July 2-3 Rains bring flooding concerns

Today's rainfall report are astonishing. It appears the heaviest rainfall was north of the turnpike. Rainfall in the Wauseon area was 2.5 inches but north of the turnpike reports of 5-7.5 inches are common across much of northern Fulton County. Below are articles reprint from 2003 edition of CORN newsletter on flooding in corn and 2006 CORN related to soybean and flooding injury.

Early Season Ponding and Flooding Injury to Corn-Dr Peter Thomison

Recent heavy rains have generated questions about flooding and ponding injury in corn. The following are some tips to consider when evaluating possible damage from water saturated soil conditions.

The extent to which flooding injures corn is determined by several factors including: (1) plant stage of development when flooding occurs, (2) duration of flooding and (3) air/soil temperatures. Prior to the 6-leaf collar stage (as measured by visible leaf collars) or when the growing point is at or below the soil surface, corn can usually survive only 2 to 4 days of flooded conditions. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. If temperatures are warm during flooding (greater than 77 degrees F) plants may not survive 24-hours. Cooler temperatures prolong survival. Once the growing point is above the water level the likelihood for survival improves greatly.

Even if flooding doesn't kill plants outright, it may have a long term negative impact on crop performance. Excess moisture during the early vegetative stages retards corn root development. As a result, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. Flooding and ponding can also result in losses of nitrogen through denitrification and leaching.

If flooding in corn lasts less than 48 hours, crop injury should be limited. To confirm plant survival, check the color of the growing point. It should be white to cream colored, while a darkening and/or softening usually precedes plant death. Also look for new leaf growth 3 to 5 days after water drains from the field. Sometimes the growing point is killed by bacterial infections during and after flooding, but plant growth continues in the form of non-productive tillers (suckers).

Disease problems that become greater risks due to flooding and cool temperatures include pythium, corn smut, and crazy top. Despite fungicide seed treatments, pythium root rot contributed to serious stand reductions in many corn fields last year. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season.

Flooding Injury to Soybeans - Anne Dorrance

Several past studies have evaluated the effects flooding on soybeans. Research projects led by Dr. Tara Van Toai of the USDA-ARS and Department of Horticulture and Crop Science. In one study, soybean plants at the V2 and V3 stages were flooded naturally due to excessive rainfall, something we are all familiar with. Two 9-m wide transects across the flooded area within each field were divided into plots of 9 m by 9 m according to flooding duration: no flooding, 1 to 3 d, 4 to 6 d, and 6 to 8 d. Yield was reduced primarily due to reduced plant populations, shorter plants and fewer pods developing per plant. Other studies showed yield losses of 20% when soybean fields were flooded for greater than 2 days, but it should be noted they still had a yield. Some varieties can tolerate flooding more than others. For those fields with greater than two days of total saturation, ponding, can expect to see some long term effects. Secondary factors, such as root rots, will also contribute to the damage. Growers should note the varieties and compared varieties that were flooded for the same length of time. Some varieties will be impacted to a greater degree than others.