Greenhouse Insect and Mite Pest Management
Insect and Mite Pests Commonly Found in Greenhouses
Caterpillars
Caterpillars are, collectively, the larvae of moths and butterflies which are members of the order Lepidoptera. Caterpillars are varied in name as some are called loopers or worms (i.e., cabbage loopers, hornworms and inchworms), some are actually soil pests such as cutworms, while other are called borers, but one fact remains that they are always moth or butterfly larvae and can be extremely destructive (See Figure 27.2). These insects are only damaging in the immature larval stage; the adults either do not feed or feed only on nectar. Adult moths can be attracted to the greenhouse by lights and fly in from the outdoors to lay their eggs.
Life Cycle
Because there are so many caterpillar species, it is difficult to generalize about their life cycles. Some species lay eggs on the plants; others lay eggs on the soil. Some caterpillars prefer to hide in the soil during daylight and emerge to feed only at night; others remain on the plants always; and still others fold leaves around themselves for protection.
Types of Damage
Most caterpillars cause damage by eating plant parts including foliage and flowers; either consuming the entire leaf or leaving the mid-vein. For instance, the preference of some species, such as the beet armyworm, for tender bud and shoot tissue can produce continued pruning of a crop such as chrysanthemums and ruin its value for cut flowers.
Monitoring
Visually inspecting plants regularly when adults are flying will also avoid crop damage from caterpillar feeding. When scouting, be sure to check those plants nearest openings such as vents, doors, louvers, and sidewalls, because this is where adults may enter, especially those openings facing corn, soybean, or vegetable fields that are in decline or have been harvested.
Cultural Management Strategies
Ensure good sanitation of the greenhouse and its environs. Remove any weeds and plant debris that may serve as host to the caterpillars. Where applicable, it is advisable that you install insect netting in all ventilation openings to prevent adults from entering the greenhouse. In addition, repair any holes or damage in the plastic walls and/or roof material and use clean planting material and plants.
Biological Management Strategies
One of the most popular and effective controls for caterpillars is the egg parasitoid in the genus Trichogramma. These tiny wasps work by laying eggs (parasitizing) in the eggs of many destructive caterpillar pests. A new wasp will emerge from the parasitized egg. These mini-wasps have a rapid life cycle of about 7 to 10 days from egg to adult, so populations can increase rapidly.
Biorational Management Strategies
Microbials. Some caterpillars can be controlled by the biological control organism Bacillus thuringiensis (Btk) var. kurstaki. It is very effective but has to be applied when caterpillars are young. The active ingredient must be consumed in order to be effective and young caterpillars don’t have to consume as much material before they die; however, larger caterpillars must eat more material before the active ingredient inhibits feeding.
Chemical Management Strategies
Insecticides are directed primarily at the caterpillar stage. Most insecticides have contact activity only, so thorough coverage of all plant parts is essential. Systemic insecticides are generally less effective against caterpillars.
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