Over the last decade, changes in the cotton farming landscape have created an environment where sucking pests have become much more important. This has occurred in large part because low-insecticide cotton production has been enhanced by boll weevil eradication and the rapid acceptance of Bt cotton varieties. The result: stink bugs and plant bugs are on the warpath.
“Economically feasible management strategies are needed to reduce the impact of the pests,” said Pat O'Leary, research coordinator at Cotton Incorporated.
To that end, CI is spearheading several comprehensive studies in the Southeast (focusing on stink bugs) and Mid-South (focusing on tarnished plant bugs) regions. Much of the research for the three-year projects has already been initiated.
O'Leary said increasing pressure from the pests mean farmers need either new combat strategies or a rethinking of old ones.
For instance, she said, researchers will be looking at the practice of “popping quarter-sized bolls and looking at internal damage to determine a threshold for spraying stink bugs. That's time consuming, so we wonder if we can come up something easier for consultants and cotton scouts.”
One possibility: research currently being conducted in South Carolina on “sniffer” technology. While not part of the CI project, O'Leary said, “They've figured out that there are certain volatiles (an aroma) associated with a boll damaged by stink bugs. If they can incorporate that somehow, it would move us away from popping bolls. Theoretically, you could carry a little gizmo on your belt and, as you move through a field, just drop bolls through it. At the end of the row, because of the volatiles present, the scout would know what percentage of the bolls had been fed upon and whether a spraying is called for.”
Like most other professionals, “Entomologists must evolve and address the most pertinent and important problems at a given time,” said Roger Leonard, research entomologist with the LSU AgCenter. “The CI project was a natural continuation of the ongoing work with budworms, tobacco budworms and other pests. CI has provided leadership and financial support of regional projects to address these issues. That will allow cooperators in many states to coordinate research and develop solutions.”
For the past three years, much of Leonard's work has focused on stink bugs. “Primarily, that's because there's very little information available on stink bugs in Louisiana cotton. There's some tremendous information available for the pests in other crops, such as field corn and soybeans. But they've been considered minor pests in cotton. Until the last five years, we didn't have much information to develop management strategies in cotton.”
The emphasis on tarnished plant bugs has also been upgraded. Leonard said research efforts with the pest are focusing on sampling methods, treatment thresholds, insecticide susceptibility monitoring (a premier concern of many Mid-South entomologists), and alternative control strategies (such as area-wide vegetation management).
“Several years ago, entomologists began to see sucking pests developing into season-long problems,” he said. “Many of us tried to be proactive and initiate research to develop solutions. But the problem seemed to pick up steam.
“We see near saturation of cotton acreage with Bt cotton varieties. And the winding down of boll weevil eradication means fewer area-wide malathion applications — which can coincidentally reduce plant bug populations. In addition, for the most part, insecticides being developed by the agro-chemical industry are target-specific, and many don't exhibit bug activity.”
The CI studies will be long-term work, said Leonard. “We probably won't have answers in six months. It will take a while to develop sustainable strategies with the limited control options currently available.”
Developing a plant bug-active insecticide, said Leonard, is the “Holy Grail for the agro-chemical industry in cotton. Very few products for the pests are near commercialization. Many companies are screening some very early candidate lead chemistry. In the near future, we won't see any products that will replace the organophosphates available to producers today.”
One new product was registered last year: Crompton Corporation's Diamond, an insect growth regulator. It will help, he said, but won't solve the problem.
“This product is relatively expensive and is active only against immature stages of the bug pests. If adult insects are migrating into cotton fields from alternate hosts, Diamond won't be an immediate fix. A contact insecticide will be required to reduce the impact of immigrating adults. However, if the population consists primarily of immature stages of tarnished plant bugs, Diamond could have a fit. This product has demonstrated considerable residual efficacy and entomologists need to learn how to efficiently use that characteristic.”
Even more important is producers are losing the effectiveness of some standard products. A population of tarnished plant bugs resistant to Orthene has been found in the hill region of Mississippi.
“Acephate has been one of the most effective insecticides for tarnished plant bugs and is also effective on stink bugs. In it's — or Bidrin's — absence, producers would have a difficult time managing the pests.”
The rapid progression of insect pests filling a niche is surprising, said Leonard. “The rate at which pests step into a void is amazing. Solve one problem and a couple more pop up. That's exactly what's happened with the bug pests. For many years everyone was saying, ‘Man, if we could just get rid of the boll weevil we'd have the pest problem licked and be in hog heaven.’ So leaders in the cotton industry and USDA/APHIS managed to eradicate the boll weevil across much of the United States. Then it was, ‘Let's do something with the tobacco budworm.’ That was taken care of with Bt cotton and now the cheer is, ‘These plant bugs are the worst insect problem ever seen in cotton.’”.
While tarnished plant bugs have grown to be a significant problem recently, Leonard doubts their ability to wreak the havoc inflicted by their predecessors.
“I don't think they'll ever have the area-wide impact that tobacco budworms and boll weevils did. Many farmers in this generation can't imagine how serious those pests were because they never had to experience (them). Just ask a producer or consultant who had to deal with those pests in the 1970s (through the early 1990s) and one can quickly understand the significance of eliminating boll weevil and tobacco budworm.”