ISSUE 9 July 9, 2009 RANKING WEED COMPETITIVENESS IN SOYBEAN
Weed scientists have developed a scale for ranking the
competitiveness of weed species, allowing producers to identify
the most problematic species and develop a comprehensive control
plan tailored to fit their weed problem. Competitive ratings are
usually based on the dry matter produced by weeds. Weed
competitiveness is highly influenced by cropping practices,
including crop row spacing. For example, narrower crop rows can
reduce weed competitiveness by 20 to 50 percent compared to crop
fields planted in wider rows. Weed competitiveness also depends
on when weeds emerge relative to the crop growth stage. In
general, later emerging weeds are much less competitive than
earlier emerging ones. Field studies were conducted at two
locations in the mid-west in 2002 and 2003 to determine and to
compare weed competitiveness as influenced by soybean row
spacing and the timing of weed emergence relative to crop growth
stage. The study was part of a Master's