Uncommon Mite Shows Up In SW MO Wheat Fields

 Winter Grain Mite
 Photo courtesy Jill Scheidt

   Jill Scheidt, agronomy specialist with University of Missouri Extension, scouted wheat fields April 17 in the southwest corner of the state and found an unusual pest she determined was the winter grain mite.
   “I was scouting wheat fields and saw a small black insect with red legs and thought it was a nest of spiders at first. Then I began to see them everywhere, by the thousands, in the field and knew it was something else,” said Scheidt.
   Scheidt scouted several fields in southwest Missouri to determine if the pest was occurring in more than just the one field.
   “I contacted the University of Missouri Extension field crop entomologist, Kevin Rice, to see if this pest was previously in Missouri,” said Scheidt.
   Rice could find no mention of the winter grain mite in previous publications. Later Scheidt spoke to a local crop consultant who said he had seen them several years back, but not in the densities described by Scheidt.
   The winter grain mite is a pest of small grains and grasses. These mites are one millimeter in length and have black colored bodies with distinct reddish-orange legs.
   The telltale identifier of this mite is the presence of an anal pore on the upper surface of the abdomen viewed when using a hand lens.     The anal pore looks similar to a water droplet on the mite’s back.
   There are generally two generations per year. The first begins early fall through December. The second, and higher populated generation of winter grain mite occurs from March to May.
   Winter grain mites are most active on cloudy days when temperatures range from 40 to 70 degrees Fahrenheit.
   They feed on plants by piercing the leaf and stippling plant cells. Injury to plants results in leaves taking on a gray to silver cast.
   Heavily damaged fields have brown leaf tips, which can progress to kill the entire plant.
   “In reading other publications, I found that winter grain mites are more common in continuously planted wheat fields with minimum tillage. This threw me off a bit, as the scouted fields are rotated and some are even tilled. The dry, cool weather may have attracted them,” said Scheidt.
   Crop rotation and minimum tillage helps break the cycle if infestations are heavy.
   If growing conditions favor wheat development, winter grain mites usually do not cause economical damage. However, high infestations, coupled with dry growing conditions or nitrogen deficiency can allow them to cause significant damage. Heavy rains aid in the reduction of winter grain mite populations.
   “There are no established threshold levels for treatment, but consider an insecticide application if large populations are present and visible symptoms appear on leaves,” said Scheidt.
   Monitor winter grain mites over the next few years. “They may not be a problem now, but it could take a few years for them to establish and cause economic damage,” said Rice.
   “We aren’t quite sure why they sporadically popped up, but monitor the presence of the pest closely if you find high populations, as damage can happen rapidly’” said Scheidt. ∆
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