Fifty Years Of Evolution In Cotton Insect Control — 1971-2021.
⋅ BY RON SMITH ⋅
It has been quite a journey to have been a part of the most evolutionary period in cotton insects. I began my career as part of the new U.S. Department of Agriculture-Extension cotton IPM educational initiative in 1972 when boll weevils were the dominant cotton insect in Alabama.
The goal of the program was to increase awareness of a management approach to controlling cotton pests, a program which incorporated scouting and economic thresholds. It has become widely recognized as integrated pest management (IPM).
During the mid-1970s, our primary cotton insecticide was the organophosphate class of chemistry — products such as methyl parathion and Guthion, which were characterized by fast-acting activity but short residual. In addition, most chemicals in this class had acute human and mammalian toxicity.
The phosphate chemistry had excellent activity on the boll weevil but brought resistance in tobacco budworm and secondary pests, such as spider mites and whiteflies. Heavy use of phosphate insecticides also caused major problems with delayed maturity of the crop. This problem was so pronounced that a special session was added to the January 1976 Beltwide Cotton Research and Control Conference.
Introduction Of Pyrethroids
In 1976, the pyrethroid class of chemistry became available, initially under an Environmental Protection Agency-issued emergency use permit (EUP). In 1978, pyrethroid insecticides (Ambush, Pounce and Pydrin) received full but conditional registration and became the major player in cotton insect control for the next decade.
For several years, pyrethroids were highly effective on most all cotton insects. Insect losses were very low, yields reached higher plateaus and maturity issues disappeared. Due to extended residual from pyrethroids, insecticide application intervals for boll weevils could be extended from five to seven days.
However, during the decade of the 1980s, tobacco budworms became resistant to the pyrethroid class of chemistry in some areas of the Cotton Belt.
Boll Weevil Eradication
After more than a decade of development, comprehensive plans to eradicate the boll weevil were finalized in the early 1980s. One of the driving forces for eradication were concerns that boll weevils might develop resistance to the organophosphate chemistry, a possibility which would have wrecked the U.S. cotton industry.
Pyrethroids had activity on the weevil but were not as effective as the phosphates and were initially significantly more expensive. The boll weevil never developed resistance to the phosphates; in fact, the phosphate insecticide malathion was the primary insecticide used for eradication.
The Boll Weevil Eradication Program began in northeastern North Carolina in the early 1980s. In the fall of 1986, the eradication effort reached Alabama, and by the summer of 1995, no economic losses to the boll weevil could be found anywhere in the state.
During the active eradication program period (1986-1995), insecticide-resistant tobacco budworms and impossible-to-control beet armyworms caused yield losses beyond anything ever observed or previously recorded.
Bt Varieties Commercialized
At the end of the 1995 season — given resistance to tobacco budworms — the outlook for the future of cotton production in Alabama was bleak. Fortunately, genetically altered Bt (Bollgard) cotton varieties, which had been evaluated for the previous four seasons, were commercialized.
The new technology was readily adopted by Alabama growers, and 77% of the 1996 acreage was planted to Bollgard varieties. This rapid adoption was primarily in self-defense following the heavy losses to worms in previous years. However, planting this new technology brought with it rules and regulations never experienced before by growers.
Word was spoken that growers would never have to treat for worms again. This proved to be incorrect when in late July 1996, news of bollworm escapes in the Brazos River area of Central Texas spread across the Cotton Belt.
Some growers wanted to give up on the new technology immediately. However, over the following years, entomologists and growers learned more about what to expect from Bollgard cotton varieties and how to manage escape bollworms, which could be controlled with a minimum of well-timed pyrethroid sprays.
The following 10 years proved to be good for growers with overall improved yields and minimal insect losses and control costs.
Bug Complex Threatens
It was during this low-spray environment that the bug complex became more damaging. In north Alabama and the Mid-South states, the tarnished plant bug had to be monitored and managed more closely. In central and south Alabama, as well as the remainder of the Coastal Plains of the southeastern United States, stink bugs became the dominant economic insect.
By the time better stink bug management was adopted, single Bt gene Bollgard technology began to lose its effectiveness and escape bollworms were more widespread. Experts had warned this would happen. The single Bt gene was nearly 100% effective on tobacco budworm but considerably less effective on the bollworm species.
Anticipating this, Monsanto had begun work on stacking a second Bt gene, which was commercialized in 2009 and reduced the escape bollworm problems by about 90%. It was followed by Bollgard III in 2018. WideStrike from Dow AgroSciences with two Bt genes was introduced in PhytoGen varieties in 2005 and was followed by the third gene (WideStrike 3) in 2014.
The diamide chemistry developed by Dupont is now available and highly effective on most worm species when applied timely (small larvae) or in the egg stage. What would have been a significant development had it not been for the introduction of Bt technology back in 1996, was the introduction (1996-98) of spinosad (Tracer) chemistry by Dow AgroSciences.
Sucking Pests, Bug Complex
More recent years of cotton insect control have been dominated by the emergence of sucking pests, such as aphids, spider mites, thrips and whiteflies (silverleaf), and the bug complex — plant bugs, stink bugs and leaf-footed bugs.
As we moved into this reduced foliar spray era following the elimination of the boll weevil and tobacco budworm, our chemical tools became more selective. The new caterpillar insecticides do not control sucking pests or the bug complex, and the sucking pest insecticides do not control the bug complex or escape bollworms.
Several insecticides targeted for the bug complex give limited control of sucking pests or escape caterpillars. Tankmixes of two or more insecticides are again often necessary.
Addressing New Advances
The future will likely continue to be dominated by our current conditions. New advances may be limited. Few new chemistries will be developed. Development cost of chemistry cannot be recouped from cotton usage alone, as was done in the earlier years. New chemistry developed today must find market share with other agronomic crops, along with vegetables, fruits and nuts.
New advances will likely come in the form of genetics. These advances take years of research and often encompass more regulatory hurdles than chemicals.
A thrips-lygus gene is nearing the marketplace and is available for planting this year through the Deltapine Stewarded Ground Breakers Field Trials. Based on research, this gene may prove most effective on thrips with moderate activity on plant bugs, but it will not help on stink bugs.
Staying Ahead Of Resistance
Our future may be described as a “stay ahead of resistance” in the decades ahead. Resistance issues are present today in the following species: thrips, plant bugs, bollworms, spider mites, aphids and possibly other species.
The greatest challenge in entomology is staying ahead of resistance and managing sporadic pests such as slugs, snails, cutworms, grasshoppers, three-cornered alfalfa hoppers, leaf-footed bugs and others. Reduced tillage has been a great advancement. However, this practice has created numerous cracks that are being filled by sporadic pests that require management inputs.
In summary, the past 50 years of cotton production and insect management have evolved in many, and in some instances, unexpected ways. What an evolution and what a ride for an Extension entomologist over the past five decades.