SUSTAINABLE POTATO CROPPING SYSTEMS FOR IRRIGATED AGRICULTURE IN THE PACIFIC NORTHWEST
Location: Vegetable and Forage Crops Production Research
Title: WEED SUPPRESSION USING COVER CROPS AND SEED MEALS
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2003
Publication Date: March 1, 2004
Citation: Boydston, R.A., Al-Khatib, K., Vaughn, S.F., Collins, H.P., Alva, A.K. 2004. Weed suppression using cover crops and seed meals. Abstracts of the First International Biofumigation Conference, Florence, Italy, March 2004.
Fall seeded cover crops were tested over multiple years to determine their effect on weed seed germination, weed emergence, and weed biomass in subsequent potato crops. Fallow and a fallow-fumigated controls were included. Cover crops included sudangrass Sorghum sudanense; winter wheat, Triticum aestivum; white mustard, Brassica hirta; and an oat-hairy vetch, Avena sativa-Vicia villosa mix. Redroot pigweed seed, Amaranthus retroflexus, was buried in nylon mesh packets at 2.5 and 10 cm deep during cover crop seeding each fall and packets recovered in the spring. Cover crops had no consistent significant effect on pigweed seed germination recovered from buried seed packets, but fumigation with metam sodium and 1,3-dichloropropene in the fall reduced germination of recovered pigweed seed 99%. Fall-seeded cover crops occasionally reduced early season weed emergence prior to herbicide application to potato. Although early season weed emergence was sometimes reduced with cover crops or fumigation, final weed biomass in potato was not affected. In greenhouse trials, Brassica hirta, B. juncea, and B. napus chopped residues added to soil inhibited emergence of several small-seeded weed species from 20 to 95% and reduced growth of weed seedlings from 8 to 90%. Redroot pigweed and barnyardgrass, Echinochloa crus-galli, germination and growth were inhibited to various degrees by eight individual isothiocyanates, with methyl- and allyl isothiocyanates being the most inhibitory. Meadowfoam, Limnanthes alba, seed meal added to soil in green house studies at 1% or more by weight reduced fresh weight of redroot pigweed by greater than 90%. In subsequent field trials 4,500 to 18,000 kg/ha meadowfoam incorporated in the top 10 cm of soil reduced weed emergence in one of two years in potato, but total weed biomass at potato harvest was not reduced.