Fusarium wilt has become a problem in fields where pre-plant fumigants did not include methyl bromide and where fumigants were applied to beds through drip-lines rather than through flat fumigation of an entire field. The changes in pre-plant fumigation methods have resulted in incomplete treatment of the soil, which has allowed pathogens to build-up to damaging levels.
This includes a host-specific strain of Fusarium oxysporum, known as
F. oxysporum f. sp. fragariae. Fusarium oxysporum is commonly found in agricultural soils throughout California but most strains are not pathogenic. Those that are pathogenic cause disease on only a narrow range of hosts, usually a single crop. The strain we have found to be pathogenic on strawberry (1) might have been derived from local strains of F. oxysporum or could have been introduced from other strawberry production areas outside the U.S.
Presently we are evaluating the efficacy of alternative fumigants and non-chemical control measures. We are also testing cultivars and breeding lines for resistance to Fusarium wilt. Results to date show that the U.C. cultivars ‘Ventana’ and ‘San Andreas’ have a high level of resistance to the disease.
1. Koike S.T., Kirkpatrick S.C. and Gordon T.R. 2009. Fusarium wilt of strawberry caused by Fusarium oxysporum in California. Plant Disease 93:1077-1077.