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Show Know Your Weeds RUSSIAN KNAPWEED Drawing and part o! description taken from Utah Agricultural Experiment Station Circular 123 RUSSIAN KNAPWEED a. Drawing showing plants arising aris-ing from underground rootstocks; b. head consisting of numerous flowers; c. seed in face view; d. seed in side view; e. pappus arm; f . bract of head. DESCRIPTION Russian knapweed is one of Duchesne County's most serious noxious weeds. It is perennial and reproduces by seeds and underground under-ground rootstocks. The stems grow 18 inches tall and are grayish-green. This weed is rather late maturing, its purple flowers appearing ap-pearing usually in June. The seed is whitish-tan, oblong, flattened and about yt inch long. Portions of the root near the surface of the soil have a characteristic grayish-black grayish-black bark or covering. OCCURRENCE Russian knapweed is said to have been introduced from Europe with alfalfa seed. It is now common com-mon in most of the western states. Patches can be found in most of the counties of Utah, and it is a very serious problem in several areas of our county. This weed has wide adaptation and occurs in cultivated fields as well as in waste places. .It seems to prefer well-drained land. CONTROL Russian knapweed is one of the most difficult weeds to control. Persistance is therefore necessary for success. Three years of clean cultivation have given almost complete com-plete control. The few remaining plants can be cleaned up by spot treatment with chemical in the crop. Heavy 'rates of 2,4-D are required to even burn down the top growth of Russian knapweed. These rates often damage corn and grain, so a program of cropping crop-ping and chemicals is not prac tical. Where the plants have 'been weakened through clean cultivation cultiva-tion or spraying with 2,4-D for two years, establishing ' a good stand of pasture has held it in check and seems to have reduced the stand. If this is used, clipping should be done when necessary to keep the weed from going to seed. In treating a solid stand where there is no crop, from two lbs. to 8 lbs. per acre of any one of these three chemicals, 2,4-D ester, 2-4D amine, or 2-4-5-T, applied each year for four years has given giv-en an average of 95 per cent kill in Colorado. In waste places such as ditch banks, fence lines, or even small spots in crop land, the use of a soil sterilant is probably the best and most sure control measure. Pollybore-chlorate at eight lbs. per acre ot atlacide at six lbs. per acre give excellent control, also a heavy application of 2,4-D at about 80 lbs. per acre has resulted re-sulted in almost complete kill. |