I have been getting lots of questions about what our exceptionally warm spring weather means for tobacco pest management. I’ll have another post next week addressing the impact of warm winter weather and spring rain on thrips and tomato spot wilt virus (TSWV) incidence. Before we transplant, however, the key insect management questions I get center around pests in greenhouses, and if any year is going to result in potentially damaging insect populations in greenhouses, this is it.
This week, I had two phone calls about chewing injury in tobacco greenhouses. It’s very difficult to determine what insect or other pest is the cause of this type of damage unless you can find them in the act. The most likely suspects for chewing injury in the greenhouse are:
Crickets - Cricket feeding leaves ragged holes and will often be localized along edges of beds or outside walls. Cricket populations can be minimized by eliminating places they can hide (debris, soil bags, empty trays, etc). Crickets are active at night, so areas with injury should be observed at night to determine if crickets are present.
Slugs - Slug feeding appears similar to to cricket feeding, and slugs are also active at night. Slugs will leave distinctive “slime” trails near their feeding area. Slugs are attracted to alcohol and can be trapped in shallow bowls or plates filled with beer (use the cheap stuff).
Caterpillars – Many generalist caterpillars may feed on tobacco seedlings, but they are rarely active this early in the year. This spring, however, many caterpillars are out and about and may feed on tobacco. Caterpillars may be both day active or nocturnal, but they will often stay on and near plants when not feeding. Barrel shaped “frass” (insect feces) are also distinctive of caterpillar feeding.
Several commonly found insects in greenhouses are not likely to be pests of tobacco, and it’s important to understand which are which.
Fungus gnats - Fungus gnat larvae feed on decaying plant material and are rarely pests. They are present in soil and can be distinguished by their dark heads and legless bodies. The large amount of water in tobacco greenhouses can attract and foster large populations of fungus gnats, which will complete more generations with our warm weather. In the rare event that fungus gnat larvae do damage plants, their feeding would occur on roots, not leaves, and adult fungus gnats do not feed on plants.
Unusual weather can often result in unusual pests, so please don’t hesitate to contact me or your county extension agent if unexpected creatures begin to appear in your greenhouse. We want to know!