The challenge was how to effectively spray a small vineyard on a steep slope to keep Powdery Mildew at bay. For some locations, there may be ample space during vineyard installation to terrace wide, flat rows between vines so that a tractor or other four wheeled vehicle (such as a Gator) can be loaded with a sprayer and carted between the rows. (Our property is relatively small and so we didn't terrace the land.) A simple backpack sprayer takes approximately two days and is much trouble as the liquid seems to always get clogged, and the spray in uneven. Another possibility was to purchase a motorized backpack sprayer. This would work, providing a good mist on the vines, but is heavy to carry around. Last year, Frank Bons of Sunfresh Vineyards, who operates a vineyard management company in San Diego County, sprayed the vineyard with a long hose (approximately 300 feet) connected to a large tank on his truck, first stationing the truck at the bottom of the vineyard, then driving by paved road to the back of the property. This operation took another person to manage the hose. Not all vines were reached, and a couple of sections needed to be done with a backpack sprayer. Says Frank, when it comes to spraying, "I don't like your vineyard."
As the Blue-Merle is a difficult vineyard to spray, careful attention is paid to monitoring the mildew index using the University of California, Davis system to make sure spraying is done only when absolutely necessary. Secondly, Frank suggested using a spray such as Rubigan which is effective for 14 - 21 days, depending on the weather. Frank came up with an approach that worked. He brought a 30 gallon pump on wheels to the property, hauling it to the top of the hill, connected to his 300 foot hose. (Next time, remember to drive the pump to the back gate, and lower it using 2 X 4's.) From there, he marched up and down the rows, moving the pump down the hill and across the property as required. The actual spraying operation took less than one hour. Strong pressure from the hose meant he only had to spray one side of each row.
We used 2 oz of Gowan Rubigan (Fenarimol). According to the label, the recommended dosage for wine grapes is 2 - 4 ounces per acre. We have approximately 2 acres of vines and thought we would recharge the 30 gallon sprayer once and so mixed 2 oz. of Rubigan into the machine. It ends up that we used slightly less than 30 gallons (there are approximately 1,150 vines on the property). As this was the first spraying of the season and there was no sign of mildew, Frank thinks a light spraying may have been better. Meantime, we'll continue to monitor the temperatures to keep track of the mildew pressure, preparing for another spraying later this month, using a different spray to avoid resistance buildup.
(Picture above shows grapes infected with Powdery Mildew in early June last year.)