Some tobacco transplant buyers have indicated that they will no longer permit any acephate applications to tobacco that they intend to purchase under contract. Acephate, sold as Orthene and under other generic brand names, is an older organophosphate insecticide and has been an important tool in managing tobacco aphid, cutworms, and flea beetles in greenhouses and fields. As a result, tobacco growers are scrambling to find alternatives for insect control, particularly in greenhouse float systems.
Tobacco aphids (Figure 1) reproduce rapidly, both in fields and greenhouses through asexual reproduction. There are no male tobacco aphids; each female gives live birth to more females. This, combined with a short generation time, can result in rapid aphid buildup. However, aphid problems are much less common on younger transplants until a week or so before transplanting.
For aphid problems that develop late, tray-drench applications with a neonicitinoid (Admire, Platinum, or generics) made 5 days before transplanting will effectively manage aphids on transplants.
There are limited alternatives to control aphids in greenhouses in the weeks prior to transplanting. Selective materials for greenhouse use include insecticidal soap or azadirachtin. Insecticidal soap has worked well on tobacco transplants in greenhouses in North Carolina where growers are using it to spot spray individual infested trays or hot spots. A re-treatment may be needed 5 to 7 days later. Since these materials are applied as foliar sprays, excellent coverage underneath leaves is critical to successful control.
Some neonicitinoid products are labeled for foliar application; however, this is not recommended in tobacco float systems due to concerns of potential phytotoxicity when applied to smaller plants more than 5 days before transplanting.
Variegated cutworms are an occasional pest of tobacco in float systems. Cutworm injury in float beds first appears as clusters of missing or damaged plants (Figure 2), often in roughly circular patterns. Cutworms are typically active at night and burrow into the soil during the day, but can they occasionally be found on the plants early in the morning.
Cutworms can be controlled with foliar applications of Bt insecticides (Dipel, etc.), but these are only effective against relatively small cutworms.
Both insecticidal soaps and Bt insecticides have relatively short residual activity and thus would be best used for controlling emerging insect problems. Effective use will require frequent scouting of float beds to detect and treat problems early, and follow-up treatments may be required 5 to 7 days after the initial treatment.
Ric Bessin, Extension Entomologist and Bob Pearce, Extension Tobacco Specialist