Insects – Greenhouse Pests
Crickets (many species) seek out the shelter of tobacco greenhouses to overwinter as adults and may also feed on seedlings. Cricket feeding results in large, ragged holes.
Red imported fire ants (RIFA, Solenopsis invicta) are a common presence in crop fields throughout North Carolina but are typically thought of more as human pests, not crop pests. On occasion, RIFA can become a pest in tobacco greenhouses, feeding on seeds. RIFA is attracted to greenhouses as they search for warmth and water sources in winter and spring. If RIFA establish in areas near greenhouses, treatment with baits is advised. One bait is labeled for use in crop land (Extinguish, (S)-Methoprene). RIFA baits should be applied when ants are foraging. Check for foraging using the “potato chip test”. Place a potato chip or other salty snack near mounds. If ants have found this food source within 30 minutes, it is a good time to treat, if not, treatments should be made on a more favorable day. Because baits act against developing ants and can eventually eliminate colonies, they take several weeks to reach full effectiveness. In some cases, mound treatments may also be necessary.
Read more about the two-step method for fire ant management.
Slugs are attracted to the warm, wet environment of tobacco greenhouses. Slug feeding results in irregular holes in leaves and associated slime trials. Slugs are active at night and may not be readily detected during daytime observation. To determine if slugs are still present, and therefore require treatment, shallow bowls or plates baited with beer can be placed in greenhouses. Slugs are attracted to and drown in the beer. If slugs are present in greenhouses, they can be best treated with baits. Both conventional and organic baits are available for use in tobacco.
Occasionally vertebrates may become pests of tobacco in greenhouses. If arthropods are ruled out, it is worth trapping for mice and rats to determine if these are responsible for damage observed.
Thresholds and Management
If an adequate supply of transplants is threatened, treatment may be justified. Keeping greenhouses clear of debris which shelter insects will minimize their populations. Sealing greenhouses well during summer and allowing them the to heat will kill insects present from spring.
Few insecticides are registered for use in tobacco greenhouses, but broad spectrum materials are effective against foliar feeding insects. Bait materials are available for slugs and fire ants and are the most effective options for these pests.
See the North Carolina Agricultural Chemicals Manual for registered materials and use recommendations.