The two-spotted spider mite is a small pest that was a big problem in fields this summer.
⋅ BY AMANDA HUBER ⋅
The master of surviving high temperatures, the two-spotted spider mite was a frequent pest to peanut fields this summer. The climate in many states offered the perfect conditions for a population explosion. Further, within one to two weeks, the life-cycle from egg to adult can be completed, and each spider mite female produces 140,000 newly hatched individuals in the third generation, which can be in three weeks’ time.
The outbreak this season was not a surprise to now-retired North Carolina State University Extension entomologist Rick Brandenburg, who said earlier this year that the spring weather has a major impact on spider mite populations later in the growing season.
“I began working on spider mites in 1977, and over those many years, there has been a consistent trend,” Brandenburg said. “If we have a warm and dry April, we have an increased chance of spider mites in the summer.
“In many areas, we did see a dry April. Not necessarily a warm month, but a dry one. My experience indicates that if we have a hot and dry July and/or August, the dry April makes the likelihood of spider mite problems in peanuts much higher,” he said.
Avoid Mowing Field Edges, Flaring With Fungicides
By mid-June, dry conditions in peanut fields were again prompting a warning on spider mites from NCSU Extension state specialist David Jordan.
“Some areas of the state have become dry or have remained dry,” he said. “Avoid mowing ditches and paths close to peanut fields if at all possible. This can keep spider mites out of the fields. Mite populations build in non-crop areas and move into crops as they expand. Mowing vegetation will increase the pace of movement of mites into peanut fields.”
Then another tip a few weeks later.
“Hot and dry conditions are favorable for spider mite infestations, and fungicides, especially chlorothalonil, can reduce activity of a fungus that adversely affects spider mites,” Jordan said. “Many areas of the region are primed for spider mites given the hot and dry conditions that are anticipated.”
A Side Benefit To Tropical Weather Systems
In mid-September, Alabama Cooperative Extension Service entomologist Scott Graham said that spider mite calls had significantly picked up in the past week with reports of mites in peanuts from across south and central Alabama. At the time, the few rain showers had not tempered the mites’ march across fields, but he did expect tropical weather to have an affect on the tiny pest.
“With the storms coming, I would wait to treat in most situations,” Graham said. “While it may not kill or eliminate the mites, it should greatly reduce their activity. This will buy us some time until we can get back in the field.”
Also in September, University of Georgia Extension entomologist Mark Abney said that two-spotted spider mites were widespread in Georgia peanut fields as growers were reaching the final few weeks of the 2024 growing season.
“Spider mites thrive in hot, dry conditions, and they are often more abundant in fields where broad-spectrum insecticides have been applied,” Abney said. “The recent cooler, cloudy, rainy conditions in the state may have slowed mite population development, but the sun is shining now and mites are doing just fine.
Factors To Base Treatment Decisions On
Abney said decisions on spider mite management need to be made on a field-by-field basis taking into account the current mite pressure, the condition of the field and the time to harvest.
“Finding and treating mites before the population gets huge is important. If mites were present in July or August, treating them would be a no-brainer,” he said. “When the mites show up in mid-September, it is not so easy. We are closer to digging, days are getting shorter and temperatures are hopefully lower. Whether a low-level mite infestation will explode into a major problem in any given field in the coming days is impossible to know.
Abney suggested that fields with less than two weeks to dig that were in decent shape would probably be fine even if the mites get heavy. However, he said he would be reluctant not to treat mites in fields with three or more weeks to go before digging with heavy mite infestations.
Graham echoed those same recommendations at season end.
“Portal and Comite II are the only two labeled options we have in peanuts. When to terminate applications for mites can be a tricky call,” he said. “Ultimately, when to stop treating mites will come down to a field-to-field decision. How far out until digging? How big is the population? What is the immediate weather?” PG
