PCA Brad Schrenk shares his tips for taming the late-season mite flare ups and sour rot spread in northern California and what growers can do now to prepare for the 2012 season.
Late Season Mite Flare Ups
Based out of Simplot Grower Solutions in Lodi, Schrenk covers wine grape vineyards in northern San Joaquin County in an area known as the Delta. This part of the state experiences coastal weather influences, giving it a cooler climate than surrounding areas. The cooler temperatures and heavier dews in the Delta usually mean less pest pressure—especially less mite pressure since mites are a hot weather insect.
“Normally, we would be done with our insect control by now, but we’re still watching mite populations grow,” Schrenk says. Most fields were treated for mites earlier in the year, but some growers have been forced to retreat high populations.
Because the 2011 spring was unusually cool and wet with late rains, growers predicted they would have less pest pressure, says Schrenk. “That was true. However, in the last 30 days or so, pest pressure has spiked,” he says. According to Schrenk, the population spike came later than normal this year, threatening grape maturity and harvest.
Schrenk encourages growers and PCAs to watch vineyard hot spots where mite populations have historically flared, especially any dry areas where vines may be stressed.
Spraying for mites this close to the wine grape harvest limits the control materials growers can use because short preharvest intervals are essential. A product like Acramite® 50WS from Chemtura AgroSolutions can be very helpful in these situations by combining powerful knockdown of key mite species with a preharvest interval of 14 days and reentry interval of only 12 hours.
Watch Out For Sour Rot and Botrytis
Schrenk reports sour rot is spreading in some of the thin-skinned grape varieties, mostly Zinfandel. Also known as vinegar rot because of its distinctive smell, sour rot breaks down the berry and spreads as the berry’s juices run down onto neighboring berries.
Unfortunately, says Schrenk, there aren’t many treatments available for sour rot. He recommends a copper-sulfur dust to slow the disease down and help dry it up. “Many growers also manage sour rot by sending out hand crews to cut out the worst clusters,” he says.
Botrytis is another disease growers need to watch for. “Although Botrytis dried up over the summer, if we have any sort of rainfall between now and harvest, a lot of that Botrytis will come alive and be a problem,” says Schrenk.
Viticure® fungicide is a systemic sterol inhibitor fungicide with a short, 7-day preharvest interval that can clean up any late powdery mildew in addition to suppressing Botrytis.
Vigilance, says Schrenk, is the most important component to a successful harvest this fall. “This time of year, growers are busy getting their equipment ready, lining up crews, talking to wineries, scheduling and worrying about sugar. They’re not always out in their fields looking at the crops so it’s very important that they have a PCA watching those crops and making sure that everything finishes out as expected with no surprises.”
Setting the Stage for 2012
Fall is a great time to address fertility, says Schrenk. He recommends soil testing, applying potash and putting a little fertilizer through the drip to put the vines to rest with nutrients. Fall is also a good time to apply compost or manure in organic systems. “The most important thing to remember when it comes to fertility management is to put on the right type of fertilizers at the right time,” Schrenk says.
Growers should also start thinking about their winter weed control programs. “Look at the weeds that escaped this summer to help you determine what your weed management program should look like,” suggests Schrenk.
Finally, growers should make note of mealybug-infested fields. If mealybug populations were close to treatable levels in 2011, growers should plan on spraying for mealybug in 2012.
Schrenk tells growers to monitor their fields for mealybug and evaluate their control programs to make sure that they’re scheduling fields that need to be treated next year. “Don’t wait to treat until you see mealybugs,” warns Schrenk. “If you wait until you see them, you’re too late and you won’t get them under control.”