Scouting for Tobacco Splitworm
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Collapse ▲When to scout for tobacco splitworm
Tobacco splitworm infestations can occasionally develop post transplant, particularly in areas where white potatoes, another host of this small caterpillar, are grown. However, splitworm infestations are most common and problematic when they develop post topping, near harvest. Tobacco splitworms may have 2 to 3 generations per year in commercial tobacco. A small, typically not economically significant generation can occur in mid summer, just following topping. Fields where this midsummer generation is observed are at risk for damage near harvest and should be carefully scouted for the rest of the season. Fields where the midsummer splitworm generation is not observed are rarely at risk for harvest period damage and additional scouting is not necessary.
What part of the plant to scout for tobacco splitworms
Early season tobacco splitworm larvae may feed throughout the entire plant. Mid- and late-season tobacco splitworm larvae feed on the lower 1/3 of plant unless leaves have been harvested. Following harvest, larvae may feed on the lowest stalk leaf available. Therefore, if you are determining if a field is at risk for harvest period damage, observe the lower 1/3 of plants for the month following topping.
How to scout for tobacco splitworm
Tobacco splitworm larvae are leaf miners and create yellow to brown “blotch mines” in leaves.
Tobacco leaf with several splitworm mines containing live larvae, circled. Photo: Hannah Burrack
Mines remain on leaves even after tobacco splitworm larvae have left them, so when scouting is important to determine if a mine contains a live larvae or is old. Tear open the mine and check for a small cream, tan, or pinkish caterpillar. Mines may also contain brown “frass” or insect droppings, which can resemble soil or loose cigarette tobacco.
Tobacco splitworm larvae in opened mine. Photo: Hannah Burrack
Mines may darken and tear open after larvae develop, and leaves many contain a mixture of active mines containing live larvae and old mines.
Splitworm feeding creates brown or yellow mines in the leaves. This damage can accumulate on leaves over the course of a season. Photo: Hannah Burrack.
Tobacco splitworm thresholds
There is no research-based economic threshold for tobacco splitworms, but if 10% or more of plants are infested with ten or more mines treatment may be justified. Few, if any, insecticides are effective against tobacco splitworm larvae, and timely harvest may be the more effective means of curtailing an infestation.