- Worms are becoming more of a headache for soybean farmers this year, but at this point population levels are spotty. While worms may be present, they don’t always cause yield loss. If a farmer finds worms in his field, he should assess the injury they are causing.
NORTH CAROLINA farmers should stay calm, cool and collected when scouting for plant bugs. Many times infestations are at levels that won’t cause yield loss.
Plant bugs are proving to be more of a challenge in North Carolina this year with infestations being found and treated farther into the Coastal Plains than usual, but North Carolina State University Extension Entomologist Dominic Reisig stresses that the situation can be easily managed with proper scouting.
“Although it looks like plant bugs may be an issue this year, we don’t need to panic,” Reisig said. “What I mean by don’t panic is that we shouldn’t spray if it’s not needed. Growers in the Midsouth contend with plant bugs at much greater densities and frequencies than we do. Managing plant bugs is as easy as managing any of our other pests if you have a scouting plan and stick to it.”
Reisig encourages farmers to use a calm, cool and collected approach when scouting for plant bugs. Many times infestations are at levels that won’t cause yield loss. Spraying isn’t always necessary and if farmers are too aggressive in spraying, they can drive up resistance to the insecticide.
“It seems like a lot of our fields treated for plant bugs in the past have experienced pressure once cotton blooms and corn dries down. With that in mind, it will pay to be vigilant, although not over reactive, to plant bugs,” he said.
For cotton, it is important for farmers to monitor square retention and check for plant bugs.
“Plant bugs aren’t the only cause of square loss- other stresses in the environment can cause this. So you don’t want to spray a field where bugs aren’t the problem,” Reisig said. “Also, plant bugs are extremely mobile, and can rapidly move in and out of fields. Sometimes they may be present (especially adults), but not causing square loss.”
Worms are becoming more of headache for soybean farmers this year, but at this point population levels are spotty. After scouting numerous fields, Reisig said he has found areas where corn earworm and tobacco budworm are present.
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While worms may be present, they don’t always cause yield loss. If a farmer finds worms in his field, he should assess the injury they are causing.
“Our threshold is triggered at 30-percent defoliation throughout the entire canopy before beans are blooming,” Reisig said. “Our threshold of 30 percent is very conservative. Recent research from the Midsouth confirms that we can tolerate defoliation at levels much higher than 30 percent without a yield loss. You can rest easy with a spray at 30 percent, knowing that beans can compensate for the lost foliage later in the season.”
Reisig points out that one thing to consider is larval size.
“If you have very large larvae, they can eat more, but they may cycle out soon,” he explains. “It might be better to let this happen, rather than spray, if you are below threshold. If there are still a lot of small or mid-sized larvae, you might need to spray if you are at, or near threshold. We want to avoid spraying unless we really need to at this point in the season to preserve beneficials. Fields that are sprayed at this point in the season run the risk of getting on the pesticide treadmill. This is where we spray one pest (for example worms), flare another (more worms or spider mites), spray that pest, flare another, etc.”
Reisig stresses that once you reach threshold and know what species you have, product selection is key.
“If corn earworm is your pest, a pyrethroid should work fine early in the season. Although corn earworm is becoming more and more tolerant of pyrethroids every year, they tend to be more susceptible early season,” he explains. “Later in the season we probably select for survivors that are more tolerant of pyrethroids. At this point we will need to switch to more worm-specific materials. If you have tobacco budworm, you will need to spray one of the worm-specific materials."