Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 18, 2005
Publication Date: July 25, 2005
Citation: Fravel, D. R., Deahl, K. L., and Stommel, J. R. 2005. Compatibility of the biocontrol fungus Fusarium oxysporum strain CS-20 with selected fungicides. Biological Control. 34:165-169 . Interpretive Summary: Fusarium wilt is a plant disease that can cause large economic losses in tomato. A beneficial, biocontrol fungus, Fusarium oxysporum strain CS-20 that is related to the fungus that causes the disease, can reduce the number of plants that become infected with the wilt fungus. Two types of tests were conducted to assess the compatibility of strain CS-20 with seven fungicides commonly used on tomato. First, different concentrations of fungicides were mixed with agar medium and the growth of strain CS-20 on the agar was recorded. Secondly, tomato plants were treated with CS-20, planted in soil with the wilt pathogen, and fungicides were applied on a regular schedule as recommended on the product label. The amount of disease was recorded. On agar, three of the fungicides were toxic to strain CS-20 and the other four fungicides did not significantly affect growth. One of the fungicides that reduced growth in agar also prevented strain CS-20 from protecting plants from wilt disease. This fungicide is commonly used as a seed treatment. This information will be used by scientists integrating biocontrol into systems for producing tomato.
Technical Abstract: Fusarium oxysporum strain CS-20 reduces incidence of Fusarium wilt in tomato and other crops. We assessed the compatibility of strain CS-20 with seven fungicides recommended for tomato in Maryland. Radial growth of strain CS-20 was recorded on agar medium amended with various concentrations of the fungicides. Thiram (Thiram), chlorothalonil (Bravo), metalaxyl + chlorothalonil (Ridomil Gold Bravo), mancozeb (Manzate) and azoxystrobim (Quadris) significantly reduced radial growth at 10 ppm a.i. Mancozeb + copper (Mankocide), mancozeb (Manzate), metalaxyl (Ridomil Gold), and metalaxyl + copper (Ridomil Gold Copper) did not affect radial growth at 100 ppm a.i. In greenhouse tests, tomato seedlings were treated with strain CS-20 and transplanted into field soil infested with the pathogen. Plants were treated with fungicides at the highest label rate at the most frequent schedule labeled. Manzate is labeled as both a seed treatment and a spray, and was applied each of these ways as separate treatments. Wilt incidence of plants from seeds treated with thiram and strain CS-20 was not different from those in the pathogen only control, indicating that thiram was toxic to strain CS-20. Other fungicides toxic in vitro were less toxic in greenhouse tests, probably because of the way they are applied.