Acarina
Family:
Penthaleidae
Species:
Penthaleus major (Dugès)
Size: Adult:
1 mm long; eggs, .25 mm long.
Colour:
Adult is dark brown to almost black with red legs; nymph is brownish with orange legs; a young larva is bright pink to orange but darkens to light brown after one day; freshly deposited eggs are smooth, kidney shaped, and reddish orange, but within minutes become wrinkled and after several days become a straw yellow colour.
Description:
The adult is relatively large compared to other spider mites and is the only mite of economic importance with the anal pore (a tan to orange spot best seen with microscope, but can be seen with a hand lens) on the upper surface of the abdomen.
Hosts:
Small grains, including wheat, barley, and oats, are susceptible to winter grain mite. Other hosts include grasses, especially bluegrass, bentgrass, ryegrass, and fescue. The mite also infests and damages legumes, vegetables, ornamental flowers, cotton, peanuts, and various weeds.
Infestations of winter grain mite were detected in several wheat fields in Chesapeake and Virginia Beach in 2002 and again in 2006. Winter grain mite, also known as the blue oat or pea mite, is not related to Virginia’s more common two-spotted spider mite. It is widely distributed throughout the temperate regions of the world.
It is active during cooler periods of the year (mid-fall to late spring) with peak populations in winter months. Infestations in Virginia first occurred during the months of January and February and appeared to be more common in fields that had been previously treated with sludge.
Populations declined to unobservable levels in late February to early March, but re-emerged in early April – indicating a second generation. The early spring infestations were associated with dead patches where plants began dying in January.
However, researchers are still not certain that plant death was the result of mite injury alone, or if it was associated with additional plant stress caused by a high soil pH condition and manganese deficiency that is common in that area of the state.
Winter grain mite infestations have also been reported in several orchardgrass fields in Virginia including Bedford, Orange, Culpeper, Page, Campbell, and other counties.
Discussions with mite experts and perusal of Web information have not provided a clear understanding of whether mites are capable of killing large areas of wheat or orchardgrass, or what the economic thresholds might be. Information on product efficacy is limited.
The material in this publication is a summary of observations from various sources.
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