Gummy stem blight is more common and more severe on fall cucurbit crops than crops grown in the spring. The cooler weather and longer dew periods in the fall provide an ideal environment for the fungal pathogen to grow and spread. Gummy stem blight is most common on watermelon and may also be seen on cantaloupe, cucumber, pumpkin, and winter squash foliage. Butternut squash fruit are susceptible to black rot, the fruit rot phase.
All growers—conventional and organic—should follow two proven steps to eradicate (eliminate) the gummy stem blight fungus from infested fields.
Rotate away from all cucurbit crops for 2 years to allow time for the gummy stem blight fungus to die out in infested crop debris. The timeline starts when the first (diseased) crop is disked. It takes a full 24 months for 90% of the debris to decay under South Carolina weather conditions.
Promptly disk cucurbit crop debris after harvest to stop the spread of airborne ascospores from fruiting bodies that form on vines, stems, crowns, petioles, tendrils, and leaves. Burying crop debris helps it decay faster.
Four fungicides provide good control of gummy stem blight on watermelon, the most susceptible cucurbit grown in the fall: Miravis Prime (FRAC Codes 7 + 12), Switch (FRAC Codes 9 + 12), Inspire Super (FRAC Codes 3 + 9), and Luna Experience (FRAC Codes 7 + 3). Note that because these fungicides share active ingredients in FRAC groups 3, 7, 9, and 12, the only products that can be rotated with each other are Miravis Prime and Inspire Super. Another option is to rotate a generic formulation of tebuconazole (FRAC Code 3) with Miravis Prime or Switch. None of these fungicides controls downy mildew or anthracnose. See Watermelon Fungicide Guide for 2021 for a sample spray program for fall watermelon that covers all major foliar diseases.
The SC Specialty Crop Association is offering a new grant opportunity, the Enhancing Crop Packaging Cost-share Program. With this new cost-share program, growers can receive reimbursement up to $1,800 per grower for packaging needs. All that is required in addition to the application are copies of receipts used for purchasing packaging materials. You will also be required to fill out two surveys, one initially and one 12 months after submitting the application. All information is confidential. For more information, contact LauraKate McAllister. The application can be downloaded below.
Zack Snipes reports, “We are in a summer weather pattern with warm, muggy days and occasional thunderstorms. Most crops have finished up or are in the process. Now is a great time to sit down and do some crop planning and field rotation planning. I collected many soil and root tissue samples lately and had them analyzed for nematodes. I was surprised at how many nematodes were present in the fields. Nematodes can interfere with growth, cause stunting, and lower overall yields. Sometimes the symptoms of nematodes can be very discrete so sampling right now is the best way to get a baseline of your populations and how to properly manage and rotate fields. If left unchecked, thousands of dollars are wasted before the first seed is planted into a field.”
Justin Ballew reports, “It was another fairly mild week with high humidity and some pretty decent rain. Not much has changed on the disease front. We’re still seeing plenty. Growers are still prepping fields for planting fall crops. Some fall cucurbits and brassicas have been planted already. More are on the way. As soon as brassicas go in the ground, start scouting for worms. Remember, we can perform bioassays to screen for insecticide resistance in diamondback moths populations. Reach out to your local fruit and vegetable agent when you start seeing worms to schedule one.”
Bruce McLean reports, “Vegetable crops are harvesting well, with good volumes of squash, zucchini, cantaloupe, watermelon, cucumber, butterbeans, peas, tomatoes and okra. Sweet corn is beginning to wrap up. Late season blueberries are still being harvested in some volume, but will be finishing soon. Muscadines are sizing well. Vineyards that were only slightly affected by the Easter freeze are looking good and should have a good crop. Vineyards that were more significantly affected by the freeze are very short on crop this year. Grape root borer traps in muscadine vineyards are starting to catch moths in all locations. Spotted wing drosophila (SWD) trap captures (in blueberries) have dramatically increased over the past few weeks, showing that even in late season when fruit is becoming less and less plentiful, the fly is still very active and must be managed.”
Andy Rollins reports, “I identified a major scale problem on peaches. A grower from middle part of state called about red spots on peaches. Earlier in the year across the whole state we had red spots on leaves. We found prunus necrotic ring spot on all of those samples last year but we are still unsure of the origin. In this case, it is something much different. This is an insect that feeds on the fruit and the tree itself. The adult stage of this insect doesn’t move but the crawlers do. After consulting with Dr. Brett Blaauw, regional entomologist for Clemson, the grower decided to go ahead and treat now. On Friday, he sprayed Movento at the label rate. There is great concern because with this high of a population, the life of the entire trees at risk. The plan is to follow that application with chlorpyrifos and oil at low rates after the leaves drop. You have to be careful when doing this as the oil can damage the next years bud crop if temperatures are too hot. We will be trapping using black electrical tape wrapped around the limbs then double sided scotch tape around that. We will then look for the crawlers on the scotch tape. This ensures money isn’t wasted killing a pest that has already been controlled.”
Long-time Horticulture Agent Tony Melton retired earlier this month, finishing out a 40-year career with Clemson University. Tony is best known for his passion for working with fruit and vegetable growers in the Pee Dee Region, as well as his frequent appearances on SCETV’s Making It Grow.
Tony first began his career with Clemson University in 1980 in the Horticulture Department before earning his Master’s degree in Horticulture and becoming an Extension Agent in 1989. He attributes his passion for horticulture to the time he spent working with the McLeod family of McBee, SC in his teens. To honor his dedication, the McLeods later created and funded a Clemson University scholarship in Tony’s name.
In addition to his work with the farming community, Tony worked closely with the Master Gardeners in the Pee Dee and wrote weekly articles for the Florence Morning News. He was also involved in fruit and vegetable research, managing 20 acres of research plots at the Pee Dee Research and Educations Center in Darlington. As part of this work, Tony was recently awarded a Specialty Crop Block Grant to develop heat tolerant butter beans.
Throughout his career, Tony has earned numerous awards including the Distinguished Public Service Award from the Clemson Alumni Association, the County Agent of the Year from the SC Beekeeper Association, and the Distinguished Service Award from the SC Association of County Agricultural Agents.
Tony is well respected by his peers and is known for his love of work and staying busy. He’s even been known to show up on farms before the sun comes up. His kind-hearted personality and vast knowledge will be greatly missed as we all wish Tony well in this next chapter. Thanks for everything you’ve done and the impact you’ve made, Tony!
Dr. Tony Keinath’s remarks on fungicide stewardship:
Growers who are applying newer fungicides that are pre-mixes of two active ingredients do not need to add another fungicide to the tank mix. Pre-mixes can easily be identified by the two FRAC Codes on the label in the top right corner. Please consider the following points:
Many newer fungicides are sold as pre-mixes to reduce the risks of fungicide resistance in fungal and water mold pathogens. Mixing two active ingredients often is a way to prevent or slow resistance development, as long as both active ingredients work against the same disease.
Sometimes two active ingredients are mixed to expand the range of diseases controlled. For example, Quadris Top controls both anthracnose (the Quadris part) and gummy stem blight (the “Top” part, which is Inspire).
Mixing more than 2 pesticides, whether they are 3 fungicides or 2 fungicides plus an insecticide, increases the risk of pesticide injury (burn). Risks may be greater if a spreader-sticker is added, or when air temperatures are above 90 F.
Adding another fungicide to a pre-mix fungicide increases fungicide costs, often without increasing disease control.
Growers should contact their Extension agent before adding another fungicide, even a protectant, to a pre-mix fungicide to be sure it’s really necessary.
Justin Ballew reports, “Not much has changed in the midlands over the last week. We’ve received some scattered rain and it has been warm and humid. As a result, we are still seeing disease issues. We’re still picking tomatoes, squash, zucchini, cucumbers, sweet corn, and a few greens. We’re at an in-between stage in several fields where the spring crops have been finished and folks are preparing to plant fall crops. Some have already started fall cucurbit plantings. For anyone planting strawberries this fall, if you are still deciding which varieties to try, take a look at the NCSU’s 2020/2021 variety comparison data (pages 9 and 10).
Bruce McLean reports, “Vegetable crops are looking pretty good across the Pee Dee. Fields that have received rain or are irrigated look very good. Fields that have missed the rain are a bit drought-stressed. Sweet corn, peas, butterbeans, tomatoes, squash, watermelons, cantaloupes, and cucumbers are all being harvested in good volume. Okra is just beginning to be harvested well. Growers are still fighting cucurbit downy mildew (CDM) on cucumbers. Fields that have been sprayed with fungicides for CDM (Orondis Opti, Gavel, Ranman, and Omega) are relatively clean and producing well. Fields that have not received those products are in severe decline. Cowpea curculio is still being a challenge. Some growers have asked about adding PBO8 (Piperonyl Butoxide) synergist to their insecticide application. Research has shown some efficacy, so it does help. But, it is not the silver bullet that everyone is looking for. There really is no alternative to having a robust spray program, spraying every three to five days starting prior to bloom.
Many varieties of blueberries have already finished up, with only mid-late and late rabbiteye blueberries going now. Blackberries have finished up, as well. Summer primocane tipping and floricane removal has begun. Be sure to apply a broad-based fungicide to all open wounds/pruning cuts to prevent disease development (I.e. cane blight, etc). Muscadines are sizing up pretty well. Grape root borer traps have been placed in vineyards, but no moths captured yet.
Kerrie Roach reports, “Things in the Upstate were a little wet the last few days and it looks like showers will continue into the middle part of the week at least. Continue preventative measures for disease control and if/when a plant seems too far involved, remove and dispose of the entire plant to prevent further spread. Squash vine borer has been one of the continued problems in market garden production in the last 2 weeks. At this late point in the season and lifecycle, monitor plants closely and as soon as frass is seen, carefully cut the stem longitudinally and remove/kill the larval stage of the borer. You can mound soil on the cut part of the stem to help encourage new root growth. If done early enough, plants can continue to thrive despite the slice in the stem. New plantings of cucurbits set out in the last week or so should mature after the adults have finished laying eggs, but monitor closely for any wilting. Crop rotation, row covers, traps (yellow bowl of water), and pesticide applications can also be used as a part of a good IPM program. Check out the crop handbook for more specifics.
Andy Rollins reports, “We are having thrips issues on 3 crops peaches, pepper and cucumber. Thrips as seen in the picture cause surface damage to the outside make it aesthetically less appealing and marketable. On pepper they damage the leaves and can transmit viruses to the plant (on cucumber also). They are much worse in greenhouse and high-tunnel settings. I have been recently concerned about presence of chili thrips and I am waiting on definite identification. This is a good website about this new pest. I also found a rare disease called foot rot of squash in the upstate. It was identified by Dr. Tony Keinath. Rotation is very important with all of our vegetable crops. We are picking some excellent quality peaches in the upstate. Cold damage has limited our wholesale picking.”
Rob Last reports, “Crops are generally coming to market with good quality from cucurbits through corn, tomatoes and peppers. Be on your guard for foliar diseases, given the temperatures and humidity there are a large number of diseases present from anthracnose, powdery and downy mildew, and alternaria. Fungicide applications will help.to manage diseases applied in a timely manner.”
Zack Snipes reports, “The tropical storm brought some wind and heavy rain in some parts of the Lowcountry. We received 3.86 inches at the CREC in Charleston. Most fields have dried out and things are back to normal. I have seen an increase in bacterial spot on tomato and a rise in the spider mite population. Remember that using pyrethroids (group 3 insecticides) (Brigade, Bifen, Karate, Warrior, Tombstone, Mustang Maxx, etc.) will kill spider mites but will also kill all beneficial insects. In most cases, spider mite numbers are higher 5-7 days after a pyrethroid spray than they were before. There is also resistance to some pyrethroids in spider mite populations. Bottom line…don’t use pyrethroids to control spider mites. We have plenty of registered, spider mite specific products in our tool box.
Justin Ballew reports, “Tropical Storm Elsa came through the midlands in the early morning hours Thursday and brought 1.3 inches of rain (at my house) with it. Disease is still the big story here in the midlands. It’s been very warm and humid and we’re still seeing plenty of downy mildew, powdery mildew, anthracnose, and bacterial spot. For anyone planting strawberries this fall, now is the time to start soil sampling. Some folks held onto their strawberries well into June this year. If that was you and you plan to replant the same fields this fall, start removing plastic and discing ASAP to destroy the crop residue.”
There seems to be some confusion about what is a proper crop rotation to manage diseases caused both by pathogens that survive a few years in soil and pathogens that survive in soil longer than anyone can measure. Here are some rotations I have heard about that are not proper crop rotations.
1. A susceptible crop in year 1 and a different susceptible crop in year 2. Example: Pepper followed by tomato or tomato followed by pepper in a field infested with Phytophthora capsici, the water mold that causes Phytophthora blight. Simply switching between two susceptible crops is not proper crop rotation.
2. A susceptible crop in the spring and another crop in the same plant family in the fall. Example: Watermelon in the spring and cucumber in the fall on the same plastic. There are too many potential disease problems with this crop sequence to even mention all of them. Gummy stem blight, root knot, and Phytophthora blight are among the top three.
3. Multiple plantings of a short-season crop in the same field in the same year, then rotating the following year. Example: pickling cucumbers. The same comments made in #2 apply here. Root knot nematodes on an early summer crop will infect a crop planted later in summer.
4. A susceptible crop in the fall and a different susceptible crop in the spring in the same field. Although I don’t have a specific example this time, the short break over winter is not long enough to reduce pathogen levels.
In general, a proper crop rotation is a sequence of crops that are in DIFFERENT plant families. Although not every disease affects all plants in the same family—e.g. early blight on tomato and potato but not on eggplant or pepper—enough diseases do affect closely related vegetables that it is best to avoid planting them too often right before or after each other.
Dr. Tony Keinath reports, “Basil downy mildew was found in mid-June in Charleston. Symptoms start as faint yellowing of leaves, which eventually show brown spots surrounded by yellow areas. To see the spores, look on the bottom of a symptomatic leaf. Sometimes it helps to hold the leaf up to a light source (but don’t look directly into the sun). Seeing spores is useful to rule out nutrient deficiency or sunburn on leaves. Growers who use conventional fungicides should rotate two of these three labeled fungicides: Revus, Presidio, or Ranman. See page 203 of the 2021 Southeastern U.S. Vegetable Crop Handbook. Potassium phosphite products can be used as a preventative and by home gardeners. I do not know of any cultivars that truly are resistant or any organic biopesticides that are effective. Once downy mildew spores arrive in South Carolina, the disease will be present until frost kills the basil host.”
Zack Snipes reports, “Crops are still looking good coming off. Typically July 4th week is our busiest week in the field. One thing I saw this past week in some melon fields was crown decline. Crown decline is characterized by a yellowing of the crown leaves which makes the plant look weak overall. The disease can be mistaken for a nutrient deficiency. This disease is important to diagnose because yields can be reduced and fruit quality can be impaired at the middle to end of the season which can impact your bottom line. Read up on this disease and management options here. I am seeing some gummy stem blight and anthracnose in watermelon right now as well. Get your fungicides out before the tropical storm this week.
Justin Ballew reports, “Things are progressing well in the midlands. Temperatures have been pretty mild and we saw about half an inch of rain at my house Thursday afternoon. It looks like Tropical Storm Elsa will be coming through Thursday, so plant diseases will continue to be our major issue for at least a little while longer. I’ve been seeing plenty of downy mildew, powdery mildew, anthracnose, and bacterial spot over the last week. Japanese beetle numbers are pretty high right now also.”
Tony Melton reports, “Sweetpotato vines are covering the beds. We’re starting to harvest processing tomatoes. We’re planting fall butterbeans and peas and picking processing peppers for the second time.”
Downy mildew was found on watermelon this week in Allendale and Barnwell counties. Although downy mildew does not infect fruit, it reduces sugar content once 1 in 4 leaves (25%) are infected.
All watermelons should be sprayed with a fungicide effective against downy mildew. See pages 214-215 in the 2021 Southeastern U.S. Vegetable Crop Handbook. Any fungicide listed there can be used except Aliette, Previcur Flex, or Curzate. Do not use these fungicides to manage downy mildew on watermelon, as the isolate on watermelon in 2020 was resistant to them. Gavel, Ranman, and Elumin are the least expensive choices. Growers should apply a downy-mildew specific fungicide this week, a protectant (chlorothalonil or mancozeb) next week, and repeat this sequence until one week before the last harvest. See the following publications for more info on watermelon disease management:
Rob Last reports, “Peaches and blackberries are coming to harvest with good quality and volumes. As yet we are not seeing any issues with spotted winged drosophila. Vigilance will be required as this pest can be troublesome in blackberries. Watermelons and cantaloupes are coming off well. However we are seeing cucurbit downy mildew in watermelons. Spray programs will need to be robust through to the end of harvest to manage the disease. The disease is characterized by brown or yellow spots on the leaves with a Grey’s purple sporulation on the underside of the leaves. Anthracnose is also starting to show up as angular lesions on the stems, leaves and fruit in some fields. Tomatoes and peppers are looking good with some anthracnose fruit rot being seen. There are active spider mites too in some crops. Vigilance and scouting is the order of the day to keep on top of disease and pest issues.”
Zack Snipes reports, “Everything from arugula to zucchini is coming in right now in the Lowcountry. This next week is usually one of the busiest weeks for us as July 4th approaches. Cucurbit crops are starting to look rough after multiple pickings, disease pressures, and lots of rain. The tomato crop and watermelon crops are coming off nicely. I am seeing a good bit of blossom end rot and sunscald in pepper. Blossom end rot is a calcium deficiency that is usually seen when we have uneven soil moisture levels. When its hot and there is a heavy crop load, you may need to water more than you think. In our sandy soils, more frequent, shorter irrigation cycles (45 minutes or so) is better than letting irrigation systems run all night. Sunscald is common when there is poor canopy coverage in the pepper allowing the sun to directly shine on the pepper. This is usually a result of a root rot or poor fertilization which inhibits a good leaf canopy to develop.”
Tony Melton reports, “Picking peppers and tomatoes hard. Using a lot of sun protection products on crops. Thrips are really bad on peaches losing about 1/3 of #1s. Weeds are bad because of all the rain we had when we should have been plowing – especially pickles and sweetpotatoes. Butterbeans and peas are in fair abundance.”
Bruce McLean reports, “Vegetable crops have been growing well, as of late. Sweet corn, peas, tomatoes, peppers, cucumbers, squash, snap beans and zucchini are all being harvested in good volumes. There have been a couple of tomato fields where Southern Blight was seen pretty widespread across the field. Cucurbit Downy Mildew (CDM) is widespread across the Pee Dee, as well as Cowpea Curculio. Growers that are spraying more targeted (management) fungicides for CDM (like Orondis Opti, Gavel, and Ranman) are controlling the disease much better than those applying preventative sprays like Bravo and mancozeb. Seems like everyone is having trouble controlling the Cowpea Curculio, though. Watermelon, cantaloupe and okra should be ready for harvest in about a week. Blueberries are still going pretty strong with good volumes and quality. Blackberries are winding down. Muscadines are coming along, but the crop looks like it may be a bit short this year.”
Kerrie Roach reports, “Strawberries are finished and blueberries are king in the upstate. Weather in the region has be varied, and irrigation is key to smaller market producers right now. Spotty showers across the area have left hit & miss spots that may need supplementation. Summer pruning is on the horizon for apple producers… more info to come on a meeting in July.”
Dr. Keinath reports, “Cucumber growers should consider adding Presidio back into their fungicide rotations to manage downy mildew. Isolates of downy mildew in Charleston were sensitive to Presidio in 2018, 2019, 2020, and again in 2021. In spring and fall 2020, susceptible slicing cucumber cultivar, Speedway, sprayed with a weekly rotation of Presidio and Bravo had the lowest diseased leaf area and yielded 2.6 times more than nonsprayed cucumbers. Profits were about $3600/acre with Presidio/Bravo compared to $1000/acre with no fungicide calculated after all production costs were accounted. The same efficacy was seen again in spring 2021. It is risky to rely only on two fungicides, Ranman and Orondis Opti, to manage cucumber downy mildew. Adding another fungicide to the rotation will reduce the likelihood that cucurbit downy mildew will become resistant to Ranman or to Orondis.”
Rob Last reports, “Given the rainfall and humidity levels, we are seeing increases in foliar and fruit diseases on a range of crops. This includes cottony leak in cucumbers, anthracnose in pepper, tomatoes, and cucurbits. Also, please be aware cucurbit downy mildew is very active now. As a result, it is going to be really important to maintain fungicide programs in both a timely manner and to be robust. That being said, we have some great quality melons, both cantaloupe and watermelons, coming to harvest, as well as good volumes of quality peaches, blackberries, and a host of other vegetable crops.”
Zack Snipes reports, “We had some heavy downpours this past week which has beat some crops up. Hopefully everyone got their fungicides out ahead of the rain. The CREC hosted their annual Field Day last week. A special thanks to all that attended. I learned a good bit about herbicide carryover damage and direct herbicide damage from Dr. Matt Cutulle. I think the cool weather this spring made our plants and herbicides have some unusual reactions.”
Justin Ballew reports, “After a pretty dry week, Tropical Depression Claudette came through over the weekend and dropped a lot of rain (a little over 3 inches at my house). More rain is forecast for this week, so again, be sure to stay on top of fungicide sprays. This past week we started seeing bacterial spot on tomatoes, anthracnose fruit rot on peppers, and Southern blight remains active on several crops. We’re getting close to the end for the spring brassica crops. Tomatoes, squash, zucchini are being harvested and sweet corn will be coming soon.”
Tony Melton reports, “Thank goodness the rain was not as heavy as predicted for the tropical storm. We are fighting belly rot and downy mildew on pickles with all the possible controls. Hard to get sweet potatoes laid-by and fertilized with the wet conditions. Snap beans are doing and yielding well but processors are having trouble keeping up because of labor problems. Bad thrips problems on peaches losing 1/3 of #1 yield.”
Kerrie Roach reports, “Things are looking pretty good in the ‘golden corner’ area. Heavy rains over the weekend have caused some ponding and erosion, but nothing major. Disease pressure continues to be high with the perfect conditions (humid and warm), so growers should continue to practice preventative control methods. Insect pressure has still been considerably low for this time of year, but we’ve seen a subtle increase in populations in the last 2 weeks. Monitoring is extremely important for management strategies to be successful, in general nymphs or the juvenile form of most insects are much easier to manage than adults. Strawberries are just about done, with most growers doing some final pickings this week.”
Andy Rollins reports, “Phytophthora can be a devastating disease of Pepper. We have suffered extreme losses on one farm. The worst fields had been planted for 2nd year in pepper which is not recommended. Rotation is highly encouraged. Grower had treated with Ridomil twice and used phosphite repeatedly. It is believed there is resistance in this field to Ridomil, but testing hasn’t been completed yet. Dr. Tony Keinath has a complete description of this disease and control options in this article. We are mostly finished with strawberries at this point and preparing for next year. We are picking some peaches in the upstate although picking is very light do to extreme cold damage from April 3rd. We are picking some tomatoes in high tunnels. Early blueberry crop was observed last week but picking is very light there also.”