Field Update – 6/8/20 (Downy Mildew Arrives in SC)

Statewide

Downy mildew was found in Charleston, SC late last week on cucumbers. This is the first confirmed report of the 2020 season. If not already doing so, all cucumber and canteloupe growers should begin applying protective fungicides to help prevent or manage downy mildew. Ranman tank-mixed with a protectant such as chlorothalonil, mancozeb, or Zampro is a good option for protecting plants prior to symptom development. For more info, see Dr. Tony Keinath’s CDM Management publication.

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Downy mildew symptoms on the top side of a cucumber leaf. Note that the spots are angular in shape and are delineated by the veins in the leaf. Photo from Justin Ballew.

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Dark-colored downy mildew spores developing on the underside of a cucumber leaf. Photo from Justin Ballew.

Coastal

Zack Snipes reports, “It is a very busy time out in the fields. Every crop is coming in right now and folks are busting it to get crops out and keep the remaining crops healthy.  Keeping up with fertility, fungicide, insecticide, and herbicide programs can really help with the bottom line as now is when our crops need a little help. With the mild temperatures and cloudy, wet days last week, I saw some diseases appear and spread.  On tomato, I am finding increased bacterial spot that is starting to make plants turn yellow. This will cause a yield drag and the spots can be found on the fruit if the infection is not slowed down. Downy mildew was found in cucumber last week so be sure to be proactive and keep an eye out for that. I saw some other cucurbit diseases last week including gummy stem blight and Alternaria. The stink bug population has also increased in the past week or so with some damage showing up on tomato. Please refer to the 2020 Southeastern Crop Handbook for details on management programs for insects, diseases, and weeds.”

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Bacterial spot is increasing causing yellowing of the plants. Bacterial spot can reduce yields and develop spots on the fruit. Photo from Zack Snipes.

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Downy mildew found in cucumbers last week. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “Last week was warmer and actually a little dry. Lots of irrigation has been running. Crops are progressing quickly. Strawberries are mostly done now. The silks on the earliest planted sweetcorn are browning and harvest isn’t far off. Tomatoes, peppers, eggplant, squash, beans, and cucumbers are also progressing well. Downy mildew has been found in the state, so be sure to start preventative fungicide sprays on cucumbers.  Let us know if you’d like help scouting fields for downy.  Collards, cabbage, and kale are still being harvested and are looking good.”

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Silks are turning brown on the earliest sweet corn plantings. Photo from Justin Ballew.

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Tomatoes are developing well. It won’t be long before harvest starts. Photo from Justin Ballew.

Lalo Toledo reports, “Downy Mildew has been diagnosed in Charleston County. However, Downy Mildew has not been found in Orangeburg county.  Please be advised that it is a matter of time before we start seeing symptoms. Please refer to the vegetable handbook regarding fungicide applications. It’s recommended to stay on a Fungicide schedule and to apply protectants even before we start seeing symptoms. Bacterial Wilt on tomatoes is present in many fields in Orangeburg county. Please contact your local extension office for proper recommendations.”

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It’s only a matter of time before downy mildew shows up in cucurbits in Orangeburg County. Photo form Lalo Toledo.

Pee Dee

Bruce McLean reports, “Field conditions really improved this past week. Cucumbers are being harvested in good volumes. Overall, quality is good. Downy mildew is starting to show up in cucumber fields that were affected by recent heavy rains. Squash and zucchini are beginning to be harvested, as well. Snap beans and southern peas are flowering heavily. Some acreage of snap beans were lost due to ponding caused by recent heavy rains. Many fields of sweet corn are tasseling well and beginning to silk. Watermelon, cantaloupe, and peppers are growing very well. Blueberry quality is beginning to improve. Much of the rain-damaged fruit has been removed. Currently, the blueberry crop looks good. Muscadine fruit set is good, but thrips and aphid activity is high, which could cause problems in yield. Scouting is necessary to determine pest presence and necessary insecticide application.”

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Downy mildew really showing up in rain-stressed fields. Photo from Bruce McLean.

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Snap beans affected by ponded water from recent heavy rains. Photo from Bruce McLean.

Tony Melton reports, “Some areas got 10 inches of rain in one day. Hundreds of acres of beans and cucumbers are drowned. Cucurbit downy mildew is here on cucumbers. Weeds are awful.”

Upstate

Kerrie Roach reports, “With heavy rains a few weeks ago, high humidity and heat this past week, we are seeing some disease problems pop up across the board… make sure you are following prevention practices that fit into your growing style. Conventional, organic, or somewhere in between, all growers should be managing disease through preventative measures. Crop rotation is arguably one of the most important strategies in an Integrated Pest Management (IPM) program. If you’re a grower that hasn’t moved crops around within your site in years, now is that time!”

Andy Rollins reports finding black knot of plum. “Prune out these galled up branches as quickly as possible before they begin to sporulate. I also recommend sterilizing or at least sanitizing the pruners as much as is possible between cuts.  Treat with 2 lbs of Captan foliarly as soon as possible after pruning to try and keep those wounds free from other problems.  This problem can come in on the purchased trees, but can also come in from wild cherry trees or wild plum surrounding the orchard.  It is always a good thing to kill any and all wild cherry and plum trees directly adjacent to a commercial orchard.  Penn State has some good information here.”

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Black knot on plum branches should be pruned out before sporulation begins. Photo from Andy Rollins.

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