There are symptoms for the various Fusarium races and all look similar. The only way to confirm Race 4 is through lab analysis.
Telltale signs of Race 4 are:
• Blank areas of a cotton field where there are no plants or plants are dying.
• These areas may be small initially, but can expand down the rows and across fields in year two or three, especially if the field has a history of susceptible varieties.
• Surviving plants adjacent to the blank areas will have wilted, splotchy foliar chlorosis and/or necrosis and nearly continuous, dark brown vascular staining in the tap roots
• Race 4 vascular dark brown staining will be most evident on tap root.
• Verticillium wilt symptoms appear later in the season and vascular staining is generally lighter with verticillium, more discontinuous and usually evident in lower stems as well as in root tissue.
• Limit soil movement from infected fields.
• Pressure wash implements, sprinkler pipe, machinery from farms even suspected of having Race 4.
• On known Race 4-infected fields, avoid land planing or other leveling that moves soil and consider reduced, conservation tillage in those fields.
• Restrict irrigation tail water movement off infested fields.
• Limit equipment traffic through Race 4 infested areas of fields.
• Keep gin trash from infested fields off ground.
• Avoid using manure from cattle corrals using gin trash for bedding or cattle fed with cottonseed from known Race 4-infested fields.
• Do not allow seed production from infested fields or even fields next to known infested fields.
Management of Race 4
• Plant only varieties with the highest level of Race 4 resistance. UC/USDA screening tolerant/susceptible variety trials are available at cottoninfo.ucdavis.edu.
• Rotation to non-host summer crops or summer fallow will likely reduce inoculums, especially in multi-year rotations.
•Long term weed free fallow may reduce inoculum.
• Soil solarization with fumigants/tarping for one to two months may reduce inoculums.