Winter wheat is one of the few crops that are currently in the ground and subject to the adverse effects of flooding. Reports indicate that many winter wheat fields have been flooded for varying periods in January. Some areas of Louisiana have received in excess of 15 to 20 inches of rain within a one-week time period. Not surprisingly, there is considerable concern about the impact that flooding or waterlogging will have on the 2013 winter wheat crop.
Crop injury from waterlogging is primarily caused by the lack of oxygen. When soils become saturated, the amount of oxygen available to plant tissues below the surface of the soil (or water level during flooding) decreases as plants and microorganisms use up what is available. The movement of oxygen from the air into water/saturated soil is much slower than in well-aerated soil and much less than needed by the crop and other organisms in the soil.
The depletion of oxygen rate in saturated soil is dependent on a number of factors, but temperature is the most important and predictable factor. The higher the temperature, the faster the rate of oxygen depletion. Under cooler temperatures, the negative effects of flooding take longer to impact plant tissues. Fortunately, the temperatures that have accompanied all of excess rainfall received in January have been relatively cold to mild.
The extent of water damage to a particular field largely depends on the length of time that there was standing water and the size of the area of the field that was affected. It should be easy to tell whether the wheat plants were flooded for too long; they either die or become rotted and stunted, with a chlorotic appearance (light green-yellow discoloration).
A major question arises as to whether or not these chlorotic, stunted plants will be able to recover and produce a reasonable grain yield. While this is a difficult question to address, it is still early in the growing season, so the potential exists for these affected plants to recover.
One thing is certain: if these affected areas don’t receive any 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 to 30 pounds of nitrogen per acre as soon as possible.
If the plants do respond to this fertilizer application by greening up and tillering, then chances are good they will develop into plants that are capable of producing some level of grain 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. 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. 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. Saturated and poorly drained areas favor plant diseases such as root rots. Downy mildew is a fungal disease that is also associated with poorly drained areas of a field.
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. Some infected plants may produce some upright growth, but they may have twisted heads and malformed leaves. Plants usually have yellowish lower leaves and these may have a leathery feel. No chemical treatments are available for root rots or downy mildew.
One final issue for the present time deals with wheat vernalization. In 2012, there were issues with partial or lack of vernilization with some wheat varieties. Vernalization is the response to cold temperature that overcomes dormancy and allows the wheat plant to start forming heads. The best vernalization temperatures are in the 40- to 50-degree range, not at colder temperatures. Vernalization is a biological process and plants have to be biologically active, not frozen, to occur.
Most winter wheat varieties grown in the Southeast require three to seven weeks of vernalization. If you recall in 2012, weather conditions were relatively warm during certain time periods in the winter months, and some varieties may have only received partial vernalization. These fields took on a “ragged” appearance after the plants headed out. 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.