Integrated Pest Management

Damping-Off on Direct-Seeded and Transplanted Vegetable Crops

Posted on by Tim Bryant

By: Anthony Keinath, Vegetable Pathologist, Clemson Coastal REC

Originally posted on SC Grower: https://scgrower.com/

“Damping-off” refers to root and stem rot on young seedlings of direct-seeded crops. “Stem and root rot” is used to describe the same disease on transplanted crops. I use the term “seedling disease” when information below applies to both types of crops.


Stem and root rot on a watermelon transplant. Note the brown, water-soaked, discolored area on the stem just above the soil line.


Stem and root rot on a tomato transplant. Note the tan, collapsed area on the stem just above the soil line.

In South Carolina, the water mold Pythium is the most common cause of seedling diseases, especially on cucurbits, tomato, and pepper. The fungus Rhizoctonia also occurs on seedlings of certain crops, including beet, onion, radish, arugula, and head and stem brassicas (broccoli, cabbage, cauliflower) along with collard and kale. (Note that head and stem brassicas, collard, and kale are, botanically, Brassica oleracea, which is more susceptible to Rhizoctonia than mustard, Brassica juncea). Most vegetable crops can be infected by both pathogens. For example, 49% of diseased arugula seedlings were infected by Pythium and 54% by Rhizoctonia on an organic farm in the Lowcountry in an on-farm study in 2011.

At a recent vegetable grower meeting, summer squash was voted the crop most susceptible to damping-off out of a list of direct-seeded crops that included beets, onions, parsley, and cilantro. Squash and other cucurbits are susceptible to at least 9 species of Pythium, 3 warm-season species and 6 cool-season species. Thus, squash and other cucurbits are susceptible to seedling diseases year-round.


Recovery of Pythium species from transplants of cucumber, watermelon, Hubbard squash or bottle gourd, 2017 to 2019, Charleston and Lexington counties.

Fungicides and Biofungicides
The standard conventional fungicide Ridomil Gold applied via drip irrigation is recommended to reduce seedling diseases. Research in another state showed that Ridomil Gold is more effective applied as soon as possible after transplanting rather than several days or weeks later. Ridomil Gold will not completely prevent seedling disease, but, typically, it reduces the number of diseased plants. Biopesticides and NOP/OMRI organic-approved products generally have little effect on seedling disease in the field. They are useful in the greenhouse to prevent damping-off in seedling flats.

Cultural Practices
Plastic mulch is such a common production practice that I almost forgot how much it significantly reduces stem and root rot on transplants. I was reminded, in dramatic fashion, in an experiment in cooperation with the University of Georgia in spring 2015 that included mulched and not mulched plots of transplanted seedless watermelon. It’s very possible that some growers are seeing so much damping-off on summer squash because it is typically planted on bare ground.


Stem and root rot of seedless watermelon transplants in a field naturally infested with multiple species of Pythium at Coastal REC, Spring 2015

Resistance
No cultivars of any vegetable crop have genetic resistance to seedling diseases. As the graph below shows, however, there may be some differences among cultivars that could be called “field resistance,” a term used when certain cultivars have less disease under field conditions than is expected based on greenhouse testing.


Seedless watermelon cultivar Melody had significantly less Pythium stem and root rot than Citation and Fascination, Coastal REC, Spring 2015

Recommendations

  1. Transplants generally have less seedling disease issues than direct-seeded crops, because all vegetable crops become more resistant to stem and root rot as they age. This is not to say that stem and root rot doesn’t affect older plants, but it’s less likely.
  2. If you replace transplants that died from stem and root rot, do not set the new transplant in the same hole. Move the planting hole at least 6 inches away, because there might be fewer pathogen propagules in a different spot. The numbers of pathogens in soil is very variable.
  3. Overseeding at a higher rate of seed/foot or seeding a bit more shallowly than normal can improve stands of direct-seeded crops.

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Small Grains Field Day at Clemson’s Pee Dee REC

Posted on by Tim Bryant

Clemson Extension is hosting a small grains field day on Thursday, April 25th at the Pee Dee Research and Education Center. Registration will begin at 8 am and the program will be from 9 am – 12 pm. Lunch and 3 pesticide credit hours will be provided for registered attendees. Topics covered will include high yield intensive management, disease control, weed control, and insect pest management. If you plan to attend please RSVP with Pat McDaniel (pmcdani@clemson.edu), or call 803-484-5416.

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Advanced IPM: Anaerobic Soil Disinfestation Strategies Workshop

Posted on by Tim Bryant

On Thursday February 15, 2024 the South Carolina New and Beginning Farmer Program is hosting a workshop on anaerobic soil disinfestation strategies as part of the advanced IPM workshop series. The event will be held from 10 AM – 4 PM at Clemson’s Coastal Research and Education Center in Charleston, South Carolina.

Learn how to use a cutting-edge advanced IPM (Integrated Pest Management) technique for reducing soil-borne pests, especially nematodes. Anaerobic Soil Disinfestation (ASD) has been used in Asia and northern Europe for some time now but is slowly making its way into the Southeast region of the United States. With the loss of methyl bromide as a soil fumigant, this technique, which uses available sources of biologically derived carbon, is a promising strategy.

Anaerobic Soil Disinfestation (ASD) has been used in Asia and northern Europe for some time now but is slowly making its way into the Southeast region of the United States. With the phasing out of many fumigants, this all- natural pre-plant soil treatment technique (that uses available sources of biologically derived carbon) is proving a promising strategy for both conventional and certified organic applications.

Register for the event and other events as part of this series here, and find more information on the advanced workshop series here.

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South Carolina New & Beginning Farmer Program Now Accepting Applications

Posted on by Tim Bryant

The Clemson Extension SC New & Beginning Farmer Program is now accepting applications for the Class of 2024!

The SCNBFP is focused on enabling new and beginning farmers to be successful, productive, and innovative members of their local agricultural community by providing them with the tools, knowledge and skills necessary to be successful entrepreneurs; sound business managers; exemplary stewards of SWAPA (soil, water, air, plants, and animals), and successful marketers of the unique products they create; and, perhaps most importantly, individuals who have a sense of pride and quality of life as a result of their investment and participation in the agricultural community of South Carolina.

Applications due March 3, 2024

South Carolina New & Beginning Farmer Program
Class of 2024 Program Snapshot

  • ‘Core’ Program Dates: May – December 2024, consisting of a series of 10 full day events (9 core training workshops and a graduation event) and optional advanced programming.
  • Cost: $350.00/Person
  • Core Workshop Locations: Some workshops will be held in-person at the Lexington County Clemson University Extension office, and some will be held online via Zoom.
  • Who May Apply: Any current resident of SC, age 18 or older who has been actively farming for less than 10 consecutive years.  Current land access not required.
  • How to Apply: Online applications only at www.scnewfarmer.org
  • Deadline to Apply: 11:59 PM, Sunday, March 3, 2024
  • Detailed Program Outline and Course Schedule and Description available at: www.scnewfarmer.org

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Clemson IPM Program and SC SARE Joint Open Forum

Posted on by Tim Bryant

Flyer

The annual Clemson IPM program and South Carolina SARE open forum will be held this Thursday, January 11, from 10am to 2pm at the Sandhills Research and Education Center in Columbia, SC. This open forum is an opportunity to hear an update on ongoing activities from the Clemson IPM program, SC SARE, and SC State University SARE, ask any questions you may have, or provide input on future directions for these programs. A schedule of the event can be found below. To register, visit this site.

Agenda

10:00 am – 10:15 am: Welcome and introductions

10:15 am – 10:45 am: IPM Program overview and updates

10:45 am – 11:15 am: SC SARE Program overview and updates

11:15 am – 11:30 am: Updates from SC State University SARE

11:30 am – 12:00 pm: Guest speaker(s)

12:00 pm -1:00 pm: Lunch

1:00 pm – 2:00 pm: Open discussion & brainstorming for 2024

2:00 pm: Adjourn

 

We look forward to meeting with you!

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Preparing a stink bug pest management plan for field corn

Posted on by Tim Bryant

Stink bug overview and identification

The brown stink bug, Euschistus servus, and southern green stink bug, Nezara viridula, can be damaging pests of field corn in South Carolina. While it has a high potential for injury, it is considered a sporadic pest because it does not occur at damaging levels in every field every year. Due to the sporadic nature of this pest, it is important to understand potential risk factors for infestation and have a plan in place before the growing season to be ready to address it efficiently and effectively if damaging populations occur.

Stink bugs are shield-shaped insects, which are similar in shape and size across species. As the name suggests, the brown stink bug is dark brown in color. There is a beneficial stink bug species that may be confused with brown stink bugs, but can be distinguished by the presence of pointed and sharp shoulders (i.e. pronotum), which the pest brown stink bug does not have. Nymphal brown stink bugs are light green in color and have a distinctive brown patch on their abdomen. Southern green stink bugs are slightly larger than brown stink bugs and green in color. The nymph of southern green stink bugs have a series of pink, white, and black spots on their abdomen, which can easily distinguish them from other species. Other species that can occur in corn but are either far less common or not pests of corn in South Carolina are the brown marmorated stink bug, green stink bug, and rice stink bug.

Brown bug on green plantSmall green bug on white sheet of paper
Left: adult brown stink bug. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org. Right: fourth instar brown stink bug nymph. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org

shield shaped green buggreen, pink, and black bug on leaf

Left: Adult southern green stink bug; note the presence of tachinid fly eggs. Right: fourth instar southern green stink bug nymph. Image credits: Russ Ottens, University of Georgia, Bugwood.org.

Injury to field corn

Field corn is susceptible to injury during three key stages of field corn development: 1) emergence (VE) – six-leaf stage (V6), 2) two weeks prior to tasselling (VT) during the earliest stages of ear development, and 3) the first two reproductive stages of development (R1 and R2). During the early vegetative stages (i.e. VE-V6), stink bugs feed directly on the growth point of young plants, which can lead to stunted plants, tillers, leaf holes, deformities, or plant death in severe cases. Prior to tasseling and pollen shed, feeding on the early stages of ear development leads to a characteristically “banana-shaped” ear, which limits overall yield potential and can expose the ear to secondary pests and pathogens. It is important to note that during these stages, the ear is not yet visible, but stink bugs can use their straw-like mouthparts to penetrate into it. Beyond pollination, direct feeding on kernels has limited potential to directly impact yield but can introduce grain quality issues in the form of fungi and mycotoxin contamination if bugs are at a high enough density.

young corn plants with multiple shootssmall corn plants between larger corn plants
Early vegetative injury from stink bug feeding. Left: plants stunted with multiple tillers. Right: Severely stunted plants. Image credit: Tim Bryant, Clemson University. 

young corn ear with curved shapemature corn ear with severe crook shape
Banana-shaped ears as a result of stink bug feeding during late vegetative stages prior to tasseling. Image credit: Tim Bryant, Clemson University. 

Corn ear with discolored kernelsCorn ear with discolored kernels
Discolored kernels and fungal growth as a result of stink bug feeding during early reproductive stages of corn development. Image credit: Tim Bryant, Clemson University. 

Population dynamics and management

Identifying at-risk fields can help save time in deciding when and where to scout for stink bugs. During early vegetative stages, fields that are planted into heavy cover crop residue can potentially be at higher risk for large populations and injury. Proper seed slot closure can be affected by this heavy cover and expose more sensitive portions of the plant to feeding, increasing injury potential. Fields that were planted with soybeans in the previous season can also be at a higher risk for early-season infestations. Later in the season, the interface of wheat and corn is at high risk for stink bug infestations. Wheat is an excellent early-season host for stink bugs, which can easily move into nearby corn during wheat harvest. Wheat harvest often coincides with the later vegetative stages of corn development, which are susceptible to stink bug injury.

For early vegetative infestations, insecticidal seed treatments, which are applied almost universally to commercial corn seed, can provide some protection from early season injury. Generally, fields with a history of stink bug pressure or at risk of injury from soil pests may benefit from increased seed treatment rates. Additionally, foliar insecticides can effectively manage stink bugs throughout the season, but it is critical to scout and only apply an insecticide at the economic threshold level for the given growth stage. The economic threshold is 1 bug per 10 plants from V1 to V6, 1 per 4 plants from V12-VT, and 1 per 2 plants at R1 and R2. The two most important considerations for applying an insecticide are achieving good coverage and timing the application properly. Ensuring canopy penetration is especially critical during the later stages of corn development. Bifenthrin is generally the most effective material to target brown stink bugs specifically. Applying an insecticide only at the economic threshold level will also preserve naturally occurring biological control agents in the field that broad-spectrum insecticides would otherwise kill.

For more detailed biology and management information on brown stink bugs in field corn, see this Land-Grant Press article.

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Transgenic Bt Corn Research at Clemson University

Posted on by Tim Bryant

Contributing Author: Dr. Francis Reay-Jones

More than 80% of field corn grown in the U.S. has been genetically engineered to express one or more insecticidal toxins from Bacillus thuringiensis, called Bt toxins. Bt corn was first commercialized in the U.S. in 1996, expressing a single Bt toxin targeting the European corn borer. Newer Bt corn hybrids express two or more Bt toxins, which has increased the number of target pests to include the corn earworm and the fall armyworm. Benefits of planting Bt corn can include protecting yield from insect damage, reducing the need to use insecticide, and improved grain quality. However, such benefits can be impacted by the development of resistance in target insects.

Corn earworm larvae feeding on corn ear.
Corn earworm larvae feeding on corn ear.

Dr. Francis Reay-Jones is continuing this year to evaluate the efficacy of Bt traits and the impact Bt toxins have on the life cycle of the corn earworm, with implications on resistance evolution. “We have been conducting field efficacy trials with a range of Bt traits since 2009. Since then, we have seen some traits become less effective over time because corn earworm has developed resistance. We saw in particular a shift in 2015 when resistance to some of the Cry toxins expressed in Bt corn became more widespread not just in South Carolina, but across the southeastern U.S.” Although the corn earworm is generally not a significant economic pest of field corn, the same species is a serious pest in cotton, where it is known as bollworm. Because Bt cotton expresses the same or similar toxins as Bt corn, selection for resistance in Bt corn is likely driving resistance issues to Bt cotton. “Planting a non-Bt refuge is the only tool we have to manage resistance. Preventing resistance development in Bt corn is crucial so that the insect does not cause more damage to Bt cotton later in the season, where the corn earworm (or bollworm) is a major economic pest.”

Corn trials at the Clemson University Pee Dee REC in 2023.
Corn trials at the Clemson University Pee Dee REC in 2023.

While resistance in corn earworm is widespread to most Cry toxins used in Bt corn and Bt cotton, one toxin, called Vip3A, remains highly effective. Trials in South Carolina continued this year to evaluate Bt corn hybrids expressing Vip3A. Examination of hundreds of corn ears in 2023 showed that these hybrids remain highly effective, with no ear injury found due to corn earworm feeding. In corn, this toxin is expressed in Trecepta, Optimum Leptra, and Agrisure Viptera products. While Vip3A remains effective, reports of unexpected injury in recent years in the mid-south underline the need for continued resistance monitoring. Vip3A toxins are also expressed in new Bt cotton varieties, and planting of non-Bt refuge in corn is crucial, since only a single Bt toxin is currently available with very good activity for this key pest.

 

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Clemson’s Vegetable Entomology Program

Posted on by Tim Bryant

Dr. Tom Bilbo, Clemson’s vegetable and strawberry entomologist stationed at the Coastal Research and Education Center in Charleston, began his research and extension program late in 2021. Since starting here at Clemson, Dr. Bilbo has rapidly expanded his program and has started addressing a number of different economically important pest concerns for vegetable and strawberry growers. “The primary goal of my research program is to enhance sustainable food production through protection of yields from crop pests and enhancement of yields through conservation of beneficial insects” Dr. Biblo says. The primary areas of focus for his research are 1) developing new biological control strategies for key pests, 2) reducing pest potential through modification of farming practices and systems, and 3) improving insecticide use and managing insecticide resistance. When it comes to Extension and stakeholder interaction, focus areas include 1) identifying key entomological issues in vegetables and strawberries, 2) encouraging adoption of improved practices through demonstration of efficacy and profitability, and 3) improving stakeholder knowledge of advances in IPM and IRM.

Headshot of a man with brown hair.
Dr. Tom Bilbo, Clemson’s vegetable entomology specialist

“Overall, my research uses our understanding of insect ecology to reduce pest problems and enhance the role of beneficial species, especially predators and parasitoids” Dr. Bilbo says, “much of my research is conducted on commercial farms in coordination with local growers.” The reason for much of the research being conducted with collaborating growers in twofold. 1) Insect ecology entails insects moving around, and insects don’t care about the arbitrary plot borders researchers construct. So small plot experiment station trials make it difficult to tease apart treatment effects as well as not being a realistic representation of how insects behave on vegetable and fruit farms. 2) On-farm trials allow Dr. Bilbo to build relationships with growers to understand the pest problems better and create management strategies that are feasible, economical, and effective.

A man and a woman working in a field of leafy greens
Research assistants Wyatt Witman and Caroline Dukes artificially infesting collard plants with diamondback moth larvae to determine parasitism rates at varying distance from flower strips.

Some of Dr. Bilbo’s on-going projects include pest management in brassicas, strawberry, tomato, watermelon, and cucurbits. In brassicas, the primary focus is effective integrated management of the diamondback moth, the major economic pest of most brassica crops worldwide. His work on diamondback moth includes determining how predator and parasitoid activity varies with the use of intercropped flowers (to optimize flower plantings), evaluating mating disruption as a potential management strategy, and determining which plants are best at attracting natural enemies of diamondback moths and other pests in both spring and fall crops. Much of this diamondback moth research is conducted in collaboration with specialists at NC State, Virginia Tech, and Tennessee State University. These types of regional efforts allow for a greater understanding of pest status and management options on a larger spatial scale.

A woman working in a field of leafy greens.
Research assistant Lindsey Newton setting up diamondback moth pheromone dispensers as part of a mating disruption experiment.

In strawberry, his primary research focus is on enhancing the role of beneficial predatory mites to manage spider mites. A survey of commercial farms for the presence of these beneficial mites will provide a baseline level of knowledge on their natural occurrence and role in suppressing pest mites. Other projects include evaluation of tomato and watermelon cultivars for spider mite preference, evaluating pheromone traps for pickleworm moth in cucurbit crops, continued Bt resistance monitoring in corn earworm, and conducting insecticide trials to evaluate new and existing products for important pests. All of this research and subsequent extension work to disseminate the results of these studies will directly benefit vegetable growers in South Carolina by maximizing their pest management and providing a full range of tools to effectively address those pests.

A man and a woman working on insect traps.
Research assistants Wyatt Witman and Caroline Dukes setting up a trapping experiment for pickleworm moth in zucchini

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Edisto REC Hosts Field Corn Field Day

Posted on by Tim Bryant

On Thursday, July 27, a corn production field day was held at Clemson University’s Edisto Research and Education Center in Blackville, SC. The field day was well attended by growers and other stakeholders to learn about the latest research and recommendations for corn agronomy, disease and nematode management, insect management, and soil fertility management.

Dr. Michael Plumblee, Clemson’s corn and soybean extension specialist, organized the field day in addition to providing updates on his on-going work with double cropping corn and soybean, corn variety trials, and corn fungicide efficacies. Double cropping corn and soybeans is a new strategy that Dr. Plumblee and his graduate student, Bennett Harrelson, are exploring as a potential mechanism for growers to increase profitability in the long South Carolina growing season. In this system, corn is harvested early and soybeans are immediately planted. Dr. Plumblee’s research seeks to identify best management practices for this system including planting date, harvest date, soybean variety, and nematode management.

Dr. John Mueller, a field crop pathologist and nematologist, provided updates on several nematacides that are commonly used by growers, Counter 20G and Velum. On-going trials conducted by Dr. Mueller will help determine which of these products provides effective control for growers. Dr. Mueller also spoke about corn fungicide trials that are on-going in collaboration with Dr. Plumblee. Dr. Mueller says the good news for growers this season is that it has been a relatively light disease year so far.

Dr. Mike Marshall, a field crop weed specialist, provided an update on a number of different pre and post emergent herbicide programs that could be used by growers in the field. There are many different herbicide programs that growers can utilize, and continued efforts to test the efficacy of these programs allows growers to be informed and not use herbicides which may not provide good levels of control.

Man speaking in front of corn field.
Dr. John Mueller discussing several different nematacides.

Dr. Francis Reay-Jones, a field crop entomologist, provided an update on the state of insect pest management in corn. Dr. Reay-Jones emphasized the importance of planting non-Bt refuge corn each year to delay the continued development of Bt resistance in corn earworm populations. While corn earworm is generally not an economic pest of corn, it is a major pest of cotton, where it is known as bollworm. Since cotton expresses many of the same Bt toxins that corn does, resistance management in corn continues to be a critical strategy to prevent further issues in managing the insect in cotton. Tim Bryant, provided an update of the state of stink bugs in field corn. Stink bugs are the most important economic insect pest of corn in the Southeast, but it is also a sporadic pest, so scouting is critical for growers to effectively manage it.

Man talking to crowd of people.
Dr. Francis Reay-Jones providing an update on the state of Bt resistance management in corn earworm populations.

Finally, Dr. Bhupinder Farmaha provided an update on soil fertility practices for corn. Soil samples should be taken in the field and sent to the Clemson Agricultural Service Laboratory to provide a full break down of the nutrient contents of the soil in a field, allowing growers to amend the soil in a targeted and effective way. Dr. Farmaha also stressed the diminishing returns seen from soil amendments beyond a certain amount, emphasizing the importance of these soil tests.

Man speaking to a classroom of people
Dr. Bhupinder Farmaha discussing soil fertility in corn.

All of these biotic and abiotic factors play an important role in the success growers have with corn production. Integrating all these decisions with each other in a synergistic manner is the cornerstone of a truly integrated pest management program.

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Management of Alternaria Black Spot on Conventional and Organic Kale Grown in the Fall

Posted on by Tim Bryant

Contributing Author: Dr. Anthony Keinath

Black spot, also known as Alternaria leaf spot, is considered to be the most important fungal disease on organic kale in South Carolina. It tends to be more prevalent in the fall than in the spring. The primary cause is the fungus Alternaria brassicicola (AB), found worldwide on brassica crops. In South Carolina and Georgia, a second species, Alternaria japonica (AJ), also is present. AJ is more cold tolerant than AB, so it is more likely to be found on fall crops or overwintered kale than on spring crops.

Kale leaf with yellow and brown patches
Kale infected with Alternaria black spot.

In October 2021, two fields at Coastal REC were each transplanted to 14 kale cultivars representing four types of kale: curly, Tuscan (lacinato), Siberian, and Portuguese. One field was organic certified, and one was conventional. The same rates of organic and conventional fertilizer were applied to each field. Transplants were spaced 1 ft apart in single rows on a 3-ft-wide bed with drip irrigation and white-on-black plastic mulch. Leaves were cropped in early to mid-December and again in late December to early January. Leaves were sorted into healthy and diseased categories, then counted and weighed by category. The diseased category included leaves with any leaf spots on them, even very small ones.

Rows of different kale crop types and cultivars
Various kale types and cultivars planted to test their yield potential and susceptibility to Alternaria black spot.

Average yields differed by the type of kale. Summed over both harvests, Siberian kale grew the fastest and yielded the most, followed by Portuguese kale, curly kale, and finally Tuscan kale. Cultivars did not differ much within kale type, except White Russian yielded more than Red Russian and Russian Royale when the yields from both harvests were added together.

Figure showing kale yield of various varieties
Kale yield by type.

Kale type also differed in susceptibility to black spot when plants were sprayed with spores of Alternaria. Portuguese was the most susceptible and had more diseased leaves, 70%, than any other type or cultivar. Tuscan was the least susceptible, while curly and Siberian were intermediate. Curly kale cultivars didn’t differ in susceptibility at the first harvest, but when regrowth was harvested, Oldenbor had more disease (57% diseased leaves) than the other four curly kale cultivars. The red curly kale curly Roja had less disease than the four green curly kales, but it also had low yields. Among Siberian kales, Red Russian had less disease than White Russian. Toscano Tuscan kale had more disease than cultivar Lacinato.

Figure showing percentage of diseased plant with different kale types
Percentage of Alternaria black spot diseased leaves by kale type.

Another potential way to increase kale yields is to grow plants in double rows rather than single rows. At Coastal REC we did this in fall 2020 by transplanting two rows of kale on a 6-ft-wide bed with drip irrigation and white-on-black plastic mulch. The popular cultivars Darkibor and Winterbor were used. One plant at the end of each plot was inoculated with spores of AJ. Three plants in the middle non-inoculated portion of each plot were harvested, and the inoculated plant plus the plant next to it were also harvested. Leaves were sorted as described above.

Yield of healthy leaves was increased for both cultivars in double-row plots compared to single-row plots. This yield increase was observed on both inoculated and on non-inoculated plants. Black spot decreased yields of Winterbor in double rows but not single rows and not with cultivar Darkibor at either spacing. Double rows did not increase disease as much as might be expected because the hours kale leaves stayed wet was similar in both row spacings: 17.3 in single and 18.8 in double. This study demonstrates the importance of type and cultivar on disease prevalence. Selecting a type based on the balance of yield potential and disease resistance is an important part of an integrated management program for Alternaria black spot in kale.

This work was in part supported by the Organic Transitions Program, National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2021-51106-35495.

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