Unlike other fusarium races, Race 4 is not associated with root knot nematodes. It does not need them to vector the disease. It is the only fusarium that does not require nematodes to spread. Once it is in the soil, it is there forever and if inoculum levels reach high enough, a field can be rendered useless forever for cotton production.

Although it has been around for at least two decades, concerned dwindled among growers along with cotton acreage not long after it was found. SJV acreage declined to less than 200,000 acres in 2009. However, it did not go away; it just remained dormant until cotton returned to the fields. SJV cotton acreage has increased significantly over the past couple of years and with 450,000 acres in 2011, Fusarium Race reappeared with a vengeance.

It has been identified in at least 200 fields spread out over every single SJV cotton-producing county.

“It really showed up in 2011,” said Williams.

Cotton is the only crop Fusarium Race 4 impacts, but it remains virulent for decades in soil, once a field is infected with diseased cotton. It is spread primarily by soil on equipment, sprinkler pipe and irrigation water.

University of California Extension cotton specialist and agronomist Bob Hutmacher said processing tomato, lettuce and other vegetable harvesting operations on the West Side of the San Joaquin Valley are particularly problematic in spreading Race 4, since fields are muddy at harvest time and trucks and harvesting equipment carry mud onto roadways and into other fields.

Hutmacher recommends:

  • 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.
  • Limit land planing to prevent spreading infected soils to clean areas of a field.
  • Don’t spread gin trash from infected fields to clean fields.