Diseases in cotton threaten the crop from the seedling stage until late in the season. They can lower yields and quality and, in some cases, wipe out whole stands.
Seedling diseases and nematodes: dangers to young plants
The seedling disease complex represents the most common disease problems found across the Cotton Belt. This complex includes:
- Pythium (damping-off): Seed rot and pre-emergence damping-off diseases caused by Pythium can be major problems in cotton regions where soil temperatures at planting are less than 60 degrees F. Symptoms include root decay and death, as well as light tan to dark discoloration of rotting roots and stem tissues.
- Rhizoctonia (soreshin): Seedling death resulting shortly after emergence is called postemergence damping-off. Rhizoctonia is usually the cause of soreshin, which refers to situations in which only stem girdling occurs. Disease lesions – well-defined margins and varying in appearance from water-soaked to light tan, reddish-brown or dark brown, normally below the soil line – appear mainly on the seedling’s stem below its cotyledons or seed leaves, but they can also occur on taproots.
- Thielaviopsis (black root rot): Also called black root rot, Thielaviopsis causes blackening of the taproot and rotting of lateral roots, coupled with stunting of cotton seedlings. Development of black root rot is most severe when soil temperatures at planting range from 60–64 degrees F.
- Fusarium wilt/root-knot nematode complex: The root-knot nematode (RKN) is a small, parasitic worm that injures cotton roots, allowing entry for the Fusarium disease. Root-knot nematode and Fusarium wilt are grouped as a complex because they are normally found together in sandier soils.
Verticillium wilt: A common disease in the Southwest
Once crops are past the seedling stage, cotton producers still need to manage other diseases. For example, Verticillium wilt can be a devastating disease. It occurs across the upper Mid-South, Southwest and Far West. It is especially a problem in the High Plains and Far West.
Leaf symptoms can vary according to variety, fungal isolate, developmental stage and environmental conditions. Early leaf symptoms include chlorosis, a yellowing of leaf tissue due to a lack of chlorophyll, between the veins. Verticillium wilt can result in malformed younger bolls, severely stunt plants and cause premature defoliation, yield loss and reduced fiber quality.
Bacterial blight: A widespread problem
Bacterial blight, also called angular leaf spot because of the angular appearance of the resulting lesions, can be found extensively in the Cotton Belt, with hotspots in the Mid-South and on the High Plains. Rainy, cool periods provide conditions that are conducive for this disease. Symptoms include:
- Small, dark green spots, which are first visible on the underside of leaves and later on the upper leaf surface. Lesions can also extend along the main leaf vein.
- Leaf petioles and stems may become infected and cause premature defoliation.
- Black cankers may encircle the stem or branches, causing these portions to die above that line.
- If bolls become infected, boll rot can result in rotted seed and discolored lint.
Target leaf spot: Premature defoliation and yield loss
Target spot (Corynespora cassiicola) has been identified in several cotton states, including Georgia, Alabama, Louisiana, South Carolina and North Carolina. Warm, humid conditions favor the development of this disease. Symptoms first develop as red dots that lead to the formation of irregular to circular lesions with tan to light brown centers. Lesions further enlarge into a target-like appearance formed from concentric rings within the spot. Heavy infection can cause premature defoliation, along with yield loss.
Cotton root rot: Rapid wilt and plant death
Cotton root rot, often called Texas root rot or Phymatotrichum root rot, occurs from Texas west to California. This disease often causes the rapid wilt and death of cotton in the late spring, summer and early fall in warm temperatures. Dead and withering leaves remain attached to the plant; however, infected plants may also decline more slowly during cooler weather and in fields with well-managed plants. Dying or declining plants have rotted root systems.
Managing Cotton Diseases
In addition to best management practices for cotton – such as crop rotations – several products can help manage disease resistance and greatly increase success.
Starting off with a good seed treatment is an excellent way to control seedling diseases and protect cotton above and below the ground.
- EverGol® Prime is an innovative seed treatment fungicide that protects against Rhizoctonia and promotes stronger, healthier root growth for faster crop establishment.
For cotton-growing areas with a history of disease pressure and/or conditions that are conducive to seedling disease problems, growers can maximize their stands by planting in optimal soil temperatures and protect their cottonseed investment with a premium fungicide seed treatment.
Trilex® Advanced offers complete, broad-spectrum protection from common cottonseed and seedling diseases, including Rhizoctonia, Fusarium and Pythium.It also suppresses Thielaviopsis basicola to increase early season plant growth, strengthen stands and improve yield potential. Trilex Advanced is the preferred fungicide partner for Aeris® insecticide/nematicide seed treatment.