Foggy fall mornings are nature’s warning that conditions are favorable for brassica downy mildew to get started on collard and kale.
Remember that because downy mildew affects the harvested, edible portion of the crop, control practices must be very effective to increase yields. Use the following practices to maximize control:
1. Rotate crops to new fields every year. Brassica downy mildew is believed to survive in soil.
2. Check lower, older leaves for angular yellow downy mildew spots on the top of the leaves and black lesions with white downy mildew growth on the bottom of the leaves. Even lesions 1/8-inch in diameter can produce spores.
3. Make the first fungicide spray when the first foggy morning is predicted. Fog means the leaves will stay wet all night and a good part of the morning. The lack of sunshine on foggy mornings also allows downy mildew spores to stay alive longer than on sunny mornings, when UV light will kill them in about 24 hours.
4. Potassium phosphite is a very effective, economical alternative fungicide against brassica downy mildew. It is probably “good enough” by itself during sunny periods without rain. Note that it is not labeled for certified organic production.
5. During rainy periods, rotate effective conventional fungicides, like Zampro or Presidio, with potassium phosphite. Fungicide rotation is critical for leafy brassica greens left in the field for more than 2 months when leaves are cropped repeatedly. Zampro may be applied only 3 times per crop. Presidio may be applied 3 times at the 4-ounce rate or 4 times at the 3-ounce rate.
For more info on brassica downy mildew, see Dr. Keinath and Tim Bryant’s article in the latest issue of the Clemson IPM Newsletter.
There are some reports that anthracnose may be issue in strawberries this year. In addition, we are continuing to look out for the new disease, Neopestalotiopsis. Clemson Plant Pathologist Guido Schnabel has recommended applying Zivion S (natamycin) via preplant dip to help prevent these diseases. Dr. Schnabel provided the following instructions:
Mixing Instructions. Add Zivion S while stirring to the volume of water to be applied, or to a smaller volume that is then added to more water to make the expected final volume. Continuously stir the treatment solution unless it is to be applied immediately. Application Time. Apply prior to plant as a preplant transplant root or whole plant dip treatment. Do not apply after or to harvestable commodities. Application Rate. Root or whole plant dip: mix 6-12 fl. oz. (0.04 – 0.08 lbs a.i.) of Zivion S per 10 gallons of water. Dip plants for a minimum of 2 minutes, but no more than 5 minutes. Plant treated plants after dip application.
To find Zivion contact Nelson Jameson at 800-826-8302.
Rob Last reports, “We are progressing well with preparations for strawberry planting. Some Plants are due to be delivered this week. Remember, if fumigants have been used, check to ensure the products have dissipated to prevent damage to the transplants. The same is true to make sure planting restrictions on any pre-emergence herbicides applications are observed. Always refer to the label. Finally, remember to check your plants carefully for pest and disease inoculum from the nursery. Planting any disease or pest-infected plants will lead to a more challenging. If you require any help, please reach to Extension Agents.”
Zack Snipes reports, “I thought I had moved to Seattle last week with all the rain and dreary weather. We have a good week of weather coming up and I expect that everyone will be busy in the fields transplanting greens, finishing laying plastic, and continuing the harvest of fall crops. Watermelons, squash, and winter squash are being harvested this week. Downy mildew is loving this weather and is on basil, squash, cucumbers, winter squash, and cantaloupe. I have seen many freshly transplanted fields with black rot in brassica. This disease shows up every time we plant brassica. It is essential to transplant quality transplants. If your transplant supplier is sending you diseased plants, then visit our Seed and Transplant Supplier list to find a new supplier. You might be surprised how big of a difference it makes. Carolina Farm Stewardship Association is having a webinar this week on Tuesday, October 12 at 12pm on Ginger and Tumeric production in a high tunnel. Please email firstname.lastname@example.org for link and passcode.
Justin Ballew reports, “We finally saw some sunshine this past weekend after a pretty rainy week. Caterpillar pressure has been high and lots of treatments have been going out. I’ve been seeing a decent amount of pathogenic fungi developing on diamondback moth caterpillars due to the wet conditions creating the perfect conditions for development. We’ve had a couple acres of strawberries planted and ordinarily we would be planting full steam ahead now, but strawberry plants are late coming in this year. Lots of folks are being told it will be next week before their plants come in. I’m also hearing reports that anthracnose may be a problem from nurseries this year. As a result, we are strongly recommending a fungicide dip on transplants before planting to combat this and any potential infections from the new disease Neopestalotiopsis. See Dr. Schnabel’s comments about Zivion above.”
Phillip Carnley reports, “Cucumbers are finished in Orangeburg and Calhoun counties. Fall greens are in full swing with some pressure from DBM with the occasional looper. Growers are bedding strawberry fields and applying their pre’s. We have seen heavy infestations of gummy stem blight in fall watermelons, as well as spider mite damage in blackberries.”
Sarah Scott reports, “Tree removal and field prep for new peach installations are happening around the ridge. Strawberry plants are being planted now and got a good watering in with last weeks rain. Fall vegetables are looking good, growers should keep up with scouting for disease issues in the field following the week of wet and humid weather.
Andy Rollins reports, “I am busy scouting new strawberry plantings this past week. Be on the look out for leaf diseases of plants but also check roots thoroughly for discoloration. When planting make sure crowns are still visible after planting. We are also preparing ground for new peach production going in. We are still picking a few muscadines, but that will be finishing pretty soon.”
Rob Last reports, “Fall cucurbit crops, including cantaloupes, and watermelons are ripening and approaching harvest. Disease pressure from powdery mildew and gummy stem blight have really increased significantly over the last week. Maintaining a tight spray program will be key to managing disease. As we look forward to strawberry planting land is being prepared. If you are planning to fumigate, make sure the plant back interval between fumigation application and planting is maintained. A good test can be to plant some lettuce seed in the treated area. When lettuce germinates, the risk of damage from fumigation is reduced. Finally, on any remaining fall plantings, consider using a labeled pre-emergent herbicide to help with weed management. Once the crop and weeds emerge, options are drastically reduced.
Zack Snipes reports, “Land is being prepared and fall crops are going in around the Lowcountry. Early fall crops look better with the slightly cooler temperatures and periodic rain. We are wet in some parts. I am seeing lots of bacterial spot in the fall tomato crop. We have good herbicide management plans for greens, but folks will need to take advantage of pre-emergents now.”
Justin Ballew reports, “This past week was fairly rainy. There are several fields that are pretty soft, even some sandy fields. Folks are still planting brassicas for the fall and they are looking really nice right now. Strawberry growers are also getting prepped to fumigate and lay plastic. We’ve been seeing a lot of damping off (Pythium) in young cucurbits and some brassicas lately. The wet weather is definitely creating the perfect conditions for this. A few things that can be done to help minimize damping off include planting on plastic beds, planting at the proper depth (just deep enough to cover the plug with native soil), rotating fields wisely (tomatoes are a host for Pythium), and using a fungicide at planting may also make sense when environmental conditions are right for Pythium development.”
Phillip Carnley reports, “Cucumber production is in its final stages here in Orangeburg and Calhoun counties with most growers close to or in the process of harvesting. There is still a noticeable amount of cucurbit downy mildew, but due to the dryer weather it has been easier to keep in check. Sweetpotatoes are currently being dug with yields looking to be fairly good. There have been a few issues with wireworm damage in sweet potato fields with the majority of damage being seen on the lighter colored tubers. Diamondback caterpillar is ramping up in brassica crops, especially in collards. Make sure to scout early and treat in a timely fashion, if your insecticide program is not showing the desired level of control talk with your local agent about scheduling a bioassay to screen your population’s resistance to different insecticides. Also be on the look out for black rot and other fungal problems in early transplants.”
Sarah Scott reports, “We received some heavy rain in areas throughout Edgefield and Aiken Counties last week, up to 2 inches in spots. In preparation for October planting, plastic has been laid in strawberry fields. Brassica crops are being planted as field conditions allow. Late summer plantings of broccoli are starting to get some good size on them. Pepper plants that were put out in August are setting fruit that is starting to size up nicely.”
Zack Snipes reports, “We had a heavy downpour of rain last week surpassing 2.5 inches in some spots. I am seeing downy mildew in cucumbers and lots of gummy stem blight in winter squash and pumpkins. The worm pressure has lessened in the past few weeks. I am seeing lots and lots of black rot in transplanted brassicas. Inspect your plants before planting them to make sure the disease is not coming from the nursery. Once a brassica is planted in the field, there is not much we can do to slow the spread except hope that environmental conditions (rain, humidity) are not conducive to spread the disease. I am also seeing lots of early weed pressure in fall planted crops on both bare-ground and plastic. We have some very good herbicide options to apply preplant. Once you plant the crop, we have very few herbicides that can be used over the top of the crop. Right now is the time to get down strawberry herbicides before the season starts. As the old proverb goes: an ounce of prevention is worth a pound of cure.”
Justin Ballew reports, “We received about an inch of rain (at my house), which we really needed. The temperatures over the last week have been very mild and it has started to feel like fall. Fall crops are doing well. We’re still planting brassicas and keeping an eye on caterpillars. Muscadines are being harvested now. Growers are reporting good fruit quality, but lower yields than last year. This is most likely due to the late cold weather that affected muscadine growers across the state. On pecans, black aphid populations and scab incidence are both high. It appears both of these pests are going to significantly reduce yield on sensitive varieties if growers didn’t stay on top of sprays.”
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Justin Ballew reports, “We’re getting a little dry here in the midlands and folks have been running irrigation a lot. We got a shower last night (9/6) at my house, but it didn’t amount to much. Our fall crops are looking really good right now. The dry weather is holding down disease though we are still seeing some insects, mainly caterpillars. Squash, zucchini, cucumbers, peppers, tomatoes, turnips, and other brassicas are all growing pretty well.”
Phillip Carnley reports, “Muscadine production is in its final stages here in Orangeburg and Calhoun counties with most growers preparing to harvest or in the process of harvesting. There is still a noticeable amount of angular leaf spot on many vines, but this late in the season, it is not much of an issue. Continue to keep an eye on the population of grape vine borer with the use of traps. Also keep an eye on water, as it is needed for nice plump fruit.
Bruce McLean reports, “Soils are getting pretty dry in many locations. Even though dry weather would greatly benefit the muscadine growers, we could use a little rain. Vegetable crops are looking pretty good. Spider mite activity has increased over the last couple of weeks, especially on tomatoes. Bedding and fumigation (for strawberries) is getting ready to begin. Wine and juice muscadine harvest is upon us. Muscadine harvest is going to be a bit tricky this year. In many locations, half the crop is ready to pick and half the crop needs a little additional time, especially Carlos and Doreen cultivars. This is likely due to the late spring freeze that we experienced this year. Primary growth (that recovered from the freeze) is giving us a timely crop. Secondary growth (growth from secondary buds) is a little delayed. Watch harvesting too much under-ripe fruit. Under-ripe fruit does not contain the sugars or the juice, and will reduce your overall juice yield and total sugars.”
Kerrie Roach reports, “Things have significantly slowed down in the Upstate with the Labor day weekend signaling the true end of summer. The growers who are doing fall vegetable production are in the thick of things with insect and disease monitoring of utmost importance. I would typically be posting about apples and the harvest for this season, but the late cold event from April 22, 2021 has put a significant damper on local orchards. Growers have apples available, but u-pick operations are very limited, if not cancelled for this season. Orchard management is imperative even when the trees are not producing, and can be a good opportunity to get weed control and pest management under control.”
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Justin Ballew reports, “Last week was warm and humid again. Some of our sandier fields got dry enough early in the week that crops were wilting in between waterings. We got a bunch of rain over the weekend, though (a little over 2 and a half inches at my house). Overall, fall planted crops are coming along nicely. Some of the earliest planted fall squash and zucchini is being picked now. We’re still seeing the same disease problems that have plagued us all summer, though growers seem to be managing them fairly well. As far as caterpillars go, I’m seeing mostly diamondback moth and armyworms with a few loopers here and there. Get ready. This could be a high pressure fall for caterpillars.”
Phillip Carnley reports, “Not much has changed here in Orangeburg or Calhoun Counties. Its been hot and humid and we’ve had a few untimely showers delaying cucumber harvests. There is still plenty of downy mildew to go around. We are seeing loopers on pickling cucumbers that are ready for harvest. At that stage the loopers should be treated prior to harvest with Coragen, Harvanta, or Radiant. Fall brassica, peas, and tomatoes are just now being planted. We are seeing increased amounts of scab in pecans this year, due to the rain and humid weather. For insect and disease management in pecans, have a look at the UGA Commercial Pecan Spray Guide.”
Andy Rollins reports, “Excessive rains have caused cracking of fruit at several upstate muscadine farms. Powdery mildew is also present but I’m not sure how much of a role it is playing on the cracking part. The powdery is damaging the skin of the fruit. Topsin M is labeled and recommended with Captan but have to wait 7 days to pick so have to watch your PHIs. Also finding some insect pests in peach. Oriental fruit moth and sap beetles have been found last week but only a small amount of affected production. Herbicide control has been difficult this year because all the rain has caused excessive grass growth, especially in new orchards.”
Zack Snipes reports, “Its hot and humid in the Lowcountry. Fall tomato and watermelons are in the ground and enjoyed a week of mostly dry weather. Okra and sunchokes, aka Jerusalem artichokes, are loving this heat. With the exception of those crops, there aren’t too many crops in the ground right now. I am seeing lots of summer cover crops. I love the idea of using a mixed species of cover crop. One reason is, it spreads out the risk that one of the species in the mix won’t germinate or will be eaten by deer. So by using multiple species, you can almost guarantee that something will be there covering the soil. Multi-species mixes also provide different benefits to the farm. Cowpeas may fix nitrogen while sorghum X Sudan hybrids may be a deer deterrent and shade out weeds.”
Justin Ballew reports, “Not much has changed here in the midlands over the last week. Its been warm and humid and we got a little rain a couple times throughout the week. Recently planted fall brassica and cucurbit crops have gotten off to a good start. We are seeing some caterpillar activity already. We are seeing increased amounts of scab in pecans this year, thanks to the rain and humid weather. I’m seeing some black pecan aphids causing damage as well. For insect and disease management in pecans, take a look at the UGA Commercial Pecan Spray Guide.”
Phillip Carnley reports, “It’s that time of year to be on the look out for Southern stem blight (Athelia rolfsii) in hemp. To avoid possible infections of this pathogen, avoid planting in fields that have previously had tomatoes, peppers, eggplant, or peanuts. Crop rotation is your best avenue for mitigation as there are no fungicides labeled for control of Southern blight in hemp at this time. Also be on the lookout for plant stunting from girdling roots. For information on chemicals labeled for hemp checkout the EPA website.”
Kerrie Roach reports, “Late summer season crops are still producing in the upstate, but many market producers are starting to lose the disease battle. When something is finished for the season, make sure to remove all parts of the crop. Do not leave diseased plant material in the field. Dispose of the diseased crop in an area far away from your fields or garden. Do not use diseased plant material for compost. Most home compost piles do not reach consistent and uniform temperatures at which pathogens will be killed. Dead plant material harbors insects and pathogens that can and will cause issues for fall season crops as well as next year’s crop.”
Most growers probably have heard that it’s possible to infest a “clean” (pathogen-free) field by moving soil on equipment. The question is how much infested soil is too much. The answer depends on the pathogen and where the soil is deposited.
Some pathogens are present in soil at very high numbers. One of the worst is the clubroot organism that infects all brassica vegetables. According to a new report from North Dakota, presented at the 2021 Plant Health meeting last week, there are enough spores in 1/8 teaspoon of moist soil to infect one plant. So, if all the soil stuck on a small dozer, like the one shown here, landed in one spot at the edge of the field, a patch of clubroot surely would develop there.
In addition to the clubroot organism, root-knot nematodes and the water mold that causes Phytophthora blight are pathogens at high risk of being spread in infested soil. They’re not as concentrated in soil as the clubroot organism, but moving as much soil as is on the dozer above is enough to create a patch of diseased plants. It takes only about 1/3 cup of soil with young nematodes in it to cause a gall on a susceptible crop.
On the other end of the spectrum, since 2005 I have had a field at Coastal REC infested with Fusarium oxysporum f. sp. niveum, the fungus that causes Fusarium wilt on watermelon. As far as I know, the pathogen has not spread, or has not spread enough, to other fields to cause Fusarium wilt, even though the equipment is not cleaned after it is used in the infested field. Even though Fusarium is present in the soil, it’s not at high enough levels to be spread easily.
It’s true that environmental conditions must favor the pathogen for disease to develop from the pathogen inoculum moved in soil on equipment. However, all four pathogens mentioned in this blog are long-term soil residents. They will simply wait in the new field until environmental conditions are right for them to infect a susceptible crop.
The bottom line is equipment, especially dozers that carry a lot of soil with them as they are moved from field to field, must be cleaned by power washing every time they are used in a different field. Power washing should be a standard practice, not just done when the equipment is used in a “known” infested field, because sometimes you don’t know if a field is infested until it’s too late to take precautions.
Rob Last reports, “Generally speaking, we are in the change over period from spring to fall crops, with some fumigants being applied to next year’s strawberry plantings. If fumigants are to be used, make sure soil moisture is good and beds are firm to gain maximum efficacy. One thing we have observed in blackberries and blueberries in the area is the emergence of bark scale. Bark scale is a new pest to South Carolina and has previously been noted in ornamentals. However reports for Asia, where the pest is native, indicate the bark scales can survive on Rubus species.
The images show the egg sacks and adults of the bark scale. The insects appear white and are very waxy, similar in appearance to mealybugs. The wax coatings can make management complex, preventing insecticides from penetrating the layer to be effective against the insects. The addition of crop oils to the pesticide solution may enhance efficacy by helping to strip off the waxy coatings. In blueberries, adults can be found underneath the exfoliating bark, again making contact with the insecticides more difficult. When crawlers emerge, they will be pink and barely visible to the naked eye, and monitoring will be easier with the aid of a hand lens. We will find crawlers hatching in April or May, with a second flush emerging in late summer. An excellent way to detect crawler movement is to wrap the branches in double-sided sticky tape to help to catch the crawlers. Contact insecticides can be very effective against the crawlers. Insect growth regulators may also be effective for management. Unfortunately, systemic materials such as imidacloprid appear to have little effect. Please get in touch with an Extension Agent to help with identification and management options.”
Zack Snipes reports, “It’s wet in the Lowcountry. We are getting heavy rain showers what seems like everyday. This is making it hard to get equipment in fields to spray or prepare for fall plantings. I have seen some watermelon and tomato fields and they look ok considering the rain and soggy conditions. I saw some bacterial spot on pepper and expect to see the same on fall tomato with the rain and humidity we’ve had. Get out your preventative fungicides, if you can. I also saw some leafminer damage on these crops which is unusual in my tenure. It seems plants were impacted a few weeks ago but the new growth looks to be unaffected. Melonworms were found in cucumbers, so get ahead of them.”
Justin Ballew reports, “This past week was a relatively nice, mild week compared to the week before. We had some rain to start the week and more to finish it out. Planting of fall crops continues and what’s been planted seems to be growing well. I looked at a few fields this week of seedling brassicas and I’m already seeing diamondback moth caterpillars and armyworms feeding. Remember to start scouting as soon as plants go into the ground. It doesn’t take many caterpillars to eat up seedlings and small transplants. Don’t forget we can run field bioassays to screen for insecticide resistance, so call us when you start seeing worms.
Bruce McLean reports, “Vegetable crops are still harvesting well, for the most part. Other than cucurbit downy mildew affecting cucumbers and some powdery mildew affecting squash, there are no widespread vegetable diseases seen in the fields. Cowpea curculio is still widespread on peas and must be intensively managed (starting prior to bloom) to minimize damage. Spotted Wing Drosophila is still very active in late-season blueberries, with trap counts showing very high capture numbers. Grape root borers (GRB) emergence is starting to increase in muscadines. Trap captures for GRB is on the rise. Much of the state is outside the window of Chlopyrifos application for GRB… except on late harvesting cultivars (more than 35 from application to harvest) and maybe some wine grape cultivars in the Upstate. Pecan weevil emergence is just getting started (in pecans). Ground and lower canopy application of Carbaryl and/or a trunk application of Tanglefoot are effective methods of control. Monitor traps and weevil movement through September (especially after rains). Re-treatment of Carbaryl will be necessary and can be reapplied at (up to) 7 day intervals. Pecan scab is becoming more evident in pecan orchards. Also, fall armyworm numbers have exploded over the last two weeks. This is a pest that can affect a wide variety of crops.
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.