After 41 years in the business, one might think that an entomologist would run out of new things to talk about.
Not so, says Ron Smith, long-time Auburn University Extension entomologist, who says there’s always something new and different in the world of crop insects.
There are sporadic and incidental pests and then there are others that can be counted on to cause problems every year, said Smith, speaking at a recent Certified Crop Advisor Training in Auburn, Ala.
One of those sporadic pests is the garden fleahopper, a small insect that has been found in Mobile County, Ala., in recent years, he says.
“This past year they were also in Baldwin and Monroe counties, on cotton as well as in peanuts. They will speckle every leaf in the field. One of our growers applied a pyrethroid this past season, but it wasn’t very effective. We think it’s an economic pest in those fields where it occurred.”
Grasshoppers continue to be a problem from central Alabama into the southern portion of the state, especially in reduced-tillage situations, says Smith.
“They’re in the field during the cotton seedling stage — when they can cut off the stems — and they’re out there by the thousands per acre. I would call them a risk insect because they’re a risk to stands, and with the cost of seed and technology today, you have to manage this risk just as you would an insect later in the season.
“I don’t think we’ll ever have an exact, established threshold for grasshoppers, and the problem is much greater where we have reduced-tillage.
“When growers do their winter wheat burndown in March or April is when we’d want to mix something in there with the herbicide to target grasshoppers in the immature stage,” says Smith.
Almost anything labeled for cotton at the lowest labeled rate will kill immature grasshoppers, he continues.
“We could add a couple of ounces of Dimilin, and that would give us some residual control through the spring because there’s always the possibility there would be some infestation from field borders again.
“If you wait until later, like in May, most of the grasshoppers will be adults and you can’t kill them with a sledgehammer. There’s nothing you can do to wipe out adult populations. The problem ends when cotton gets to the fourth or fifth true-leaf stage,” says Smith.
The three-cornered alfalfa hopper also can be a pest of cotton, he says. “I wouldn’t say they were tremendously economic, but you’ll see a stunted, peculiar type of red cotton plant associated with girdling by three-cornered alfalfa hoppers. You’ll also see that problem in soybeans. On cotton, they’re worse during dry springs and in field borders.”
Smith says he gets a lot of call each spring about the burrower bug, but the consensus is that it’s not an economic pest of seedling cotton. It’s a different species from the one that causes problems on peanuts, he adds.
Brown marmorated stink bug
“The brown marmorated stinkbug is one we’ll likely see in the future on both cotton and soybeans, but probably more in home gardens and on vegetables and fruits,” says Smith.
“It’s a native of Asia. It first showed up in Pennsylvania around 2000, and it’s moving south into the Carolinas, causing severe problems on fruits and vegetables. It’s now in soybeans in Virginia and North Carolina.
“We know they like cotton and corn, and they will be a lot more damaging than the stinkbugs we have today because their snout is bigger and stronger, and they can go through an older cotton boll better than our regular brown and green stinkbugs. They also can go through a corn ear more readily. They will be a major pest at some point.
“They are good hitchhikers, so we either already have them here or we’re going to have them — it’s just a matter of time. We should be okay with controlling them with the materials we have, such as the pytrethroids.”
Snails, slugs and pillbugs all can cause economic stand losses in cotton, but most of the losses are from slugs, he says.
“They’re under the crop residue in the daytime, and people associate their damage with the pillbug. But of these three, slugs pose the greatest threat. They’re more common in cotton planted behind corn because there’s more residue, and they’re more common in wet springs.
“There are no effective controls for any of these — you just have to take the loss and replant if necessary.”
The kudzu bug has become a popular topic of conservation for growers, says Smith.
“They are very small when they are hatched, and the adults are not as big as a stinkbug. A lot of people don’t see the immature stage on the stem, and that’s probably the most critical damaging stage.
“In 2009, they were found around Athens, Ga., and in 2012, they were spread throughout Alabama and scattered into Mississippi and Tennessee. They’re also great hitchhikers.
“They are a major pest of soybeans in the Carolinas and in Georgia. Yield losses are up to about 50 percent, but on the average, where they’ve conducted a lot of trials, the average loss is about 20 percent in the untreated plots.”
Kudzu bugs are stress inducers, says Smith, causing fewer pods per plant, fewer seed per pod, and reduced seed size.
They move from kudzu to other hosts such as soybeans in mid-June to mid-July, and early planted beans are at the greatest risk.
“You can survey them with a sweep net or visually survey them. We’re looking for one adult per sweep, but the key is the presence of these immature bugs on the plant stem.
“That’s when we want to spray. If you spray whenever you see adults in a field, you’ll be spraying every week all summer once they get into soybeans.
“My counterpart in Georgia last year properly timed one insecticide spray and controlled them in Tifton. That was around July 20-25.
“I’m saying one or two well-timed insecticide applications will be all that is needed. In Alabama, that would be from July 15 near the Gulf Coast to Aug. 1, in the Tennessee Valley.”
Several insecticide options
Several insecticides give effective control of kudzu bugs, he says, including pyrethroids. “If you spray too early they will come back on you,” notes Smith.
The red-banded stinkbug is a native of South America and was first found in Louisiana, he says. It can be damaging on soybeans.
“They’re more difficult to control than the green stinkbug, and we’ve seen them near the Gulf Coast and as far north as Prattville, Ala. They are susceptible to cold weather, so they should stay a problem in the southern part of the state.”
Caterpillar pests of soybeans include soybean loopers, green clover worms and velvetbean caterpillars, says Smith.
“Last year we had a mixed population throughout the state with all three species. If you’ve got any loopers in the population, you have to switch chemistry. The pyrethroids do a very good job on clover worms and velvetbean cateripillars. If you’ve got loopers, you’ll have to go with a different chemistry.”
Cowpea aphids were seen this past year in peanuts, he says, and imidacloprid chemistry is recommended for their control. It was the first time aphids had been observed feeding on peanut pegs in Alabama.
“Fall armyworms have been with us on pasture, hay and turf for three consecutive years. We’re not doing a good job of detecting them as early as we need to.
“They will feed on soybeans and peanuts, but they don’t like cotton. You’ll need to look at pastures on a schedule with a sweep net. They will stay with you from early summer up until frost.”
The future of Meymik 15G, the aldicarb replacement for Temik, remains uncertain, says Smith.
“The active ingredient is still waiting in China for a formulating plant to be approved, funded and constructed in south Georgia. So, there will be no Temik replacement for 2013, likely not in 2014, and maybe never.”
Smith adds that methyl parathion will no longer be available after the 2013 season.
New scouting techniques, thresholds
Sweep nets, says Smith, have proven to be a good insect survey tool in peanuts, soybeans and even in cotton for those who want to look for live stinkbugs rather than damaged bolls.
The more drilled beans you have, the more you’ll need a sweep net, he says.
This past year, Smith says Extension began promoting a new threshold for making foliar sprays for cotton thrips.
“The first true leaf stage is the ideal time to apply foliar sprays. We want to do that especially where cotton is planted before May 10, because that would be in the heavy thrips window. This is based on multi-year, multi-state research from Alabama to Virginia.”
As the pigweed problem continues to spread, and growers increasingly move to residual herbicides, some of those herbicides will stunt the growth of cotton and inhibit root growth, says Smith. “Anything that inhibits growth below ground also impacts it above ground and keeps it in the susceptible thrips window for a longer period of time.”
Smith says he thinks stink bugs remain the greatest potential economic insect of cotton, particularly in central and south Alabama.
“Populations have been low in the last couple of seasons, but I don’t think they’ll always be low. We think the colder winters of 2009 and 2010 repressed stinkbug populations during those growing seasons, and the extreme heat and drought in June of 2011 suppressed the populations.”
It’s important to remember that stink bugs have two key reproductive periods, he says.
“Corn and other non-pod hosts are used by stink bugs in the spring, and then there’s a late-summer population explosion on soybeans. They don’t do much reproducing on peanuts, and they do a limited amount on cotton.
“It seems that in wet seasons, stink bugs carry more boll rot organisms on their snouts, which they use to penetrate and get into the bolls. So you get more boll damage in wet seasons than in dry seasons.”
When scouting for stink bugs in cotton, pull a random boll sample, advises Smith.
“Looking for stink bug damage on bolls is the best tool for cotton. We want to pull one boll per acre and no less than 25 per field. Then, we want to crush those bolls and look for any signs of warts or deteriorated tissue.
“Early on, there aren’t a lot of bolls at risk, and this threshold changes as we get into summer. Stink bugs cause the most damage at about week three through six of bloom, about a four-week period.
“Use a 10-percent damage of internal boll threshold. Crushing bolls takes a lot of time, so crack the bolls until you reach a threshold. If you pull 25 bolls, after you reach the third one with internal damage, you’re over 10 percent, so you throw away the rest of them. That’ll save a lot of time.”