Refining weed management strategies in organic agriculture

Carolina Zamorano-Montanez, Purdue University


Weed management in organic agriculture relies heavily on alternative control methods such as the use of weed-suppressive cover crops, the use of mowing as a replacement for late-season cultivation, and the use of living mulches. The primary objective of my research was to examine and potentially refine elements of these weed management practices. First I evaluated the potential use of mowing to control late-season weeds and reduce weed seed production in a soybean-tomato and tomato-soybean rotation. I evaluated the effect of seed rate and planting date on the potential of sorghum-sudangrass planted as a summer cover crop to reduce weeds as an alternative to fallow. In order to better understand the effect of residue height on cereal rye decomposition rates, I conducted a litterbag experiment in which I varied litter height and followed decomposition during the growing season. Finally, I examined the effect of delaying the emergence of a common weed, velvetleaf (Abutilon theophrasti), and a cover crop proposed as a living mulch, crimson clover (Trifolium incarnatum), on tomato yields. My research suggests that late-season mowing does not provide consistent weed management results and has some potential to reduce crop yields. My research does not support the use of late-season mowing in tomatoes or soybeans. Weed suppression was improved when sorghum-sudangrass was planted in July rather than in June but increasing seeding rates from 22 kg ha-1 to 44 kg ha-1 did not improve weed control. Substantial biomass was produced by sorghum-sudangrass, which may limit its use before fall vegetables. Litter height did not affect cereal decomposition rates in my study; a simple exponential model using days after rye termination provided an excellent fit to the decomposition data. Including litter height in decomposition models appears to be unnecessary. Finally, I found no effect of crimson clover on tomato yields, regardless of when the cover crop was seeded. The effect of delayed velvetleaf emergence on tomatoes varied between years and appeared to be related to differences in velvetleaf height and biomass. Cumulatively, my research provided information that can be used to refine weed management practices in organic agriculture.




Gibson, Purdue University.

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