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Title: EFFECTS OF WEED COMPETITION ON SOIL MOISTURE, PLANT NITROGEN LEVEL AND YIELD IN GLYPHOSATE RESISTANT CORN

Author
item KALAHER, CHAD - UNIV OF ILLINOIS
item HART, STEPHEN - UNIV OF ILLINOIS
item BELOW, FREDERICK - UNIV OF ILLINOIS
item STOLLER, EDWARD

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/12/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Weeds can compete with crops for resources that may affect crop growth and yield. The effects on corn grain yield from varying duration of early- season weed competition are highly variable. Field studies were initiated in 1998 at Urbana and DeKalb, Illinois, to determine when grain yields begin to decline and if competition for soil moisture and Nitrogen are major contributing factors to yield losses due to early-season weed competition in glyphosate-resistant corn. Glyphosate was applied postemergence to glyphosate-resistant corn when giant foxtail reached 5, 10, 15, 23, or 30 cm in height. Rates of glyphosate were 0.84 or 1.12 kg ai ha-1. Major weed species and densities were giant foxtail (645 plants m-2) plus common waterhemp (760 plants m-) and giant foxtail (375 plants m2) plus velvetleaf (290 plants m) at Urbana and DeKalb, respectively. Corn and weed tissue was sampled at R1 and R6 corn growth stages, in addition to prior to each glyphosate application. Nitrogen concentrations were determined using a Fisons NA 2000 plant analyzer standardized with atropine. Percent volumetric water content was measured in the row immediately prior to each glyphosate application using time-domain reflectometry with open reflection waveform. Data were subjected to ANOVA using PROC GLM in SAS. Significant reductions in corn grain yield were initiated when giant foxtail was 10 and 15 cm at Urbana and DeKalb, respectively. A significant yield reduction was also noticed at DeKalb when a glyphosate application was made when giant foxtail was 5 cm in height. This was due to a significant weed reinfestation after application. Weeds in check plots reduced yields 67 and 39% at Urbana and DeKalb, respectively.