Saturday, October 16, 2021

What’s Lurking In The Field?

A late-season foe came early in 2021, and a new miticide looks promising for control.

• By Amanda Huber •thrips damage in peanut

Thrips were prevalent in many fields of late April- and May-planted peanuts. University of Georgia Extension entomologist Mark Abney says thrips injury varied in severity from minor feeding scars on fully expanded leaflets to severely deformed or dead terminal buds.

As to whether a foliar insecticide should be used, Abney says, “Most of the time I do not think an insecticide application at four weeks after planting will pay for itself; however, if peanut terminals are being severely injured, immature thrips are still present, and the plants are experiencing drought and/or herbicide stress, treatment might be warranted.

“In my experience, thrips injury typically peaks around 30 days after planting. After that, thrips numbers tend to decline, peanut growth increases rapidly and we forget about thrips for another year.”

It is tomato spotted wilt virus, Abney says, that is transmitted by thrips which is the more serious problem.

“Fields planted after May 10 that were treated with phorate (Thimet) will be at reduced risk compared to earlier planted fields with no at-plant insecticide or with a different one. It is important to remember that foliar insecticide sprays will not reduce the risk of TSWV in peanut.”

Treat At Threshold

Dry conditions in May also set fields up for pests such as lesser cornstalk borer, Abney says.

“In June and beyond, LCB is the most common and severe dry weather pest of peanut. Scouting and timely decision making are the keys to managing this pest.”

Abney does not recommend preventative insecticide applications. Even in heavy LCB outbreak years, not every field will need to be treated.

“We do not have to prevent infestations from occurring; we just have to find and treat them in a timely manner.”

He has the same recommendation with foliage-feeding caterpillars: Do not treat until threshold is reached.

Early Spider Mitesspider mites on peanut

Two-spotted spider mite is an insect pest that often occurs later in the season, but the dry weather brought on this pest in some areas earlier. South Carolina Extension peanut specialist Dan Anco says crop consultant Drake Perrow found spider mites in peanuts he was scouting on June 1.

“Yes, this is early, and the more obvious, yes, we are dry,” Anco says. “Rains will help a natural fungus to attack the mites and bring the population back down.”

Abney says, “Mites often occur in large numbers in peanut fields where pyrethroid insecticides have been applied. Avoid pyrethroid insecticides in non-irrigated peanut fields to prevent flaring mites. While we do not usually see treatable populations of mites in peanut in June, the decision to apply a pyrethroid in June or July can dramatically increase the risk of infestation later in the season.”

New Miticide Looks Promising

Although it is easy to flare spider mites with an insecticide, options for treatment are either expensive, hard to purchase or provide only a modest level of control, says Rick Brandenburg, North Carolina State University Extension entomologist.

“On top of all that, many of the products we use today are more than 30, 40 and even 50 years old. This illustrates that we have not developed a lot of effective products in recent history.”

However, he says a new product, Portal Miticide/Insecticide, manufactured by Nichino America, has potential. Brandenburg evaluated the product in 2020 and was impressed with its spider mite control.

“While I have only tested it one year and in only one location, Bertie County, I decided to add it to our recommendations. When used on a wide basis, we will find out how good it is, but I believe it can be a very effective option for spider mite control in the future.”

Brandenburg also hopes that it will be priced at least competitively with other miticide products when it becomes more widely available.

“Other spider mite products have often been hard to find in the past. It seems when it gets hot and dry everyone needs them at the same time.”

He is evaluating the Portal again in 2021 to gain more data on its use, but he already thinks the registration is a welcome addition to the spider mite control toolbox. PG

 

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