There’s no new breakthrough on cherry powdery mildew management, but a diligent approach to the basics still works to keep orchards clean.
“A lot of this stuff is going to sound familiar, but if you follow it every year, you are going to have more success than if you skip it,” said Matt Smith, a crop consultant with Northwest Wholesale.
Smith was joined by Justin Wiggs of G.S. Long Co. to share their insights into powdery mildew management at the North Central Washington Stone Fruit Day, held in Wenatchee on Jan. 21. The event is part of a series of grower education days organized by Washington State University Extension and the North Central Washington Fieldmen’s Association, with support from the Washington State Fruit Commission.
“Scouting is important, but for mildew, being aggressive from the get-go is the best way to be successful,” Smith said.
Prevention starts with big pruning cuts that open up trees.
“Light penetration and airflow is the only thing that’s free,” Smith said. “It’s something that is going to work for you 24/7.”
Wiggs recommended delaying the start of the irrigation season, when possible, to delay the start of the cherry powdery mildew cycle. He also said that applying sprays with higher water volumes allows more product to drip into the stem bowls of developing fruit, and he warned against stretching your spray intervals.
“If your target is seven days and it gets windy and you are out to 10 days, you’re probably fine. If your interval is 10 days and it gets windy and you go out to 14, you’re not fine,” he said.
Also, remember to rotate your modes of action. FRAC Group 3 fungicides are showing resistance, according to WSU research, Smith said.
Managing powdery mildew well is worth the money, Wiggs said in closing. The difference between a 70 percent packout and a 90 percent packout can be $20,000 an acre.
“That’s way more than your chemical bill,” he said.
The afternoon session had an economic focus, with talks about cherry retail dynamics, pricing and the growth of Chinese cherry production.
Even WSU physiologist Matt Whiting embraced the economic lens for his talk on crop load management from the perspective of the carbon economy in the tree.
Growers usually try to balance the carbon supply (leaves) and demand (fruit) in fruit trees by thinning the fruit so that there’s an optimum level of resources available for high-quality fruit. But Whiting shared a promising finding from taking the opposite approach and boosting supply.
In an experiment using Extenday reflective fabric to boost the light available to the canopy in a Sweetheart orchard, crop load increased from 10.8 tons per acre to 14.6, Whiting said. But, critically, that increase in tonnage was big fruit, with gains in the 10-, 9.5- and 9-row sizes.
“So, this is actually valuable increase in tonnage,” he said. “We improved the light relationships in the tree, shifted the supply side of the equation and got more light to the shaded leaves so the trees could actually handle more fruit.” •
