Scouting is the best way to discover this and other yield-robbing pest problems.
⋅ BY AMANDA HUBER ⋅
Peanuts are popping up in fields, and scouting should begin in earnest to get ahead of any potential pest problems.
“Last year was a record-breaking lesser cornstalk borer year. So, that should still be top of mind for most everyone,” says FMC technical service manager Blaire Colvin. “You want to scout weekly, and depending on the location and weather, they can show up earlier than you ever realize.”
University of Georgia Extension entomologist Mark Abney says LCB is the most damaging insect pest of peanut in Georgia.
“It feeds on stems, pegs and pods, and it will reduce yield and increase the risk of aflatoxin contamination. Lesser cornstalk borer thrives when it is hot and dry,” he says.
There are two big mistakes to avoid, Abney says, both of which can be prevented with scouting.
“First, not every field will need to be treated with an insecticide. Spraying every field because lessers ‘might’ be present is a bad idea. We do not need to use insecticides to prevent LCB infestations. When the pest reaches threshold, we can treat it, kill it and move on.
“Second, missing an LCB infestation will result in significant losses.”
When To Treat
Scouting for LCB is an important task, Colvin says of this pest that can be hard to find.
“Look in areas where the vines are wilted or any skips in the row for any signs of the pest. You may not see the caterpillar, but instead find the silken tubes they have made.
“The best way to check for insects on peanuts is to vigorously shake or slap the vines. This will knock caterpillars from the vines to the ground. Then, pull the vines back and see what has been knocked off onto the ground.”
Colvin says there can be a variety of species in peanut from multiple types of armyworms, tobacco budworm, corn earworm, redneck peanut worm, velvetbean caterpillar, green cloverworm, soybean looper and lesser cornstalk borer.
“Typically, it will be worth it to spray if you have four to eight caterpillars per row foot. That’s the range that should trigger an application to protect your yield,” Colvin says.
Abney says to use the lower end of the range if vines are small or growing poorly and use the higher threshold value when plants are vigorous and rank.
“Finding caterpillars by the fence row, field path, pivot point, etc., does not necessarily mean a field needs to be treated. If the average number of caterpillars per foot of row from at least 10 random samples is less than the threshold, it will not pay to treat,” he says.
Colvin says another rule of thumb is if 30% of the places you check have signs of LCB, you probably want to make an application to prevent yield loss from that pest.
“It can be damaging if you don’t realize you have them. There are really only a couple options for what you can spray in that instance, and Vantacor is an excellent choice that has a long residual and is very effective on LCB,” she says.
Vantacor’s rate ranges from 1.2 ounces to 2.5 ounces, but Colvin recommends 1.4 ounces per acre. “We’ve gotten good results with that rate for lessers. It’s a low-use rate. With good coverage, you’ll typically get two to three weeks of residual control. It has minimal impact on beneficials, which is important, and you are not going to flare spider mites.”
Besides Vantacor or chlorantraniliprole, which is a reformulation of Prevathon, Abney says novaluron, or Diamond, is also listed for lepidopteran species in peanut. However, he cautions against using anything else.
“Using a less-expensive product that doesn’t work will not save you any money. Using a product that contains a pyrethroid will put you at increased risk for spider mites,” he says.
When To Move On From LCB
Abney also says rain does not kill LCB and they can’t be irrigated away, either.
“If we experience lower temperatures and regular rainfall, we will see numbers dwindle. Once peanut vines lap the row middles, irrigated fields that are watered adequately will rarely experience LCB populations above threshold.”
As the name implies, LCB bore into stems, pegs or pods of developing peanuts. However, a different pest can strip a field of all its leaves if not caught in time, thus the reason to scout weekly and correctly identify the insect pests found.
“It is important to know which caterpillars you have when scouting, and one reason is because of the difference in the speed of defoliation of various ones,” Colvin says. “If I see velvetbean caterpillar, we’re going to get the sprayer out very quickly.
“Velvetbean caterpillar tends show up later in the season, which is another reason to continue scouting.”
Look For Disease As Well
While scouting for insects, also scout for disease.
“When I think of late season, I think of disease, particularly leaf spot, and keeping your vines intact so you can dig and get them out,” Colvin says. “If you lose more than 50% of your leaves, you might get pod shedding.
“You should have a solid fungicide program going, but depending on the year, if leaf spot starts to blow up, you may want to make an additional spray. However, if you’re all the way at 120 to 125 days and if your vines are in good condition in regard to disease and defoliation, then you probably don’t need to make another application if you’re going to dig at 135 days.
“A lot of peanuts have been going later, so if it’s more like 140 days, then it’s about the condition of the vines from whatever stresses they’ve had,” she says.
Colvin recommends FMC’s Lucento, which she says is excellent on early and late leaf spot and white mold disease.
“Thinking about the whole peanut season, my main encouragement is to get out there and scout. Get out of the truck, walk into the field and shake some vines around,” she says. “If you have a consultant, great. But there are also great resources in Extension and in the industry. Primarily, you’ve got to know what’s going on in the field. Make the correct identification, know the application threshold and put out the correct pesticide to protect yields. PG