Drought could cause spider mite outbreak in corn
High Plains and South Plains corn producers need to be scouting their fields because the extreme drought and high temperatures are conducive to spider mite outbreaks, according to a Texas AgriLife Extension Service specialist.
Higher temperatures cause spider mites to have a higher reproductive rate, according to Ed Bynum, Ph.D., Texas AgriLife Extension Service entomologist.
Already the numbers are much greater in the fields where they have been found in than in most years.
However, not all fields have high populations, so producers need to be scouting to determine if treatment is needed, he said. Mites are most often found on the underside of the leaves in the lower portion of the plant.
"One thing we've noticed this year is the infestations seem to have been blown across the whole corn field where they have established themselves," Bynum said. "And now that the corn is beginning to tassel or moving into the reproductive growth stage, mite reproduction increases will be even greater."
He said mite reproductive rates can be as much as four times higher in the reproductive stage of corn as it is in the vegetative stage.
"So with the high temperatures and movement into the reproductive stage, we can expect to have damaging infestations of spider mites," Bynum said.
The AgriLife Extension corn guide that provides an economic threshold for making treatment decisions, based on crop value and cost of control, can be accessed at http://amarillo.tamu.edu/files/2011/06/Panhandle-Pest-Update-v3i5-7-1-2011.pdf.
Spider mites, as they feed, puncture the individual cells of the plant and suck the juice out, causing cell death, Bynum said. As the populations get higher, the damage begins to spread over the entire leaf. Populations can get high enough that the mites will begin killing the leaves.
The populations generally move up the plant as the colony gets larger, he said.
As the leaves are damaged, yield is reduced.
"Typically, we can have about 20 percent yield loss," Bynum said. "But with this potential situation, we could see even higher levels of losses. These mites could further add to yield losses for producers who have already had to abandon some fields of corn due to the drought, but are still trying to take other acreage to grain."
The entomologist did advise, however, that producers don't just start spraying before making sure the mite population is there and is still active "because we have seen mite predators within the colonies. If you don't see the live mites with a hand magnifying lens, then the predators may have controlled the population."
The most common mite predator seen this year is the six-spotted thrip, which at times can clean up the mite population, Bynum said.
If a spray is necessary, he said a good, even coverage across the field is needed for best control with the miticides that producers have available for use. If infestations are already rather high, the maximum label rate of the product should be used.
"And it would be advised for aerial applications to be made with no less than five gallons per acre. This will help to get more of the chemical into the canopy."