With hot temperatures, growers may be more likely to note stress-symptoms resulting from damaged root and vascular symptoms caused by plant-parasitic nematodes and/or Fusarium wilt. While there is nothing to be done now, growers should note where nematodes and Fusarium wilt are causing damage in a field and let us help them make decisions for the next cropping season. We are finding some fields that contain pockets of Fusarium wilt in Colquitt County. Fusarium wilt is usually found in association with infections by the southern rootknot nematode, which has a synergistic effect on this disease.
The most visible symptom of Fusarium wilt is the presence of wilted and dying cotton plants in a field. Some plants may be stunted and the leaves may yellow between the veins (also know as interveinal chlorosis). Root-knot nematodes alone can cause wilting, but the synergistic effect with the Fusarium fungus is usually required to kill plants, unless the soil is extremely dry for prolonged periods. Fusarium-infected plants wilt even if soil moisture is adequate because of damage to the vascular system that carries water throughout the plant. A preliminary diagnosis of Fusarium wilt can be made fairly easily in the field by slicing through the plant stem at a shallow angle to expose the vascular tissue. Fusarium wilt will cause a noticeable browning of the vascular tissue. This discoloration is the result of damage to the vascular tissue which prevents adequate flow of water and nutrients. If you carefully dig up the root system of wilting plants, you will also usually see significant galling caused by
root-knot nematodes.
As the cotton crop continues to develop and approached bloom, remember that Target Spot can be a significant issue, especially along the Coastal Plain and where cotton vegetative growth is rank/excessive. Growers in such conditions, especially where target spot is currently detected or has been problematic in the past should consider options for management including timing of first application (as early as first bloom in some situations) and choice of fungicide.
Bob Kemerait, UGA Plant Pathologist, has developed a target spot risk management assessment to help determine if a fungicide application will make you money. This risk management assessment takes into account factors such as field history, plant growth, irrigation, weather, and crop rotation. This It can be seen in the link below.
cotton target spot checklist
BACTERIAL BLIGHT on cotton: Bacterial blight is being noticed in Colquitt County in several different cotton varieties. It is too early to tell how much impact there will be for this season. We have nothing to spray to contain the disease-reducing leaf wetness periods (e.g. managing growth and irrigating at night) can help to slow the progress of the disease. Below are two photos of bacterial blight in cotton.
