INSECT, PLANT DISEASE, & WEED SCIENCE NEWS [No. 87-24] [September 11, 1987]

In This Issue: Weeds in Winter Wheat Rangeland Weed Control with Atrazine Musk Thistle Control Field Bindweed and Other Perennials Weeds in Winter Wheat Wheat seeding is underway. The seeded land may appear clean, however, if set-a-side acres or the 1987 crop had a pennycress or wild brome problem, chances are there will be a similar problem for the 1988 crop. Our worst weeds in winter wheat are those that germinate in the fall with the crop -- blue and tansy mustard, pennycress, wild mustard, cheat, hairy chess, and downy brome. Rangeland Weed Control with Atrazine Downy brome, hairy chess, pennycress, and mustards can be effectively controlled in rangeland with atrazine. It\u27s not necessary to wait until late fall. Actually the most effective control would be from applications made in early fall. Winter annual weeds start growth in late August and September. Atrazine applications in September would be most effective on the newly germinated weeds. Use 1 to 2 pints of atrazine or AAtrex 4L or equivalent amounts of other atrazine formulations. Bluegrass and intermediate wheatgrass may be injured by the treatments. Aerial or ground applications can be made. According to the label, livestock should not be grazed for 7 months after making fall treatments. Musk Thistle Control October and early November are excellent times to control musk thistle providing the weather cooperates. A good fall control program normally eliminates the need for spring control. This is because plants that would flower next summer are normally growing in the fall. However, the success of a fall control program depends on adequate fall rainfall. Most areas of the state have received moisture sufficient to germinate musk thistle. Dry weather reduces musk thistle seed germination and plant establishment. Where the weather has been dry, there may be no plants to control. Examine the site and determine if the thistle population justifies spraying. Herbicides and per acre rates to use on musk thistle are Tordon 22K at 6 to 8 fluid ounces, 2,4-D + Banvel at 1.0 lb. + 0.5 pt., and 2,4-D at 1.5 to 2.0 lb. These treatments are ranked in order of effectiveness for fall application. Under very dry cool conditions only Tordon can be expected to perform well. Treatments should be applied after October 1. Field Bindweed and Other Perennials Perennial weeds including field bindweed, Canada thistle, and leafy spurge can be effectively treated with herbicides in the fall. Food storage in the root system of these plants is taking place in the fall. Herbicides applied at this time to plants with excellent top growth readily move down to the roots along with the food. In the fall, temperatures and soil moisture are generally more favorable for plant growth than during ,the summer, a condition required for best herbicide performance