The objective of this study was to determine if diseases of grapevines could be reduced by the application of "alternative" fungicides other than those used traditionally.

Methods and Materials and Experimental Design

On May 15, 2001, three varieties of French/American hybrid grapes were planted at the Fruit Research and Extension Center, Biglerville, PA. The varieties planted were Chambourcin, Chancellor and Vidal. Plants were rooted in a potting mix prior to field planting. These varieties were chosen because of their economic importance as wine grapes and because of their susceptibility to major grape diseases.

Plant spacing was six feet between vines and nine feet between rows. The three varieties were randomized and planted within one block (each block containing one test vine per treatment per variety). The experimental design is a randomized complete design with varieties as subplots. To ensure that treatment plants received only the designated treatments, buffer blocks were established between each treatment block and a buffer row was established between each treatment row. A total of eight treatments were applied. The experiment was replicated four times.

Treatments, description and rates
Treatments 1 and 2 - Aerated Compost Teas (CT)
Aerated compost teas were made from two compost sources. One source consisted of compost obtained from Roth Vineyards, Fairfield, PA (treatment 1). This compost consisted of 52% hay, 17% mushroom aggregate, 18% fresh wood chips, 12% raw, litter-free chicken manure and 1% calcium sulfate (gypsum). The other source was vermicompost, obtained from Orner Farms, Rockton, PA. Vermicomposting is a process in which red worms (Eisenia foetida) digest organic materials and produce a compost-like product (vermicompost). The compost tea was made by placing 3 lbs of vermicompost or 3 lbs of Roth compost in a volume of 25 gallons of non-chlorinated water. At this time, a nutrient solution consisting of various ingredients to increase microbial populations was added.

Compost teas were brewed for an average of 24-36 hours using a custom built brewing system. The brewer was designed and built by S. Bashar Jarjour. The brewer capacity was 30 gallons and was surrounded by a wooden frame. To provide adequate aeration, Mazzei injectors were installed within the tank. To agitate the compost tea during the brewing period, a Shertech closed coupled centrifugal pump, which delivered 19 gals/min, was used. Within the brewer, a 6-gallon, 20 mesh screened bucket was used to hold the compost amounts during the brewing process.

A Symphony Dissolved Oxygen meter, model SBSoD, was used for monitoring the oxygen concentration throughout the brewing process. At the end of the brewing period, a 2% solution of the surfactant Nu-Film-P was added to the final tea to increase the adherence of tea microorganisms and nutrients to grape leaves and clusters. At application time, the compost teas were sprayed onto treatment vines undiluted.

The Roth compost and vermicompost were analyzed for 21 parameters by the Agricultural Analytical Services Lab at Penn State, to determine the major compost nutrients (Table 1). At application time, a small volume of each compost tea was removed and plated onto selective media to give an estimate of the microbial population of the tea at that time. On June 5 and July 9, compost tea samples were sent to Soil Foodweb Inc., NY for a complete microbial analyses (Table 2).

Treatment 3 - Nutrients alone
To determine the effect of the nutrient solution used in the brewing process, the nutrients were mixed in 25 gallons of non-chlorinated water and applied immediately to test plants. These nutrients consisted of: Seaweed plus Hydra-Hume-AN (Helena Chemical Co., Biglerville, PA, 118ml), SP-85, a formulation of humic acid (ORGANIC APPROACH, Lancaster, PA, 22 g), molasses (113g), corn oil (1/4 tsp.) and fish Hydrolysate (Neptune Harvest, Agway, 5 ml).

Treatment 4 -Ele-Max, Foliar 4-0-20
Ele-Max is a liquid fertilizer derived from urea and potassium phosphite (Helena Chemical Co.). This formulation consisted of 4% urea nitrogen and 20% soluble potash. The amount of Ele-Max used was 14.78 ml/gal, which is approximately equal to the rate of 3.75 pints/acre.

Treatment 5 - Armicarb 100
Armicarb 100 is a contact foliar fungicide consisting 85% potassium bicarbonate (Helena Chemical Co.). Armicarb was applied as a dilute spray (13.6 grams/gal) at the rate of 3.0 lb/acre.

Treatment 6 - First Choice pHortress, 0-37-25
First Choice pHortress is a water soluble foliar fertilizer of macronutrients. It consists of 37% phosphoric acid, 25% soluble potash, 0.2% chelated manganese, and 0.2% chelated zinc. The rate used was one oz per gallon, which converts to approximately 6.25 pints per acre. The product was obtained from Agrium Retail/Crop Production Services (jcoburn@agriumretail.com).

Treatment 7 - JMS Stylet Oil
JMS-Stylet Oil is a technical grade white mineral oil marketed by JMS Flower Farms, FL. The rate was a 1.5% solution.

Treatment 8 -no spray control

Field application and data collection
Treatments were applied once per week except for JMS Stylet Oil, which was applied at 10-14 day intervals. All treatments were applied in the morning or evening when possible to protect the microbes in the compost teas from UV light and desiccation. Treatments were applied using a covered-boom dilute sprayer also built by Bashar.. At application times, the wind speed and ambient temperature was recorded (Table 3). Treatment applications began on May 7 and ended on August 22. Scouting for the presence of disease symptoms began on June 9. The diseases of concern included powdery mildew and downy mildew. Grape leaves and clusters were both observed for symptom development. Powdery mildew on leaves began showing up on August 14.

For cluster infection, the percent incidence was expressed as the number of clusters infected by each disease divided by 10 clusters per variety per treatment multiplied by 100. For leaf infection, the percent incidence was expressed as the number of leaves infected by each disease divided by a total of 25 leaves per variety per treatment multiplied by 100.

Severity was determined by rating 10 clusters per variety per treatment and 25 leaves per variety per treatment using the Horsfall-Barratt scale for assessing disease. These ratings were then converted to percentage values for averaging and data analyses .

Summary
See the report published in Biological and Cultural Tests for Control of Plant Diseases, Vol. 19, 2004, for a complete summary of this research and data analyses.

Discussion
The question to ask is, "Why didn't the compost teas reduce disease?" The teas were applied 16 times during the growing season; either early in the morning or in the evening (Table 3) to protect the tea microorganisms from adverse environmental conditions and ensure their survival on leaves and clusters. The brewing and application of compost teas is not a simple process. Within the source compost are potentially disease suppressive microorganisms, which need to be extracted within the compost tea. The biomass of these organisms, primarily bacteria and fungi, has to be "balanced" so that their numbers are high and they can compete with diseases that are on the vines. To achieve this "balance," CTs have to be micromanipulated. To know the numbers (biomass) of the tea organisms, CT samples need to be analyzed immediately after brewing. In our study, two samples of each compost tea were sent to the Soil Foodweb Laboratory (SFI, Table 2). Results showed that both teas (Roth, vermicompost) were bacterial in nature. This means that the fungal biomass was low. To achieve a higher fungal biomass, additional humic acids need to be added to the next brewing cycle. This "adjusted" compost tea then needs to be re-sampled by SFI to determine if a balanced biomass has been achieved. In theory, this sampling process should be preformed for each compost tea at each application time so that a fully balanced, disease suppressive tea via micromanipulation can be achieved. In our studies we found that the microbial analyses of compost teas provided us with valuable information, however, was expensive. For our studies, the micromanipulation and testing of each individual brew was impractical with respect to resources. Compost teas may be able to reduce diseases on grapevines; however, additional research into the enhancement of the microbial communities of these teas for disease suppression is needed.

In the future, we will continue to look at economically feasible alternative methods to reduce diseases of grapevines.