Keep Spider Mites in Mind When Planning Burndown
From Cotton Grower Magazine – February 2017
They’re out there, overwintering and waiting for the right time to appear.
“They” are two spotted spider mites. And growers should be looking for them now while planning their preplant burndown applications.
“In overwintering, spider mites are going to be just like most other insects, in that they are going to be influenced by temperature,” said Dr. Sebe Brown, LSU AgCenter Extension entomologist, while speaking at the Beltwide Cotton Conferences. “If growers go out and survey the weeds in their fields right now, they’re probably going to find red or orange adult females in diapause. As temperatures start getting warmer, the mites will transition back to their green color.
“If you see henbit and notice little red spots on it, take a close look,” he suggested. “It might be spider mites.”
Brown noted that henbit does a good job of holding soil in place, acting much like a cover crop. But it’s also a favorite hiding place for spider mites – much like other possible sources such as tree lines, and Palmer amaranth, soybeans and corn in-season.
“Some of the worst spider mite infestations we have in cotton come from tree lines,” pointed out Brown. “Research shows that spider mites will overwinter in the bark of trees. Come spring, they’ll emerge and balloon out over the trees.”
Growers should keep a few considerations in mind to help manage spider mite problems:
- Early season spider mite outbreaks are more common following poor or late pre-plant burndown of weeds. “We see this every year, especially when we get plenty of late winter or early spring rainfall where growers can’t get in the field on a timely basis,” said Brown.
- Hot, dry weather is also a good guarantee of outbreaks. “In areas where growers don’t get good rainfall, they can anticipate problems with spider mites,” he cautioned. “In hot, dry conditions, it’s not a question of if outbreaks will happen, but when.”
- Insecticide applications targeting other pests can also a problem in spider mite control. Brown noted that long-time products like acephate and pyrethroids take out beneficial insects that help naturally control spider mites, but have no activity on mites at all. “This also includes bifenthrin, which is labeled for use as a miticide,” said Brown. “We’re not getting any control from it, and it may be making the problems worse.”
Brown suggested that the most effective way to manage spider mite outbreaks is to eliminate the green bridge in and around fields. It all begins with the preplant burndown.
“It’s important to get a good, complete burndown if possible,” he explained. You want a minimum of 4 to 6 weeks to give weeds time to desiccate. And as those weeds die, spider mites are going to concentrate to other green areas. If the green areas shrink, they’re going to overcrowd themselves and disperse.
“If growers can control green patches in their fields, it releases spider mites to look for another crop.”