Pythium in Vegetable Production

Alyssa Koehler, Extension Field Crops Pathologist;

A few weeks ago, we discussed Pythium in field corn, but it can also cause problems in sweet corn, snap beans, and a number of other crops. Wet spring conditions and low or poorly drained areas of the field can all favor root rot and other diseases caused by the oomycete pathogen, Pythium.

Sweet Corn

While seed rot can be caused by a number of organisms, we most frequently observe Pythium as the causal organism. Whenever there are cool, wet soils or other factors that delay germination, the seedling has a greater chance of being exposed to Pythium in the soil. Seedlings may fail to make it out of the ground, or may germinate and display symptoms of yellowing, wilt and leaf drop, stunting, or death (damping-off) (Figure 1). When dug out of the soil, infected plants typically have brown, rotted roots and mesocotyl. Pythium is usually worse in early season plantings, but could appear at any planting date due to the range of Pythium species found in our soils. Chemical and biological seed treatments are available to help reduce damping-off.


Figure 1. Corn seedlings with post-emergent damping-off caused by Pythium spp

Figure 1. Corn seedlings with post-emergent damping-off caused by Pythium spp.


Snap Beans
In snap beans, Pythium can be a problem at different stages throughout the season. Root rot can occur early in the season or into the summer, while cottony leak of pods occurs on mature plants near harvest or postharvest when beans are in transit to processing facilities. Cottony leak (Pythium Blight) is typically worse when there is rainy weather with cool temperatures. Look for thick, white, cottony growth on leaves, stems, or fruit (Figure 2). To reduce chance of disease, avoid close planting and maintain proper air circulation. It is also recommended to avoid harvesting and packing during wet weather. ProPhyte, K-PHITE, Phostrol, Rampart, and Ridomil Gold Copper are also options to help reduce the damage from Pythium blight.


Figure 2. Snap bean cottony leak

Figure 2. Snap bean cottony leak