ALEXANDRIA, La. - Rainfall totals across Louisiana have been excessive during the last week. Since May 11 most cotton growing parishes, with the exception of the Shreveport area, have received from 4 to 15 inches. What will be the ultimate effect on the crop that has been planted?
At this point we really do not know the answer. The largest cotton plants in the state are at the four- to five-leaf stages. These plants will likely resume normal growth once the fields drain and sunshine returns. The youngest cotton in the state was planted just before the rains occurred and plants had not emerged. Some of these fields will likely be replanted. A great many acres are somewhere between these two extremes.
Cotton can generally tolerate 24-36 hours of submerged, waterlogged conditions, but decay becomes apparent with more prolonged periods of standing water. The bottom line is that older and larger cotton plants are more likely to tolerate this problem and recover normally.
There is little that a producer can do to improve crop health until some drying occurs. Once that happens we will have a better feel for where the crop is in terms of growth and development.
In the meantime, there are some issues to consider. The first question addresses potential nitrogen losses. Some cotton has already received side dress applications and there is concern over the need for additional nitrogen fertilization to maximize yield potential. While some nitrogen has been lost due to leaching, the primary loss of N is likely to be from denitrification under the anaerobic conditions present in flooded soils.
To answer the question of how much has been lost, one opinion may be as good as another. I suspect the losses are minimal. Cotton does not have a very high nitrogen requirement until squares and blooms appear on the plant. Therefore, I would caution to delay any decision on additional nitrogen until you know the condition of the crop after fields dry, and until cotton plants begin squaring and have a higher N requirement.
The second issue to consider is also related to “supplementing” a waterlogged crop. Following excessive moisture, drought, hail, or just about any other stressed condition, there is always a temptation to make applications of foliar fertilizers or plant growth regulators to jump start the crop. Rarely do these treatments ever have any real economic benefit. This is particularly true on small cotton plants. For supplements to be of value, foliar uptake is required. Plants simply do not have much leaf area available for product uptake. Moreover, stressed leaves normally are unable to efficiently absorb and translocate foliar products.
Pre-bloom cotton has a relatively small nutrient demand. This cotton crop needs a recipe of dryer soils, sunlight, and heat units more than anything else. There will be no substitute in a jug for improved field conditions.
Several fields I have observed in the past few days have portions (usually an end) that have been under water or wetter than more well-drained areas. I think many of these fields will have areas of stunted plants even though replanting is not necessary. It will be imperative to factor in these areas when considering applications of products that are time-sensitive or targeted to a particular growth stage. This includes over-the-top glyphosate applications, Envoke, and mepiquat to name a few.
Without a variable rate application, there is no hard and fast rule for managing fields with variable stages of plant growth. We all have some experience with this situation, so it is not something new. However, it may be more common and result in severe plant injury based on the amount of rainfall many areas have received. This will be another factor that must be considered when developing the best crop management strategy during the next few weeks.
Dr. Sandy Stewart is Extension cotton specialist with the LSU AgCenter.