Downy Mildew Found on Watermelon in SC

Downy mildew was found yesterday, June 17, 2020, in one watermelon field in Bamberg County, South Carolina. All growers should immediately spray watermelon with Ranman, Revus, or Gavel to protect their crops from downy mildew. In addition to direct yield loss, loss of vine cover can expose fruit to sunburn (when the sun comes out again). Growers who find downy mildew in a field should apply Orondis Ultra or Orondis Opti in a weekly rotation with Ranman or Gavel. For more information on downy mildew, see the updated Cucurbit Downy Mildew Management for 2020.

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Downy mildew symptoms on watermelon foliage. Photo from Dr. Tony Keinath.

Field Update – 5/26/20

Statewide

Dr. Tony Keinath reports, “Powdery mildew was found late last week on watermelon at the Coastal REC, Charleston. All watermelon growers should look at the photo below to be sure they can identify powdery mildew in the early stages. The spots are pale yellow, and, unlike squash, may not have white powdery growth under the spot on the bottom of the leaf. See Powdery Mildew on Watermelon Land-Grant Press 1019 for spray recommendations (https://lgpress.clemson.edu/publication/powdery-mildew-on-watermelon/).”

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Light yellow spots on watermelon leaf from powdery mildew. Photo from Dr. Tony Keinath.

Coastal

Zack Snipes reports, “I saw a good bit of powdery mildew last week on all cucurbit crops. I have had several questions this spring about injury to watermelon. I think the strong winds, sand, and spraying damaged the crowns of melons. They are growing out of it now but have had some folks concerned. Bacterial wilt is showing up in tomato as temperatures climb and fruit is loading up in the crop. Keep up with scouting for insects and diseases. Overall things look great.”

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Crown injury on watermelon due to high winds and sandblasting. Photo from Zack Snipes.

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Conditions have been perfect for the development of powdery mildew on cucurbit crops. Photo from Zack Snipes.

Rob Last reports, “Watermelons generally look very good with great color and potential with early fruit set occurring.  Fusarium wilt is active at low levels in some places, as to be expected in areas of impaired drainage.  Also, I observed a little hail damage to watermelons and cantaloupe in Bamberg County.

Midlands

Justin Ballew reports, “It’s been raining a lot in the Midlands, but we really needed some rain. I’ve had almost 6.5 inches at my house since last Monday (5/18). This has slowed down strawberry picking and we have a ton of water damaged berries. Botrytis is loving all the moisture. Most fields look like they will keep producing for a few more weeks,  just stay on top of fungicide programs. The moisture and warm temperatures have most other crops growing rapidly and looking good. Keep an eye out for disease.

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These strawberries sitting in water will be damaged and need to be removed from the field before botrytis begins to develop. Photo from Justin Ballew

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Tomatoes are loving the warm weather. Photo from Justin Ballew.

Pee Dee

Tony Melton reports, “Anyone have an ark?  Many fields are flooded. Nutrients are washing away and strawberries are water-soaked.  Some strawberry farmers have stopped picking.  Water-logged soil causing crops to stop growing and we have to rely on airplanes to spray crops.  Weeds are enjoying the rain.”

Bruce McLean reports, “Last week was rainy in most locations, and this week looks like more of the same. Disease pressure is elevated due to excessive moisture. Seeing gummy stem blight showing up in cucumbers and bacterial spot in tomatoes. Thrips pressure had been high going into last week (especially on beans, peas, and cucumbers), and could still be high in the few locations that missed the heavy rains. But everywhere else, the heavy rains likely reduced thrips activity. Strawberries are finishing up. Heavy rains damaged most of the remaining red fruit. Blueberry harvest is starting to increase. Prior to rains, fruit was looking really good. The excess moisture did cause some fruit splitting, but no long term damage to the crop. Haven’t seen much thrips activity in muscadines yet, but now concerned with increased problems with calyptra release, a condition known as stuck cap. It’s a little early to tell, but could reduce yields.

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Thrips damage to southern peas. Photo from Bruce McLean.

Upstate

Kerrie Roach reports, “We are building the ark to send down to Tony in the Pee Dee!  Lots of flooded fields last week (and today) with many places seeing 4-6 inches of rain over 3 days. Strawberry growers halted picking and worked around the rains. Vegetable producers are replanting washed out crops and draining fields.  Peaches and apples continue to be on track for a good season. Localized hail damage is showing up on apples in Mountain Rest from one of the storms a few weeks ago.”

Field Update – 5/18/20

Statewide

Dr. Tony Keinath reports, “With the cooler-than-normal spring weather, two cool-season pathogens also may be active longer than normal. Downy mildew on brassicas, especially kale and collard, mainly affects the lower leaves. Sometimes it will move up onto the larger leaves in the middle of the plant. With a hand lens, you can see white mildew growth in lesions on the bottom of the leaves. In my spring 2020 trial, Presidio, potassium phosphite, and Zampro rotated with potassium phosphite worked well. Organic growers can use Badge X2 copper, which also performed well.

Fusarium oxysporum f. sp. niveum, the soilborne fungus that attacks watermelon, infects roots when soil temperatures are below 82F. At Coastal REC, I am still seeing new plants showing wilt symptoms. Remember that all control measures, and I want to stress all of them, must be applied before or at transplanting. There is nothing that can be done at this stage of crop growth. It is too late to apply fungicides, which will be a waste of money.”

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Tiny dark flecks of downy mildew on the bottom of ‘Blue Dwarf’ kale. Photo from Dr. Tony Keinath.

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Sporulation of downy mildew on the underside of ‘Tiger’ collard. Photo from Dr. Tony Keinath.

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Wilting and yellowing of lower leaves due to Fusarium wilt on watermelon 6 weeks after transplanting. Photo from Dr. Tony Keinath.

Coastal

Zack Snipes reports, “Things are coming along in the Lowcountry.  It has been very windy and I’ve had several farmers tell me that crops are using more water now because of the wind than if it were hot and humid.  Squash, zucchini, cukes, potatoes, and greens are coming off in good volume right now. Tomatoes are just a few weeks away and are in the sizing up stages right now. I have not seen any major pests or diseases as of late.  The conditions are ripe for the development of Powdery Mildew so be on the lookout when scouting watermelon, squash, brassica, and tomato.”

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Tomatoes are looking good and are just a few short weeks away. Photo from Zack Snipes.

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Powdery mildew on the shaded side of a collard leaf. Photo from Zack Snipes.

Midlands

Justin Ballew reports, “It’s dry in the midlands. It’s been great because we haven’t seen much disease lately (especially on strawberries), but we need some rain. The forecast looks like we may get some this week. Strawberries are still yielding fairly well, though we’re starting to see fewer blooms. Fruit size is getting smaller, but taste has still been great. The first few plantings of sweet corn are tasseling now. Brassicas are still growing well, though there is some black rot out there.  Tomatoes, peppers, and cucurbits have been growing fast the last few days also.”

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The earliest plantings of sweet corn are tasseling. Photo from Justin Ballew.

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Black rot symptoms on the margins of cabbage leaves. Photo from Justin Ballew.

Sarah Scott reports, “Peach season is here! Picking several early varieties now and running packing lines. The crop looks good for this season. Bacteriosis started to show up on leaves and fruit in fields. Still picking strawberries. Summer crops like bell pepper and squash are progressing nicely.”

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Phomopsis or twig blight in a peach orchard. Lesions on twigs cause dieback, gumosis and curling at tips. Remove damaged wood and burn. Photo from Sarah Scott.

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Twig dieback from Phomopsis twig blight. Photo from Sarah Scott.

Lalo Toledo reports, “Cool temperatures have slowed down the growth of many vegetables, but most vegetable plants are looking great. Please be aware of possible diseases coming in this week. Wet and hot conditions will be conducive for pests and diseases. Please spray accordingly and scout every two days, if possible.”

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Grasshopper damage on eggplant. Photo from Lalo Toledo.

Pee Dee

Tony Melton reports, “Hail has destroyed at least 10 A squash, 200 A peaches, 30 A strawberries, 8 A blackberries, many acres of field corn, tobacco, rye, and wheat.  Damaged another 35 A strawberries, 300 A peaches.  Thank goodness that the wind has let up for a while and temperatures have risen on tomatoes, peppers, peas, beans, and sweet potatoes.  Thrips have been awful and imidacloprid is only partially controlling them. If labeled use dimethoate, acephate, etc.   More herbicide damage than usual this year because of cool temperatures and wind, even on labeled crops and drift to non-labeled crops has been awful.”

Upstate

Kerrie Roach reports, “With a week of good growing conditions, things are looking great in the Upstate for fruit & vegetable producers. In higher elevations, there were some losses of young tender plants during isolated frost events early last week. With rains expected most of this coming week, things should start to really push for our market vegetable growers. Peaches and apples are on track for a good season.