Georgia Cotton: Yields at Risk Without Plant Growth Regulators

    A University of Georgia Cooperative Extension agronomist says managing vegetative growth is key for cotton farmers. Yields and profits may be at risk without the use of plant growth regulators (PGRs).

    A PGR is chemical compound that limits the vegetative growth of a plant — in this case, cotton. Managing the plant’s growth is often necessary because of Georgia’s environment, climate and the growth characteristics of varieties used by growers, said Jared Whitaker, a crop and soil scientist with UGA Extension.

    “In Georgia, we’ve got a relatively long growing season,” Whitaker said. “In most cases, we do an excellent job of providing the plant what it needs in regard to soil fertility and irrigation, if available. We know that this situation sets up good yield potential but often creates more vegetative growth than needed and wanted. When uncontrolled, excessive vegetative growth can delay maturity and make the canopy too large and thick.”

    “With this excessive growth (often referred to as rank cotton), there can be issues with boll rot and more potential for target leaf spot disease,” Whitaker said. “It’s more difficult for spray to penetrate into the canopy and it can make harvest more difficult and slow.”

    Whitaker said boll rot could be a big concern in rank cotton. An overgrown plant increases the potential for high moisture down in the canopy. When bolls crack open slowly, they rend up retaining too much moisture, setting the stage for rot and potentially significant yield loss.

    Many factors to consider before application

    Whitaker said multiple factors have to be considered when applying PGRs, including temperature, soil moisture, irrigation and field history. The PGR needs also vary among different cotton varieties.

    For several years, up to 85 percent of cotton planted in Georgia was the variety DP 555 BR, an aggressively growing cotton requiring intensive PGR management. UGA cotton experts and Georgia farmers knew the variety very well and knew how to manage it best.

    However, that variety is no longer available, and farmers have worked to fill that void with a diverse collection of varieties. These varieties all have different growth characteristics and PGR needs. Some grow aggressively and require heavy management. However, some are sensitive to growth regulators, and farmers risk overusing PGRs and damaging their yields, Whitaker said.

    “What we try to do is manage growth, but what we don’t want to do is overdo it,” he said. “Ultimately, if we overdo it, we can potentially limit plant growth and end up with too few fruiting positions to maximize yield. Our hot and humid environment along with unpredictable rainfall patterns tend to limit fruit retention, so we often need a large plant to have enough positions in order to reach optimum yield potential.”

    Plant growth regulators are generally applied more than once per year and up to three or four times during the growing season. Whitaker has conducted a significant amount of research with PGRs and new cotton varieties to see which methods work best. More detailed information can be found at the UGA cotton website or by contacting UGA Extension agents at 1-800-ASK-UGA1.

    According to the UGA Center for Agribusiness and Economic Development, cotton generated $1.2 billion in Georgia in 2014 and accounted for 42 percent of the state’s row and forage crops.

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