Wednesday, November 7, 2007 - 10:30 AM
252-5

Intercropping as a Tool for Disease Management in No-Spray and Reduced-Spray Peanuts.

Barbara Shew, North Carolina State University, Raleigh, NC 27695 and Mark Boudreau, Hebert Green Agroecology, Inc., 20 Battery Park Ave., Suite 817, Asheville, NC 28801.

We have evaluated the potential of intercropping to reduce early leaf spot (ELS) and late leaf spot (LLS) on peanuts over seven seasons in eastern NC. In all trials, four-row strips of peanut were alternated with four rows of another crop in 16-row x 15-m plots, using various Virginia-type cultivars susceptible to ELS except as noted below. A randomized complete block design with 4-5 blocks was used each year, employing standard cultivation and weed and insect management practices. The treatments evolved through three phases over time. During 2000-2002, corn was intercropped in low-disease-pressure locations at Castle Hayne or Butner, NC. LLS occurred at very low levels but ELS was reduced 30-73% (p<.05) compared to the monocrop with no reduction in yield. During the 2003-2004 period trials were relocated to the high-disease location of Lewiston-Woodville and a cotton intercrop added. Corn was no longer effective, but cotton reduced ELS AUDPC by 25-41% in unsprayed plots, and by 60% in combination with a reduced-spray schedule (p<.05). Intercropping appeared to act by delaying epidemic onset, so in 2005-2006 the cv ‘Perry,' with moderate rate-reducing resistance to ELS, was introduced to complement this mechanism. However, intercropping did not reduce disease in either year in unsprayed or reduced-spray plots, probably due to the unexpected prevalence of LLS, to which ‘Perry' is highly susceptible. The potential for intercropping to reduce peanut leaf spot may be limited to new production areas with low background inoculum, or in combination with some resistance to LLS and/or ELS. Nonetheless, intercropping may be a useful component of a toolkit for reduced-input and particularly organic peanut operations.