Johnny Morgan, Harrison, Stephen A., Twidwell, Edward K.
BATON ROUGE, La. – Winter wheat is one of the few crops currently in the ground and subject to the adverse effects of flooding.
Reports indicate that many winter wheat fields have experienced flooding for varying periods in January, according LSU AgCenter forage specialist Ed Twidwell.
“Some areas of Louisiana have received in excess of 15-20 inches of rain within a one-week time period,” Twidwell said.
Experts are concerned about the effect that flooding or waterlogging will have on the 2013 crop.
Crop injury from waterlogging is primarily caused by the lack of oxygen, Twidwell said.
“When soils become saturated, the amount of oxygen available to plant tissues below the soil surface decreases as plants and microorganisms use up what is available,” Twidwell said.
The movement of oxygen from the air into water or saturated soil is much slower than in well-aerated soil and much less than needed by the crop and other organisms in the soil.
Oxygen depletion in saturated soil depends on a number of factors, but temperature is the most important and predictable.
The higher the temperature, the faster oxygen is depleted. Under cooler temperatures, the negative effects of flooding take longer to affect plant tissues.
Fortunately, the temperatures that have accompanied excess January rainfall have been relatively cold to mild, Twidwell said.
The extent of water damage to a particular field largely depends on the length of time there was standing water and the size of the area that was affected.
It should be easy to tell whether the wheat plants were flooded for too long, said LSU AgCenter plant breeder Steve Harrison. They either die or become rotted and stunted, with a light green-yellow discoloration.
A major question is whether or not these stunted plants will be able to recover and produce a reasonable yield.
“While this is a difficult question to address, it is still early in the growing season,” Harrison said. “So the potential exists for these affected plants to recover.”
Harrison says one thing is certain: If these affected areas don’t receive some nitrogen fertilizer, there is no way they will be able to recover.
It might be wise for growers to consider making an application in the range of 20-30 pounds of nitrogen per acre as soon as possible, Harrison said.
If the plants do respond to this fertilizer application by greening up and producing more stems, then chances are good they will develop into plants that are capable of producing some level of yield.
If the plants don’t respond to this fertilizer application, then no further inputs should be added.
Growers will have to analyze the extent of the damage to their fields, and make decisions about fertilizing the affected areas accordingly, Harrison said.
“If these affected areas do respond to this initial nitrogen fertilizer application, then an additional application will be needed in about mid-February, after the first node becomes visible,” Harrison explained.
Total nitrogen applications to these affected areas — and all other fields as well — should range from 90 to 120 pounds per acre.
Another consequence of the recent flooding events is the presence of wheat diseases, Harrison said.
Saturated and poorly drained areas encourage plant diseases such as root rots.
“Downy mildew is a fungal disease that is also associated with poorly drained areas of a field,” Harrison said. Plant symptoms produced by downy mildew are variable.
“Some diseased plants tiller excessively and are severely dwarfed, with many tillers growing only a few inches tall,” said Harrison.
Some infected plants may produce upright growth, but they may have twisted heads and malformed leaves.
Plants usually have yellowish lower leaves that may have a leathery feel. No chemical treatments are available for root rots or downy mildew.
In 2012, weather conditions were relatively warm during certain time periods in the winter months, and some varieties may have only received partial vernalization, or chilling time.
These fields took on a “ragged” appearance after the plants headed out, Harrison said.
“We have already had enough accumulation of cool temperatures for proper vernalization in 2013, so issues involving vernalization should not be a concern this year,” Harrison said.