Alabama Cotton, Peanuts: Excessive Rainfall May Cause Field Issues

Image from Alabama Cooperative Extension

Producers from all areas of Alabama have had planting or harvesting delays and are now making management decisions based on excessive rainfall.

The summer months of 2016 ended in a late-season drought that devastated some row crops and forced cattle producers to make difficult management decisions. The onset of 2017 with continued droughty conditions seemed imminent until rain began falling in late May and early June. Now, less than 7 percent of the state is currently experiencing “abnormally dry” conditions.

Alabama Cooperative Extension System professionals are working to assist farmers as they make herbicide applications and crop re-plant, planting or harvest decisions.

Soil Nutrient Levels a Concern with Persistent Rainfall

Dr. Audrey Gamble, an Alabama Extension soil health specialist, said heavy rainfall throughout the state has likely caused significant nutrient losses in some soils.

“Nitrogen, sulfur and potassium are susceptible to leaching under heavy rainfall, particularly in sandy soils with low organic matter content,” Gamble, who is also an assistant professor in Auburn University’s Department of Crop, Soil and Environmental Sciences, said. “Although phosphorus is not as likely to leach, it can be lost as runoff during rain events.”

With many areas of the state receiving heavy rainfall recently, producers may consider re-testing soil nutrient levels.

Gamble said soil testing is vital to determining whether to apply additional fertilizer following heavy rain.

Many crops grown in Alabama require nitrogen applications. Test reports don’t include soil nitrogen concentration levels because these levels fluctuate based on temperature, soil texture and other factors.

Gamble said nitrogen recommendations are based on type of crop being grown. Supplemental N applications may be beneficial to prevent yield losses.

“It is also important to point out that conservation practices, such as cover cropping and reduced tillage, are important for reducing erosion/runoff and storing additional nutrients in the soil,” she said. “The surface residue and improved soil structure from conservation practices, help to increase water infiltration and reduce erosion.”

Crop Herbicide Injury Caused by Excessive Rainfall

Some producers experienced herbicide injury after substantial amounts of rainfall were recorded in late May and early June.

Alabama Extension weed scientist Dr. Steve Li said checking the crop stand is the first step before making a re-plant decision. If the stand is inadequate, then producers should consider a replant.

“If the stand is acceptable and seedling burn is the only issue, wait to see if the seedlings begin putting on first true leaves,” Li said. “Usually the plant recovers and no visible injury can be seen on true leaves as long as true leaves start growing.”

Li, also an Auburn University assistant professor in the Department of Crop, Soil and Environmental Sciences, said varieties with high seed vigor may get a better stand and grow out of initial injury sooner.

He said producers are also concerned about yield losses because of soil herbicide injury. Li reports no significant cotton and peanut yield reduction from soil herbicides in the past two years of his trials. He said no crops suffered significant losses as long as herbicides were applied using label rates.

“Herbicide injured cotton and peanuts can usually grow out of initial injury and stunting in three to four weeks under normal growing conditions,” Li said. “However, if these crops suffer further stresses—such as prolonged water-logging, thrips, snails, rhizoctonia, fusarium and other pests, yield loss may be possible.”

Li said managing other pests and stresses in the field will be important in order to secure yields.

For more information, read Herbicide Damage After Excessive Rainfall with more detailed information about herbicide injury.

Controlling Excessive Vegetative Growth in Cotton

Alabama Extension cotton specialist Dr. Trey Cutts said one of the issues facing producers following heavy rainfall is excessive vegetative growth on cotton plants.

“For dryland producers, heavy rainfall years—like this one—will require a change from a more moderate plant growth regulator (PGR) approach to a more intensive approach,” Cutts said. “If continued rain patterns persist—no matter your irrigation setup—getting the first PGR application on before the first bloom is crucial to managing excessive growth later in the season.”

He said producers cannot rely on late season applications alone to control excessive growth.

Cotton PGRs do not stimulate flowering, help plants produce more bolls or have any significant effect on yield. However, a PGR can help improve boll retention (especially in the lower canopy) and help manage excessive canopy growth. Canopy growth management will likely help prevent lodging, boll rot incidence and may reduce impedance of insecticides, fungicides and defoliants. All of these factors increase the likelihood of higher yield potential, as yield potential is very environmentally dependent.

When deciding to apply a PGR, Cutts said producers should consider several factors: management options, variety selection and environmental factors.

Irrigated cotton will require more intensive PGR management. Planting date is also an important variable.

“With a late planting date, more intensive PGR management may help the crop to mature faster,” he said. “Producers pushing yield potential with heavy fertilizer and other inputs should expect a more intensive PGR use to also be required.”

Finally, producers should consider environmental factors. The historical growth in the particular field and the current and future growing conditions may affect PGR effectiveness.

Find more in-depth information on plant growth regulators online in an Alabama Crops Team webinar, presented by Dr. Cutts. See Dr. Cutts’ Timely Information sheet: Plant Growth Regulator (PGR) Management Under High Rainfall Conditions

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