Beneficial Insects, Limited Insecticide Use

Urged for Second Generation Tobacco Budworms

Jack Bacheler, Extension Entomologist

North Carolina State University

 One of the more perplexing insect problems confronted by mostly southern North Carolina cotton producers at this time of year is effectively managing early season (second generation) tobacco budworms. In some years, 15 to 25% of the state's cotton acreage must be treated for this generation (for example, 1990 and 1993), while in other years (1991, 92, 94 and 95), treated acreage is as low as 5-8%. Only 0.5% of our acreage was treated for early budworms in 1997. In addition to this variability in population levels, the relationship between June (or early July in some cases) square loss, maturity delays and yield loss often seems to defy common sense. Research conducted here and in South Carolina consistently suggests that cotton plants compensate for moderate to even high square loss prior to bloom. Finally, with pyrethroid resistance by tobacco budworms now confirmed in Georgia for the past two years, the merits and penalties of using pyrethroids against early tobacco budworms must be weighed carefully. Let's look at a few options in managing these early budworms and bollworms:

Non-pyrethroid larvicides - Although most non-pyrethroids (Tracer discussed separately below) have some advantages over pyrethroids in certain situations (armyworm activity, control of some secondary pests and in resistance management programs), their lower efficacy against budworms and bollworms, their higher costs, high effective use rates and probable greater treatment frequency (typically, the higher a compound's efficacy, the longer a producer can afford to wait to see if beneficial insects will lower or hold budworm populations to sub-economic levels) renders these materials less desirable than pyrethroids in areas where pyrethroid resistance has not been found, if treatment of early populations and pyrethroid use in general remain low. Additionally, in situations where pyrethroids, carbamates and organophosphates happen to share the same mode of action for resistance, the use of the above non-pyrethroids may also contribute to the development of tobacco budworm resistance to the pyrethroids.

Research here has shown that Tracer, even at the low 0.45 lb. active/acre rate, is as active as pyrethroids at their standard industry rates against June budworms. Tracer, a fungus-derived compound of the naturalite insecticide class has looked very promising against second generation budworms in North Carolina at these low rates in initial testing. Additionally, Tracer spares most beneficials. Although somewhat pricy at the 'industry standard' rate of 0.067 lb. active/acre (approximately $12/acre), the effective 0.045 rate for early budworms, if banded, puts this product at a more reasonable cost of just under $4/acre. Our (and other) data so far suggest that Tracer will likely provide a good alternative to pyrethroids for controlling this generation of budworms and should probably be regarded as the material of choice.

Pyrethroids - If used with restraint, pyrethroids still offer North Carolina cotton growers a realistic option for profitably controlling our early tobacco budworms and bollworms, subject to the following:

1) Growers are advised to use the 1998 higher June thresholds of 15% budworms in terminals, or 8% live budworms on squares, and not respond to this generation on the basis of egg numbers. Following this threshold should result in very limited cotton acreage in North Carolina being treated with any insecticide for June budworms.

2) A single pyrethroid application is recommended for this generation.

3) Producers should keep abreast of pyrethroid resistance expansion in Georgia or into South Carolina.

For managing budworms in the June to early July time frame, utilization of beneficial insects, following higher thresholds and the sparing use of Tracer or a pyrethroid will help sustain North Carolina's cotton producers' ability to inexpensively and effectively manage budworms over an extended period of time.