University of Illinois Extension

Mite Activity During Dry Weather

Mites are nearly microscopic in size, yet can cause a mighty amount of damage during dry weather, said Richard Hentschel, University of Illinois Extension horticulture specialist.

"Mites are really more closely related to spiders and ticks than our typical insects," Hentschel explained.

"One clue that you have spider mites will be fine webbing the mite creates to move about. This webbing can often be seen on the very tip of branches where the new buds are when an infestation is really high."

If you suspect spider mites, using a white sheet of paper placed below a branch and quickly shaking the branch will have the mites falling onto the paper, from there you will see these very small dots moving about. Mites can have a range of colors, most often red, but orange, orange brown, green or even black are not uncommon.

"Damage is most evident during hot, dry weather, when the plant comes under stress," he said. "The mites feeding and life cycle occur during cooler weather, prior to when we typically see the symptoms. The feeding symptoms appear differently, depending on the plant."

Deciduous plants will show up as mottled or dappled spotting on the leaves; on evergreens, the needles will show the feeding damage by browning and often times those needles on the interior of the evergreen where the mites have a protected place to live. In either case needles or foliage can drop prematurely or cause branches to die.

"During our warmer weather a generation of mites can be completed in less than two weeks, allowing for large numbers of mites very quickly," Hentschel said. "The eggs themselves can hatch in as little as five days if conditions are right."

There are few organic treatment options for homeowners. One is using a forceful stream of water to dislodge the mites. Other organic methods include using canola, clove or cottonseed oil. Most of our inorganic control materials work well against most insects, but not mites. Be sure to thoroughly read the labels to be sure the product will control mites. Repeat applications are often needed 5-7 days later.

"When considering any pesticide, homeowners should read the label before the purchase to be sure mites are on the label as a pest that will be controlled along with the plant to be treated," he said. "Ignoring one or the other will lead to a pest that is not managed or damage to the plant from the pesticide application."