Frost, mildew lurk, could undo April’s vineyard progress


The long wait is over, and the grilling, golfing, gardening and grape-growing season is finally upon us once again in the Walla Walla Valley.

Thanks to a benign dome of high pressure, sunny skies, light winds and warmer-than-normal temperatures in the low 70s have graced Southeast Washington for the past couple of days. Spring is now in full flower with a vast array of colors and scents (along with the pollen that drives many of us to distraction with our various allergies), and the outdoors beckons Walla Wallans emerging from their winter cocoons to revel in the light and warmth of early April.

In the vineyard, the sunshine and mild temperatures will gradually warm the soil and encourage buds to break to reveal the new green growth that will eventually develop into the canopies that support this year’s bounty of grapes.

However, before this happens, the tender new vegetation must undergo the rigors of frost season which — depending upon the severity of the year — may test it to the limits of its tolerance. Vineyard managers will be closely attuned to thermometers and weather reports for the next month or so. They will be ready to act at a moment’s notice should near-freezing temperatures necessitate the starting of wind machines or overhead sprinkler systems to ward off the imminent danger to their vines.

The general outlook for the next five to six weeks is nail-biting days followed by sleep-interrupted nights, and vineyard managers everywhere will collectively breathe a deep sigh of relief around the second or third week of May, when the chances of a damaging frost drop to next to nil.


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Powdery mildew grows on grape leaves.

Frost is not the only potential problem lurking in the vineyard this month. Powdery mildew, which has been slumbering away in its overwintering structures known as chasmothecia, is ready to pounce on new green growth as soon as a combination of rain and mild temperatures releases the spores contained within. This will mark the beginning of the spray season to control this ubiquitous fungus — the single costliest grape disease worldwide.

The season will normally last into early or mid-August, when grapes begin to take on color and sugar. Vineyardists can look forward to treating for powdery mildew every two to three weeks (depending upon which compound is used to control it) from now until then. It’s a nuisance to be sure, but a task that, if ignored, can have very serious consequences for fruit quality as the growing season moves along.

In the meantime, it appears as if the next several days will be almost ideal for any sort of outdoor work or recreation. A weak cold front is forecast to slide across our area tomorrow with just a 20 percent chance of a brief shower to mark its passage. Slightly cooler weather will ensue in its wake, but afternoon readings will still remain in the 60s as we head through the week.

The outlook remains generally dry and mild until about April 15, when the 16-day Global Forecast System indicates the possibility of a little rain. An average April will yield 1.69 inches of rain here in Walla Walla, and daily high temperatures will climb from a normal of 60 degrees at the beginning of the month to an average of 67 by month’s end. Nighttime lows will range through the 40s, which means starting out the day with three or four layers of clothing and ending it with one (or none, if the opportunity presents itself.)

Get out (or stay in) and enjoy our lovely spring weather!

A lifelong fan of both the weather and the Baltimore Orioles, Jeff Popick is an instructor at the Center for Enology and Viticulture at Walla Walla Community College and manages the school’s teaching vineyard. Send your questions and comments to him at


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