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Disease Management

The most effective ways of managing ARR are through the use of resistant cultivars (Figure 5, 16), management practices that improve soil drainage, and avoidance of highly infested fields. Resistance has been identified in alfalfa, bean, pea and red clover and breeding for resistance to ARR has been most successful for alfalfa and bean. In pea, however, combining horticultural and consumer-accepted traits with host resistance has been problematic.

Crop rotation has been used to slow the rate of inoculum build-up in pea production areas. However, this practice is ineffective in reducing high inoculum levels due to the longevity of oospores. Once a field is determined to have a high ARR potential, growers are advised against planting a susceptible host. To assess ARR potential in a given field, soil samples are collected yearly and evaluated in greenhouse trials (Figure 17) following protocols originally developed at the University of Wisconsin-Madison in 1958. Other control strategies for ARR include preventing or correcting saturated soil conditions and compaction.

Figure 16

Figure 17

Fungicides, soil fumigants and biological control options, have been explored but have proven ineffective for use in commercial production. Additionally, A. euteiches is insensitive to metalaxyl, a chemical effective against many oomycetes such as Pythium and Phytophthora. The non-target effects of herbicides were studied in the 1970s as a means to lower the severity of ARR of pea. Dinitroaniline herbicides were shown to be detrimental to A. euteiches and were used to lower the severity of ARR in commercial pea production. Pendimethalin and trifluralin are active ingredients of the dinitroaniline herbicides that have a suppressive effect on ARR of pea. In Wisconsin, 50% of the commercial pea acreage is treated with pendimethalin and 5% with trifluralin.

Cover crops and green manure crops have been studied as means to lower the severity of ARR of pea. Although using oats as a green manure has been successful, cruciferous plants have shown the greatest potential as an economical means of controlling of ARR. Isothiocyanates, thiocyanate ions, nitriles and epithionitriles are released from Brassica leaf or seed tissues by hydrolytic enzymes. These volatile compounds have detrimental effects on numerous microbes including A. euteiches. Although less feasible for large commercial acreages, the use of crucifer species as green manure crops has practical application for fresh market and organic growers who typically produce on a smaller scale.

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