By John Tooker
Winter grain mites (Penthaleus major) are small black mites with orange legs. About five years ago, I had my first encounter with them when a scout in Chester County found a small population of mites on a dairy farm. Last spring and this week, I have had additional encounters with winter grain mites when crop scouts in Berks, Franklin, and Lancaster Counties have encountered triticale and rye fields with struggling plants that were teeming with mites. I encourage folks growing small grains annually to check their fields for this type of damage and the presence of the mites.
This mite species appears to be most common in Great Plain states where continuous small grain production is common, but it is distributed across the U.S., and it can feed on rye, wheat, barley, triticale, oats, and some native grasses, among other plants species. Prior to recent years, it had been rarely reported in Pennsylvania, but with many dairy farmers growing two silage crops annually for forage, this pest is becoming more common. As its name suggests, it is active during the cool part of the year. It is also nocturnal and, during the day, retreats to the base of the plant or soil to hide, though it can emerge on cloudy days. When temperatures get too warm, it enters the soil for a summertime hibernation, then becomes active again in fall. The mites cause damage by sucking out the contents of individual cells, leading to the silvering and then browning of plants.
Winter grain mite is most often a pest of continuous small grain production, which is becoming more common as dairies embrace annual production of silage from winter small grains. Growing winter rye or triticale annually can build mite populations. Because they do not have wings, mites are unlikely to spread quickly, but their infestations will grow with time. Because they are active during winter, they are largely protected from natural enemies, which tend not to be active at lower temperatures.
Some of the populations that we have encountered appear large enough to cause economic damage, but unfortunately, economic thresholds have not been developed for this pest species. Some universities recommend chemical controls to help avoid yield loss if plants are suffering from damage and mites are abundant on plants. Some formulations of lambda-cyhalothrin appear to be labeled for mites in some small grains, but be sure to check labels to be sure the formulation is allowed for your situation.
Scouting is key for winter grain mites to be sure that you can control the pest where it is causing damage rather than spraying whole fields unnecessarily. In the long term, if the populations and damage persist, rotating infested fields to soybeans, sorghum, or alfalfa will likely eliminate the problem.
Source : psu.edu