Lygus has moved to the front of the line as one the most troublesome cotton pest in the U.S. It is a promotion by default, according to University Arizona Entomologist Peter Ellsworth, based at the Maricopa Ag Center in Central Arizona.
The bollworm/budworm complex continues to rank as the No. 1 cotton pest Beltwide, reducing yields by 1.5 percent, but lygus is a close second with 0.95 percent loss. In some areas lygus losses are much higher than that with the plant bug as the No. 1 pest.
According to Michael Williams, Extension entomologist at Mississippi State University, lygus is emerging as a sectionalized pest, with Lygus lineolaris infesting the Mid-South and Lygus hesperus infesting the western United States. Cost of control for this pest Beltwide was $10.49 per acre in 2005.
Ellsworth, was on a panel of entomologists with Williams reporting on cotton yield losses to insects at the recent Beltwide Cotton Conference in San Antonio, Texas.
He said lygus have long been part of the insect pest complex that threatens U.S. cotton. For years, however, lygus has taken a back seat to boll weevil, pink bollworm and other lepidopterous pest. Now that weevil has been all but eradicated and worm pests have been brought to their tiny knees with Bt cotton, lygus has become the bad boy down the cotton rows.
Lygus is not taking a significantly larger share of cotton yield losses, but it is taking a bigger percentage of growers' pest control costs, said Ellsworth. In Arizona it accounts for 40 percent of a grower's pest control cost. Beltwide it is 20 percent.
The UA entomologist disagrees with those who say lygus represent the next generation of cotton pests.
“Lygus is not really a new pest, just a bad actor that we have not had to deal with for some time. Its prevalence and prominence are just increasing,” said Ellsworth.
“Lygus has become the No. 1 pest in Arizona and has been since 1997,” said Ellsworth. Similar situations exist in other parts of the Cotton Belt, particularly in Louisiana and the Mid-South.
The year Ellsworth mentioned is important because that was when worm pests started to be shoved to the back of the class with the introduction of Bt cotton, which greatly reduced the need to treat for damaging worm pests with insecticides.
Bt cotton is only one of the reasons lygus have gained prominence. The other is boll weevil eradication and the use of more selective pesticides and more narrow-spectrum pesticides and IGRs to control pests like whitefly. Fewer treatments for non-lygus pests and the use of selective pest control chemistries for pests other than plant bugs has meant reduced control of lygus. When broad spectrum products were used, there was some collateral lygus control.
New seed treatments and more soil applied pesticides are two other reasons lygus is sitting on the front row now.
“Changes in the landscape” also have contributed to a greater lygus presence, added Ellsworth. By that he means the growing use of conservation and or reduced-tillage is providing more habitat for lygus.
Plant bugs are more mobile than some other cotton pests with a wide array of host crops and weeds and for those reasons represent When lygus numbers get high enough, nymphs and young adults create rank plant growth as well as lint quality problems like higher micronaire and reduced fiber strength as a result of carbohydrate imbalance in the plant caused by high fruit loss. Ellsworth calls these reduced quality factors the “hidden costs” of lygus damage.
In 2005 test plots where Ellsworth evaluated control measures, the untreated plot yielded only about a third of a bale of cotton per acre in a state where the average yield is well over 1,200 pounds per acre.
Fortunately, there are pesticides to control lygus. Orthene remains the effective standard, but Ellsworth said the issue of resistance looms with so few products to control lygus.
He said this is changing with newer, more selective lygus control products that are easier on beneficials and which fit into a resistance management program.
Sampling techniques also are being employed Beltwide to monitor the pest and schedule IPM measures.
Ellsworth's recommendation to producers for 2006 is that they “avoid the problem at all cost.” This means monitoring adjacent crops and non-crop areas for lygus buildups that could migrate and damage cotton.
And if control treatments are necessary, Ellsworth reminded growers to take “selective measures.”