Last month, I posted about the potential for greater and more usual insect activity in tobacco greenhouses due to our warm winter and relatively mild spring. Spring has become less mild in the last few days, but interesting insects are cropping up in tobacco greenhouses in eastern North Carolina. Two unusual insect issues appeared recently in Wilson County.
Distinctive tobacco splitworm mines were found in two tobacco greenhouses in Wilson County in the last two day, along with what appear to be splitworm pupae. Neither of these greenhouses were near potato fields or gardens with potatoes, which are common early season hosts of tobacco splitworm (known as potato tuber moth when feeding on potato). They were, however, near weedy area or areas were weeds had recently been killed. Tobacco spitworm will also feed on horsenettle, nightshade, and other related weeds, so it is possible that the insects in the greenhouse migrated in from these areas. Damage was limited, but early splitworm activity in tobacco is of concern because these insects can increase their populations rapidly. This is a scenario where transplant insecticide applications may make sense if damage continues.
Splitworm damage is relatively easy to diagnose–if you see larvae present nothing else in tobacco looks like their leaf-mining feeding injury. The second type of injury Norman Harrell noticed was more surprising, and at first, more confusing. While visiting a tobacco greenhouse to out of concern for pythium root rot, Norman and the grower noticed several dead caterpillars in the float bed water.
David Stephan at the NCSU Plant Disease and Insect Clinic confirmed that these larvae were black cutworms, which are occasional post transplant field pests in tobacco. Upon closer inspection, they found a few trays with plants characteristically cut near the soil line. It appears that the larvae were moving downward in search of a place to pupate and drowned. Damage in this tobacco greenhouse was also limited, but early cutworm activity may translate to the field, so growers should be prepared to scout for damage following transplant. Cutworm damage typically begins on field edges and moves inward, and injury greater than 10% could result in economically significant losses and should trigger treatment. I generally do not recommend preventive treatment for tobacco cutworm because they are relatively uncommon and preventative treatments have a limited longevity.
I’d love to hear any additional reports of unusual insect activity in tobacco greenhouse and as we move into transplant. Keep your eyes peeled!