A key insect pest is one that often triggers the first insecticidal treatments in a field, and the three-cornered alfalfa hopper (TCAH) apparently has reached that status in Georgia peanut production.
“These first insecticide treatments then influence other pest activities if conditions are appropriate for their development, thus leading to more insecticidal inputs,” says David Adams, University of Georgia Extension entomologist.
Over time, he adds, key pests may change in crops. “At one time, we put out Lorsban for lesser cornstalk borers, and that might have been considered a key pest because some of the practices out in the field actually led to problems in other areas. Resistance in cutworms is one example, and sometimes it might flare problems in caterpillars,” says Adams.
That first spray could then influence what occurs in a field for the remainder of the season, he says. “When we started spraying for lesser cornstalk borers, we could count on having worm problems from that point on.”
The boll weevil on cotton was a prime example of a key pest, says Adams, because when growers had to make sprays on young seedling cotton, it caused other problems in the field with worms.
“The same thing can happen with peanuts, and we’re particularly concerned now with the three-cornered alfalfa hopper. Years ago, we knew we had three-cornered alfalfa hoppers, and sometimes we’d spray for them and sometimes we wouldn’t. We had more limiting factors that created more problems than the three-cornered alfalfa hopper,” he says.
The problem now with peanut insect pests such as the three-cornered alfalfa hopper, is that there is a research deficit as far as when and how to treat, especially over the past four years or so, says Adams. Management systems for three-cornered alfalfa hoppers now are judgment calls, with some degree of scientific backing.
After peanut production moved away from the single-variety Florunner systems, researchers started to see that yield was being lost to the TCAH, he says. “They did find that three-cornered alfalfa hoppers — at high populations and at certain periods of time — could cause enough damage to peanuts that it would be economical to treat them,” says Adams.
Limited research, he says, has shown that different peanut varieties have different levels of susceptibility to feeding from TCAH. “With this information, we would be able to tolerate higher populations in some varieties and lower populations in others. But research hasn’t kept up with the new varieties that have been introduced – it’s a judgment call.”
Since the first migration of adults occurs in late June and early July, this would be the best opportunity to control the egg-laying adult population, severely limiting the subsequent and most damaging nymph populations in August and September, says Adams. “Being a key pest, that might be the best time to spray for it because the can become indigenous in the field,” he says.
The judgment, he says, is whether there are enough three-cornered alfalfa hoppers in the early populations to warrant a treatment. It is an easy decision if there is one adult per foot of row, but what if there are only one per 3 feet of row? If this is the only limiting factor in high-yielding peanuts, then one might choose to piggy-back a treatment with a fungicide application.
“If as an agent/consultant/grower you have experience with the various varietal responses to TCAH, then it is better to yield to your best judgment. The one parameter we do know is that if peanuts are within 30 days of digging, no treatments are necessary,” says Adams.
Three-cornered alfalfa hoppers, he says, girdle the stem of the peanut plant. They feed directly into the food source of the plant as opposed to the water source. “They’re feeding into food transport system, taking out sugars that are flowing down to the plant and down into the root system, depriving the peanut plant of nutrients.”
The stem, he explains, often will be smaller below where the feeding takes place since the sugars are being reduced.
“In addition to reducing the supply of nutrients, they’re also laying eggs. The scars you often see on the plant during that early population are the egg lays. The eggs are hidden from parasites and predators, which isn’t good for the grower. If a sucking insect injures the stem, and spores are introduced into the plant, then you might have a higher level of disease in the field.”
Generally, insect management problems in Georgia peanuts were less significant this past year compared to the past several years, according to Adams. However, significant problems were encountered and insecticides were applied to many problem fields. Tobacco budworm populations occurred in mixed populations of corn earworm. In fields that needed treating for budworm/bollworm, the ratio was commonly 60/40, respectively. In 2009 county Extension agents, consultants and growers identified the budworm and initiated the appropriate insecticides for control, he says.
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