Scout Small Grains for Aphids, Winter Grain Mites and Cereal Leaf Beetle

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Recently we are receiving reports of high levels of aphids in barley and wheat fields. The fluctuating temperatures as well as continued dry conditions have been favorable for aphids. As indicated in a previous newsletter, cool, dry conditions generally favor spring outbreaks of aphids. This type of weather allows the aphids to survive and reproduce. Although natural enemies can keep aphids under control, cool dry weather in the spring often allows aphids to reproduce rapidly whereas their natural enemies reproduce slowly. Beneficial insects that attack aphids reproduce slowly at temperatures below 65°F, whereas aphids can rapidly increase when temperatures exceed 50°F. A number of insecticides are labeled for aphid control in wheat including: Baythroid, Baythroid XL, Dimethoate 4E, Lannate LV, Mustang MAX, Penncap-M, Proaxis, and Warrior. Materials labeled for aphid control in barley include Lannate, Penncap-M and Warrior. Check the labels for restrictions and harvest intervals. The recent Virginia Ag Pest Advisory from Ames Herbert indicates that they are hearing of many wheat (and some barley) fields with unusually high aphid numbers. Please use the following link for his comments on aphid management in wheat. (http://www.sripmc.org/Virginia/View.cfm?lngNewsID=487)

We continue to receive report of wheat fields with damage from winter grain mites. Remember, this mite is favored by cooler conditions. No thresholds are available for this mite pest. As indicated in the most recent Virginia Ag Pest Advisory written by Tom Kuhar, these mites have been found almost exclusively in no-till wheat situations. Very little is known about this sporadic pest; however, experience in Virginia this season indicates that that high densities of these mites can significantly affect plant vigor and growth. Although we have no experience with winter grain mite control in wheat, materials that have appeared to provide control in areas to our south include the pyrethroids (Warrior, Mustang MAX) and certain organophosphates (dimethoate). Note that dimethoate may not be effective when temperatures are below 60°F. Be sure to follow the rates and usage restrictions on the labels.

As temperatures increase in April, be sure to look for cereal leaf beetle adults, especially along field edges that border woods or in protected areas. Adult beetles feed along the veins of grain leaves leaving characteristic narrow linear holes parallel to the leaf veins. Although they do not cause much damage, you should routinely check these areas since this is where you are likely to find the first eggs and larvae. Larvae can feed heavily on leaves, especially flag leaves, and can quickly cause significant yield reductions if they exceed the economic threshold of 25 eggs/young larvae per 100 tillers.

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