Particularly devastating is the fact Race 4 FOV renders fields pariahs as a cotton planting seed production fields. Plant pathologists are insistent that no seed be produced in known Race 4 FOV infected fields and all seed fields be tested for the presence of the fungus. It is so serious it has actually impacted the economic value of land.

And Hutmacher believes many cotton growers will unfortunately discover that fact for the first time this year.

He explained that with the expanded 2011 SJV cotton acreage, fields are being seeded to cotton after several years out of cotton, periods during which prior problem areas could be forgotten and farming practices continued to move around inoculum capable of spreading the disease. These scenarios are generating phone calls as growers search for why some cotton stands are disappearing.

If Race 4 FOV has been present in those fields, it could have been easily and unknowingly spread throughout fields with the movement of infested soil on equipment or in irrigation water, likely primary methods for its spread. Also, infested soil on farm equipment or sprinkler pipe unknowingly moved from infected fields to clean fields can also spread inoculum of Race 4 FOV.

As the weather warmed, Hutmacher’s phone started ringing with growers seeking a reason for the wilted and dying seedling cotton. The cooler weather of late may allow Race 4 FOV infected plants to survive longer only to succumb to the disease as the weather warms again. On the flip side of the cool weather, the plants could be put under additional Race 4 FOV stress that may compound impact of the disease. Either way, Hutmacher told a recent UC Cotton Workgroup meeting in Tulare, Calif., he expects to see much more Race 4 fusarium this season.

Unfortunately, other parts of the U.S. Cotton Belt may also see more of Race 4 FOV.
USDA-ARS research plant pathologist Rebecca Bennett told the cotton workgroup meeting isolates similar to the Race 4 FOV found in California have also turned up in Mississippi and Alabama.

Researchers collected 39 samples of the fusarium wilt fungus from infected cotton plants in the U.S. and compared them to known reference strains. Some samples from Alabama and Mississippi were similar to this strain (Race 4) that is particularly damaging in California. To date, however, Race 4 has not been reported as causing serious disease problems in the Southeast. However, these preliminary results document the potential for increased problems with fusarium wilt in the Southeast.

All samples from Texas were related to known strains that were previously documented. These findings alert cotton breeders to potential disease problems that may warrant expanded breeding efforts for fusarium wilt resistance.