|Buhler, Douglas - Doug|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/1996
Publication Date: N/A
Interpretive Summary: The percentage of a weed's seedbank that emerges each year is important information that allows crop consultants and producers in the Corn Belt to fine-tune their weed management strategies. We studied emergence percentages of several weed species at ten locations from Ohio to Colorado, and Missouri to Minnesota. Emergence percentages are not stable from one year to the next. For example, although the average emergence percentage of a species like giant foxtail was 31%, it varied from 9 to 100%, depending upon site and year. We determined that an important cause of this variation was abnormal spring weather conditions. If the top inch of soil warmed to about 90 degrees F for only a single day in early spring (April), the seeds of giant foxtail were induced into dormancy, and they apparently would not germinate for the remainder of that year. In contrast, if the upper inch of soil remained cool (less than 90 degrees F) until June, then maximum germination and emergence occurred. In these latter years great emphasis would need to be placed on giant foxtail control, whereas in the former years a more relaxed attitude toward giant foxtail control could be afforded. Thus, a basic understanding of the ecology of weed seed dormancy aids in predicting weed pressure and in anticipating weed management strategies.
Technical Abstract: Field experiments were conducted from 1991 to 1994, generating information on weed seedbank emergence for 22 site-years from Ohio to Colorado, and Minnesota to Missouri. Early spring seedbank densities were estimated through direct extraction of viable seeds from soil cores. Emerged seedlings were recorded periodically, as were daily values for air and soil temperature, and precipitation. Percentages of weed seedbanks that emerged as seedlings were calculated from seedbank and seedling data for each species, and relationships between seedbank emergence and microclimatic variables were sought. Fourteen species were found in three or more site-years. Average emergence percentages (and coefficients of variation) of these species were as follows: giant foxtail, 31.2 (84%); velvetleaf, 28.2 (66); kochia, 25.7 (79); Pennsylvania smartweed, 25.1 (65); common sunflower, 17.7 (107); common purslane, 15.4 (135); common ragweed, 15.0 (110); green foxtail, 8.5 (72); wild proso millet, 6.6 (104); hairy nightshade, 5.2 (62); yellow foxtail, 3.4 (67); pigweed species, 3.3 (103); common lambsquarters, 2.7 (111); and wild buckwheat, 2.5 (63). Variation among site years, for some species, could be attributed to microclimate variables that were thought to induce secondary dormancy in spring. For example, total seasonal emergence percentage of giant foxtail was related positively to the first date at which average daily soil temperature at 5 to 10 cm depth reached 16 degrees C. Thus, if soil warmed in early spring, secondary dormancy was induced and few seedlings emerged; whereas many seedlings emerged if soil remained cool until summer.