The distribution, growth habits, and control of German velvetgrass (Holcus mollis L.) in Western Oregon Public Deposited


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  • A study was conducted on German velvetgrass (Holcus mollis L.), a weedy, rhizomateous perennial grass introduced in the United States in relatively recent years, The purpose of this study was to learn more about its distribution, growth habits, and control under conditions found in Western Oregon. German velvetgrass infestations of economic importance were found in localized sections of Linn, Marion, and Clakamas Counties. These infestations were found to occur almost exclusively on four closely related soil types, Olympic, Polk, Aiken, and Cascade. All of these soils are well drained, residual soils developed on consolidated bedrock and derived almost entirely from basalt, andesite, or other igneous rocks. These soils are referred to Iocally as, "red hill soils." While the acreage now infested is small, this species should be considered as a potential threat to large areas of Western Washington, Western Oregon, and Western California having soil and climatic conditions similar to those found on the "red hill soils" of the Willamette Valley of Oregon. Steps should be taken to stop its spread and eliminate existing infestations. While this species is reported to produce little seed in its native area of adaptation, it was found to produce large amounts of seed under Western Oregon conditions. Seed yields of over 400 lb/A were found. The seeds, which are somewhat similar in size and shape to those of Kentucky bluegrass, were found to remain viabre in the soil for a number of years. When buried at one inch, seeds remained viable for two and one-half years. After four and one-half years burial, seed at the four and eight inch depths still showed 8 and 19 percent viability. Seeds of this species emerged and became established from depths of one to one and one-fourth inches but failed to emerge when buried at greater depths. Temperature but not light affected germination of this species. Maximum germination occurred at 15°C. Rhizome formation on new seedlings occurred 35 to 40 days after emergence and when the seedlings were well stooled, three inches or more in height, and had at least 40 leaves. A study of the vertical distribution of rhizomes indicated that they were distributed throughout the tilled portion of the soil profile but did not penetrate below the tillage zone. The rhizomes formed an almost solid mat within the tilled zone which amounted to 14,392 lbs. dry matter/A in the field sampled. Observations made in established Highland bentgrass seed fields showed that German velvetgrass made a continual advance into bentgrass sod. In a very heavy sod the invasion front moved forward about seven-tenths of one foot/year. In a less dense sod the advance was about one foot/year. Rhizomes of this species were found to be destroyed by various outside influences. Burial of the rhizomes to depths greater than eight inches, exposure to temperatures above 100°F or below 20°F for short periods of time resulted in death of the rhizomes. Ethyl N, N-di-n-propylthiolcarbarnate (EPTC), when applied at rates from two to six lb/A gave season long control of German velvetgrass. When applied for three consecutive years established stands were eliminated. crops such as corn, alfalfa, red clover, flax, and crimson clover were grown following treatment with EPTC allowing crop production during the control period.
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