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Effects of Brassica cover crops on weed dynamics.
Haramoto, Erin*,1, Gallandt, Eric1, Molloy, Thomas1, 1 University of Maine, Orono, ME, USA
ABSTRACT- Allelopathic cover crop residues may contribute to weed management by reducing weed establishment and suppressing the growth of weed seedlings. Members of the Brassicaceae contain glucosinolates (GSLs), which degrade to compounds that are toxic to a variety of organisms. Brassicas used as cover crops include, but are not limited to, canola (Brassica napus), rapeseed (also Brassica napus), and yellow mustard (Sinapis alba). Glucosinolate content of these cover crops varies widely, with canola having very low GSL concentrations, yellow mustard typically having very high concentrations, and rapeseed being intermediate between the two. During the summer of 2002, two experiments were conducted in Stillwater, ME, to examine the effect of different cover crop residues on weed and crop emergence and the effect of these residues on growth and reproduction of redroot pigweed (Amaranthus retroflexus) and green bean (Phaseolus vulgaris). Weed and crop emergence was measured following incorporation of six cover crops--three brassicas (canola, rapeseed, and yellow mustard) and three non-brassicas (buckwheat (Fagopyrum esculentum), crimson clover (Trifolium incarnatum), and oats (Avena sativa)). Incorporated cover crop residues reduced weed and crop emergence by 33% (p=0.036). However, emergence following brassicas and non-brassicas was similar. In the second experiment, monocultures of redroot pigweed, green bean, and a mixture of the two were seeded into incorporated residues of canola and yellow mustard. Redroot pigweed grown with green bean was smaller than redroot pigweed grown alone; the same was true for green bean. However, no residue effect on growth or yield of redroot pigweed or green bean was found. Despite the presence of glucosinolates in the incorporated residues, the residue-mediated effects of brassicas on weed dynamics appear to be similar to other commonly grown cover crops. Brassica cover crops may not provide distinct advantages for weed control, but may suppress other soil-borne pests.
Key words: cover crops, weed management, Brassica spp.