Avoid pyrethroids on early budworms

Unlike the case with bollworms, North Carolina cotton producers almost always fare better than their southern and Mid-South counterparts when it comes to both early- and late-season tobacco budworms on conventional cotton.

Second generation (often mid- to late-June or early-July) budworms are rarely an economic problem, even on our conventional cotton acreage.

In some years, however, when budworms eliminate most squares and terminals in scattered cotton fields, maturity delays and yield losses can occur. Although these early-June tobacco budworms in cotton are not considered a serious problem here, when treatable situations do arise, pyrethroids should still be avoided. It is imperative that pyrethroids be saved for our later, more damaging late-July and August budworm and bollworm generations, and are available as a cost-effective option for controlling green stink bugs.

For the past decade, an average of fewer than 5 percent of North Carolina's conventional cotton acreage was treated for this early budworm generation. One reason for the reluctance to treat is the low correlation between pre-bloom square loss vs. maturity delays and yield losses.

Square removal research conducted here and in South Carolina and Virginia consistently suggested that cotton plants can compensate for moderate to even high square loss prior to bloom.

Because of the increased tolerance of bollworms and tobacco budworms to pyrethroids in North Carolina, if our present threshold of 10 percent and 15 percent live worms on squares and in terminals, respectively, is reached, non-pyrethroid alternatives should be utilized for this generation.

A few options in managing these early budworms follow:

(1.) Biologicals and Ovicides — In concept, this ‘soft’ approach to managing June/ early-July budworms in conventional cotton is appealing. In reality an ovicide (Curacron, Lannate, Larvin, or pyrethroids at low rates, etc.) or a biological material such as a sprayable B.t. would likely translate into adopting much more protective thresholds and treating more cotton acreage, which often would have been protected solely by beneficial insects in our area.

In addition to plant compensation for June square loss, high mortality of small budworms in June is also commonly observed, particularly in terminals. This ‘soft’ approach would also probably require twice per week scouting and probably multiple applications to be effective.

(2.) Organophosphates and Carbamates — Although OP's and carbamate insecticides have some advantages over pyrethroids in certain situations (control of some secondary pests and in resistance management programs), their lower efficacy against budworms, their potential disruption of beneficial insects at caterpillar rates, and their 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 than an ideal choice for early budworm and bollworm control.

(3.) Pyrethroids — Pyrethroids, although inexpensive and moderately effective against this early budworm generation, should be limited for use against our economically damaging, major late-July to early-August bollworm generation(s). North Carolina producers growing non-Bt cotton can not afford to potentially squander this important chemical class to avoid minimal damage prior to bloom.

Though not predicted to occur any time soon, the loss of bollworm efficacy in Bt transgenic cotton lines, if it occurred, would significantly elevate the importance of this class of insecticides.

(4.) Tracer and Steward — Tracer, a fungus-derived compound of the naturalite insecticide class, and Steward, a nerve transmission blocker, and Denim have looked promising against second-generation budworms. Both products also spare most beneficials.

Although pricey at the their ‘industry standard’ rates (approximately $12 to $14 per acre), a June treatment could be banded, with the material cost reduced accordingly.

Additionally, lower rates are often effective against this early generation. These products should be regarded as the materials of choice if pre-bloom budworm thresholds have been met.

(4.) Non-treatment — In replicated tests conducted from 1993 though 2002 in southern North Carolina, pyrethroid treatments against different levels of budworms (budworm pressure varied from light to very high) and hand-removal of squares and terminals, resulted in no yield increases unless most or all of the squares and terminals were removed.

Because our probably over-protective June budworm thresholds of 15 percent live budworms in terminals or 10 percent in squares are met so infrequently here, very little of this state's cotton acreage has needed treatment for this generation.

Reliance of beneficial insects (non-treatment) should be regarded as the primary option for dealing with up to at least moderate levels of June budworms.

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 Steward should help sustain North Carolina's cotton producers' ability to inexpensively and effectively manage early budworms and bollworms on our remaining conventional cotton acreage over an extended period of time.

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