Processes Involved in the Weed Suppressiveness of Hairy Vetch and Implications for Weed Management in Vegetable Production
Addressing sustainable weed management is critical. The use of allelopathic species could be a key component in improving weed management in sustainable systems. Legume cover crops, like hairy vetch, are gaining importance because they address three key issues: species diversity, soil quality, and weed suppression. Though several studies document the ability of hairy vetch residue to suppress weeds, several key questions remain. Our goal is to quantify the weed suppressive effects of hairy vetch, determine the role of allelopathy in the weed suppressiveness, and measure the susceptibility of weed species, as well as crops, to hairy vetch extracts.
Objective 1. Study of the response of weed populations to hairy vetch residue.
Objective 2. Determination of the role of allelopathy in the weed suppressiveness of hairy vetch.
Objective 3. Measurement of the effects of timing of cucumber planting after hairy vetch kill on yield.
Laboratory experiments were conducted by using a completely randomized design to study the effect of the water-soluble extracts of hairy vetch and cowpea on germination and subsequent radicle elongation in seven vegetable and six weed species. Lyophilized water extracts of hairy vetch were dissolved in distilled water, yielding seven concentrations of 0.00, 0.25, 0.50, 1.00, 2.00, 4.00, and 8.00 g/L. Each treatment had 4 replicates and the full experiment was repeated.
In general, seed germination was not affected by extracts of hairy vetch. However, radicle growth of all species tested was affected by the hairy vetch residue extract. Low concentrations of the extract stimulated the radicle growth of carrot, pepper, barnyardgrass, common milkweed, and velvetleaf. The order of species sensitivity to the hairy vetch extract, as determined by the IC50 (concentration required to produce 50% radicle inhibition) values, was common chickweed > redroot pigweed> barnyardgrass 1 > carrot 1 > wild carrot > corn > carrot 2 > lettuce > common milkweed > tomato > onion > barnyardgrass 2 > velvetleaf > pepper > cucumber (most sensitive to least sensitive). This study shows that at low rates, water-soluble extracts of hairy vetch are stimulatory to some vegetable and weed species. However, at higher concentrations all species were negatively affected, a situation that is beneficial for weed control, but negative for vegetable stand establishment.
To date, one article has been published from this work in HortScience.
Hill, E. C., M. Ngouajio, and M. G. Nair. 2006. Differential Response of Weeds and Vegetable Crops to Aqueous Extracts of Hairy Vetch and Cowpea. HortSci. 41:695-700.
Currently, we are in the process of trying to publish an article on the effects of methanol and ethyl acetate extracts of hairy vetch on the germination and radicle elongation of 3 weed and 3 vegetable species. Field studies examining the effect of hairy vetch residues on cucumber stands and yields and on weed species densities are also in line for publication.
The results of these studies have been presented at the Great Lakes Fruit, Vegetable, and Farm Market Expo, the North Central Weed Science Society’s annual meeting, and the American Society for Horticultural Sciences annual meeting.
Impacts and Contributions/Outcomes
This work uses hairy vetch to improve weed management and the sustainability of vegetable production systems. The expected short-term outcomes include: increased awareness of growers to the benefits of introducing cover crops (specifically hairy vetch) into their rotations and augmented appreciation of integrated weed management practices. The intermediate-term outcomes include: herbicide savings, fertilizer savings, and the potential for the development of new bioherbicides. The long-term benefits to this research could include: improved weed management, increased sustainability and yields of vegetable production systems using hairy vetch as a cover crop. The short-term and intermediate-term outcomes will be monitored via grower surveys and attendance at our presentations.
Thus far this work has been welcomed by growers. Continuing to distribute the information gained from this study will further help growers increase the sustainability of their weed management systems, diminish nutrient leaching, and reduce erosion.