Heavy rains in the region have caused flooding, ponding, and plant damage across low field areas. Prolonged soil saturation affects crop growth and yield. Corn is very sensitive to flooding in the early vegetative stages (especially prior to the 4th or 5th leaf stage). In early growth stages, corn or soybeans can survive for only two to four days under water in anaerobic conditions. Moderate water movement can reduce flood damage by allowing some oxygen to get to the plants, keeping them respiring and alive. Drainage within one to two days increases the chance of survival. The most susceptible crops to flooding are dry beans and potatoes. Only a day or two of flooding can cause plant death or damage so that full recovery is never attainable.

The extent of injury to seedlings is determined by the plant stage of development at ponding, duration of flooding and the air/soil temperatures as well as if auxiliary buds are present on damaged plants. If temperatures are warm during flooding (greater than 77 F), plants may not survive 24 hours. Cool temperatures may prolong survival. However, cold, wet weather favors disease development. Seed treatments may provide some protection from pathogens, but under extreme conditions are limited in the level of protection they can provide. Seedling development slowed or delayed two to three weeks allows soil-borne pathogens a greater opportunity to cause damage. Seed rots, seedling blight, corn smut and crazy top affect corn plant development later even though ponding occurred earlier.

Delayed soybean growth allows diseases such as Fusarium root rot, Phytophthora rot and Pythium rot to establish and weaken or destroy seedlings. Limited hybrid and variety resistance to these diseases and difficulty in predicting damage makes evaluation difficult.

On surviving stands, remember that favorable weather for plants after ponding is important. Cultivation of adequately dry soils will open and aerate surface soil and promote root growth. Be careful working the soil. Working wet soil causes compaction that can retard root and crop growth.

An additional nitrogen application in corn may be necessary in fields that show signs of yellowing or uneven growth. See the article on Nitrogen Status of Corn for recommendations for assessing the need of additional N.

Phillip Glogoza
Regional Extension Educator—Crops