Flooding, ponding and saturated soils continue to impact crops across southwestern and south central Minnesota. Intense rains, ranging from six to eight inches or more in several counties in southwestern Minnesota July 3, exacerbated the wet conditions.

Potential damage to crops depends on several factors, including:

• Crop stage during the flooding/ponding

• Duration of the flooding/ponding

• Air/soil temperatures

• Rate of drying and soil type

Crop development stage is quite variable this season due to a wide range of planting dates.

Partially submerged plants have a better chance of survival than completely submerged ones, although root development and nutrient uptake will still be impacted.

Corn at the V5 stage (five leaf collars) can generally survive two to four days of flooding, although plants may not survive more than 24 hours when temperatures are above 77 degrees Fahrenheit.

Corn at the V7 to V10 stage can generally tolerate standing water for seven to 10 days, depending on the temperature.

During pollination, corn is more susceptible to flooding, as this is one of the most critical stages for corn development in determining yield potential.

In general, significant yield losses can be anticipated after two to four days of standing water at this growth stage. Yellow corn, a sign of nitrogen deficiency, can be observed in fields across the region due to excessive moisture and prolonged saturated conditions.

Nitrogen deficient corn can respond to nitrogen applied as late as pollination, but at this point in the season, no more than about 30 pounds of nitrogen per acre would be recommended.

If nitrogen is broadcast on tall corn, urea is the safest nitrogen source. Yield potential of the crop and the ability to increase yield with nitrogen is likely compromised at this stage in the growing season, so it is important to take a hard look at the cost-benefit of the application in each situation.

Soybeans can generally survive being under water for 48 hours.

Four days or more of flooding stresses the crop, delays plant growth and causes the plants be shorter with fewer nodes. Flooding for six days or more can depress yields significantly. 

Flooding for a week or more may result in significant (or entire) losses of stand.

Ideally, once the flood waters recede, drowned-out spots should be planted to non-crop covers to suppress weeds while reducing the effects of fallow syndrome.

Fallow syndrome can occur if “good” fungi that help in nutrient uptake die off since there are no living roots to survive on. This can impact yield potential of the crop the following year. Be sure to match cover crops with any applied herbicides, and follow rotational restrictions listed on the herbicide label if grazing or feeding of the cover crop is desired. A low-cost option for drowned-out spots is soybeans, although soybeans planted beyond mid-July may not produce a harvestable crop.

Planting soybean into a soybean-on-soybean situation is not preferred. Even very small areas of soybean-on-soybean can lead to reservoirs of soybean pests and diseases that will affect subsequent soybean crops for years to come.

More detailed information on flooding impacts on crops can be found at z.umn.edu/floodedcrops. 

– Information and photo provided by Liz Stahl, University of Minnesota Extension Service educator, Jeff Coulter, Extension corn specialist, Seth Naeve, Extension soybean specialist and Fabian Fernandez, Extension nutrient management specialist