Impact of fall and early spring herbicide applications on insect populations and soil conditions in no-till soybean

Field studies were conducted at three Missouri locations in 2004 and 2005 to evaluate the effects of fall and early spring herbicide applications on soil temperature, soil moisture content, and insect populations in no-till soybean production systems. All three experiments received herbicide applications in the fall, 60 days prior to planting, 30 days prior to planting, and seven days prior to planting. During a period from April I to May 31, chlorimuron plus sulfentrazone plus 2,4-D applied 60 days prior to planting did increase soil temperatures at a 2.5 cm depth compared to the untreated when soil temperatures were above 20 degrees C. However, differences in soil temperature were inconsistent when temperatures fell below 20 degrees C. Significant treatment differences in the percent volumetric soil moisture content were present at two weeks before (WBP) and two weeks after planting (WAP). Two WBP, soil moisture in the untreated averaged 46.0% volumetric soil moisture content, while the herbicide treated plots ranged from 48.8% to 50.8%. Two WAP, the untreated averaged approximately 5.0% less soil moisture than any of the herbicide treatments. Shake-cloth samples taken at five and seven WAP revealed significantly higher numbers of total insects per 0.8 m(2) in the untreated compared to the herbicide treated plots. At five WAP the untreated averaged 12.5 total insects per 0.8 m(2), while the herbicide treated plots ranged from 0.8 to 1.5 total insects per 0.8 m(2). Seven WAP the untreated averaged almost 19 total insects per 0.8 m(2) while the herbicide treated plots averaged only 2.1 to three total insects per 0.8 m(2). (C) 2007 Elsevier Ltd. All rights reserved.