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.”
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, “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.”
The Coastal Research and Education Center Field Day is coming up this Thursday, June 17 beginning at 8:30. You must have registered to attend this year.
Zack Snipes reports, “We received some welcomed rain but 5+ inches in a day or so was a bit much. Conditions this week will dry things out. I cannot stress enough how important it is to get out fungicides once you can get in the fields. I saw a few squash fields going downhill last week. Upon closer examination, I found thousands of squash bugs. They tend to congregate on the crown of the plant and will hide under the plastic when you look for them.
Justin Ballew reports, “More rain fell in the midlands this past week. We’re up to a little over 4 inches of rain at my house for the month of June, more than March and April combined. Some places have received much more. Crops have been loving the rain, but it does come with a cost. As expected, we’ve seen diseases pop up here and there. We’ve seen some Southern blight and bacterial wilt in tomato fields, fusarium in watermelons, and more black rot in brassicas. Weeds are loving the moisture as well. Keep up with fungicide applications, as diseases can get out of hand in a hurry in these conditions.
Bruce McLean reports, “Vegetable crops are growing well. Sweet corn, squash, cucumbers are being harvested in good volumes. Downy mildew was observed in a smaller planting of cucumbers. Powdery mildew was seen on a smaller planting of squash. Tomato harvest is just beginning. Blossom end rot has been an issue on some early tomatoes. This can be contributed to environmental stresses to the plants (high UV, extremely low humidity, high air temps) from a couple of weeks ago. Blueberries are being harvested in good volumes. The quality of the blueberries is good (for the most part), but a bit undersized. Blackberries are looking good, but botrytis (gray mold) is likely right around the corner. Muscadines are looking good in most locations. Even with the frequent rains, calyptra release has been good. Thrips activity has been low so far. Some early-season ALS (Angular leaf spot) is starting to show. Rally is a good product to control ALS. Some fields are getting a bit wet, limiting equipment and harvest activity in the field.
Tony Melton reports, “Peppers and tomatoes are rotting at bottom of the plants from too much rain. Belly rot and Pythium leak is bad on cucumbers. Pickleworm is here and needs to be controlled. Southern stem blight is getting bad on tomatoes. Peas that are flowering need to be sprayed for cowpea curculio. Lots of potassium phosphide, metalaxyl, and mefenoxam are being used to keep down rots. Started side dressing, laying by, applying bifenthrin, and boron to sweet potatoes.”
Andy Rollins reports, “Bacterial canker of peach is much worse this year in the upstate. This disease is caused by a Pseudomonas sp. that is different than the bacteria that causes bacterial spot (Xanthomonas sp.). It is common in younger plantings, 3 to 6 years old. A common tell is dead blooms that remain on the tree. This is one of many sites where the bacteria will invade the plant. Fall pruning is a huge mistake as it creates even larger openings for bacteria to enter. This disease can be part of a disease complex (Peach tree short life) or can act independently. The presence of ring nematode would contribute in this case. Cold damage from southwest injury to the trunks is very common and also provides entry. Unfortunately, there is very little that can be done to remedy this problem after being found. Trying to limit the above mistakes is helpful and some research has shown positive results from painting pruning wounds. Other Rutgers research recommended early winter copper applications for bacterial canker in cherry.
The Coastal Research and Education Center Field Day is coming up on June 17 beginning at 8:30. You must register to attend this year. Registration may be found here.
Dr. Matt Cutulle reports, “The coastal rain events of the past week resulted in a lot of weeds popping up. For fields not planted yet this is a perfect opportunity to burn down the flush of weeds to reduce the weed seed bank in the field.”
Rob Last reports, “After some welcome rain in the area over the weekend, crops are looking good. However, given the humidity and rainfall, we are likely to find disease pressure increasing. Strawberries are all over. The wet humid conditions have spiked infections of botrytis and water soaked berries. Blueberries, blackberries and peaches are all coming to market with good quality and volumes with few insect or disease pressures being seen currently. Watermelons and cantaloupes are developing well with some early planted crops coming to harvest. In response to rainfall and increased humidity, keep an eye out for diseases such as bacterial spot in pepper and tomatoes. In addition, some cantaloupe crops are beginning to show Alternaria leaf spot. Make sure fungicide timings are good using a robust program.”
Zack Snipes reports, “We finally got a little bit of rain last week which knocked the dust down some. We could use more and hopefully we will get some this week. Incidence of Southern blight increased last week in tomato. Make note of these fields and avoid planting them in tomato, eggplant, pepper, squash, or melons next season. Overall, the crops look solid. We are in the thick of things when it comes to tomato harvest and rabbiteye blueberry harvest is starting this week as well. We have really humid and wet conditions coming this week so don’t forget to use protectant fungicides. I know everyone is busy, but during the busy season is when most of our insect and disease pressure spiral out of control.”
Justin Ballew reports, “We finally got some significant rain in the midlands this past week. I’m up to 1.8 inches at my house and there is a good chance in the forecast for more. It has been warm, overcast, and very humid the last several days, which is the perfect recipe for disease development. Make sure you are using preventative fungicide where necessary. Insects seem to be picking up a bit as well. Caterpillars are going strong, we’re still seeing plenty of mites on various crops, and I’m getting reports of stink bugs here and there. We’re harvesting brassicas, squash, zucchini, cucumbers, and herbs.”
Sarah Scott reports, “Much needed rain has occurred throughout the area this week with more predicted. With rain may come an increase in disease cases, growers should be aware of brown rot as it has been seen in several orchards this week. Removing fruit mummies and diseased fruit if possible can remove some inoculum from the field and limit future spread. Bacterial spot still isn’t being seen on a widespread basis, but again, after the moisture moving in for the extended forecast, growers should keep an eye out. Strawberries are wrapping up with some harvest still happening. Peppers and eggplants are progressing nicely and will also benefit greatly from some rain.”
Tony Melton reports, “1 pickle worm was found in a local squash. Processing and fresh market peppers will be ready to harvest on the week of June 13. Early tomatoes are just beginning to ripen. The rains have been mostly very beneficial but some spots have had excessive. Mudding through to pick pickles in spots. Very difficult to apply timely application of chemicals and some have to be reapplied after rains.”
Kerrie Roach, “Things are looking good in the Upstate with warm season crops starting to come off. It’s still early for too many disease and insect issues, but high humidity and a couple days of spotty rain will most likely increase pressure significantly.”