Control of Botrytis by Compost Tea Applications on Grapes in Oregon Vineyards
Powdery mildew was a serious disease problem at vineyards in the Willamette Valley of Oregon this year, as it was last year. In the vineyards used for this study, powdery mildew outbreaks were largely controlled, or their severity reduced, in areas sprayed weekly with compost tea. Organism biomass in the teas, and therefore leaf surface coverage by microorganisms, particularly fungi, was not sufficient to prevent infection. Weekly compost tea applications reduced the number of applications to one to as many as three applications of chemical fungicide needed to control powdery mildew over the summer growing season.
Changes in soil micororganisms between 2001 and 2002 were also documented. In general, bacterial activity was higher in 2002. Fungal biomass declined in some areas sprayed with compost tea. Organism biomass in soils from conventionally-treated areas followed similar patterns, however, so most likely these changes are in fact seasonally related and not the result of compost tea application. Thus, it is clear that SOIL organism biomass changes were due to other environmental factors or management practices, and not to the application of compost tea. Foliar sprays did not significantly improve soil biology in this two year study.
Miscommunications and inconsistencies between protocols and application rates in the different vineyards have made it clear that all sites must be under the control and the responsibility of one grant-paid person, not the manager of each vineyard. Next year, a project manager will be responsible for all treatment applications and sample collection.
To assess the ability of different compost teas to reduce disease in grapes.
Why are differences in ability to control diseases observed? Why is control of foliar diseases nearly 100% in some cases, but in other cases, control is no better than without tea? The probable explanation for such variation between teas is that tea quality is not the same way in each case. Differences in tea recipe, in tea aeration, in the initial compost used (and therefore the complement of organisms present to compete with and control disease) are probably the explanation for the differences. Which tea recipe, production method, application method, or compost gives the best control of disease? To understand our choice of factors to test, several salient facts need to be understood.
In the first two years of this project, we have identified levels of organism biomass needed in compost tea in order to suppress powdery mildew. We have documented reduced severity of powdery mildew infection, and reduced need for chemical fungicides to control outbreaks.
We had only asked for funding to do field work in years one and two, but we will try to continue into year three. In the coming year, we will only work with two of the vineyards (Broadley and Wren), and only have one compost tea plot, compared with conventional grape production. Fungi in the compost will be maximized by adding a special inoculum into the compost and this compost will be properly maintained through the summer. The plots will be sprayed once a month starting at bud break and will include a soil drench. When the mildew alert is issued by the Extension Service, then sprays will be put out once a week until color change. Only if botrytis is a problem will spraying continue after that point.
Impacts and Contributions/Outcomes
ACRES USA, December 2002, seminar to 65 growers on the Soil Foodweb
ACRES USA, December 2002, Compost Tea 501, 500 growers interested in compost tea and how to use it.
Compost Tea seminar, November 2002, Soil Foodweb Inc., Corvallis, 70 growers
– Meeting of the U.S. Composting Council, January 2003
Reed and Reynolds Vineyard/Oregon Vineyard Supply