The biological control of Pea Root Rot and damping off on lettuce by effective microorganisms.

Abstract

Pea root rot Aphanomyces euteiches is an important pea (Pisum sativum) disease world wide. Previous trials with suppressive composts had shown a suppression of pea root rot by up to 57 percent. A verified bioassay was used to measure the level of biological control offered by two concentrations of effective microorganisms (EM) (a commercial mixture of microorganisms including yeasts, fungi, bacteria and Actinomycetes), with water and water + molasses controls, against three inoculation levels (0, 5x102, 5x103 spores/ml) of Aphanomyces euteiches zoospores. There was no significant difference between the EM treatments, water or water + molasses. There was a highly significant difference in infection levels between the three zoospore inoculum levels. Previous trials with composts have indicated that the presence of Acremonium spp., Fusarium spp., and Paecilomyces spp. improved disease suppression in the composts while Penicillium spp. increased disease development. This may have a bearing on the failure of EM to control pea root rot. Control of damping off in organic production systems is difficult, due to the prohibition of synthetic fungicides. A successful biological control agent would be of considerable benefit for organic agriculture. A trial was set up to evaluate the potential of EM for control of damping off in lettuce. Soil, with a history of high levels of damping off, from the Biological Husbandry Unit at Lincoln University, Canterbury, New Zealand, and a control of commercial seed raising mix was placed into 7.5 cm pots and planted with ten lettuce seeds (Lactuca sativa, cv. Red Sails). Treatments were EM at standard and double strength, water + molasses, water, bokashi (a compost fermented with EM), and bokashi plus EM. The peat based seed raising compost received a water treatment and EM treatment. A very low rate of emergence of lettuce seedlings in all treatments appeared to be caused by high temperature dormancy. The trial was repeated in lower temperatures without success. The number of weed seedlings from the first trial were analysed but no clear trend was apparent. Keywords. Effective microorganisms, EM, lettuce, Lactuca sativa, pea, Pisum sativum pea root rot, Aphanomyces euteiches, biological control, damping off.