May 26, 2011

How long can a plant survive under water? Should you expect it to survive two or three days?

My experience has been that crop loss to drowning in a flood is quite variable. In general in areas of the field completely covered with water, the plant will likely die in 24 hours. In some instances, depending on a number of variables, it can live longer. Plants in partially flooded areas are likely to survive unless the wet condition persists for a long time. Cooler air and water temperatures, as we’ve seen this week, will help increase the odds for survival.

Evaluating plant survival can be difficult. Mud in the whorls of plants will make them yellow and sick for some time, or until the growing leaves push the mud out. A good rain may help plants recover by washing off this mud.

If the weather following the flood is mild, plants which are not likely to survive can look better than they should for some time. To determine root health and the plant’s potential for survival, dig up and wash plants in a bucket of water. If the roots are solid and healthy, the plant will likely be okay. If the roots are mush, the verdict is likely dire. In the latter case, contact your crop insurance agent for an evaluation as soon as possible so you can consider your options and do a timely replant, if needed.

Replanting Options

Replanting corn in portions of the field that were killed or severely damaged should be done to make harvest as easy as possible. At the end of the season damaged plants will likely dry down on a different schedule than the rest of the field, which will complicate harvest.

When replanting:

• Plant mid season hybrids to June 5. After June 5 you might switch to early or mid-early season hybrids. Steer away from super early wonder hybrids which are likely adapted for the Northern Plains.
   
• Don’t dramatically increase planting rate.
   
• Make sure the hybrid you replant has corn borer traits. Corn borer will seek out late planted fields.

After last year’s hail in Gage and Johnson counties, we saw a huge influx of southern corn rootworm (cucumber beetles) that even overwhelmed fully stacked hybrids. If you don’t want downed corn, plan to scout even if you’re planting stacked hybrids.

In many instances, depending on amount and rate of rainfall, the fertilizer you already applied may still be in place (see related story). Denitrification of nitrogen can start after a couple days underwater and could be significant in extended periods of flooding.

When replanting, use a starter fertilizer. Consider creating a reference strip of higher rate application to evaluate the need for nitrogen before the side-dress period is over. You could apply it with your planter by driving slowly to apply the fertilizer without seed or you could just buy a 50 lb bag of urea at the coop and spread it down a few rows by hand. Herbicides are likely to be gone, so go with post options that best fit the program in the rest of the field, unless this replant area is easily separated.

Replanting Soybeans

If you’re replanting soybeans, you’ll want to pay special attention to two aspects. Make sure the seed is treated with a fungicide as replanted soybeans are more prone to seedling diseases. Rhizobia bacteria do not fare well in flooded fields. Make sure you innoculate the seed with fresh Rhizobia.

As with corn, mid-season or mid-early soybeans are a good choice. There is no reason to alter populations. I would not recommend switching corn to soybeans or vice-versa. If you have reason to do this, make sure there are no major herbicide concerns.

Additional Options

Farm operations with a livestock component have several more options. One, there is no concern with replanting corn, no matter how late you plant. This corn can be grazed, chopped, or baled.

You also could replant to forage crops like forage sorghum, sudex, or pearl millet.

Paul Hay
Extension Educator in Gage County