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Monday, May 23, 2011

Tobacco budworm update

Calls about tobacco budworm have begun in earnest this week, and the main questions I am hearing are "What is the difference between BeltTM(Bayer CropScience) and Coragen® (DuPont)?" and "I used BeltTM/Coragen®, how long should I wait before I decide if I need to treat again?"

First instar tobacco budworm larva in eastern North Carolina tobacco. Photo via Loren Fisher.

What is the difference between BeltTM and Coragen®?
BeltTM and Coragen® are two recently registered insecticides for use in tobacco against Lepidopteran (caterpillar) pests. Both these insecticides share a common, and novel, mode of action. They act on ryanodine receptors, which form calcium channels in muscle cells, and inhibit muscle contraction. The Insecticide Resistance Action Committee (IRAC) places both of these materials in Group 28 (ryanodine receptor modulators). In other words, BeltTM and Coragen® kill insects in the same way and using one following the other does not represent a rotation.

In our research trials over the last 3 years, BeltTM and Coragen® perform similarly to one another when applied as foliar treatments. They also perform similarly to the standard insecticide used for tobacco budworm control, Tracer (spinosad, Dow AgroSciences). The key difference between BeltTM and Coragen® is the potential in-plant movement of the latter. Coragen® is xylem mobile, which means that it moves in the plants water channels when applied to the soil. Coragen® has a transplant water label in tobacco, but our data on the efficacy of this application method is limited.

I used BeltTM/Coragen®, how long should I wait before I decide if I need to treat again?
Both BeltTM and Coragen® slow or stop feeding quickly. However, larvae may appear alive, but sickly (or moribund) for up to 4 days after treatment. Another insecticide application should not be made until sufficient time has passed to allow for the insecticide to work. If another treatment is considered necessary, growers should be sure to rotate to another mode of action.

As always, when I discuss treatment thresholds (10% infestation) for tobacco budworm, it is important to understand that these thresholds are very conservative, meaning that yield loss has rarely been documented due to budworm feeding, even at much higher infestation rates than 10%.

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