Velvet Bean as a Biological Control of Weeds and Pathogens

View the project final report

• 2002 annual report

Commodities

• Agronomic: sorghum (milo)

Practices

• Soil Management: general soil management

This series of experiments answers a few important questions regarding velvetbean's effectiveness as a suppressor of some weeds and possibly fungi, as well as the potential of 'GA Bush' velvetbean and sunn hemp for improving the organic matter content and fertility of soils in two important agricultural areas of Georgia. The data collected and presented also provides a reference for farmers in the Southeast region regarding planting dates and specific effects that can be anticipated when using velvetbean as a cover crop and as part of a comprehensive crop rotation plan. Significant biomass and nutrient accumulation was seen when velvetbean and sunn hemp were grown for 60- 120 days in the two locations, with more variability as days after planting increases. In Watkinsville, it may be best to plant 'GA Bush' velvetbean after April, unless a grower has the ability to grow the crop for 120 days. The data began to show a trend of increasing biomass with planting after April, however, this is through extrapolation of existing data due to damage to the crop from pests that terminated the project before all data collection was complete. This shows a need for some type of protection of ‘GA Bush’ velvetbean from deer and other pests when grown in the Watkinsville area.

Sunn hemp also accumulated substantial biomass and nutrients after 60 DAP, however, biomass accumulation began to level off for the later plantings (June and July) harvested in the late Fall. Allowing 90 days for growing sunn hemp was optimal for both locations.
Velvetbean proved to be effective in suppressing the growth and germination of the common horticultural weeds of the Southeast that were tested in this series of experiments. Though, the stirred extract of velvetbean seed produced better weed suppression results, a technique that sterilizes the extract without destroying the allelopathic effects needs to be explored due to the considerable fungi that contaminated the petri dishes in this portion of the study. The biomass residue collected from the April planting in Watkinsville also exhibited weed suppression, although better inhibition was seen for the biomass harvested 60 DAP than for that harvested 90 DAP for redroot pigweed and for sicklepod. For Florida beggarweed and crabgrass significant inhibition of weed growth was seen for the residue harvested 90 DAP. The best suppression was seen using the stirred velvetbean seed extract.
Velvetbean may have some suppressive effect on P. capsicii, however insignificant to no inhibition was seen for R. solani. This series of experiments begins to explore ‘GA Bush’ velvetbean as a biological control of weeds and fungi and shows that ‘GA Bush’ velvetbean may be a good alternative for farmers interested in growing a summer cover crop that needs only a short time to accumulate significant biomass and nutrients and at the same time will help inhibit weed growth through allelopathy and competition.

Introduction

For centuries, people have been growing cover crops as part of an agricultural system to improve the fertility and structural composition of their soil. Today, cover crops are still grown as part of a total agricultural system that promotes sustainability. Some of the long-term benefits obtained from the use of cover crops include weed suppression through competition or allelopathy, shorter fallow periods, possible insect control through rotation, and less monetary input through the decreased use of herbicides, pesticides, and water. Velvetbean (Mucuna spp.) and sunn hemp (Crotalaria juncea) are two tropical legumes in the Fabaceae family that have been used for many years in agriculture and may fit well in a sustainable vegetable production system in the Southeastern Region of the U.S. Traditionally used in agricultural systems in places such as Hawaii, the Philipines, and Meso-America, velvetbean was also once used in the early 1800s in the Southeastern United States. Here it was used as a green manure in orange orchards and in rotation with cotton and corn, because it helped lower external inputs and created a more sustainable system. Sunn hemp (Crotalaria spp.), also in the Fabaceae family, is one of the earliest, most distinctly named fibers of India; and one of the most widely grown green manure crops throughout the tropics (Cook et al., 1996). Grown usually in rotation with several different crop species, sunn hemp shows promise as a green manure/cover crop for the Southeast region due to its high N content, fast-growing habit and ability to prevent soil erosion. In recent years little research has been done on sunn hemp and velvetbean as cover crops in the United States. This results in a lack of information regarding when to grow and when to harvest sunn hemp and velvetbean for the most nutrients and biomass production as part of a sustainable vegetable production system in the United States. Though some research exists on velvetbean as a weed suppressor, this study examined the allelopathy in velvetbean seed and above-ground biomass. This study also sought to examine velvetbean’s effect or non-effect on common horticultural fungi, since very little research is published on the topic.

One objective of this series of experiments was to analyze the biomass and nutrient accumulation of 'GA Bush' velvetbean and sunn hemp (Crotalaria juncea) through field experiments. This part of the study included growing Sunn hemp (Crotalaria juncea) and ‘GA Bush’ Velvetbean (Mucuna pruriens) to collect the previously mentioned data on these somewhat common cover crops from the Fabacea family. This experiment was performed Spring/Summer/Fall of 2002. Lab experiments utilizing the residue from the field experiments will also help to determine velvetbean’s allelopathic affects toward four common southern horticultural weeds (sicklepod, redroot pigweed, crabgrass, and beggarweed). This study also examined velvetbean seed as a suppressor as weeds. These experiments began in May of 2002 and were completed May 2003. Another objective of this series of experiments was to determine any suppression velvetbean may have toward Phytophthora capsici and Rhizoctonia solanii, common southern horticultural fungi. These experiments began in summer 2002 and were completed May 2003.