Effect of Alternative Fungicides on Alternaria solani Control and Productivity of Organic Tomatoes
The effectiveness of compost teas and organic fungicides to control Septoria lycopersici in organic tomato production was evaluated. Initial results indicate that compost teas, a watery-based compost extract, and Serenade, a fungicide approved for use in certified organic production, did not reduce disease severity caused by Septoria lycopersici. Champion, a copper-based fungicide approved for use in certified organic production, did reduce disease severity. Furthermore, additions of Bravo or Quadris, conventional fungicides, to Champion did not increase yield or decrease disease severity.
The objective of this research was to: 1) evaluate the efficacy of organic fungicides,
2) investigate the efficacy of compost tea made from either windrow composted cattle manure (WCCM) or vermicomposted cattle manure (VCM), and 3) compare the efficacy of organic fungicides with conventional fungicides to control S. lycopersici in organic tomatoes.
The first of two field seasons was completed this year. I am currently working on a growth chamber experiment to evaluate the efficacy of various compost teas to control Septoria lycopersici under a controlled environment. A second field season is planned for the summer of 2004. I am collaborating with a professor at the University of Kansas, to evaluate a source of vermicomposted cattle manure used to make a compost extract.
Impacts and Contributions/Outcomes
Weather conditions this year were particularly favorable for Xanthomonas campestris pv. Vesicatoria (Doidge) resulting in an epidemic of bacteria spot prior to field inoculation with S. lycopersici. It was virtually impossible to distinguish between symptoms caused by X. campestris and symptoms caused by S. lycopersici on plant leaves in the field.
Results from last season’s field trial will have three impacts on tomato producers. First, results indicate that Champion, a copper- based fungicide approved for use in certified organic production, can be used to reduce disease severity caused by the bacteria speck/spot complex and Septoria lycopersici. Treatments that received copper fungicides yielded 60% more marketable fruit than treatments that did not receive any copper fungicides. Furthermore, the conventional method of adding Bravo or Quadris, conventional fungicides, to copper fungicides is not necessary. Finally, because compost teas or Serenade were not able to reduce disease severity when the pressure was high, farmers may want to consider using copper fungicides in areas where disease pressure is severe.
Last season’s results were published in the Iowa State University Annual Fruit and Vegetable Progress Report. At this time, other publications are not being considered until work has been accepted for publication into a peer-reviewed journal; submission is expected in the fall of 2004. An abstract has been submitted to the Annual Society for Horticulture Science to present at the annual meeting in July 2004.