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Title: Fusarium Race 4: Management Recommendations for Growers

item HUTMACHER, ROBERT - University Of California
item Ulloa, Mauricio
item WRIGHT, STEVEN - University Of California
item DAVIS, R. MICHAEL - University Of California
item KEELEY, MARK - University Of California
item DELGADO, RAUL - University Of California
item BANUELOS, GERARDO - University Of California
item MARSH, BRIAN - University Of California
item MUNK, DANIEL - University Of California

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/18/2011
Publication Date: 5/1/2011
Citation: Hutmacher, R.B., Ulloa, M., Wright, S.D., Davis, R., Keeley, M.P., Delgado, R., Banuelos, G., Marsh, B.H., Munk, D.S. 2011. Fusarium Race 4: Management Recommendations for Growers. National Cotton Council, Memphis, TN. pp. 188-192.

Interpretive Summary: Fusarium wilt is a disease of cotton that is caused by a soil inhabiting fungus. This fungus has several strains, or races, that vary in their ability to attack cotton, and in the timing and severity of disease symptoms. Because the fungus can survive for long periods in the soil, it is nearly impossible to eliminate from infested fields. In recent years, a specific race (race 4) has severely impacted cotton production in the San Joaquin Valley of California. Over the past seven years numerous observations of plant symptoms of Fusarium wilt caused by race 4 have indicated the importance of inspecting fields for infection while cotton plants are still seedlings. Management recommendations for reducing the spread of this fungus include removal of infected plants from the field, limiting movement of irrigation water through or out of infested areas, and taking care to minimize movement of infested soil by workers or farm equipment. At present the best approach to minimize yield losses from race 4 of Fusarium is to plant cotton cultivars with resistance to the fungus. Adoption of these management recommendations is important to efforts to prevent or reduce the continued spread of this disease in California.

Technical Abstract: Over the past five to seven years, race 4 of the fungal pathogen Fusarium oxysporum spp. vasinfectum (race 4 FOV) has been widely studied and has increasingly impacted cotton fields in California’s San Joaquin Valley. Findings from field and greenhouse research and observations can be summarized as: (1) most Pima cultivars show more severe symptoms, higher levels of stunting and plant mortality from race 4 FOV than seen with most Upland cotton cultivars; (2) some moderate to highly-resistant commercial Pima cultivars have been identified from several seed companies; (3) several USDA-ARS experimental Pima germplasm or breeding lines moderate to highly-resistant to race 4 FOV have been identified; and (4) most Acala and non-Acala Upland germplasm tested for susceptibility to race 4 FOV were less severely impacted in terms of plant stunting or mortality rates than most Pima cultivars but were still infected by race 4 FOV. In order to improve abilities to detect race 4 FOV in the field, plant sampling and scouting for disease symptoms need to be done between early seedling development through no later than first flower. Race 4 FOV has been observed in the field to affect and even kill plants as early as the 1 to 2 leaf stage, but more typically at the 4 to 10 node stage. This is much earlier in the growing season than past typical timing (after peak bloom, early boll maturation) for field inspections of seed and production fields for weeds and presence of wilt disease symptoms associated with another fungal pathogen, Verticillium. In fields where the FOV has been confirmed as present in the plants and soil, recommended management considerations include: removal of infected plants from the field, limitations for irrigation and drainage water movement out of infested into non-infested areas, and restricting personnel and equipment traffic through and out of infested areas of fields. Improved sanitation practices associated with human traffic (weeding crews, others) and farm implements moving through and out of infested areas will not eliminate the possibility of movement of the pathogen, but can significantly reduce the amount of inoculum moved out into non-infested field areas. To date, no crop rotation or short-term fallow practices are known to greatly reduce survival of this pathogen, but more research is needed to investigate these tactics. The most effective current approach for growers wanting to continue with cotton plantings in infested soil areas or where there is a threat of infestations is to plant cotton cultivars known to possess a good level of resistance to race 4 FOV.