Tolerance to Phytophthora root rot refers to polygenic resistance. There are two sources of major gene resistance. There are several races of SCN, but both sources of resistance are effective against the Iowa populations. Varieties that do not lodge readily generally are less susceptible. You should make disease resistance a priority if a potentially recurring disease was a problem in 1994 or 1995.
Most diseases tend to recur due to pathogen buildup.
Resistance is most effective if used in combination with crop rotation and other management practices. Continuous planting of one resistant variety can lead to a breakdown in resistance to some diseases, so there is some risk to overuse of resistance. In the absence of disease, some resistant varieties may not yield quite as well as susceptible varieties, but the difference is usually small, especially when compared to the substantial yield benefit of resistant varieties in the presence of disease. A new publication, Disease Resistant Soybean Varieties for Iowa, supported by funds from the Iowa Soybean Promotion Board, is now available from ISU Extension Distribution. It also will be included in the January issue of the Iowa Soybean Review.