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.
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.”
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, “On the whole disease pressure in most crops remains low. The exception is cucurbits where we are finding powdery mildew in cucumbers as well as downy mildew. Cucurbit bacterial wilt has been found in isolated fields. This disease is characterized by wilting of one vine or the whole plant. Once cut the stem will ooze a sticky sap from the wound. It is transmitted by the feeding activities of cucumber beetles. Strawberries are beginning to slow down while tomatoes peppers and peaches are doing very well.”
Justin Ballew reports, “We had an unseasonably hot week last week followed by a much cooler weekend. Some places received a little rain early in the week and some places received a little on Saturday. However, the Midlands are very dry overall. Crops responded well to the heat last week. Brassicas and cucurbit crops progressed extremely quickly. Squash and zucchini are setting fruit and some are being picked. Brassica and herbs are still being harvested. Tomatoes are setting fruit, but we still have a little time before picking on a large scale.”
Sarah Scott reports, “Peaches are still going strong in the Ridge. Some varieties are showing more cold damage than anticipated, but there is still a good crop out there. It seems that the very early varieties and then some of the very late varieties are the ones with the most damage. Some bacterial spot is showing up but not near as bad as last season, mainly due to dry conditions. We’ve had some really hot days but this past week we finally got some relief from the temperatures and some cloudy days. Hopefully rain is in the future as growers are irrigating heavily now. Some second croppings of Camarosa strawberries are still being harvested this week. Squash, zucchini, and cucumbers are producing well. Insect pressure is starting to occur more heavily, but disease, for the most part, is still at bay.”
Bruce McLean reports, “Blueberry harvest, after getting a late start, is starting to provide good quantities. Strawberry harvest is winding down for most. Last week’s heat caused much of the strawberries to become soft and unmarketable. Some varieties are still holding up though, with limited harvest. Some early blackberries are being harvested in good volume, with very good quality. Peach harvest is light and fruit is a bit small. Tomato harvest should begin late this week/early next week. Tomatoes have been experiencing some environmental stress (heat, low humidity, high UV), causing some leaf curl. This should subside with the increased moisture and lower temperatures. Squash are starting to be harvested. Cucumbers harvest isn’t far away. Peas and beans have been affected by thrips, but are growing out of that damage. Sweet corn harvest is getting near. Vegetable planting is starting to resume with the recent moisture and reduced temps.”
Tony Melton reports, “Peppers and tomatoes are setting fruit. Harvesting pickles consistently. Applying downy mildew and pickleworm materials regularly. Finishing up first cut of collards for processing. Started 2nd cut of processing turnips. Harvesting processing cabbage. Snap beans and butter beans are flowering. Setting sweet potatoes as fast as slips become available.”
Rob Last reports, “As we mentioned last week, cucurbit downy mildew has been confirmed in cucumber crops locally. All cucurbit growers should be applying downy-mildew specific fungicides such as Ranman tank mixed with either chlorothalonil or mancozeb. Other pests and disease levels in cucurbits remain low. Tomatoes and peppers are developing well with good fruit development and low pest and disease pressure. A little bacterial spot is beginning to show in untreated crops. Applications of mancozeb or copper can help to hold the disease. Note applications are unlikely to “cure” bacterial disease. Fruit crops continue to progress with good quality and low disease. Strawberries are showing a little botrytis and anthracnose, but this is at a low level. Peaches are coming to market along with blueberries and blackberries.
Justin Ballew reports, “Dry weather has returned to the midlands. Strawberries have slowed down and while we’re still picking a few, we are seeing very few blooms. The heat we’re expecting this week is likely to cease bloom production. The heat could be a problem for tomato and cucurbit pollination as well, as we may see some blooms die. Brassicas have been growing well. There has been an increase in diamondback moth activity over the last week. If you start seeing large DBM populations on your farms, contact your local agent about doing a bioassay to test for insecticide resistance. This is a great way to figure out which materials may work best on your farm. We don’t charge anything for this service. Don’t forget downy mildew was found this past week in cucumber in multiple places in the coastal plain, so it’s time to start preventative fungicide sprays in cukes if you haven’t already.”
Sarah Scott reports, “We are in full swing with early variety peach harvest. Some peaches are developing a little smaller in size partly due to previous cold weather events. Something spotted in the field has been some nutrient deficiency. Growers may have been tempted to dial down nitrogen or calcium nitrate applications on peach blocks that suffered cold damage as they thought those blocks would not produce a viable harvest, however this could lead to leaf drop and less reserves for next year’s crop. If you skipped out on some of your fertilization keep in mind yellowing, spotting and leaf drop could occur. A soil application of calcium nitrate at 30lb/acre now and another in late July can help those trees recover some foliage and build up a nutrient supply for next year’s reserve. Be careful if you want a quick result and try foliar applications, as this could burn the leaves and cause more drop that you may not be able to afford.”
Bruce McLean reports, “Irrigated vegetables are looking good for the most part. Seeing some stress to tomatoes with a heavy fruit load – likely from very low humidity and very high UV. Nonirrigated crops are starting to show some drought stress. Strawberries are starting to wind down. Blueberries are finally starting to be harvested, much later than usual. Blooming on muscadines appears to really stretched out due to the Easter freeze. Early flower clusters on growth from primary buds appears to be somewhat on time. But, flower clusters developing from secondary buds are really behind… possibly 3-4 weeks (easily). Soil is really starting to get dry in many areas.”
Tony Melton reports, “The higher temperatures have started to speed-up crops. We will start to harvest pickles this week. Spraying downy mildew fungicides on cucurbits. Some farmers are starting to apply insecticide for pickleworm. They don’t want to put out insecticides this early but they see the gamble of an entire field of pickles being rejected because of 1 pickleworm as too much of a gamble. These farmers think we need a system set-up to detect pickleworm in the southern part of the state to give them a better indication of when pickleworm arrives. Harvesting greens, cabbage, and broccoli as quickly as possible. Started planting sweetpotatoes. Many farmers getting deer depredation permits for peas, beans, and sweetpotatoes. Also, many farmers are applying acephate and dimethoate to control thrips with the added benefits of repelling deer. Peppers and tomatoes are begin to load with fruit. Many farmers still harvesting strawberries.”
Kerrie Roach reports, “Things in the ‘Golden Corner’ are looking up for vegetable producers, despite the dismal projection for tree fruit crops because of the cold events in April. For market growers, cool season crops are at their absolute last with 90+ degree temps forecasted for this week. Warm season crops are starting to really get growing, and many growers are starting to see some potential harvests this week. With higher than normal temps projected, make sure irrigation is consistent, scheduled and set for early morning to avoid leaf wetness late in the day and overnight and reduce disease incidence.”
Cucurbit downy mildew was found in SC this week in Bamberg, Barnwell, and Calhoun Counties. In each case it was found on cucumbers and for now severity seems low. This is about two weeks earlier than in the past couple years.
If not already doing so, all cucumber and cantaloupe growers in SC should begin applying protective fungicides to help prevent or manage downy mildew. Ranman tank-mixed with a protectant, such as chlorothalonil or mancozeb, or applications of Zampro are good options for protecting plants prior to symptom development. For more info, see Dr. Tony Keinath’s CDM Management publication.
Check out the new podcast, “The SC Grower Exchange” featuring Clemson Extension fruit and vegetable agents. The podcast is moderated by Sarah Scott from Edgefield and covers a more detailed look at what is happening in the fields across the state. New episodes are recorded weekly, so listen weekly and subscribe through Spotify, Google, or Apple.
Zack Snipes reports, “Everything is progressing nicely in the Lowcountry. We got some much needed rain last week. Temperatures have been cool so things are somewhat slow from a developmental standpoint. All the crops look great especially the tomato crop. We have a really nice fruit set and very little disease. I am expecting to see bacterial spot to show up sometime soon and have been getting a few calls about bacterial wilt taking down plants. I’ve also gotten a few calls about blossom end rot. That is typical on the first fruit set and will usually correct itself provided there is ample calcium in the soil AND the soil moisture is consistent. In our sandy soils the main cause of blossom end rot is allowing the soil to dry out during the fruiting stage. Folks might want to consider multiple 30 minute to 1 hour irrigation cycles on tomatoes per day.”
Justin Ballew reports, “We got right at an inch of rain at my house this past Wednesday. While the rain was much needed, the moisture and cool temperatures has allowed plant diseases to get a foothold in numerous crops. Over the last week, I’ve seen bacterial blight in mustard, downy mildew in collards, Septoria leaf spot in Italian parsley, and of course botrytis and a little bit of anthracnose fruit rot in strawberries. Growers have been sanitizing, applying fungicides, and/or terminating old crops to manage disease. When selecting fungicides, be sure to rotate MOA groups (referred to as “FRAC Codes” in the SE Vegetable Crop Handbook) to avoid developing fungicide resistance in your fields.”
Tony Melton reports, “A major pickle company found cucurbit downy mildew on pickles in Calhoun County. I have seen 100 acres of pickles damaged by hail and another 100 acres damaged by Reflex carry over. Next year, please make sure you are planting the right variety of strawberry for the intended market. When markets get full like this year, buyers are picky of the variety they will buy and many acres were not harvested to their full potential. Remember to control thrips on small peas, cucumbers, and beans. Also, control thrips in the flowers of tomatoes and beans.
Dr. Tony Keinath reports, “For the past few years, Orondis Opti on cucumber and cantaloupe and Orondis Ultra on pumpkin and watermelon have been the best fungicides to manage downy mildew. Based on results from a spring 2020 cucumber experiment at Coastal REC, Orondis is no longer the “silver bullet” it was 2 years ago. In my experiment, Orondis Opti rotated with Bravo controlled downy mildew in the early part of the season, but disease increased significantly during the latter part of the season and ended up higher than expected. Part of the shortcoming of the Orondis Opti/Bravo spray program was the Bravo rotation. Bravo sprayed by itself every other week did not control downy mildew at all, so spraying Orondis Opti/Bravo acted like Orondis Opti sprayed every other week, which was not enough. The labels for Orondis Opti and Orondis Ultra say they must be rotated with another fungicide. For the rest of the 2020 season, use Orondis Opti/Ranman + chlorothalonil on cucumber and cantaloupe, and Orondis Ultra rotated with Gavel or Ranman + chlorothalonil on pumpkin and watermelon. Always use the high rate (2.5 pints/acre) of Orondis products. Note that the mancozeb in Gavel or adding chlorothalonil helps to manage other foliar diseases like gummy stem blight and anthracnose. Yield data and input costs from my experiment are being analyzed to see if spraying Orondis leads to a higher net return despite the higher cost of this fungicide. Results will be presented at the virtual Cucurbit meeting in February 2021 to help growers plan downy mildew fungicide programs for the 2021 season.”
Rob Last reports, “Fall crops continue to grow well in the area. Given the current weather patterns pests and disease are active in some crops particularly where there are volunteers remaining from previous crops. Vigilance will be required in scouting an pesticide management programs. If In doubt scout.”
Justin Ballew reports, “It’s been cool, cloudy, and kind of pleasant outside this past week, though that has the vegetable crops growing a little slower. We’ve gotten some decent rains in most areas around the midlands as well. Bacterial spot is really showing up on fall tomatoes as a result of all the recent rain. It could be a bad fall for bacterial spot if the weather stays like this. Caterpillars are already out there on fall brassicas. It doesn’t take long once they’re planted. Start scouting, scout often, and rotate insecticides. Remember to contact one of us about screening your farm for insecticide resistance in diamondback moths once you start seeing populations build up.”
Bruce McLean reports, “Both fruit and vegetable development has slowed a bit due to cloudy conditions. Sunny conditions needed. Sweetpotatoes are sizing well and will be ready for harvest soon. Fall cucumbers and squash should soon be ready to start harvesting. Fall brassicas are being planted now. Muscadine crop is getting close to harvest. Noble is around 90% ripe; Carlos is around 60%; Doreen is still around 25%. Brix (sugar content) is off due to rain and cloudy conditions. Noble and Carlos brix are averaging around 11% with a low of 9.2% and a high of 15.0%. Doreen is averaging less than 10%. Did find a few Doreen that brix was over 19%… candy. Sunny conditions definitely needed.”
Tony Melton reports, “Beginning to harvest processing sweet potatoes but some have been stunted and delayed by excessive rain. Spraying processing peas for cowpea curculio. Starting to plant processing greens by seed. Even though lots of rain and having to mud through fields cucumbers for pickles are being harvested and still being planted.”
Andy Rollins reports, “Blueberry pruning is best served for the dormant time of year late January-late February. I met with a commercial grower who was anxious about getting started early partly because he has many plants completely unproductive for the second year in a row. I like to call this revenge pruning as that is the primary motivation. Be careful, you could end up hurting yourself more in the long run. In his case, it was all about light and proper pruning to encourage light down through the canopy. The orignial spacing of Rabbiteye type varieties was very close so we also considered killing every other plant to get more light into the bushes but this would not replace the need for properly selectively removing a few of the oldest canes each year, spacing them out so there is better light penetration. For a detailed explanation, please see NCSU Blueberry specialist Bill Cline’s presentation.”
Rob Last reports, “In our area crops are generally looking good with watermelons and cantaloupes coming to harvest. From a pest perspective, we are finding some early pickleworm and melon worm damage occurring. In addition, cucumber beetles and squash bugs remain active. Cucurbit downy mildew is being found in the area and as such protectant fungicide applications remain viable options. If in doubt scout.”
Zack Snipes reports, “Last week was full of heavy rain and heat. It finally feels like June. Crops are either going one of two ways right now: they either look great or they are succumbing to disease. Tomatoes are picking great and I’ve seen some really nice watermelons finish up this week. Peppers are loving this heat but I have seen an uptick in bacterial leaf spot (BLS) in the crop. Keep up with spray programs (copper and Manzate) for BLS in pepper. Tomatoes are also starting to look rough with all the heat and rain. If your tomato crop dies, please identify the culprit so we can better manage it next year. Soilborne diseases such as bacterial wilt and southern blight will not go away next year. I will be more than happy to work with folks on crop planning, cover crops, and rotation on their farms so we can avoid crop failures.
A quick cut of the stem of a wilting plant and a dip into water can help to positively identify Bacterial Wilt in tomato. The presence of the pathogen will yield a clear to white ooze coming from the plant after a few minutes in the water. Photo from Zack Snipes.
Bacterial Leaf Spot is spreading in pepper due to the heavy rains and increased heat. Photo from Zack Snipes.
Justin Ballew reports, “We finally got some widespread rain mid-week and it has rained in places most days since. Some areas received enough rain to cause temporary flooding in lower-lying fields. Remember, according to produce safety guidelines, any produce that was flooded may not be harvested. We should expect diseases to worsen in the coming weeks. Powdery mildew in cucurbits and bacterial spot in tomatoes has certainly increased in the past week. Crops are still developing very rapidly and we are picking lots of squash, zucchini, cucumbers, tomatoes, eggplant, sweetcorn, greens, beans, etc.”
This field of cucumbers was temporarily flooded by the heavy rain last week. Photo from Justin Ballew
A crew picking squash in Lexington. Squash and zucchini are growing like wildfire in the midlands. Photo from Justin Ballew.
Tony Melton reports, “Raining almost every day some storms causing downed trees. Root rot bad applying a lot of potassium phosphide. A few strawberry growers still picking around rains. Downy mildew bad but Ranman and Orondis are doing a good job of control. Peas are maturing and will not be too long until harvest. We need to hurry to get the second crop planted on the same land. Still planting sweet potatoes. Okra and tomatoes just started to bare. Southern stem blight is bad and we’re spraying Fontelis. Some first crop butterbeans are being harvested.”