North Carolina Tobacco: What Foliar Insecticides Are Recommended for 2017?

The insecticide toolbox in tobacco has changed significantly during the past year. As many growers and extension personnel are aware, registration for the active ingredient flubendiamide was canceled due to concerns about non target effects on aquatic invertebrates.

The Environmental Protection Agency proposed cancellation in March 2016, and following a failed appeal of the cancellation, it went into effect at the end of July.

Flubendiamide was labeled as Belt in tobacco, and marketed by Bayer CropSciences. This cancellation is particularly significant for tobacco because Belt was one of the most commonly used foliar insecticides, applied to a reported 46% of acres grown during 2015.

Belt was used so extensively because it was highly effective against tobacco budworm, which are particularly hard to control with insecticides (see Table 2, below). Belt was also effective against hornworms, the most significant post topping foliar pest in tobacco.

Belt was one of two Group 28 insecticides that were registered in tobacco, the other is Coragen, containing the active ingredient chlorantraniliprole, which is still registered. Insecticides with this mode of action act on insect muscle cells and stop insect feeding quickly, but generally have “low” mammalian toxicity (LC50 values of >5000 mg/kg in test animals).

In the absence of Belt, we need to revise our recommendations for tobacco budworm and hornworm control. There are a number of other effective insecticides registered in tobacco. However, there are constraints limiting the utility of a number of these materials.

Table 1. Insecticides labeled in tobacco with activity against tobacco budworm and hornworms.

The two most significant constraints on Belt alternatives are long pre harvest intervals (Group 3A materials such as Besiege, Brigade, Karate, and Warrior cannot be used after layby) and tobacco purchaser concerns about pesticide residues (see Table 1, last column).

Issues of pesticide residues in tobacco are complicated and beyond the control of farmers, so for the purposes of grower recommendations, we try to avoid recommending materials for which purchasers have indicated that they are concerned about residues.

Of course, the most important consideration when recommending an insecticide is efficacy. In order to compare efficacy of Belt alternatives over time, we calculated the average percent control in field efficacy trials, as compared to an untreated control, from 2009 through 2014.

Table 2. Relative efficacy of insecticides against tobacco budworm, 2009-2014. Brigade was not included in trials during this period, but one trial included Capture LFR, a different bifenthrin formulation. Bt, Karate, Warrior, and Orthene were not included in efficacy trials during this time period.

Taking into account residue concerns, pre harvest application constraints, and efficacy, Blackhawk, and perhaps Denim (although it was screened only in a limited number of trials), appear to be essentially the only foliar applied materials we can widely recommend for tobacco budworm.

Coragen foliar treatments are also highly effective against budworms, but at this time, at least one purchaser has raised concerns about residues. Transplant water applications of Coragen are effective against tobacco budworm only if infestations occur during the period which they are active, 4 to 6 weeks after transplant.

This is inconsistently the case in North Carolina, although transplant applications of Coragen have produced higher efficacy in Georgia and South Carolina and may be quite effective against hornworms.