Organic vegetable producers have limited options for managing weeds. They cite weed management as their number one research priority. Studies were conducted in 2004 and 2005 at the Black Sea Agricultural Research Institute, Samsun, Turkey, to determine the weed suppressive effects of summer cover crops in organic kale production. Treatments consisted of grain sorghum, sudangrass, hairy vetch, grain amaranth, pea, and fallow. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 d after incorporation (DAI) of the cover crops. Kale was transplanted 14 DAI and hand weeded once after last weed evaluation (56 DAI). All cover crops produced at least 1 ton/ha (t/ha) biomass; grain sorghum produced more dry matter than all other cover crops in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer species, lower weed density, and total weed dry biomass compared with other treatments. Cover crops suppressed emergence of common purslane, common lambsquarters, redroot pigweed, European heliotrope, field pennycress, annual sowthistle, black nightshade, shepherd's-purse, wild mustard, sun spurge, Persian speedwell, annual mercury, and jimsonweed up to 56 DAI. Total kale yield in hairy vetch treatments was more than double that of the no cover crop, and was significantly higher than yield from the other cover crop treatments. These results indicate that hairy vetch, grain sorghum, and sudangrass have ability to suppress early-season weeds in organic kale production.
Nomenclature: Annual mercury, Mercurialis annua L.; annual sowthistle, Sonchus oleraceus L. SONOL; black nightshade, Solanum nigrum L. SOLNI; common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea L. POROL; European heliotrope, Heliotropium europaeum L. HEOEU; field pennycress, Thlaspi arvense L. THLAR; jimsonweed, Datura stramonium L. DATST; Persian speedwell, Veronica persica Poir. VERPE; redroot pigweed, Amaranthus retroflexus L. AMARE; shepherd's-purse, Capsella bursa-pastoris L. Medik. CAPBP; sun spurge, Euphorbia helioscopia L. EPHHE; wild mustard, Sinapis arvensis L. SINAR; grain amaranth, Amaranthus cruentus L.; grain sorghum, Sorghum bicolor (L.) Moench spp. Bicolor SORVU; hairy vetch, Vicia villosa Roth.; kale, Brassica oleracea L. var. acephala DC; pea, Pisum sativum L.; sudangrass, Sorghum bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan