Alternative control methods


Weeds may harbor aphids both inside and outside the greenhouse. Pull weeds or use commercially available herbicides; use barriers to prevent weed growth.

Insect screens

Screens on vents and doors will help prevent aphids from getting into the greenhouse, but often the most effective screens reduce air flow. The maximum hole size to exclude cotton aphid is 341 |j (micrometers). Be sure to screen the greenhouse before the crop growing season, when the potential for aphid problems is still low.

Host plant cultivar

Aphids feed preferentially or reproduce at different rates on different cul-tivars of chrysanthemum. In one experiment, for example, 40 times more green peach aphids were found on the cultivar Tuneful than on Portrait. Green peach aphids were found to reproduce much faster on Tuneful than on Golden Princess Anne.

Chemical control Localized infestations and high populations that need to be reduced before predator or parasite introduction can be spot-sprayed with selective chemicals. Insecticidal soap can effectively control aphids, but should be used only if no predators, including predatory mites, or adult parasites are present because it will affect exposed natural enemies. Once the soap is dry, however, it is nontoxic.Thorough coverage of infested surfaces is essential,and more than one application may be required.

Horticultural oils, both refined petroleum distillate products and those made from vegetable oils, can kill aphids and other insects.These horticultural oils may be toxic to some plants. Many brands are registered for use on vegetables and ornamentals in greenhouses to control many pests, including aphids.

Pyrethrins are insecticides derived from the flowers of the pyrethrum daisy, Chrysanthemum cinerariaefolium. They are extremely fast-acting and cause immediate knockdown, but most insects can recover after a brief period of paralysis. Other ingredients can be added to prevent this recovery. Most pyrethrin products are sold commercially as a premix with rotenone,with piperonyl butoxide, or with piperonyl butoxide and diatomaceous earth.

Kinoprene is an insect growth regulator registered for use on ornamentals for control of aphids and other insects. It can be used when aphid mummies or predators are present. It has minimal activity on natural enemies but may damage some plants. Some rose varieties show delayed damage.

Azadirachtin is another insect growth regulator that can be used in rotation with kinoprene, although it generally acts as a feeding deterrent for aphids. This is a commercial formulation of an extract from the seeds of the neem tree (Azadirachta indica). Several formulations are registered for use on greenhouse ornamentals and vegetables.

Available natural enemies and their potential for control

Bacillus thuringien-sis (Bt) can be very effective against young caterpillars, but other natural enemies are of limited value.

Order Lepidoptera: Butterflies, moths, and skippers

Family Noctuidae: Owlet moths and underwings

Beet armyworm, Spodoptera exigua

Black cutworm, Agrotis ipsilon

Variegated cutworm,

Peridroma saucia

Cabbage looper, Trichoplusia ni

Corn earworm or tomato fruitworm, Helicoverpa zea

Family Pyralidae: Pyralid,grass, and wax moths

European corn borer,

Ostrinia nubilalis

The larval, or caterpillar, stages of several moths are occasional pests of many greenhouse crops, especially in summer when lights inside the greenhouse attract moths at night from outside through open vents. Beet army-worms are common on carnation, chrysanthemum, cyclamen, geranium, snapdragon, and other crops. Cabbage loopers are particularly damaging on carnation, chrysanthemum, geranium, nasturtium, and crucifer sets. Corn earworms prefer the buds of chrysanthemum,gladiolus,and rose,as well as small tomato fruits. European corn borers tunnel into the stems of plants, particularly chrysanthemum and dahlia. Variegated cutworm, a climbing species, is one of the most common species on ornamentals and often causes damage to tomatoes, carnations, and chrysanthemums. Black cutworms damage seedlings, vegetables, and flower crops. Many other species of cutworms, loopers, or other caterpillars may occasionally infest greenhouse crops.


Caterpillars chew off pieces of foliage and leave plants ragged in appearance. Some species also feed directly on flowers or fruit, which is often when people first notice the infestation. Foliage losses usually matter less than damage to buds. Damaged buds don't produce flowers but axillary shoots instead. Shoots tunneled into by European corn borers wilt and do not produce flowers.

Description and life cycle

The female moths, which are nocturnal, lay eggs on plants or other surfaces in the greenhouse.The caterpillars that hatch from these eggs feed on the underside of the leaf for several days, often leaving the upper leaf surface intact. As they grow larger they eat through the whole leaf and may feed on fruits or flowers. Caterpillars often feed at night or on cloudy days and hide during the day at the base of the plant or in camouflaged positions along midribs, leaf edges, or petioles. Caterpillars of noctuid moths can reach 2 inches (5 cm) in length.The different species vary in color.They all pupate on or just under the soil surface.

The grayish brown beet armyworm moths are about 3/4 inch (2 cm) long. Females lay 100-150 eggs in small piles on the undersides of lower leaves.The smooth, green caterpillars have a wide black stripe down each side and grow to 1V8 inches (3 cm) long. After about 2 weeks they pupate in a loose cell on the medium surface.

Black cutworm adults are dark red to blackish-brown in color, with indistinct dark markings on the wings. The females lay eggs singly or in small groups on leaves or stems. The greasy-appearing larvae are gray to black along their back and pale underneath.They grow to 11/4-13/4 inches (3.0-4.5 cm) long.They pupate under debris on the medium surface.

The adult variegated cutworm has a wingspan of about 11/2 inches (4 cm). The wings are a mottled dark gray with a purplish tint and two indistinct spots in the upper middle of each wing.The eggs are laid in clusters of 200-500 on the undersides of leaves.The caterpillars are gray or brown with blotchy gray and black markings and a row of pale, small, almost diamond-shaped spots along the sides.They grow up to 13/4 inches (4.5 cm) long.They pupate in the soil.

The 1-inch (2.5-cm) cabbage looper moths are mottled dark-brown and have a silvery figure 8 on each forewing.They lay round, white eggs singly or in small groups on the undersides of leaves.The caterpillars are light-green with faint white stripes down each side, and they taper from the tail toward the head, so the rear is fatter than the front.They grow up to 11/2 inches (4 cm) long.The caterpillars move with a characteristic looping motion produced by holding on with the front legs and arching the middle portion of the body to bring the prolegs (hind legs) forward, then extending the front of the body while holding on with the prolegs. Pupation occurs in a loosely woven cocoon attached by one side to a plant leaf.

Corn earworm moths vary considerably in color and markings, from tawny with faint markings to reddish-brown with heavier markings.The 3/4-inch (2 cm) females lay 500-1000 eggs singly on foliage.The caterpillars grow to 11/3 inch (3.5 cm) long and are highly variable in color—red, maroon, orange, yellow, green, and nearly black—with a yellow head and alternating dark and light stripes along the length of the body. They bore into the soil to pupate.

Female European corn borer moths are about 3/4 inch (2 cm) long, vary in color from yellow to light-brown, and have two zigzag lines across the outer parts of their wings. Males are slightly smaller and light-brown with yellow zigzag lines. Females lay 400-500 eggs in masses of 15-20, with the flat eggs overlapping each other like fish scales.The eggs are white when first laid but turn darker just before hatching.The caterpillars grow to 1 inch (2.5 cm) long and range in color from light brown to dark brown to pink or gray, always with a dark head and an indistinct stripe on the back.They pupate within flimsy cocoons inside tunnels in stems, or in other protected locations.


Moths are often attracted to a greenhouse's production or security lights, then enter through openings and proceed to lay eggs. Adult populations can be detected—and low numbers controlled—with blacklights or, for some species, pheromone traps.Small green fecal pellets near chewed foliage often indicate a caterpillar attack. Search plants for egg masses or young caterpillars when moths are caught in traps. These pests may also be brought into a greenhouse as eggs or young caterpillars on cuttings, so new shipments should be carefully inspected.

Natural enemies

Numerous parasites and many predators attack caterpillars, but few are suitable for control in greenhouses. Of the many nematodes, viruses,and bacteria that are used commercially for control of caterpillars, only one bacterium is useful on greenhouse crops.


Trichogramma spp. Trichogramma wasps attack the eggs of over 200 species of moths and butterflies.These almost microscopic wasps (1/64 inch, 0.5 mm) are very important in preventing crop damage because they kill their hosts before the insects can cause plant damage.The female Trichogramma lays an egg into a recently laid host egg. As the wasp larva develops, the host egg is killed and turns black. Each female parasitizes about 100 eggs.The wasp's short life cycle of 8-10 days allows their population to increase rapidly.These wasps are harmless to people, animals, and plants.There are many commercially available species, such as T.pretiosum, T. minutum, and T.platneri.


Many general predators will feed on caterpillars or their eggs. Larvae of the commercially available green lacewings Chrysoperla (=Chrysopa) carnea and Chrysoperla rufilabris are voracious predators that will feed on moth eggs and very small caterpillars. (See "Aphids"for more information.) Lady beetles and minute pirate bugs may also feed on eggs or small caterpillars if other prey is not available.

Trichogramma minutum wasps have a short life cycle allowing their population to increase rapidly.


Bacillus thuringiensis. This pathogen, commonly known as Bt, is a naturally occurring, soil-inhabiting bacterium that is highly selective and active mainly against caterpillars.There are many types of Bt and they differ both in specificity to and potency against a range of target insect species. Only two varieties are toxic to insects other than caterpillars: one affects the larvae of mosquitoes, blackflies, and some other types of flies; the other affects certain beetles. The varieties kurstaki and aizawi are available in commercial formulations for control of caterpillars.This bacterium is nonpolluting and safe to humans.

During sporulation Bt forms a parasporal body, or crystal, which is the source of its insecticidal properties.The crystals dissolve in the gut juices of susceptible insects and release toxic compounds. Later the spores germinate, and bacteria grow in the insect body.The first observable reaction after a caterpillar ingests Bt is paralysis of the gut and mouthparts, followed by cessation of feeding. Paralysis may happen in a matter of minutes, but death usually takes 30 minutes to 3 days following ingestion. Bt is available in several commercial formulations.

Possibilities for effective biological control

Bt can provide good control of the most common greenhouse caterpillar pests. However, Bt does not provide persistent control under greenhouse conditions because it does not disperse well enough and breaks down rapidly in ultraviolet light. It must be applied whenever pest populations develop and in a manner similar to conventional insecticides. Applications should not be made on a regular schedule, but should be timed based on the occurrence of eggs or caterpillars on the plants. Monitor moth flights to determine when to begin scouting for eggs. Because Bt must be eaten to be effective, apply it where the target insects are feeding. If infestations are localized, make spot applications. Bt is not effective against caterpillars feeding within plant tissues—for instance, inside stems, buds or nests of webbed leaves. Bt is more effective against earlier instars than later instars.

Caterpillars &

Enemies egg -caterpillar- pupa adult

Trichogramma spp. Predators

Bacillus thuringiensis

™ Natural enemy attacks the host * Effectiveness depends on species of enemy Width of bar indicates degree of effectiveness

Trichogramma wasps provide good control of certain species of caterpillars in outdoor crop systems. In most greenhouses, caterpillar infestations are sporadic and minimal. Under these conditions egg parasites are not very effective, and spot applications of Bt would be more efficient. However, if large caterpillar infestations occur regularly, Trichogramma released at the first sign of moth flight through peak egg laying can provide control. Regular scouting to detect the appearance of caterpillar eggs is necessary to determine when wasps should be released so the appropriate stage will be available to maximize Trichogramma effectiveness. Most suppliers of Trichogramma can make recommendations about the species and number of wasps to release. Rates should be determined on an individual basis.

The wasps are shipped as immatures inside moth eggs glued to small cards that can be attached by hand to infested plants. Keep the cards in a warm, humid place out of direct sunlight until the emerging adults can be seen as small dots moving around in the closed container. A few tiny worms may also be found in the container because it is very difficult to obtain 100% parasitization of the moth eggs, but these worms are harmless to plants.When most of the adults have emerged, place the opened containers in a shaded spot in areas where you suspect moths are laying eggs.The adult wasps will fly onto the plants in search of new host eggs to attack. Do not put the cards out before the wasps start to emerge from the moth eggs because ants and other predators may eat them.The best time to make releases is early morning or evening when direct sunlight will not hit the cards. Avoid making releases when the temperature is above 85°F.

Alternative control methods


Numerous plants can serve as reservoirs for beet armyworms or other caterpillars. Remove weeds that can be alternate hosts for these caterpillars from inside and outside the greenhouse. Sterilize new soil that may contain cutworm eggs, larvae, or pupae before bringing it into the greenhouse. Check new plant material entering the greenhouse for eggs or larvae and treat or quarantine any that are infested.

Insect screens

Screens on vents and side walls will prevent moths from getting into the greenhouse.

Hand picking

Frequent plant inspections and removal of all visible caterpillars may be impractical for large plantings, but is an option for small or spotty infestations. Inspect plants thoroughly to catch eggs and newly hatched caterpillars or those that may have escaped earlier detection.


Cutworms are attracted to bran baits. One recipe from the 1930s suggested moistening 12 pounds of bran with a mixture of 1 pint molasses, 1 ounce banana oil (amyl acetate), and an insecticide in about 1 gallon of water. Spread the poisoned bait late in the day so it will be fresh when the cutworms come out to feed.

Chemical control

Spinosad is an insecticide derived from natural metabolites produced under fermentation conditions by the actinomycete Saccharopolyspora spinosa.It has a high level of contact and oral activity and rapid speed of action. It is especially effective against caterpillars, leafminers, and thrips, but has low to moderate impact on beneficials. It is registered for control of many pests on landscape ornamentals; check with your chemical supplier on availability for use on greenhouse ornamentals.

Green lacewing larvae can provide quick control of small, localized infestations. They prefer to feed on aphids, so their effectiveness will be limited if aphids are present.Where caterpillar eggs are present, releases should be made as described in the "Aphids" section.

Available natural enemies and their potential for control

Nematodes, Bacillus thuringiensis (Bt), and predatory mites can provide excellent control of fungus gnats.

Order Diptera: Flies

Family Sciaridae: Darkwinged fungus gnats

Family Ephydridae: Shore flies

Fungus gnats, Bradysia impatiens and B.coprophila

Shore flies, Scatella stagnalis

Fungus gnats and shore flies, although only distantly related, both occur in the same environmental conditions. Both are nuisances, but only fungus gnat larvae injure plants directly, feeding on a variety of plants and on cultivated mushrooms.


Fungus gnat larvae usually feed on soil fungi,algae,and decaying organic matter. However, when populations are high, they may feed on root hairs and tunnel into roots and stems just under the soil surface. Affected plants may turn yellow, appear stunted, or wilt during the day under severe attacks. Cuttings, prior to setting callus tissue, and tender root systems of young seedlings are most susceptible to feeding injury by fungus gnat larvae. Plants may eventually die.In addition,adult fungus gnats deposit fecal droppings on plants that may reduce the aesthetic quality of the crop.The adults often get trapped in surface moisture on leaves, making plants less salable because they look "buggy."

Shore flies are algae feeders and do not normally damage plant material directly, although larvae will feed on roots infected with fungi. Black drops of excrement deposited by the flies on leaves can make the plant less attractive.

Both shore flies and fungus gnats can transmit some fungal diseases, including Botrytis, Fusarium, Phoma,Pythium, and Thielaviopsis basicola when they are larvae, and Pythium, Fusarium, and Verticillium when they are adults.

Description and life cycle

Adult fungus gnats are 3/16 inch (4-5 mm), dark brown to black flies that rest on the potting medium or plants. The delicate adults are thin with long legs and antennae.They run rapidly and are weak fliers.The wings have a distinct Y shape in the middle. Females lay clusters of 2-30 eggs on moist medium surfaces, producing a total of 100-300 small white eggs during a 7-10 day life span.The larvae are slender maggots that have a distinct black head and a transparent white body that is 1/4 inch (6-7 mm) long by the third and final instar.They live on or near the surface of the medium.The larvae feed for 5-14 days, then pupate in the soil and emerge as adults about a week later. Fungus gnats are most prevalent in wet soil mixes that are high in organic matter and new media that are micro-bially active.

Shore fly adults are about the same size as fungus gnats, but are darker and more robust, with short legs and antennae.They breed in algae and standing water or water-soaked areas in the greenhouse. Females scatter eggs on moist soil or algae.The larvae that hatch in 2-3 days live just below the soil surface, feeding on bacteria,yeasts, and algae for 3-6 days.The adults emerge after a 4-5 day pupal period and feed on algae.


Yellow sticky cards or stakes are very effective in monitoring adult fungus gnat populations. Blue sticky traps may be more attractive to shore fly adults than yellow cards. See "Whiteflies"for more detailed instructions.

Potato wedges cut into 1/4-inch sections and placed into the growing medium surface can be used to monitor fungus gnat larval populations. Leave the potato pieces on the medium for 72-96 hours. Fungus gnat larvae feeding on the exposed potato surface can be counted.

Natural enemies

Several natural enemies attack the larvae of fungus gnats and shore flies. A naturally occurring diapriid wasp para-sitoid attacks fungus gnats in British Columbia, but little is known about it or any other parasitoids. A few predators and many pathogens, including bacteria, fungi, and nematodes, attack fungus gnat or shore fly larvae in the soil. Only a few have been examined and are useful for control of these pests in greenhouses.


Hypoaspis (=Geolaelaps) miles. This laelapid mite is a native American soil dweller that feeds on many soil-inhabiting arthropods, including fungus gnat larvae. It is an aggressive predator that attacks individuals many times its size. The brown adult females are about 1/25 inch (1 mm) long; males are much smaller. Adults consume one to five fungus gnat larvae daily, killing more small prey than large prey.When insects are scarce,H. miles can survive by scavenging on algae and plant debris. Females deposit one to three eggs per day.Nonfeeding,six-legged larvae hatch in 2-3 days; they molt into eight-legged nymphs within about a day.This stage lasts 4-5 days, during which the nymphs consume 16-33 young fungus gnat larvae. All stages of the mite are found in the top inch of the soil or potting medium, and prefer moist soil with an open structure.They become inactive below 59°F, but do not diapause in the winter.H. miles is offered commercially.


Bacillus thuringiensis var. israelensis.

There are many types of the naturally occurring Bacillus thuringiensis,a soil-inhabiting bacterium commonly called Bt.The types differ both in specificity and potency against a range of target insect species. Most are highly selective and active against caterpillars (the larvae of butterflies and moths), but the variety israelensis (Bti) is toxic to the larvae of fungus gnats, mosquitoes, blackflies,and some other types of flies. Fungus gnat larvae stop feeding and become limp within 24 hours of ingesting Bti. After 2 days the larvae disintegrate. Bti is more effective against earlier instars than later instars.This bacterium is commercially available as a microbial insecticide. See "Caterpillars" for more information on Bt.

The soil-dwelling laelapid mite Hypoaspis miles.

1 k V

0 0

Post a comment