The use of products derived from plant material to control pests appeals to many consumers and nursery operators because there are fewer pesticide residues and worker exposure to pesticides is reduced (McDade and Christians, 2000; Young, 2004). However, poor efficacy or high cost of many natural products have limited their use. Corn gluten meal is a byproduct from corn wet-milling and has been used to control weeds in turf and other crops (Liu et al., 1994; Liu and Christians, 1997; McDade and Christians, 2001; Nonnecke and Christians, 1993). Five dipeptides present in corn gluten meal have been identified that are responsible for the herbicidal effect (Liu and Christians, 1994, 1997)
Another byproduct of ethanol production with potential herbicidal activity is dried distiller grains with solubles (DDGS) which is commonly used as cattle feed. Developing new uses for DDGS could increase the overall profitability of ethanol produced from corn. DDGS typically consist of 10% moisture, 27% crude protein, 11% fat, and 9% fiber (<http://www.iowacorn.org/ethanol/ethanol_11.html>) and typically contains 4.4% N–0.16% P–0.79% K, and 0.5% S in our laboratory testing. The high nitrogen content of DDGS makes it appealing as a potential fertilizer supplement in nursery production.
Preliminary research found that DDGS inhibited growth of several plant species when applied as a surface mulch (Vaughn, unpublished data). The research reported here determined the effect of DDGS on two common weed species and three transplanted perennial ornamentals when it was added to pine bark potting mix and when it was applied to the surface of potting soil. Separate experiments evaluated potential causes of the herbicidal effect and measured the effect of DDGS on microbial respiration. Methanol-extractable compounds present in DDGS are being evaluated for other value-added uses, so additional experiments were conducted to determine whether the herbicidal properties of DDGS are maintained after methanol extraction.
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