Fruit Rots

Gray Mold (Botrytis cinerea): Symptoms of gray mold include light brown areas on fruit; a powdery gray growth produced on rotted fruit and leaf tissue; and whole rotted berries that retain their general shape but become tough and dry.

Gray mold is a serious problem because it often attacks other living plant parts in addition to developing on harvested fruit. The fungus overwinters in living plant tissue and proliferates in the spring as leaves die. Favored by cool, wet weather, the fungus establishes itself on dead or aging leaves, moving to healthy tissue as more and more spores are produced. Petals and other parts of older flowers are likely to be attacked first. These infections may destroy developing fruit immediately or become dormant until the fruit begins to ripen. Secondary infections may occur when spores that cling to ripening fruit germinate in moist packaging conditions after the fruit is harvested, causing uncontrollable storage rots.

Management: It is important to maintain proper spacing between plant rows and to keep plant rows narrow to allow good air circulation. This will promote rapid drying of foliage, blossoms, and fruit during periods of high humidity, rain, irrigation, or dew and lessen the chance of Botrytis spores germinating on plant surfaces. Beds that become too crowded are likely to promote Botrytis fruit rot. Heavy nitrogen applications, particularly early spring applications, also promote Botrytis development.

If Botrytis is a chronic serious problem or in years with a lot of rainfall during bloom, fungicides should be applied during the bloom period. Frequently rotate fungicide chemical groups (FRAC numbers) to prevent the development of resistance.  See pest management schedule below for recommended materials and timing.

Leather Rot (Phytophthora cactorum): Symptoms include: fruit with dull and lifeless appearance; infected areas of immature fruit turn brown to dark brown, while infected areas on ripe fruit appear bleached to lilac to normal in color; infected fruit is tough and has a bitter taste. After harvest white fuzzy growth may appear under moist packaging conditions.

This organism is a common soil inhabitant that attacks many species of trees, shrubs, and perennial or annual herbs. The leather rot organism also causes a serious crown rot. Rainy weather promotes infection by splashing spores along with soil particles onto flowers or fruit. Maturing fruit in contact with wet soil may become infected. Frequent fog or morning dew may supply adequate moisture for the “swimming” spores to cause infection. Fruits may be affected at all stages from blossom to maturity.

Management: Proper plant spacing and weed control for good aeration to promote rapid drying of plant surfaces. Clean straw mulch placed under plants and between rows keeps maturing fruit from getting rain-splashed soil on the surface. (Note: plastic mulch may “puddle” and actually make leather rot worse.) When conditions are very wet, and leather rot has occurred in a field, fungicides may be needed. See pest management schedule below for recommended fungicides and spray timing.

Anthracnose (Colletotrichum spp.): Symptoms of this disease include circular, sunken, water-soaked tan to black lesions on both green and ripe fruit. In wet or humid weather, creamy pink to salmon-colored spore masses occur in the centers of these lesions, and the fungus can produce fluffy white growth at the border of the lesion and healthy tissue. Under dry conditions, or if secondary organisms do not cause soft rots, the fruit may become mummified and black.

This fungus is an extremely important pathogen of strawberries in the Southeast. In addition to fruit, this fungus may also attack stolons, petioles, and strawberry crown tissues. The same fungus may cause fruit rots of crops such as apples, blueberries, raspberries, grapes, peppers and tomatoes.

The incidence of anthracnose fruit rot may be directly related to unusually warm, damp weather in spring. Spore production, germination, and host infection are all favored by warm and humid environmental conditions. Spread of the fungus from infected tissues to uninfected fruit and crowns occurs primarily by splash dispersal and is aided by wind-driven rain. However, spread may also occur on runners and by the movement of people or equipment through the field, especially in wet weather.

Management: Control of strawberry anthracnose is difficult, especially under warm, wet conditions. Initial planting of uninfected crowns is important, and rotation out of strawberries for a period of time before replanting may be helpful, as the fungus overwinters on infected plant tissues or infested debris in the soil. Fungicides may be helpful in reducing infection, but may be less effective in hot, humid weather. Overhead irrigation of fields with infected plants or fruit and the movement of people or equipment through wet fields can increase spread of the pathogen. However, the retention of a straw mulch between rows will help reduce splash dispersal of the fungus. See pest management schedule below for recommended materials and timing.

Foliar Diseases

Bacterial Angular Leaf Spot (Xanthomonas fragariae): Angular leaf spot is a bacterial disease that is not a consistent annual problem. Early symptoms on the leaves are tiny, water-soaked areas. When viewed against a bright light, lesions are translucent, but when viewed against a normal or dark background, the lesion areas are dark green. As the disease progresses, it may develop into symptoms similar to common leaf spot, leaf scorch and Phomopsis leaf blight. Chlorotic halos will form, areas of tissue will appear red, and the lesions on leaves and petioles will join together into large, irregularly shaped areas. The most severe problem, from a marketing perspective, is that the calyx, or cap, of the berries may become infected, turning it brown and making the berries less attractive.  In New England, the disease can damage plants and limit growth, but does not cause plant mortality.  Reports from California indicate that infections can become systemic and will occasionally kill plants.

Inoculum for the first lesions in the spring comes from infected dead leaves. The bacteria are very resistant to drying and other harsh conditions, and may survive for a long time in the old leaves or in buried plant tissue in the soil. The pathogen does not move in the soil, or survive free in the soil. The bacteria may move from new lesions to other plants. It can be spread by rain or irrigation, or carried from plant to plant when fields are being worked. Wet, cool weather in the spring encourages the bacteria to build up to damaging levels. Long periods of rain, or frequent irrigation at times when the day temperatures are around 65˚ F, and night temperatures near 35˚ F, will encourage growth and spread of this disease. It is often more prevalent in the fields that have been irrigated frequently for frost control.

Management: In general, antibiotics (streptomycin or oxytetracycline), copper-containing pesticides or hydrogen dioxide are used to treat bacterial plant diseases. While some sources say these treatments will protect against angular leaf spot, field tests have shown only moderate success at best. Copper applications can damage strawberry plants and should not be applied when plants are in bloom.

In the absence of any better information, it is best to take a two-pronged approach where angular leaf spot has been a problem. First, in fields with a history of this disease, inoculum should be reduced by removing as much leaf debris as possible from the field at renovation. Rotate out of severely infested fields for at least a year. Second, begin scouting fields with a history of this disease as soon as buds extend from the crown. Continue scouting until bloom. Symptoms often first appear near sprinkler heads. If symptoms are observed, discontinue irrigation unless needed for frost protection or when excellent drying conditions prevail. Minimize the time leaf and blossom tissue is wet. Also, avoid worsening the problem by working in the field when the leaves are wet.

Leaf Spots

Fungal leaf diseases may occur as soon as the first leaves unfold in early spring and continue until dormancy in the late fall. Generally, these diseases do not exceed an economic threshold that calls for chemical control. The primary damage of leaf diseases is a loss of vigor through reduced leaf area that is needed to support the plant. If outbreaks of these leaf diseases become significant, the plants will become weakened during winter dormancy and become more susceptible to root diseases and winter injury.

The three major leaf fungal pathogens have a similar life cycle. Leaf spot, leaf scorch, and leaf blight all overwinter in infected dead or living leaves, producing spores and new infections during moist, warm conditions.

Leaf Spot (Mycosphaerella fragariae): Symptoms of leaf spot first appear as circular, dark purple spots. The spots enlarge and the centers turn grayish to white on older leaves and light brown on young leaves. A definite reddish purple to rusty brown border surrounds the spot.

Spores overwinter in lesions on living leaves. More spores are produced in early summer in spots on the upper and lower leaf surface, and are spread by splashing rain. Middle-aged leaves are most susceptible. Lesions also develop on fruit, stems, petioles and runners.

Leaf Scorch (Diplocarpon earliana): Symptoms of this disease consist of numerous small, irregular, purplish spots on leaves. The center of the blotches becomes brownish. Blotches may coalesce, covering the leaflet which then appears purplish to reddish to brown.

Fruiting structures are produced in the spring on lower leaf surfaces of dead leaves. Spores are produced most abundantly in midsummer. Oldest and middle-aged leaves are infected more readily than young ones.

Leaf Blight (Phomopsis obscurans): Symptoms of leaf blight infections begin as one to six circular reddish-purple spots on a leaflet. Spots enlarge to V-shaped lesions with a light brown inner zone and dark brown outer zone. Lesions follow major veins progressing inward. The whole leaflet may turn brown. In severe cases, stolons, fruit trusses and petioles may become infected which may girdle and kill the stem.

The fungus overwinters as mycelium or fruiting structures on the old leaves that remain attached to the plant. Spores are spread by rain splash early in the spring. Leaf blight is most destructive to older leaves in the late summer. Calyxes and fruit may also be infected.

Management: Leaf scorch and leaf spot are mainly controlled by use of resistant varieties. (See chart of disease resistant varieties.) No resistant varieties to leaf blight are known. Cultural practices and some fungicides recommended for controlling fruit rots are also beneficial for managing leaf spot diseases, e.g. proper plant and row spacing for good air drainage and plant vigor. Mowing or removing the tops and old leaves at renovation has benefits for managing leaf diseases. This practice is only effective for this purpose if the cut foliage is removed from the field or thoroughly incorporated into the soil by tilling. Leaves less than 3 weeks old are susceptible to infection by leaf spot; older leaves are resistant. See pest management schedule below for recommended materials and timing.

Powdery Mildew (Sphaerotheca macularis): Symptoms include white powdery growth on the lower leaf surface, causing the leaf edges to roll upward. (Note: Some herbicides will cause leaf rolling on certain varieties.) Infected flowers and ripe fruit may also become covered with white growth; and infected green fruit may fail to ripen and will remain hard.

This fungus overwinters on living infected leaves. Infection periods are favored by humid weather and temperatures between 58-68˚F. Thus, if a severe foliar infection occurs, it does so either early or late in the season. Controlling these foliar infections with fungicides does not apparently increase yields. However, by controlling foliar infections, the amount of inoculum available to infect the spring growth is reduced. Crop losses occur as a result of flower and fruit infections.

Management: See pest management schedule for recommended materials and timing, and variety selection chart for resistant varieties.

Root Rots

The strawberry root system is composed of three types of roots: the perennial and structural roots that originate from the crown, and the transient feeder rootlets that originate from the perennial or structural roots. The structural roots are light in color with a well developed cortex. The perennial roots are dark due to the sloughed cortex surrounding woody secondary growth and are more or less permanent. They store food reserves to maintain the plant through winter dormancy.

Structural roots are produced from the crown during the current year. Transient feeder roots consisting of primary tissues are produced from both structural and perennial roots. They may only live a few weeks and are replaced during the growing season; they are constantly dying back and being replaced. The transient roots function to absorb water and nutrients; the perennial roots cannot. Thus, all types of roots are important in maintaining healthy plants and good yields. Death to transient rootlets by pathogens or unfavorable soil conditions is not as damaging to plant vigor if the plant is able to replace them. However, often the structural and perennial roots also become infected. When this happens, the plant is greatly weakened, producing little or no fruit. Plants may suddenly wilt, or plants which were healthy the previous season may develop slowly in the spring. Proper diagnosis of soil-borne problems requires careful examination of the roots and crown.

Red Stele (Phytophthora fragaria): Symptoms of red stele infection are numerous: wilting; young leaves with a bluish-green tint; and older red, orange or yellow leaves. Severely diseased plants may die or remain stunted, producing few runners and small berries. When roots are cut open lengthwise, the core will show a reddish-brown discoloration; however, a reddish core does not guarantee that red stele is present. Plants showing symptoms usually occur in patches where the soil is wettest.

The red stele organism causes a root rot and wilt, and is a major disease of strawberries where cool, wet soil conditions occur. The spores actually swim and need water in the soil in order to find and infect roots. The disease enters the main perennial roots and grows along the stele, the plant’s food and water transport system. Roots begin to rot from the tip within a few days after infection. Depending on the extent of the infection and the plant’s resistance, stunting or wilting and collapse of the plant may result.

Management: Good soil drainage, texture, and planting in raised beds in wet areas will discourage disease infection. Purchase planting stock only from nurseries that have been inspected and certified disease-free. Disease resistant varieties are available. Consult your nursery supplier for more information. Pre-plant soil fumigation may reduce P. fragaria infestation in soil but avoiding wet sites is more reliable. Pre- and post-plant treatments with a systemic fungicide is also an option. See pest management schedule for materials and timing.

Verticillium Wilt (Verticillium albo-atrum): Symptoms of Verticillium wilt are marginal and interveinal browning and eventually collapse of outer leaves; inner leaves are stunted and may wilt but tend to remain green until the plant dies.  This fungus has a wide host range among annual and perennial crops and weeds. Verticillium is spread from field to field by water, wind or on infected planting stock, and crop and weed debris. Plants that are fruiting are affected more severely, and the first symptoms are noticeable as temperatures increase in late spring.

Management: Do not use solanaceous crops (such as tomato or potato), or squash or raspberries for rotation crops. Do not use alfalfa as a rotation/cover crop. In addition, control pigweed and lamb’s-quarters which are also hosts for Verticillium. Preplant soil fumigation may help in managing this disease. See disease resistant variety chart for selection of resistant varieties.

Black Root Rot: Above-ground symptoms of this disease are similar in appearance to red stele, including a general lack of vigor and eventual collapse of plants especially during dry weather. Underground symptoms consist of blackened feeder roots and, eventually, structural and perennial roots. Structural roots will rot from the outside to the center, leaving the core white for a period of time, unlike red stele where the core is usually red.

Black root rot has no simple causes or remedies. It is a disease complex, involving several pathogens combined with plant stress. The key pathogens include Rhizoctonia, Pythium, and lesion nematode. The pathogens involved in this disease are commonly found in soils but usually don’t cause disease symptoms on healthy plants, but stressed plants are more susceptible. Strawberry plants may be stressed by drought, winter injury, root feeding insects, nematodes, poor nutrition, soil compaction, and improper herbicide use. Stresses reduce the plant’s resistance to disease.  Root rotting pathogens may infect and continue to damage plant roots and crowns long after the initial stress.

Management: Control of black root rot in an existing field is difficult. Stress management is the key to black root rot management. Therefore, replacing winter mulch that has blown off, irrigating during dry weather and after renovation, maintaining good nutritional status in the plants, and not allowing the soil to be compacted are important practices to reduce plant stress and reduce the possibility of black root rot developing in the field.

The long-term strategy for managing black root rot relies on site selection and crop rotation. Choose a site which has well drained soil with good soil organic matter content and has not grown strawberries recently. Where black root rot has been a problem, a rotation of a 3–6 year period without strawberries is recommended. This long rotation is needed because causal organisms can persist in the soil for a long time. Using a variety of crops and cover-crops in this period is recommended to help break up the disease cycle. Banded or in-row applications of strobulurin fungicides may reduce or delay infections in infected fields.

Soil fumigation for controlling black root rot can work well, but can also fail under certain conditions. Fumigation sterilizes the soil of pathogens and beneficial organisms. Organisms reintroduced in this “clean” soil grow rapidly in the absence of competition or predators. Pathogens, even in very small quantities, in soil from non-fumigated areas carried into fumigated areas on shoes, equipment or roots of strawberry transplants, may allow pathogens to quickly build up to high levels. Thus, soil fumigation runs the risk of favoring black root rot rather than controlling it. Moving to a planting site which has not grown strawberries recently, and is well-drained, is the best method of managing this disease.

Virus Diseases

Viruses are disease-causing organisms so small they cannot be seen with an ordinary microscope. Several viruses infect strawberries in the Northeast, and it is not uncommon for two or more viruses to be found within the same plant. Viruses in a plant may not show obvious symptoms. However, their presence does weaken the plant.

Loss of vigor and yield caused by viruses are more likely to show up when growing conditions are unfavorable and plants are stressed. Virus symptoms on strawberries, include chlorotic (yellow) spots or irregular patches on leaves. Leaves may crinkle, or otherwise be malformed. Herbicide injury and virus symptoms may be similar.

Management: Once strawberry plants are infected with a virus, they cannot be cured. The infection is passed on to all daughter plants via runners. Most viruses are spread from plant to plant via aphids. Chemical insecticides will not kill aphids before they are able to transmit viruses and may even stimulate aphids to feed. Planting virus-free material will decrease overall damage from virus diseases.

Fruit Damaging Insects

Tarnished Plant Bug (Lygus lineolaris): The tarnished plant bug (TPB) is a small (1/4”) bronze-colored insect with a triangular marking on its back. The immature stage, or nymph, is smaller and bright green, resembling an aphid, but much more active. Both adults and nymphs feed on the developing flowers and fruit, sucking out plant juices with straw-like mouth-parts. This results in deformed fruit: typically “cat-faced” berries, also called nubbins or button berries. Such fruit are generally unmarketable.

Management: Controlling weeds in and around the planting may reduce populations of this insect, but insecticide sprays may be necessary. If mowing around fields, do so after insecticides have been applied (to control migrating insects). White sticky traps are available for monitoring tarnished plant bug adults. These traps are used as a indication of when plant bugs begin their activity in the spring and a relative indication of their abundance, not as an indication of when to control this insect. Immature TPB (nymphs) are sampled by shaking or tapping flower trusses over a flat white surface, like a paper plate. Thirty flower clusters should be sampled evenly from across the field (typically 6 clusters at 5 locations or 5 clusters at 6 locations). If 4 or more flower clusters are infested with nymphs (regardless of how many) a spray is recommended. A follow-up spray application may be made after bloom if TPB are still present in high numbers (check harvest interval before selecting material). See pest management schedule for recommended materials and timing. Do not apply insecticides during bloom.

Sequential Sampling: a time-saver. To save time, a sequential sampling plan may used to determine how many clusters should be sampled. By using Table 19 above, you can make a spray/no spray/keep looking decision by first examining a minimum of 15 clusters. If you find 0 TPB nymphs, you can stop and make a “no spray” decision. If you find more than 0 but less than 3, you should continue sampling. If you find 3 or more TPB nymphs, control is required in order to avoid economic damage to your crop. If the maximum of 50 flower clusters are sampled and no decision is indicated, the grower should sample again in 1 or 2 days. This method allows scouts to spend less time monitoring in fields where populations are very low, or very high. More time is spent sampling fields where TPB populations are close to the threshold.

Strawberry Bud Weevil, “Clipper” (Anthonomus signatus): The strawberry bud weevil or “clipper” occurs somewhat less frequently than tarnished plant bug. This insect is a very small beetle (1/8”) with a copper-colored body and a black head with a long snout.  The female weevil chews a small hole in unopened flower buds and lays an egg in the hole. She then girdles the stem just below the bud. The flower bud dries up and dangles from the stem, eventually falling to the ground. The immature weevils, or grubs, develop in the girdled buds, emerging as adults in the early summer, and then migrating to wooded areas.

These insects are not always present and may only cause minimal damage some years. Examine the plants before bloom for clipped buds. If the field has a history of significant clipper injury, the first appearance of clipper indicates the need to spray.

Management: Check for presence of clipper by examining new flower trusses as they first emerge from the crowns in April or May. The weevils will sometimes crawl in among the unopened buds for shelter. They are most likely to be in rows near woods or hedgerows. Later, look for shot-holes in opened flower petals and/or clipped buds of unopened flowers. In the past, the IPM action threshold for this insect is 1 clipped bud per 2 ft. of row or one live adult. Research done in recent years suggests that many more clipped buds can be tolerated without significant yield loss. A comparison of old and new sampling methods done by researchers at Cornell University (Hortscience 34 (1): 109-111. 1999) can be seen in Table 20 below. Sample at least 5 locations in the field. If you determine that the infestation is limited to the edge of a field, you may only need to spray the border rows. If you see evidence of clipper and determine a spray application is necessary, follow recommendations for materials and timing in the strawberry pest management schedule.

Brown Marmorated Stink Bug (BMSB) (Halyomorpha halys): Adult BMSB are approximately 3/4 inch long and are shades of brown on both the upper and lower body surfaces. They are the typical “shield” shape of other stink bugs, almost as wide as they are long. To distinguish them from other stink bugs, look for lighter bands on the antennae and darker bands on the membranous, overlapping part at the rear of the front pair of wings. Masses of 20-30 eggs are laid on underside of leaves. The 5 nymphal stages range in size from 1/8 - 1/2 inch. Nymphs and adult BMSB feed on many hosts including small fruits, tree fruits, vegetables, ornamentals, and seeded crops such as corn and soybeans. BMSB feeds by puncturing the fruit with piercing/sucking mouthparts, and injecting saliva which allows the insect to suck up the plant material through its mouthparts. Fruit tissue at the point of entry and just below into the flesh, then dies and the rest of the fruit grows around it. This leaves a sunken area on the skin at the point of entry, and browning, dead tissue in the flesh.

BMSM has become a serious insect pest throughout much of the mid-Atlantic states and southern New York. As of 2020, BMSB has caused minor economic injury to tree fruit in some areas of New England, but is not yet a pest of concern for most small fruit crops. It is unknown at this time whether there will be one or two generations per year.

Management: BMSB can be controlled with some of the commonly used fruit insecticides, including bifenthrin and malathion. Spray recommendations are found in the strawberryberry pest management schedule.

Spotted Wing Drosophila (SWD) (Drosophila suzukii): These are small (1/8”) vinegar flies that came into the northeastern U.S. in 2011. They originated in western Asia and attack most soft or thin-skinned fruits. The female flies can insert eggs through the skin of ripening fruit. The larvae, or maggots, are small and translucent and feed on the flesh of fruits. Each female fly can lay between 300-400 eggs. The cycle from egg to larvae to pupae to adult can be completed in as little as 14-21 days. Even a relatively small influx of flies into a field can soon develop into a major infestation. Infested fruit may contain a few to many larvae and will prematurely soften and decay. If not noticed at harvest, infested fruit will have very reduced shelf life, and larvae will be seen emerging from the remains.

Management: Although the flies are relatively easy to kill with insecticides, keeping berries free from infestation can be difficult because of the near constant pressure of countless flies throughout the late summer and fall. To date, only frequent and repeated insecticide sprays throughout the ripening and harvest period have proven effective. For June-bearing strawberries in New England, it appears that spotted wing drosophila do not build up to populations high enough to cause significant damage until after harvest is complete. It is recommended that growers be vigilant however, especially with later ripening varieties, and be ready to apply appropriate insecticides if flies are observed in the field or larvae are found in the fruit. This insect is a significant threat to day neutral strawberries ripening in the late summer and fall.

Homemade traps for the flies can be made by drilling 1/8” holes in plastic containers or cups (red or black color is most attractive). The cups should be baited with apple cider vinegar or sugar water with a pinch of yeast. Commercial traps (from Scentry or Trece) contain similar attractive odors as homemade recipes and may be more convienient. Check the traps regularly for vinegar flies. The males can be identified by a single small black spot near the top of each wing. The females have no spots. It is likely that by the time flies are found in the traps, eggs have already been laid in the fruit. Therefore, sprays would be recommended as a preventative measure on any fruit starting to ripen after the first week of August. Weekly coverage may be adequate under low pressure, but twice weekly sprays may become necessary for high pest pressures affecting fall-bearing day-neutral strawberries.

Pay close attention to days-to-harvest requirements and limitations on number of applications on all product labels. Most insecticides will be made more effective by adding sugar to stimulate SWD feeding. On smaller plantings, placing a fine screen or row cover over the plants can effectively keep flies from laying eggs on fruit, but can interfere with pollination if flowers are still present.

Field sanitation – removing all waste fruit from the field – may help reduce infestations. Carefully grade fruit before marketing, removing any soft berries which may contain larvae. Chilling harvested fruit to 32° F prior to marketing can significantly reduce emergence of larvae.

Sap Beetles (Stelidota geminata): Sap beetles cause hollowed out cavities on ripe fruit, an injury very similar to slug injury. Adults are small oval beetles about 2mm long and dark brown in color. They are often hard to see because they drop to the ground when disturbed, but they may be found in the cavities they have chewed out. They are found almost exclusively when there is ripe fruit in the field.

Management: The best management for this pest is sanitation; keeping the field as free as possible of ripe and overripe fruit. Sap beetles may be trapped with bait baskets of over-ripe fruit placed between the edges of the field and wooded areas. Spacing recommendations are not known. Place traps as soon as bait fruit is available. Insecticides may be used for control if absolutely necessary. Most can be sprayed within 24 hours of harvest, but might devastate mite predators. Read the labels carefully. See pest management schedule for recommended materials and timing.

Thrips (Thysanoptera): Thrips are tiny insects that feed on flower parts. Several species occasionally infest the flowers of strawberries. The adults are slender, winged, about 1/25 inch long, and are orange or yellow. Young thrips are smaller, wingless, yellowish, and active. These insects breed on grasses and weeds in spring, and move to strawberries at bloom. They insert their eggs in plant tissue at the base of flowers, and in tender, new foliage.

Thrips begin feeding on the seeds and the inner surface of the hull soon after the buds open. As the fruit expands and the seeds separate the thrips feed extensively on the fruit between the seeds. Thrips feed by scraping the surface cells with their mouth-parts and sucking the contents, causing cells to die. With continued feeding, the entire fruit becomes bronzed and may crack along the surface.

Management: Thrips can occasionally build up to damaging levels. Scouting for this insect can be difficult because of their small size. Fruit should be examined when they are very small, 5-10 mm in diameter. Examine under the calyx for presence of thrips, or place a sample of immature fruit in a zip-lock bag in the sun. This will drive the thrips out so that they can be counted. Canadian researchers indicate that more than 25 thrips per 50 sampled fruit will result in unacceptable levels of fruit damage (see Table 21 below). Several insecticides labeled for use on strawberries are effective on thrips. Consult the product labels.

Leaf Damaging Insects and Mites

Strawberry Leafrollers (Ancylis comptana fragariae): The immature stage (larvae) of these insects damages strawberry leaves. They are small green or bronze caterpillars up to 1/2” long at maturity. They occur in the field prior to bloom and in mid- to late July. Larvae are first found on the undersides of leaves in silken covers, then on upper sides of leaves that have been folded or rolled and tied with silken threads.

Management: Remove and destroy rolled leaves. If infestation is severe, a pre- or post-bloom spray application may be needed. Timing will depend on when larvae are present. In Southern New England they occur in mid-May so a pre-bloom insecticide spray is recommended.

Twospotted Spider Mite (Tetranychus urticae): Twospotted spider mites (TSSM) are very small (1/50”), 6- or 8-legged creatures that feed on strawberry foliage. Under heavy infestations, mite feeding destroys leaf chlorophyll and causes leaves to have yellowish or whitish speckles, then an overall bronze color. Leaves will be covered in a fine webbing. Yield reductions may occur from repeated heavy infestations. The most serious reductions in yield may result from early season feeding, so scouting for overwintered mites in early May is especially important.

Twospotted spider mites are found on the underside of leaves, are barely visible to the naked eye, and are especially active during hot, dry months. Mites generally form colonies and may be most noticeable by the webbing that they produce around their aggregations, which may occur as localized “hotspots” in the field. Therefore, when looking for mites, the grower must look over the whole field, checking first for bronzing and then looking for mites with a hand lens. Overwintered female TSSM mites are easily seen because they are orange-colored.

Management. Mites should be monitored weekly by sampling the field in 5 to 10 locations. Five to ten leaves should be sampled at each location for a total of 60 leaves. Examine the underside of the leaves for the presence or absence of TSSM. Record the information on a field map so that “hot spots” can be identified and treated. A miticide application is recommended if 25% (i.e., 15 leaves) or more of a 60 leaf sample is infested with TSSM. See pest management schedule for recommended materials and timing.

Natural predators exist which feed on two-spotted spider mites. One such predator, also a mite (Neoseiulus fallacis), is native to the northeast and often maintains TSSM populations at non-damaging levels. It is equally small but lacks the two spots on its back, is teardrop shaped, shiny, and pale yellow in color. They are also easily distinguished from TSSM by their rapid movement across a leaf in search of prey; (they resemble bumper cars moving forward and backward as they search for food). When sampling a field, presence of predators as well as TSSM should be noted.

Several companies sell predatory mites, including N. fallacis, for release in various crops. However, the benefit of releasing commercially reared mites has not been demonstrated in the northeast, where natural populations of N. fallacis are pervasive. It is important to encourage natural enemies of spider mites by reducing the use of broad-spectrum pesticides (especially carbamate and pyrethroid insecticides) which harm natural enemies. One strategy that has worked exceptionally well has been the early-season use of 1% oil with a mist blower. This inexpensive treatment is highly selective: it kills TSSM, but not predatory mites. The resulting imbalance between predators and TSSM allows predators to “mop-up” the remaining TSSM. Please note that oil-incompatible pesticides should not be applied prior to the oil spray. See the table at the end of this guide for toxicity of pesticides to beneficial insects. See resource listing in the Appedices of this publication for for sources for natural enemies such as predatory mites.

Cyclamen Mite (Steneotarsonemus pallidus): This soft-bodied mite is orange-pink, white, or green and about 1/100” long. These mites feed on the unfolding leaves in the crown of the plant, leading to distorted, purplish leaves, and buds that fail to open. Cyclamen mite is not as common as two-spotted mite in strawberries and has been known to come in on nursery stock. It is, therefore, important to buy plants from a reputable source. The mites are very small and a 15X or higher hand lens is needed to see them. Mites are most commonly found on tiny, unfolded leaves down in the crown. Look for small translucent, cigar-shaped mites.

Management: See pest management schedule for recommended materials and timing. Materials should be applied with high rates of water and a spreader to carry the chemical down into the crowns.

Strawberry Aphids (Chaetosiphon spp.): There are several species of aphids that infest strawberries. Adults are small (1/16” long), soft-bodied insects. Aphids occur on new shoots, undersides of leaves, and on buds while they are still in crown. Root aphids have been found on rare occasions. Aphids are primary vectors of virus diseases, transmiting viruses from infected to non-infected plants. Monitoring and management efforts should be undertaken when viruses are known to be a problem in the region. When present in great numbers, aphid feeding can result in stunted, malformed plants.

Management: See pest management schedule for recommended materials and timing.

Leafhoppers (Empoasca fabae): Leafhoppers are small (1/8”), green, bullet-shaped insects which take flight quickly if disturbed. The nymphs are lighter colored and do not fly. They are easily identified by their habit of moving sideways when disturbed. Leafhoppers feed primarily on the underside of strawberry leaves, causing them to yellow between the veins and become curled and distorted. These symptoms are often mistaken for herbicide injury. Feeding activity is most serious during the late spring and early summer, and is often first noted in new plantings. They reduce vigor and runner production. Insecticides should be applied only when large populations of nymphs are noted on the leaves or symptoms become apparent.

Management: See pest management schedule for recommended materials and timing.

Spittlebug (Philaenus spumaris): Hidden beneath masses of white frothy spittle are soft-bodied, tan and green, elongate bugs about 1/8-1/4” long. These insects feed on stems and blossom clusters before and during bloom. Heavy feeding activity results in reduced plant vigor and decreased yield. Early season feeding can result in stunted, off-color plants; damage appears much like that caused by cyclamen mites.

Management: Spittlebug seldom does significant damage to the plants. It is mainly a problem because customers are bothered by the froth in the field when picking. Often heavy rains and/or irrigation will wash froth from plants. This insect tends to be more of a problem in weedy fields. Insecticide applications early in the season (e.g., for tarnished plant bug) are usually adequate for keeping this insect in check. Recommended action threshold is one spittle mass per foot of row. See pest management schedule for recommended materials and timing.

Cutworms: The immature stage (larvae) of these insects causes feeding injury to plants. Larvae may reach 2” long at maturity. Color and arrangement of stripes and spots varies from one species of cutworm to another, but are often mottled or dingy gray. Cutworms may be observed on plants at night during spring and summer. Larvae consume leaves, stems, buds, flowers, and developing fruit.

Management: Consult with your Cooperative Extension Specialist for management options.

Root Damaging Insects

Root-feeding insects can cause above-ground symptoms that are similar to root diseases: general loss of vigor and collapse during dry weather. Where damage is suspected, plants can be dug with a spade to examine roots and to check soil for the presence of root-feeding insects.

Strawberry Rootworm (Paria canella): The adult form of this insect are beetles that are small (1/8”), round, and copper-colored with a dark markings on their backs. The immature root-feeding grubs are also small (1/8”), creamy white in color with 3 pairs of legs, and are actively feeding on roots in the late spring to early summer. The new generation of adults appears after renovation (late July to early August).

This insect can be most easily observed in the field as adult beetles feeding on leaves. Feeding occurs at two times during the growing season (May, and July-August), and results in small shot-holes in the leaves. The second feeding period usually is more evident because a greater number of beetles are feeding then. The earlier feeding is done by the overwintering population.

Management: As with all the root-feeding insects, control of the root-feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage of the insects. Presence of adults can be detected by feeding injury or direct sightings of the adult beetles in the field. Sticky traps used for monitoring tarnished plant bug may aid in sighting strawberry rootworm adults since they feed primarily at night. Some of these beetles find their way onto the traps.

If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again.

No threshold is established for this insect. Feeding injury, as with all the root-feeding insects, is most damaging if root diseases (i.e. black root rot) are also present. Therefore, it is advisable to keep the root-feeding population low. See pest management schedule for recommended materials
and timing.

Root Weevils (Otiorhynchus spp., Polydrusus spp.): There are several rootfeeding weevils that are damaging to strawberries; black vine weevil (Otiorhynchus sulcatus) strawberry root weevil (O. ovatus), and the rough strawberry root weevil (O. rugosostriatus) are the best known. Additionally, green leaf weevils, (Polydrusus spp.) have also been found feeding on strawberries in Massachusetts and Connecticut.

These insects damage strawberries primarily through larval feeding inside the crown and on the root system, which weakens the plants. Root feeding is especially damaging where root diseases are also present. The grubs are whitish and crescent shaped, ranging in size from 1/4” to 1/2”. They have no legs. Adult weevils feed on leaves from May through August, causing notching of the leaf margins. Adults in heavily infested fields can contaminate harvested berries. Adult feeding generally does not cause serious injury unless plants are already weakened. Under heavy infestation by root weevils, the plants decline, appear stunted and bear poorly. Infestations are generally in patches in the field.

Management: The easiest time to detect weevil activity is during harvest. Randomly pick 100 leaves from each field and count the number that have feeding notches along the margin. Greater than 50% leaf notching may indicate the need for control measures. Confirm the presence and species of weevils involved by observing them at night with a flashlight. The easiest time to detect root injury from larval feeding (and from other root disorders) is in the autumn. The foliage of plants with poor root systems turns orange-red earlier than healthy plants. Plants should also be examined in the spring if patches of poor vigor are noticed. Lift a section of row with a spade and examine the roots within a 6” layer of soil. If grubs are found, insect pathogenic nematodes should be applied in early May or late August. Be sure to keep the field irrigated during periods of active growth to avoid stress on the plants.

Predatory nematodes attack root weevil grubs in the soil. Although populations of these nematodes naturally occur, application of commercially produced nematodes can achieve faster biological control. See resource listing in the appendices at the end of this guide for sources of beneficial insects.   Available species useful against root weevils include Steinernema carpocapsae, S. feltiae, Heterorhabditis bacteriophora, and H. marelatus. The Heterorhabditis spp. have the ability to penetrate insect cuticle, which facilitates infection of white grubs. The cost and quality of nematodes can vary widely, so talk to your Small Fruit Specialist to find out more about different products. A banded spray may be very cost effective compared with application through overhead irrigation. Nematodes application should be preceded and followed with irrigation. Protect them from sunlight by applying them in the evening. Brigade^TM (IRAC 3A) is now registered to control the adults, before they lay eggs. Controlling root weevil adults requires the highest labeled rate, and is best applied at night when adults are active. This material can induce spider mite outbreaks, and may kill beneficial root weevils predators. The systemic insecticide, Platinum™ (IRAC 4A), is registered for use as a soil drench in the spring or late summer to control grubs. See pest management schedule for recommended timing and rates.

White Grubs of Asiatic Garden Beetle, European Chafer, Japanese Beetle, and Oriental Beetle: (Maladera castanea, Rhizotrogus majalis, Popillia japonica, and Exomala orientalis): Many growers have recently experienced leaf and root damage from these scarab beetles, collectively also called white grubs. Root feeding by larvae dramatically weakens the plants, especially where the root systems already suffer from diseases like black root rot. All of these species overwinter as a grub in the soil, emerging in late May through July in the Northeast. The adult Japanese beetle is copper-brown and -green in color and approximately 1/2” long.

They are often found feeding during the day on leaves in small groups. Asiatic garden beetles (AGB) are small (3/8”) and a velvety cinnamon brown color, showing a faint green iridescence in the sunlight. AGB feed at night on the foliage and hide during the day under plants. Feeding by Japanese beetle or AGB is easily distinguished from root weevil feeding because these scarabs principally skeletonize leaves (making holes within the leaves), rather than notching the leaf edge. Leaf feeding typically occurs in June through mid-August. Oriental beetle and European chafer adults are rarely observed because they do not feed much. Oriental beetles are slightly smaller than Japanese beetles, and are usually tan and mottled with darker spots. European chafers are slightly more than 1/2” long and are a uniform tan.

The larvae (or grubs) of these insects look quite similar to one another and are called white grubs. They are c-shaped, have 3 pairs of legs, grow up to 1 inch long. They are easily distinguished from the larvae of root weevils, which have no legs. White grubs are very difficult to manage after a strawberry bed has been planted.

It is unknown how much leaf feeding can be tolerated, but if leaf area is greatly reduced it could affect the following year’s flower bud formation, which is initiated in the fall. Large numbers of beetles are of concern, especially if it increases the amount of overwintering grubs. High populations of larvae can be expected the autumn and spring following a dry summer, especially where strawberry fields are surrounded by turf. These conditions favor movement of adults into strawberry fields to lay eggs.

Management: Management of grubs in the soil is possible with insecticides, and predatory nematodes may also have some value.  Chemical control of adult beetles can prevent extensive leaf damage, but is not guaranteed to prevent egg laying. Traps with combination pheromone and floral scent lures are commercially available for Japanese beetle, but their placement near strawberries may actually attract more beetles to the area. Therefore, if traps are used, they should be placed at least 20 yards from the strawberry field.

Milky spore disease is a commercially available bacterium that is incorporated into the ground and attacks Japanese beetle grubs. However, soil temperatures in the northeast are too cool for this disease to easily become established, which makes it impractical for our area.

To avoid the risk of white grub problems, do not plant on newly turned sod land. Rather, plow the field, let it lie fallow or in a rotational cover crop such as Sudan, buckwheat, or a salable crop such as pumpkins or squash for at least one season prior to planting with strawberries. Also, avoid siting a strawberry field next to large grassy fields which would be a source of these beetles. Control grassy weeds within the planting, which are especially attractive to egg-laying Japanese beetles and European chafers.

Other Pests

Slugs: Slugs are dark grey, black, yellow-gray or brown worm-like mollusks. They may also be covered with spots and range in size from 1-1/2 to 4” long. Slugs feed mainly at night, eating ragged holes in leaves and/or fruit. They also leave a trail of slime in their paths. Damage occurs primarily on fruit.

Management: Slugs thrive in moist places. If mulch is very thick and rows close together, slugs will be favored. Try to open things up a bit by removing excessive mulch and planting at lower densities which also helps manage diseases. Some growers have used diatomaceous earth for slug control. Research results are not available to verify the effectiveness of this material. Baits are also available but are not considered highly effective according to some growers. Consult with your Extension Specialist if you need help with this pest.

Garden Symphylan, (Scutigerella immaculata):The garden symphylan, also known as the garden centipede, is an occasional but very destructive pest of strawberries. Symphylans are not insects but are more closely related to centipedes and millipedes. They have 12 pairs of legs and 14 body segments. Symphylans overwinter in the soil as adults. In spring they move into the top 6 inches when the soil temperature rises above 45°F.

Eggs are deposited in soil crevices and tunnels in late April, May, and June. The eggs hatch two to three weeks later into tiny, white nymphs that resemble the adults in appearance except they have only six pairs of legs. As the nymphs develop, they grow bigger and add a pair of legs at each molt until they have 12 pairs. About three months are required to complete development from egg to adult. The adults remain in the upper 6 inches of soil until extreme dryness or cold weather drives them deeper into the soil. Mature symphylans are white, slightly less than l/4 inch inlength, with a pair of long beaded antennae. Their entire life(one to two years) is spent in the soil.

Garden symphylans feed on the roots of strawberry plants, weakening or killing them. Infestations seldom encompass an entire field, but rather involve one or more small areas within a field. Usually, the first indication of a symphylan infestation is a small area of stunted, unhealthy plants. Crop losses continue in the same area of the field year after year, with the infected area increasing in size about 10–20 feet each year.

Management: It is best to control symphylans before the crop is planted or at the time of planting. To check for symphylans, turn over at least 10 shovelfuls of soil. Sift the soil while looking for active symphylans. An average of one symphylan per shovelful signals that a treatment is necessary before planting. If symphylans are abundant, an insecticide should be broadcast and incorporated into the soil of the infested area before planting takes place.

Weed Management

Several weeds are usually cited by growers as problem species. As a general rule, always look for new or unusual weed species in fields. Attempt to cultivate or hand remove these weeds before seeds are produced. Following is some information on the most troublesome weeds with suggestions for control. Specific recommendations for any herbicides mentioned below can be found in the tables that follow.

Common Chickweed (Stellaria media): Common chickweed is a winter annual with an extended germination period. Germination can usually begin in late August or early September and continue into the next spring. Seeds are produced in late spring and early summer. 2,4-D is not effective on this weed and labeled rates of Sinbar^TM applied at mulching over emerged chickweed are generally ineffective. Cultivation is impractical since the most competitive weeds are in the strawberry row where they also receive good winter protection. Effective control can be achieved with an application of Devrinol^TM in late August. Since Devrinol^TM does not control emerged weeds, it is important to make the application before emergence. While Dacthal^TM can also control this weed from seed, residual activity is too short to make this application cost effective.

Field Pansy (Johnny jump-up) (Viola, spp.): This winter annual weed has become a serious problem for many growers. As with chickweed, germination is in the late summer, fall, and early spring. Cultivation is impractical in the strawberry row. Unfortunately, the weeds in the row are often better winter protected and produce more seed than those in the row middles. There is currently no postemergence herbicide control of this weed. The only herbicide that can provide effective control from seed (preemergence) is Dacthal^TM which should be applied in late summer; however, Dacthal^TM is rarely used in late summer because of its cost and short residual (4-6 weeks). Only the first flush can be controlled with this method. Until better control options become available, growers will continue to have serious problems with this weed.

Yellow Wood Sorrel (Oxalis, spp.): This weed is perhaps the most troublesome for many strawberry growers. Several species exist. Some are perennials and some are winter annuals. Seed production usually occurs during harvest with the plants “spitting” their seeds across the strawberry rows. This, of course, allows free spreading of this weed across the field. As with the above-mentioned weed species, germination can take place over several months making control difficult. 2,4-D provides good control of oxalis plants if they are small and not hidden under the strawberry foliage. Therefore a late fall application, prior to mulching over dormant strawberry plants, can be at least partially effective. A 2,4-D application prior to renovation is usually not effective since seed dispersal has already taken place. Sinbar^TM also has some activity on this weed. Splitting the annual use rate of Sinbar^TM into a renovation and late fall (dormant) application can also provide some control. This weed usually shortens the life of a planting due to its quick spreading habit.

Dandelion (Taraxacum officinale): While dandelion has been cited as a problem weed by many growers, acceptable control is possible. Dandelion is a “simple” perennial weed. Unlike other perennials, it does not spread by rhizomes, has a taproot, and uses seed dispersal as its primary method of reproduction. Seeds germinate in the fall and produce good size plants by November. None of the soil-applied herbicides currently registered in strawberry will control dandelion. The only effective control strategy is a late fall application of 2,4-D. This application must be made after the strawberry plants are dormant (no new growth, reddened leaves). If few plants are present, hand removal may be an option. Be sure, however, to remove the entire tap root or regrowth will occur.

The following Tables (24-26) provide information of on weed management and herbicide effectiveness in strawberries. Weeds can develop resistance to herbicides. The Weed Science Society of America (WSSA) developed a grouping system based on the mode of action of different herbicides. WSSA Group numbers can be used as a tool to choose herbicides in different mode of action groups so mixtures or rotations of active ingredients can be planned to better manage weeds and reduce the potential for resistant species. Any questions about specific weed problems or weed management strategies should be directed to your local University or Extension Specialist. See Integrated Pest Management for Strawberries in the Northeastern United States for details on alternative weed management strategies.