Organic viticulture is all about timing

Bill Powers used common materials—screen mesh, bottoms of plastic jugs—to construct his pest fan.

Melissa Hansen

The key to making organic practices effective in the vineyard boils down to timing, says organic wine grape pioneer Bill Powers. With more than two decades of organic farming experience, he’s used farmer know-how to build his own contraptions and has perfected a mental calendar of what needs to be done when, from nutrition to pest management.

The following is a brief overview of the organic viticulture practices followed at Badger Mountain Vineyard located near Kennewick, Washington.

Nutrition—In the early organic years, Powers spread blood meal from a local slaughter plant for vine nutrition. “It was pretty stinky stuff, and nobody wanted to be around it,” he said. Now, he relies on compost tea and compost to supply a goal of 100 units of nitrogen to the white grape varieties and 75 units to the red. About two tons of compost are applied annually and several compost tea applications made.

He makes compost tea in a 500-gallon stainless steel tank, using highly oxygenated water steeped with compost and other nutrients like molasses and alfalfa meal. The first compost tea application is made in early spring when vines have three to four leaves. Applications are made through the sprinkler irrigation system at the beginning of the year, but can be made as foliar sprays if the vines don’t need irrigation water. Usually two compost tea applications are made through the sprinkler system in April and one or two in May, with applications stopped around the first part of June when powdery mildew sprays are needed. Tea applications are put on hold during mildew spray season until veraison because the lime sulfur used for mildew control kills microbes in the tea. After veraison, one or two more tea applications are made before harvest, with the most important application made postharvest. Powers said the postharvest application helps dry up the leaves to eliminate overwintering of mildew.

Grapevine tissue samples are taken yearly to give a snapshot of the vine nutrient status and guide fertility adjustments in the next season. Soil tests are also taken every few years, with samples sent to a lab in Corvallis, Oregon, to test for soil microbe activity. He also tests the compost tea batches for microbe and fungi levels.

“But the biggest test is looking at those darn vines,” Powers said. “They’ll tell you if you’re applying too much or too little nitrogen.”

He’s tried growing vetch and rye as a cover crop to provide habitat for beneficial insects and nitrogen to the soil, but water needs of the cover crop didn’t always coincide with vine irrigations. Today, native grass vegetation is used to cover the row middles.

Disease—Temperature and humidity are monitored closely in the spring to identify the time for powdery mildew control. As soon as conditions are ripe for primary infection, lime sulfur sprays are applied every seven days, using sulfur dust as the sulfur source until signs of powdery mildew spores are observed, and then he switches to a liquid sulfur formulation.

Powers says that sulfur dust is cheap ($5 per acre) and goes on fast, with the spray rig able to cover six to seven acres in an hour. Because sulfur dust can burn foliage, the applicator starts early in the morning and quits when temperatures reach 70°F.

Irrigation—Vines are irrigated by overhead solid-set sprinklers. If early season irrigation is needed to fill the soil profile, care is taken to ensure that irrigation can be cut off once mildew season begins. After veraison, vines are irrigated again. An average of 13 inches of water are applied annually.

Insects—“With organic insect control, it’s all about timing,” Powers said. “If you miss the first generation, then you have to come back and treat again, or the second generation will get out of control. You have to watch temperatures and know when your populations are building.” Insects of primary concern are spotted and redbacked cutworms and grape leafhoppers. Powers says he hasn’t seen a grape mealybug on the place since 1988. Natural predators take care of most insects, but for cutworms and leafhoppers, he built a unique pest fan implement to blow and catch the insects from the vines. The fan from an old airblast sprayer was removed and over-the-row screens and a catch tray attached to collect insects blown from the vine. When the fan is used to blow leafhoppers, cooking oil is painted on the screen to smother and kill the leafhoppers.

Cutworms overwinter in the soil and vineyard debris, and climb up the trunk at night in early spring, feeding on buds and young shoots. Powers has developed cutworm thresholds to guide timing of the fan work. When buds begin to soften, the pest fan pulled by the tractor is driven at night when cutworms are active. After making a few row passes, the driver stops to count cutworms caught in the screen trap. If two or more cutworms per row are caught, driving continues. If the threshold isn’t met, the operator moves to known hotspots in the vineyard, looking for cutworm activity. If cutworms are absent, they wait a few days before driving the pest fan again.

To knock leafhopper populations down early, they use a propane weed burner to flame small suckers beginning to leaf at the base of trunks. They’ve found that leafhoppers usually first appear tucked inside the young leaves on the suckers. Flaming not only kills the insect but also kills weeds and the small suckers.

Weed control—Both the propane weed burner and a European-designed in-row cultivator are used for weed control. The weed burner is very effective on goathead weed, also known as puncture vine. Powers has used a WeedBadger, an in-row tiller and mower, but said using the implement is slow going.