Which early season soybean disease is more severe in low, poorly drained clay soils?

The correct answer is Phytophthora, which is a significant pathogen affecting soybeans, particularly in poorly drained soils. This disease thrives in waterlogged conditions, which are more common in low, poorly drained clay soils. Phytophthora sojae, the pathogen responsible for Phytophthora root and stem rot, is notorious for causing seedling damping-off and root rot in these adverse conditions.

In poorly drained environments, the excess moisture can create a favorable environment for Phytophthora to infect seedlings, leading to greater disease severity. The roots of the plants can become damaged, resulting in reduced water and nutrient uptake, ultimately leading to plant death or stunted growth.

Other pathogens listed, such as Pythium and Rhizoctonia, also affect soybeans, but they tend to be more opportunistic in a range of soil conditions. While Pythium can cause damping-off, it is primarily associated with overly wet, poorly drained soils as well, but its symptoms are often less severe compared to those caused by Phytophthora. Rhizoctonia can cause seedling disease as well, but it is generally more prevalent in well-drained soils and does not show the same level of severity in heavy clay conditions. Fusarium