Cut Flowers: Insects and Mites in Commercial Production of Field-Grown Cut Flowers

Plant bug injury on dahlia

Scouting and Early Detection

Early detection is one key to successful insect management on outdoor cut flowers. Insecticide treatments are rarely 100% effective. Regular and careful observation of the plants will help detect pest problems as they are just beginning. In greenhouses and high tunnels, yellow sticky traps may serve as a useful tool for whitefly, thrips and fungus gnats and outdoors for detecting migrating leafhoppers. Place traps among the flower crops checking them weekly to determine what pests may be present and as an indicator for the effectiveness of treatments. Plant foliage may be tapped over a white sheet of paper to look for mites and thrips. A sweep-net can be used to capture plant bugs and leafhoppers.

Insect Management

The best approach to both disease and insect management begins with good sanitation and soil management. Keep the field free of weeds and plant debris. Adjust soil fertility and pH based on soil tests and space plants to allow sufficient air circulation within plantings.

When using a pesticide, good spray coverage is important. Unfortunately, not all of the material you apply actually reaches the target insect. Therefore, even small changes in spray distribution and delivery can have a large impact on success or failure.

Many insects look similar but are very different in their biology, habits and controls. A wrong identification can result in choosing the wrong pesticide or management strategy and obtaining poor control. Things like pesticide selection and placement, cultural practices, and frequency of treatment all hinge on proper identification.

Most damaging pests are apt to attack a wide variety of plant types while a few are specific to a limited number of hosts. In any case, it is important to be able to recognize the damage that results from the feeding of particular insects so that management strategies can be applied before the damage becomes extensive, or preventative steps can be taken.

Insects Causing Damage by Chewing

Pests with chewing mouthparts feed on all parts of the plant. These pests tear or cut, then chew and swallow bits of tissue leaving a ragged leaf or flower margin in the process. The tissue is removed mostly from the outer margin inward. In severe cases, most of the leaf may be eaten, in other cases, the insect may not be able to chew completely through the leaf surface and the result is a lacy appearance to the damaged leaf. Some chewing pests prefer only the tender interveinal tissue; a skeleton of veins is all that is left after attack. Since chewing pests feed on large quantities of leaf or flower tissue, apply an appropriate pesticide on the leaf or flower surface so that the insect will ingest sufficient residue to be killed. The following is a description of some common chewing insects that are known to cause damage to cut flower crops.

Caterpillars. Several species of moths and butterflies are pests of cut flowers. One of the most important is the variegated cutworm. Larvae hatch from eggs layed in the spring and generally feed after dark. Plants may be cut off at or near the ground overnight. Some species of cutworms also climb and feed on the foliage. A single cutworm can kill several plants in a night. Newly planted annual flowers are most vulnerable. Other damaging caterpillars include beet armyworms which may bore into flower buds and defoliate plants; painted lady butterfly larvae; yellow woolybear; greenhouse leaftier; checkerspot butterfly; orange tortrix; verbena bud moth; diamondback moth; columbine skipper; corn earworm; and redbanded leafroller.

Flies (maggots) and midges. The maggot (immature) stage of some flies can cause feeding damage to cut flowers such as Helichrysum and Chrysanthemums. The sunflower maggot infests the stems of Helichrysum causing the stem to collapse. Chrysanthemum gall midge bores into the leaves, stems or buds which results in the formation of cone-shaped galls in which they develop. As a result buds become distorted and stems and leaves twisted.

Beetles. Cut flowers are vulnerable to attack by one or more species of beetles. Only a few of the more common and injurious species are covered here. Both adults and larvae have chewing mouthparts that cause damage. Adult Japanese beetles feed during the day on a large number of flowering plants. Adults emerge from the soil in June and July and feed on foliage for about 30-45 days. Just before the female adult dies, she lays about 50 eggs under the soil surface in lawns or other grassy areas. These eggs hatch into grubs that feed on roots of the grasses until cold weather drives the grub down into the soil where it can escape freezing temperatures. The grubs move upward as the soil warms in the spring and feed on the roots again until they pupate in late May then emerge as adults. Control should be directed to the grub stage as well as adult. Other beetles that cause damage include Asiatic garden beetle, various species of snout beetles, spotted and striped cucumber beetles, larvae of click beetles (wireworms), blister beetles, golden tortoise beetle, flea beetles, rose chafer, and June beetles.

Miscellaneous chewing insects. The sawfly larvae, grasshoppers, slugs and snails also fall into this category of chewing insects and can cause damage to cut flower crops.

Insects Causing Damage by Piercing-sucking

Perhaps most damaging although not as apparent, are insects and insect-relatives that suck plant juices. Leafhoppers, thrips, aphids, plant bugs and mites are among the most common.

Insects with piercing-sucking mouthparts do not chew plant tissue. They pierce the leaf, flower, roots or stem with sharp, needle-like structures. Once these structures are inserted into plant tissue, the insect pumps liquid such as sap into its stomach. At the same time a salivary liquid is pumped into the plant to facilitate food withdrawal. In some cases the saliva may cause a toxic reaction in the plant. This process of feeding also accounts for the fact that insects with piercing-sucking mouthparts can transmit viruses and mycoplasm- like organisms to healthy plants.

Damage caused by piercing-sucking insect may show up as small specks or chlorotic spots where the plant or flower was punctured. Others cause twisted, curled or deformed plant or flower growth, largely because of the introduction of the toxic saliva. Still others cause general wilting which may eventually lead to plant death. Occasionally, leaves may have holes as a result of damaged tissue that has dried, become brittle and fallen from the leaf.

Because these pests do not consume any of the plant surface, stomach poisons on the surfaces of plants don't work very well. In this case a systemic pesticide, one that enters the plant system so the insect picks up the pesticide as it feeds or a contact insecticide may work best. Insecticidal soaps have contact activity but must be come in contact with the pest because they have no residual activity.

Some insects are capable of transmitting diseases from infected to uninfected plants. The most important ones here are leafhoppers and aphids.

Leafhoppers. The aster leafhopper is the primary vector of aster yellows disease. Sometimes called the six-spotted leafhopper, it is about 1/8 inch long and buff colored with six dots on its head. It does not overwinter here, but migrates from more southern regions each season. The amount of aster yellows is related to the disease incidence occurring in the southern United States at the time if migration. Thus, disease levels can vary from year to year.

Aster yellow symptoms may appear as distorted leaves and flowers, flowers that fail to form, and/or foliar yellowing. The disease affects many cut flowers such as Annual statice, Gomphrena, Acroclimum, and Asters. While control of aster leafhopper is generally easy, controlling the disease is more complicated. The best method for disease management is to monitor for and control leafhoppers as soon as they appear.

Thrips. Thrips is a common pest on outdoor cut flowers and this pest has rasping-sucking mouthparts. This describes feeding with both piercing-sucking and chewing mouthparts. Thrips puncture the tissue, then sucks the sap and fluid that is released from the injured tissue.

Thrips are very tiny, (about the size and shape of a grass seed), cream to dark colored insects that prefer to feed in opening leaf and flower buds. Some species will feed on leaf tissue where they produce silvery depressed areas that frequently contain black specks. Thrips will attack many cut flowers including Strawflowers, Acroclinum, Bachelor's buttons and dahlies. Feeding damage appears as a dull discoloration. Flowers can be streaked, mottled or flecked with off-color areas. In some cases new growth may become misshapen and deformed, or buds may fail to open. Thrips also transmit impatiens necrotic spot virus (INSV), a serious disease in the greenhouse industry. The potential exists for INSV to cause problems in cut flower production also. Insects with rasping-sucking mouthparts make them vulnerable to insecticides with systemic and contact activity. Since thrips prefer to feed in tight, protected places such as expanding flower buds, multiple applications of insecticides are often necessary for adequate management. Photo of INSV on Snapdragons

Aphids. Aphids can occur in large numbers very quickly. Most aphids are about 1/16-1/8 inch long, rounded or almond shaped with two "tailpipes" cornicles at the rear of the abdomen. Apart from the damage they inflict directly by removing plant juices, they also are effective vectors of many virus diseases. Plants can generally cope with small numbers of aphids. However, during high temperautre, aphids have the capacity to multiply rapidly and cause extensive damage.

Plant bugs. The fourlined and tarnished plant bugs are the most injurious species and attack a large number of different cut flowers.

Tarnished plant bugs feed on many flowers including dahlia, aster, calendula, chrysanthemum, cosmos, gladiolus, poppy, salvia, daisy, sunflower, verbena, zinnia, and others. The long sucking mouthpart is inserted into the plant tissues and introduces toxic saliva into the plant as it feeds. The toxin kills cells near the feeding site. Symptoms of feeding can result in injury to flower buds, causing them to abort and drop, or the blooms not to open properly or be distorted on one side. Other types of injury include deformed leaves, scarred and discolored stems, or leaf petioles. The heaviest injury often occurs during mid to late summer and is most evident during hot, dry weather, especially adjacent to recently cut hay fields. The first few generations develop on preferred hosts such as small grains, alfalfa, wild grasses, vetch, dock, and fleabane. As hay is cut or as other plants dry out, tarnished plant bugs migrate in large numbers to succulent hosts, which may be your cut flowers.

Tarnished plant bugs can be difficult to manage due to their mobility. Besides spraying with an insecticide, a grower can manage TBP with cultural practices including the removal of weeds and the elimination of trash and other debris in areas that provide overwintering sites. Mowing grass and weeds around production areas may also help to eliminate sites where the tarnished plant bug breeds. Preventing weeds from forming young buds and flowers will keep populations lower in the weedy areas.

Fact Sheet: Field Grown Cut Flowers: Tarnished Plant Bug

Four-lined plant bugs feed on many perennials including Heuchera, Dahlia, Chrysanthemum, Rudbeckia, Heliopsis, Lavandula, Lupinus, Paeonia and Coreopsis. The adult is greenish yellow with 4 black lines running down the back. It is flat and slender and aobut ¼ in long. The immature stage is bright red or orange with black spots on the segment behind the head. As they mature, a yellow stripe appears on each side of the wing pads. They feed for about 6 weeks. Plant bugs move rapidly and try to hide out of sight when disturbed. Feeding damage appears as spotting on the upper leaf surface. The injury can resemble spotting caused by disease. Depending on the plant, the spotting on leaves may be dark or light to dark tan. The spots are caused by plant bugs feeding on the plant juices and injecting a toxin when feeding. Slender white eggs are laid in the summer, inserted within stems of many kinds of herbaceous plants where they overwinter. Eggs hatch during May to late June.

Mites. Two spotted spider mite, cyclamen mites and broad mites are three mite species that can cause problems in cut flowers. Two spotted mites are most active on the underside of the leaves, their presence being apparent by the fine stippling caused by their feeding and seen on the upper surface of the leaves. Fine webbing is produced by the mites. Leaves turn yellow or bronze, and many drop. Photo: Two spotted spider mite injury

Cyclamen mites and broad mites are invisible to the naked eye but cause a great deal of damage, particularly to Delphiniums, Aconitum, Dahlia, Chrysanthemum, and Verbena. Mite feeding causes the leaves to curl, twist, and become brittle and scabby. Flower buds may dry up and die. Light infestations may result in discolored or dark-flecked flowers. On Delphinium, leaves cup or curl and are blackened. Flower spikes are stunted and blackened. Cyclamen mites are most active during high relative humidity and cool temperatures, while broad mites are most active during high temperatures.

Whiteflies. The greenhouse whitefly and sweet potato whitefly can be important pests. Generally, these insects confines their activity to the warmth of the greenhouse. However when outdoor temperatures become favorable, they leave the greenhouse to infest suitable hosts outdoors.

Photo: Whiteflies on underside of leaf

Mining Insects

Leafminers. The larvae of this group feed within the leaves of plants. Females deposit eggs on the underside of leaves. On hatching, the maggots burrow between the upper and lower leaf surfaces and feed. Many leaves may have light green or white winding trails that eventually turn brown and die. The mature larva emerges through a slit in the leaf surface and enters a resting stage where it passes as a pupa in the soil. There are many species and lifecycles may vary a bit. Susceptible plants include Chrysanthemum, Dahlia, Dianthus, Salvia, Verbena, Delphinium, Gypsophila and Aconitum.

One method of controlling these pests is to pick off and destroy infested leaves and, in the fall to remove and destroy plant remains. Elimination of alternate weed hosts also helps reduce populations of leafminers in the field.

Photo: Leafminers

Boring Insects

The larval stage of some moths and beetles cause damage by boring into stems and other parts of plants and are known as borers. There are many borers that attack cut flowers. Stalk borers, burdock borer, iris borer, and European corn borer are common borers found in cut flowers. Flowers such as Aster, Dahlia, Iris, Monarda, Centaurea, Chrysanthemum, Delphinium, Rudbeckia, Alcea, Phlox and Salvia are all susceptible to borers. To help reduce borer populations, it is advisable to destroy old leaves and other debris in the fall or before hatching of the eggs in the spring.

Protecting Pollinators from Insecticides

Protecting pollinators, especially honey bees, from pesticide poisoning should be part of any pesticide program. To avoid killing bees, do not apply pesticides hazardous to bees during the blooming period.

Ideally, pesticides should be applied when there is no wind and when bees are not visiting plants in the area. The time and intensity of bee visitation to a given crop depends on the abundance and attractiveness of the bloom. In general, evening or early night applications are the least harmful to bees.

Dust formulations and microencapsulated pesticides are usually more hazardous to bees than sprays. Wettable powders often have a longer residual effect than emulsifiable concentrates. Ultra-low volume (ULV) formulations of some pesticides are much more toxic than regular sprays.

Table: Some pesticides labeled for insect and mite management for outdoor flower crops. Always read the label!

Common/Trade Name Aphids Beetles Borers Cater-pillars

Leaf-
miners

 Leaf-
hoppers		 Mites Plant Bugs Slugs Thrips Comments

abamectin
(Avid 0.15 EC, Quali-Pro Abamectin)

 x       x   x     x Labeled for many mites including broad mite and two-spotted spider mite. Translaminar activity that penetrates and remains inside plant tissue. Toxic to bees.
acephate
(Orthene TT&O)		 x x           x   x Spot test first to insure plant safety. Toxic to bees.
Acetamiprid (Tristar) x x   x x x       x Thorugh coverage important. Toxic to bees.

azadirachtin
1- Azatin XL,
2- Aza-Direct,
3- Ornazin 3%EC,
4- Molt-X

 x (1,2,3,4) x
(1,2,4)		   x
(1,2,3,4)		 x
(1,3,4)		 x
(1,2)		 x
( 2)		 x
(2)		   x
(1,2,3,4)		 Insect growth regulator for immature stages
Bacillus thuringiensis (BioBit HP, Deliver, Dipel Pro, Javelin WG)       x             Stomach poison that must be eaten by target insect to be effective. Insect stops feeding and dies 1-5 days later.
Beauvaria bassiana
1-BotaniGard
2-MycotrolO
 		 x
(1,2)		 x               x
(1,2)		 Contains a fungus that must contact the target pest. Do not tank mix with fungicides. Potentially harmful to bees.
bifenazate (Floramite)             x       For all life stages of two-spotted spider mite. Toxic to bees exposed to direct treatment.
Residues on treated foliage are not toxic to bees.
chlorpyrifos (Duraguard ME) x x   x x x x x   x Microencapsulated formulation. Toxic to bees.
bifenthrin (Talstar S, Menace GC) x x   x x x x x   x Thorough spray coverage needed.
cyfluthrin (Decathlon 20WP) x x       x   x   x Toxic to bees.
fluvalinte (Mavrik Aquaflow) x x   x   x x x   x Toxic to bees.
imidacloprid (Marathon II, Imida E-Pro 2F) x x   x x x       x Toxic to bees.
insecticidal soap (M-Pede)
 		 x     x   x x x   x Good coverage is needed. Works on contact.
methiocarb (Mesurol 75-W)             x   x x Toxic to bees.
spinosad (Conserve SC)   x   x x         x Toxic to bees.
fenpropathrin (Tame 2.4EC) x x     x x x       Highly toxic to bees.
permethrin (Perm-Up, Pounce 25 WP) x   x   x x   x   x See label for plant safety. Highly toxic to bees.
petroleum (Ultra-Pure Oil) x       x   x     x Contact pesticide.
pyridaben (Sanmite)             x       Toxic to bees.
pyrethrins (Pyrenone Crop Spray) x x   x x x   x   x Good coverage is needed.

References and Resources

updated 2013, reviewed 2015

Tina Smith
Extension Greenhouse Crops and Floriculture Program
University of Massachusetts