EDITOR’S NOTE— The following article was compiled by D. Eddie McGriff, Coffee County, Ga., Extension Coordinator and Mark von Waldner, Extension Coordinator in Atkinson County, Ga.

 

Georgia experienced the most severe outbreak of burrower bug damage on peanuts this year that has ever been documented.

Numerous trailer loads of peanuts have been graded as Seg. 2 due to burrower bugs. While burrower bugs may be a new problem for many growers, burrower bug damage has been a major problem for the U.S. peanut industry, especially for salted nut manufacturers, in both domestic and export markets.

The internal damage caused by the burrower bugs is considered a serious quality defect that leads to consumer complaints.

Burrower bug-damaged peanuts are graded as Seg. 2 when there is 2.5 percent or greater internal damage. Seg. 2 peanuts are designated for oil stock. Seg. 2. peanuts represent a considerable loss for growers. Local buying points informed me they are paying $330 per ton for Seg. 2 peanuts. Seg. 2. and Seg. 3 peanuts have a market loan value of $130 per ton.

Burrower bugs are small (about 1/4 inch) soil-dwelling insects with piercing-sucking mouth parts (think of them as underground stink bugs) that can penetrate the peanut’s hull and feed on the kernel. It leaves a round, yellowish-green to black spot on the kernel where it has injected enzymes to break down the kernel’s proteins and carbohydrates while feeding.

We have been conducting on-farm research on this problem since 2006. What we currently know and expect is for burrower bugs to be more of a problem in conservation or reduced-tillage, non-irrigated fields. Tillage is likely to disrupt early season burrower bug numbers and they seem to resort to feeding on peanut kernels more in drought conditions. Their damage may be more severe this year, especially in reduced-tillage fields, due to the record heat and lack of rain in some areas of Georgia.

Lorsban 15 G (chlorpyrifos) had no impact on either burrower bug numbers or peanut kernel damage in our research trials in 2006 and 2007, but the trials were not ideal for burrower bug feeding. Trials conducted in South Carolina showed granular chlorpyrifos treatments were most consistent in suppressing kernel feeding.

The 2006 trials were irrigated and conducted in a variety of conservation-tillage systems. The trial also included deep turned and disked plots.

In 2007, we were able to conduct Lorsban trials in both irrigated and non-irrigated peanut fields in which there were thousands of burrower bugs covering the ground and un-harvested peanuts from the previous year’s crop. We chose these fields specifically because of these high populations of burrower bugs. However, both of the 2007 trials were not conservation-tillage but disked and bedded before planting. This was quite a sight as most of the burrower bugs we have found previously have been in the soil and never in these numbers. We were amazed to find very little to no burrower bug damage, in spite of their high populations, in either the irrigated or non-irrigated field (which received good rainfall) and no significant difference in the untreated or Lorsban treated plots.

These trials support the premise that burrower bug damage is much more likely to occur in non-irrigated fields during drought years.

We have been able to surmise that most of this year’s Seg. 2 peanuts due to burrower bugs in Georgia have been in non-irrigated, conservation-tillage fields or non-irrigated fields where very little tillage was conducted.

South Carolina research

Research conducted in South Carolina by Jay Chapin, Clemson entomologist, demonstrates an association between burrower bug feeding and aflatoxin contamination. His research showed alflatoxin concentration was 65 times greater in kernels with burrower bug feeding.

Obviously, irrigation is the best insurance in preventing burrower bug feeding, but approximately 40 percent of Georgia’s peanut crop is non-irrigated.

The future of Georgia’s non-irrigated peanut acres may be found in the past. Growers have gotten away from deep turning peanut land with the adoption of conservation-tillage, but there is a place for both in peanut production. We believe growers need to seriously consider deep turning peanut ground in the fall after harvest and then planting a cover crop. We realize it is difficult planting a cover crop behind deep turning but the benefits will be worth the extra effort.

Let’s look at the benefits of deep turning peanut ground. First, damage potential from burrower bug is significantly reduced when fall tillage is used to plant cover crops compared to no-till planting of cover crops.

Another important benefit of deep turning is that Palmer amaranth (pigweed) emergence has been reduced 45 to 60 percent in recent Georgia tillage studies. Deep turning combined with a good cover crop has reduced Palmer amaranth emergence by up to 95 percent. Deep turning also reduces other troublesome weed emergence, most notably tropical spiderwort.

In many situations (but not in all), deep turning can greatly reduce white mold and other soil-borne diseases which can lead to significant yield increases due to just disease control. Disease control and yield increases will be more likely in fields with poor rotation or history of disease.

The best defense against burrower bugs is irrigation and tillage, but South Carolina research has shown granular Lorsban (chlorpyrifos) applied at pegging has helped suppress burrower bug injury.

It is important to note that rainfall or irrigation within seven to 10 days is necessary to activate chlorpyrifos. The longer the chlorpyrifos granules lay on the ground, especially during the hot weather we traditionally have at pegging, the less effective the chlorpyrifos will be.

Other benefits of chlorpyrifos (assuming timely activation by either rainfall or irrigation) include control of lesser cornstalk borer, Southern corn rootworm and a significant reduction in both wireworms and their damage. Wireworms are a significant problem in Coffee County reducing both yields and peanut quality in many fields. Chlorpyrifos may also aid in the suppression of white mold and three-cornered alfalfa hoppers.

The disadvantages of chlorpyrifos, besides the cost and the necessity of timely rainfall to activate it, include the increased risks of tobacco budworm, corn earworm, fall armyworm, cutworm and spider mite outbreaks.