Vegetable Crops Edition

Seasonal updates and alerts on insects, diseases, and weeds impacting vegetable crops. New Jersey Commercial Vegetable Production Recommendations updates between annual publication issues are included.
 
Subscriptions are available via EMAIL and RSS.
 
Quick Links:

NJ Commercial Vegetable Production Recommendations

Rutgers Weather Forecasting - Meteorological Information important to commercial agriculture.

January 19, 2020

Damping-off: Identifying and Controlling Pathogens in Transplant Production

It is extremely important to know which pathogen is causing damping-off problems and which fungicide to properly apply. The key to controlling damping-off is being proactive instead of reactive. Always refer to the fungicide label for crop use, pathogens controlled, and application rates.

Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off). Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia and Fusarium spp.

Control of damping-off depends on a number of factors. First, is recognizing the conditions which may be leading to the problem (i.e., watering schedule/greenhouse growing conditions) and second, identifying the pathogen causing the problem. Reducing the chances for damping-off always begins with good sanitation practices prior to transplant production.

Conditions Favoring Damping-off

Although all four pathogens are associated with damping-off, the conditions which favor their development are very different. In general, Phytophthora and Pythium are more likely to cause damping-off in cool, wet or overwatered soils that aren’t allowed to dry out due to cloudy weather or cooler temperatures. Conversely, Rhizoctonia and Fusarium are more likely to cause damping-off under warmer, drier conditions especially if plug trays are kept on the dry side to help reduce transplant growth. [Read more…]

Filed Under: Commercial Ag Updates, Organic Production, Vegetable Crops Tagged With: ,
January 18, 2020

Cucurbit Powdery and Downy Mildew: A Tale of Two Pathogens

Cucurbit powdery and downy mildew are two important pathogens of cucurbit crops throughout the mid-Atlantic region. Each disease has the ability to cause significant losses and can often show up in cucurbit plantings at the same time during the production season making control difficult. Its important for growers to remember that each pathogen belongs to a different group of fungi (powdery mildew – the ascomycetes and downy mildew – oomycetes)  which means that different classes of fungicides (i.e., different FRAC codes) are needed for the proper control of each disease. Thus, at any time of the growing season growers may have three choices: control one or the other, or control both at the same time. Before we get to control options, lets take a look at each one, and what has changed during the past few years.

Cucurbit powdery mildew

Up until 2004, cucurbit powdery was considered the most destructive disease in cucurbit production, that all changed with the re-emergence of cucurbit downy mildew. Cucurbit powdery mildew (CPM), in past years, was thought to be caused by two different pathogens, Podosphaera xanthii (formerly Sphaerotheca fuliginea) or Golovinomyces chicoracearum var. chicoracearum (formerly Erysiphe cichoracearum), with the former being reported more in the US and worldwide. In general, E. cichoracearum was more commonly found during cooler weather, with P. xanthii preferring hotter weather. What is the importance of knowing which species is present? Knowing which species are present, or more prevalent in the overall population of the pathogen will have important impacts in breeding programs, control strategies, and fungicide resistance management strategies. In 2019, researchers from IL and NY conducted a survey of CPM isolates collected from 6 different cucurbit hosts from around the US. The survey, with the use of morphological characterization and genotyping-by-sequence (GSB) methods and analysis, determined that 100% of the CPM isolates collected in the US were Podosphaera xanthii. Virulence testing with a subset of samples determined that there were some differences in the ability to cause disease, which was not unexpected. Cucurbit powdery mildew is an obligate parasite, and like cucurbit downy mildew, must have a living host in order to survive the winter, or importantly, as in the case of powdery mildew produce chasmothecia which allow the pathogen to overwinter. The production of chasmothecia shows the pathogen is reproducing sexually which gives rise to genetic diversity in the CPM population which can lead to differences in virulence as well as fungicide resistance development. Cucurbit powdery mildew is known to produce chasmothecia in different regions of the US, and has been observed in New Jersey in some years. The role of clasmothecia production and if it allows overwintering in NJ (and elsewhere) is not well understood. In general, CPM moves up the east coast each spring as cucurbit crops are planted up the coast, eventually reaching the mid-Atlantic region sometime in the early to mid summer making preventative fungicide applications necessary. The fungicides that have been used to control the pathogen in southern regions may greatly impact efficacy and control strategies in our region because of potential fungicide resistance development. Importantly, there are a number of cucurbit crops with very good genetic resistance to CPM. These varieties can help delay disease onset and may help reduce fungicide input and should be considered as a part of any disease management plan, especially in organic production systems.

Cucurbit downy mildew

As mentioned earlier, in 2004, cucurbit downy mildew (CDM) re-emerged in the US with a vengeance causing significant losses in cucurbit production. In most years prior to this, concern for CDM control was minimal, since the pathogen arrived late in the growing season (in more northern regions), or the pathogen caused little damage, or never appeared. After 2004, with significant losses at stake, and with very few fungicides labeled for its proper control, CDM became a serious threat to cucurbit production. Importantly, at the time, cucumber varieties with very good levels of CDM resistance were no longer resistant, suggesting a major shift in the pathogen population. Research done over the past 15 years has led to a better understanding of the pathogen. Recent research has determined that the CDM falls into two separate clades: Clade I and Clade II. Some CDM (Pseudoperonospora cubensis) isolates fall into Clade I which predominately infect watermelon, pumpkin, and squash, where CDM isolates in Clade II predominately infect cucumber and cantaloupe. Research suggests that isolates in Clade II can quickly become resistant to specific fungicides (NCSU). Most cucumber varieties are resistant to Clade 1 isolates, but there is no resistance currently available for Clade 2 isolates. For pickling cucumber the varieties, Citadel and Peacemaker, are tolerant to clade 2 isolates. For slicing cucumbers, the varieties SV3462CS and SV4142CL are tolerant to Clade 2 isolates. All organic and greenhouse growers are encouraged to use tolerant varieties since chemical control options are very limited (NCSU). An extended list of cucumber varieties with CDM resistance from the University of Florida can be found here. For the past decade, researchers from around the US have been closely monitoring and forecasting the progress of CDM through a website hosted by NCSU. The CDMpipe website is currently in the process of an upgrade and will now be hosted by Penn State University. All cucurbit growers are encouraged to sign up to the CDMpipe website to help them know what cucurbit crops are being infected (and where) and to follow the forecasting to know where the pathogen may move to next. As a note, in recent years, CDM control with certain fungicides has varied significantly depending on the cucurbit host and geographic region. This is extremely important since two clades of the pathogen are potentially present (affecting host range) as well as having a potential impact on control strategies. How do you know which clade may be present on your farm? Follow the reports. If CDM is mostly present in cucumber crops as it works its way up the east coast, then you are most likely to see it infect cucumber and melon on your farm first. Scout your fields regularly, especially if CDM is in the immediate region. Pay very close attention to symptom development and on what cucurbit crop(s) you see it on, this is especially important if you grow more than one cucurbit crop. Like CPM, once CDM arrives in the region preventative fungicide applications will be necessary.

Fungicide resistance development in CPM and CDM

Fungicide resistance development in cucurbit powdery mildew is well documented. In the mid-Atlantic region, resistance has been reported in FRAC code 3 (DMI fungicides – Nova, Rally), 7 (SDHIs – boscalid), 11 (strobilurins – Quadris, Pristine), 13 (quinoxyfen – Quintec), and U6 (cyflufenamid -Torino). All of these fungicides have a high risk for resistance development because of their specific modes of action. Other currently labeled fungicides for CPM control, such as fluopyram (Luna, FRAC code 7) and metrafenone (Vivando, FRAC code 50) are also at risk for fungicide resistance development. All cucurbit growers are strongly encouraged to rotate as many different fungicides with different modes of action (i.e., from different FRAC codes) to help reduce the chances for fungicide resistance development. Growers are also strongly encouraged to scout fields on a regular basis to help determine any loss of fungicide efficacy. If loss of efficacy is present, the grower should avoid using that particular fungicide (FRAC code). The good news for CPM control, there are a number of fungicides with different modes of action in different FRAC codes and the grower has a number of options to chose from. All growers should follow use recommendations on labels and avoid overusing one mode of action, even if it works well.

Loss of efficacy in the control of CDM has also been documented in FRAC code 4 (mefenoxam), FRAC code 11 fungicides (azoxystrobin), and FRAC code 43 (fluopicolide). Importantly, most fungicides labeled for the control of CDM are at-risk for resistance development because of the specific modes of action. These include Ranman (cyazofamid, FRAC code 21), Gavel/Zing! (zoxamide, 22), Tanos/Curzate (cymoxanil, 27), Previcur Flex (propamocarb HCL, 28), Forum/Revus (dimethomorph, 40), Zampro (ametoctradin, 45), and Orondis (oxathiapiprolin, 49). Importantly, just like with CPM control, there are a number of CDM fungicides with different modes of action in different FRAC codes that the grower has a number of options to chose from. Again, all growers should follow use recommendations on labels and avoid overusing one mode of action, even if it works well. As with CPM, If loss of efficacy is present, the grower should avoid using that particular fungicide (FRAC code) for CDM control.

Growers should remember that fungicides specifically labeled for CPM control won’t control CDM, and fungicides labeled for CDM control won’t control CPM. Therefore, following disease monitoring and forecasting website, scouting fields, paying close attention to host crops, choosing varieties with CDM or CPM resistance, and following proper fungicide resistant management guidelines remain critically important for successful CPM and CDM control.

For more information please see the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations.

References:

North Carolina State University

https://content.ces.ncsu.edu/cucurbit-downy-mildew

University of Florida

https://edis.ifas.ufl.edu/pp325

2018 Fungicide Resistance Management Guidelines for Cucurbit Downy and Powdery Mildew Control in the Mid-Atlantic and Northeast Regions of the US.

http://www.plantmanagementnetwork.org/pub/php/volume19/number1/PHP-12-17-0077-BR.pdf

Filed Under: Commercial Ag Updates, Disease Forecasting, Organic Production, Vegetable Crops Tagged With:
January 15, 2020

Greenhouse Disease Management: Seed Treatments and Transplant Production

Seed Treatment

Seed used in transplant production should be certified ‘clean’ or disease-free. Most commercial seed comes with certification and is pretreated with fungicide. Important diseases such as Bacterial leaf spot of tomato and pepper can cause major problems in transplant production if introduced in the greenhouse, especially if untreated seed is infested. Remember, a small amount of infested seed can be a major source of inoculum in the greenhouse and cause significant problems in the field later in the growing season.

As a rule for any crop, any non-certified or untreated seed should be treated, if applicable, with a Clorox treatment, or with hot water seed treatment, then treated pre-seeding or at seeding with fungicide(s) to help minimize damping-off diseases. Organic and conventional tomato growers who grow a significant number of heirloom vegetables, such as tomatoes, should consider using the hot water seed treatment to help reduce the chances for bacterial problems. Remember, Chlorox simply acts as a surface disinfectant, kllling pathogens that may reside on the surface of the seed. The hot water seed treatment method will also kill potential pathogens within the seed.

Hot Water Seed Treatment Method

Hot water seed treatment is a non-chemical alternative to conventional chlorine treatment which only kills pathogens on the surface of the seed. Heat-treatment done correctly kills pathogens inside the seed as well. If done incorrectly, it may not eradicate pathogens and may reduce germination and vigor. For cole crops, it is especially important to follow treatment protocols as seeds can split.

Seed heat treatment follows a strict time and temperature protocol and is best done with thermostatically controlled water baths. Two baths are required: one for pre-heating, and a second for the effective (pathogen killing) temperature. For cole crops, the initial pre-heating is at 100°F (38°C) for 10 minutes. The effective temperature is 122°F (50°C). Soaking at the effective temperature should be done for 20 minutes for broccoli, cauliflower, collards, kale, and Chinese cabbage, and 25 minutes for Brussels sprouts and cabbage. Immediately after removal from the bath, seeds should be rinsed with cool water to stop the heating process. After that, seeds should be dried on a screen or paper. Pelleted seeds are not recommended for heat treatment. Only treat seed that will be used in the current season.

As an alternative to hot water seed treatment, use 1 part Alcide (sodium chlorite), 1 part lactic acid, and 18 parts water as a seed soak. Treat seed 1-2 minutes and rinse for 5 minutes in running water at room temperature.

For more information on seed treatment methods please see page 124 in the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Transplant Production

Proper greenhouse sanitation is important for healthy, disease-free vegetable transplant production. Efforts need to be made to keep transplant production greenhouses free of unnecessary plant debris, soils, and weeds which may harbor insect pests and disease.

  • All equipment, benches, flats, plug trays and floors should be properly cleaned and then disinfested prior to use with efforts taken throughout the transplant production season to minimize potential problems.
  • Any weeds in or around the greenhouse structure should be removed prior to and after any production.
  • Any transplant brought into the greenhouse from an outside source needs to be certified ‘clean’, as well as visually inspected for potential insects and diseases once it reaches your location. Suspect plants should not be placed in the greenhouse.

Remember, disinfestants, such as Clorox, Green-Shield, or hydrogen dioxide products (Zerotol – for commercial greenhouses, garden centers and Oxidate – commercial greenhouse and field), kill only what they come into direct contact with so thorough coverage and/or soaking is necessary. The labels do not specify time intervals for specific uses, only to state that surfaces be ‘thoroughly wetted’. Therefore, labels need to be followed precisely for different use patterns (i.e., disinfesting flats vs. floors or benches) to ensure proper dilution ratios. Hydrogen dioxide products work best when diluted with water containing little or no organic matter and in water with a neutral pH. There are a number conventional and organic products labeled for disease control during transplant production in the greenhouse.

Sanitizing Greenhouse Surfaces and Treatment of Flats and Trays:

There are several different groups of sanitizers that are recommended for plant pathogen and algae control in transplant greenhouses. Alcohol is often used to disinfect grafting tools. All these products have different properties:

  • Quaternary ammonium chloride salts (Q-salts such as Green-Shield®, Physan 20®, KleenGrow™) are labeled for control of fungal, bacterial and viral plant pathogens, and algae. They can be applied to floors, walls, benches, tools, pots and flats as sanitizers.
  • Hydrogen Dioxide, Hydrogen Peroxide, and Peroxyacetic Acid containing products (ZeroTol® 2.0, OxiDate® 2.0, SaniDate®12.0) kill bacteria, fungi, algae and their spores on contact. They are labeled as disinfectants for use on greenhouse surfaces, equipment, benches, pots, trays and tools.
  • Chlorine bleach may be used for pots or flats, but is not recommended for application to walls, benches or flooring. When used properly, chlorine is an effective disinfectant. A solution of chlorine bleach and water is short-lived and the half-life (time required for 50 percent reduction in strength) of a chlorine solution may be as little as a few hours.

New flats and plug trays are recommended for the production of transplants to avoid pathogens that cause damping-off and other diseases. If flats and trays are reused, they should be thoroughly cleaned and disinfested as described below. Permit flats to dry completely prior to use. Styrofoam planting trays can become porous over time and should be discarded when they no longer can be effectively sanitized.

  • Sanitizing trays with Chlorine: Dip flats or trays in a labeled chlorine sanitizer at recommended rates (3.5 fl oz. of a 5.25% sodium hypochlorite equivalent product per gal of water) several times. Cover treated flats and trays with a tarp to keep them moist for a minimum of 20 minutes. Wash flats and trays with clean water or a Q-salts solution to eliminate the chlorine. It is important that the bleach solution remains in the pH 6.5-7.5 range and that a new solution is made up every 2 h or whenever it becomes contaminated (the solution should be checked for free chlorine levels at least every hour using test strips). Organic matter will deactivate the active chlorine ingredients quickly.

For more information on seed treatments and disinfectant products labeled for use in the greenhouse please see the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Selected Organic and Conventional Fungicides, Bactericides

An updated table for selected organic and conventional fungicides and bactericides labeled for greenhouse use will be available in Table E-11 in the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide. The table includes an updated comprehensive list of conventional and organic fungicides and biopesticides approved for greenhouse use.

Filed Under: Commercial Ag Updates, Organic Production, Vegetable Crops Tagged With: , ,
January 12, 2020

Rutgers downy mildew resistant sweet basils available around the world; Research efforts continue

Rutgers downy mildew resistant sweet basils available around the world; Research efforts continue

After a decade’s worth of research and breeding efforts Rutgers Downy Mildew Resistant (DMR) sweet basils are now available to commercial and organic growers as well as home gardeners around the world. Since 2007, when basil downy mildew (BDM) was first identified in FL, the disease has caused significant economic losses to commercial basil growers everywhere, and made growing sweet basil in the backyard garden nearly impossible. Basil downy mildew has commonly led to total crop loss for organic growers under field cultivation systems. The presence of any BMD on fresh leaves will make the product unmarketable. Of further concern is that the pathogen favors high relative humidity. Certain temperature range which can make a basil crop appear to be free of downy mildew (e.g., at times over the season or after a harvest when weather is too hot and dry), then full of disease upon arrival to the distributor or retailer because of the environmental conditions of the packaged basil during distribution and shipping which often favors its growth. Since 2009, Rutgers has been working diligently to identify and breed downy mildew resistance into commercially acceptable sweet basils that have the correct aromas, essential oils, and flavors. The first of these four new DMR sweet basils are available through  your favorite seed company in North America, the European Union, and Australia.

Each of the new Rutgers DMR sweet basils have their own unique characteristics which can be matched to meet grower needs.

Rutgers Obsession DMR: An excellent sweet basil for field or potted plant production; will also make an excellent edible landscape plant; more compact, slower initial growth than Devotion DMR and Thunderstruck DMR, but for overall season is high yielding, lends itself to multiple cuts, and has a high leaf-to-stem ratio – good for small bunches or small size clam shells – dark green, thick, glossy leaves, flowers form very late; and highly resistant to Fusarium wilt.

Rutgers Devotion DMR: An excellent Genovese-type sweet basil for field production for fresh markets; establishes in the field or pots quicker than Rutgers Obsession DMR, with uniform, upright growth, dark, green color with flat to cup-shaped leaves. The Rutgers Devotion DMR is a beautiful plant.

Rutgers Thunderstruck DMR: An excellent sweet basil with high yields needed for processing- and fresh-market production; quick establishment and fast, upright growth with medium-sized, ruffled leaves with a bright green color.

Rutgers Passion DMR: An excellent sweet basil for potted plant and field production. Exhibits vigorous growth with high leaf-to-stem ratio; larger, slightly cupped leaf and similar aesthetics to Rutgers Devotion DMR.

Over the past 10 years, great research efforts have been made around the world to better understand and control basil downy mildew.

Understanding basil downy mildew

Basil downy mildew (BDM) is an obligate parasite, just like with all downy mildews, the pathogen needs a living host to survive. In northern regions, this means the pathogen will die out when basil crops freeze with the first frost in the fall. In areas of the south, such as southern Florida, the pathogen could survive year round as long as living basil is present. In greenhouse production (even in northern regions that freeze), as long as basil is in production the pathogen could be present. Research from Israel and Italy suggest that the pathogen can undergo sexual reproduction leading to the production of oospores, much like Phytophthora capsici, the causal agent of Phytophthora blight in pepper. This has profound effects on the pathogen – the opportunity to overwinter, develop new races, and its ability to develop fungicide resistance. For growers, this means that all downy mildew resistant basils still need to be grown with excellent management and with a proper spray program to ensure excellent control season-long.

Oospore production and overwintering

Oospore production via sexual reproduction in BDM has been confirmed in Europe, but not officially in the US to date. Oospore production suggests that mating types of the pathogen may be present. One early study from Israel showed that oospores were incapable of infecting plants. Importantly, oospore production in BDM could allow it to overwinter in soils drastically changing the way growers will have to manage the disease. Instead of waiting for BDM sporangia to arrive on your farm via weather patterns from other location or from infested seedlings, transplants, or plugs coming from more southern regions, the pathogen would already be present in your soil, and as long as weather conditions were favorable, the pathogen could cause disease. Thus, in more Northern regions, BDM could show up much sooner in the growing season. More work on understanding the role of oospore production in the lifecycle of BDM needs to be done. Growers must remain diligent and closely monitor their basil crop.

Basil downy mildew race development

Downy mildew pathogens in other cropping systems are known to develop new races over time. In spinach, for example, there are over 20 races of the pathogen. Importantly, the development of new races of the BDM pathogen would allow it to overcome current genetic resistance, meaning new genes for resistance would need to be bred into the host. In theory, for every new race of BDM that might develop, a new resistance gene or set of resistance genes would need to be bred into the host. Research in understanding the sweet basil genome as well as the pathogen’s genome is still in its relative infancy, but work at Rutgers and other Universities is currently ongoing. Understanding the genetic diversity of BDM in the US is a top priority of researchers with Rutgers collaborating with colleagues at UMASS, Cornell, and the University of Florida. Importantly, finding new sources of natural genetic resistance is also a top priority for all those involved in breeding for resistance to BDM. Research in each of these important areas to ensure continued genetic and plant breeding for basil downy mildew resistance is ongoing due to funds from the United States Department of Agriculture to the US universities listed.

Fungicide resistance development in BDM

Downy mildews in other crop systems are known to develop fungicide resistance. In recent years, mefenoxam insensitivity has been found in basil in Europe, but not the US to date. This suggests, along with knowledge of other downy mildew pathogens that fungicide resistance is most likely to develop in BDM. In recent years, a number of new fungicides with different modes-of-action have been registered for use in controlling BDM. Some of these fungicides have a high-risk for resistance development because of their active ingredient(s) and specific modes-of-action. Commercial basil producers need to take all the precautions to help mitigate fungicide resistance development. This means carefully following the use restrictions on the label and rotating among fungicides with different modes-of-action (e.g., rotating between fungicides in different FRAC codes).

Is basil downy mildew seed-borne?

Research has shown that BDM can be detected on the surface of seed using real-time PCR methods, but this method does not detect whether the pathogen is viable or not. Grow-outs of infested basil seed have been somewhat mixed; with some research showing it may be possible and others showing it is not possible. More work needs to be done and as such in the interim, it is better to assume it could be seed-borne.. For commercial growers and home gardeners, seed should always be purchased from reputable seed companies and growers should not harvest and save their own seed for possible re-infestation as studies have shown that BMD is detected on the seed collected from DMR and susceptible basil varieties. Some companies now offer propriety seed treatment methods for basil seed. When purchasing seed, you should ask if the seed has been treated and/or certified free of BDM.

Using BDM resistant sweet basils

In the past few years, along with the release of the new Rutgers DMR sweet basils, other sweet basils with BDM resistance have been commercially released in the US and Europe. It’s important for basil growers and homeowners to understand that none of the new DMR sweet basils are completely “immune” from getting BDM. The new DMR sweet basils are highly resistant to the pathogen compared to commercially-available susceptible varieties. Thus, in DMR resistant sweet basils the development of disease will be delayed – hopefully to much later in the growing season depending on your location, or not at all. Commercial and organic growers are encouraged to use DMR sweet basils along with best management practices, including appropriate fungicide use and good cultural practices, to help mitigate disease development.

For more information on basil downy mildew, our research, and our new Rutgers DMR sweet basils follow us on Instagram at RutgersBasil.

 

Filed Under: Vegetable Crops Tagged With: ,
January 10, 2020

Controlling Cercospora leaf spot in beet

Cercospora leaf spot (CLS), caused by Cercospora beticola, is an important and emerging disease in beet and swiss chard production in New Jersey. Efforts to control this disease has become more difficult in the past few years in some areas of southern New Jersey. The soil-borne fungal pathogen, once established in fields, can survive in the soil for up to 2 years on infected debris and on weed hosts such as Chenopodium, goosefoot, and pigweed. The pathogen may also be seed-borne. Symptoms of infection include numerous, small tan leaf spots with distinct dark purple margins that are easily diagnosed (Fig. 1). Overhead irrigation and rainfall help spread the pathogen throughout the field.  Cercospora beticola is most damaging in warm weather (day temperature of 77 to 90° F and night temperature above 60° F).

Controlling Cercospora leaf spot with preventative fungicide applications has become challenging for some growers in New Jersey. The pathogen is known to have developed resistance to important fungicide classes in recent years, such as the QoIs (FRAC code 11) and the DMIs (FRAC code 3) in different regions of the country, based on fungicide use. This is not surprising since resistance development can occur when fungicides in these groups are used extensively over many years. In New Jersey, azoxystrobin has been used extensively for years to manage this disease.

Cultural practices to help mitigate losses to Cercospora leaf spot

There are a number of cultural practices growers can do to help reduce losses to CLS.

  • Start with certified, disease-free seed, or treat seed using hot water seed treatment method.
  • Avoid fields with a known history of CLS.
  • Rotate to non-host crops (outside of the Chenopodium family) for 2-3 years.
  • Bury infected crop residues and destroy volunteer plants and weed hosts.
  • Burn down fields after harvesting.
  • Avoid planting succession crops close together (at least 100 meters apart).
  • Avoid overhead irrigation if it will result in prolonged leaf wetness periods (e.g., late evening or at night); irrigate early to mid-day when leaves will dry fully or use drip irrigation for small plantings.
  • Using the proper fungicides, rates, and fungicide rotations.

Fungicides for controlling Cercospora leaf spot

In recent years a number of new fungicides have been labeled for CLS control. Many of these fungicides contain two different active ingredients with more than one mode of action. Growers who have relied on managing CLS with azoxystrobin (FRAC code 11) for years and suspect a loss in efficacy should consider removing it from their fungicide program. There is a good chance fungicide resistance has developed. In 2019, a field study was done at RAREC to examine the efficacy of different fungicides for CLS control (Table 1). The fungicide efficacy trial was established in field with a  history of CLS; where the field was inoculated with infected debris collected from a farm in southern New Jersey. Fungicides were applied weekly for 5 weeks with overhead irrigation to help promote disease development.

Fungicide program (application timing) FRAC code active ingredient(s) Rate per acre Labeled for beet AUDPC value
Untreated control n/a n/a n/a n/a 617 a
Kocide 3000 (1-5) M01 copper hydroxide 1.0 lb Yes 564 ab
Quadris 2.08F (1-5) 11 azoxystrobin 15.5 fl oz Yes 538 bc
Fontelis 1.67SC (1-5) 7 penthiopyrad 30.0 fl oz Yes 510 bcd
Miravis Prime 3.34SC (1-5) 7 + 12 pydiflumetofen + fludioxonil 13.4 fl oz Yes 497 bcd
Merivon 2.09SC (1-5) 7 + 11 fluxapyroxad + pyraclostrobin 5.5 fl oz Yes 471 cd
Tilt 3.6EC (1-5) 3 propiconazole 4.0 fl oz Yes 445 d

 

Cercospora leaf spot development was extremely high during the course of the study. Area Under Disease Progress Curves (AUDPC) were calculated to determine the amount of disease development under each fungicide program (Table 1). CLS development was highest in the untreated control (UTC), with no significant differences between the UTC and weekly copper applications suggesting that weekly copper applications did not help reduce CLS in this study (Table 1). Weekly applications of Quadris, Fontelis, Miravis Prime were not significantly different, but significantly lower than the UTC (Table 1). Control of CLS was best with weekly applications of Tilt and Merivon, but these were not significantly different from weekly applications of Miravis Prime or Fontelis (Table 1). Results of this study suggest that growers with resistance concerns who have relied heavily on copper and azoxystrobin for CLS control should consider using other fungicides in their weekly preventative fungicide programs. Control programs should focus on applying fungicides with more than one mode of action and focus on rotating fungicides with different modes of action. For example: (please see 2020/2021 Commercial Vegetable Production Guide), Apply Tilt (FRAC code 3) followed by Miravis Prime (7 + 12), then tebuconazole (3), then Merivon (7+ 11), then Tilt (FRAC code 3), then Luna Tranquilty (7 + 9). Remember, resistance development to FRAC code 11 fungicides (QoIs) is qualitative and controlled by single point mutations, once resistance develops the fungus is completely resistance (to all fungicides in the group). Resistance development in FRAC code 3 fungicides (DMIs) is quantitative which often characterized as a gradual loss of resistance over time. As a note, FRAC code 3 fungicides should always be applied at the highest rate, using lower rates may increase selection pressure.

Organic Control Options

Controlling CLS in organic production systems starts by following and executing good cultural practices listed above. Always purchase certified seed. Use the hot water seed treatment method to help disinfested seed. Avoiding fields with a history of the disease. Producing beet on mulch and drip irrigation in small operations should be considered. This will help reduce weed pressure (as well as potential hosts) and reduce the need for overhead irrigation. Organic copper applications may not be effective in some operations where disease pressure is extremely high. Unfortunately, control of CLS with organic and biopesticides has been difficult, therefore good cultural practices must be followed accordingly.

 

Filed Under: Commercial Ag Updates, Vegetable Crops Tagged With: ,
January 9, 2020

Copper resistance in bacterial leaf spot found in New Jersey during 2020 growing season

Copper resistance has been detected in bacterial leaf spot of tomato and pepper and in Pseudomonas chicorii, the causal agent of bacterial leaf spot in basil, in New Jersey. While not surprising, copper resistance has been known to develop for decades now; however, this is the first time it has been confirmed in vegetable crops in New Jersey. Copper applications for the control of bacterial diseases in many crops has been a mainstay for decades now and is often applied in weekly protectant fungicide programs. In 2019 and 2020, with help from Dr. Nrupali Patel and Dr. Don Kobayashi, bacteriologists in the Department of Plant Biology located on the New Brunswick campus, a survey was begun to determine which species of bacterial leaf spot are most prevalent in New Jersey vegetable crops. Bacterial leaf spot can be caused by four species of Xanthomonas: X. euvesicatoria, X. vesicatoria, X. perforans, and X. gardneri. Currently, there are four races of BLS found in tomato (T1-T4; one for each of the 4 species stated above) and eleven races found in pepper (0-10). Differential tests in southern New Jersey using various bell pepper lines over the past 15 years has suggested that the number of races of BLS in pepper has increased over time; with all races present in the State to date. Lab testing results from samples collected from the small number of NJ vegetable farms the last two summers has shown the presence of X. euvesicatoria in pepper, as well as X. euvesicatoria and X. perforans in both tomato and pepper in the state, with ~50% of all samples testing positive for copper resistance.

How do you know what species of bacteria are present on your farm?

The only way to determine which species of bacteria are present in tomato or pepper crops on your farm are to have them identified through laboratory methods.

How do you know what races of the pathogen are present on your farm?

That’s a difficult question to answer. Up to now, the only way to know is through differential testing. That means planting a number of different bell peppers with varying BLS resistance packages and monitoring which cultivars develop symptoms. For example, if you detect BLS development in Aristotle X3R (which has resistance to races 1,2, & 3); then you possible have races 4-10 present on your farm. If you were to plant Turnpike in that same field and you have BLS development in it, then you possibly have race 6 or 10 present, because Turnpike has resistance to BLS races 0-5 and 7,8,9. It’s extremely important to know what races of BLS are present so you can chose the proper cultivars to grow. Choosing the proper cultivar will do two things: significantly reduce the chances of BLS development and significantly reduce the number of copper applications on your bell pepper crop. As a note, there are a few non-bell peppers available with BLS resistance packages (see 2020/2021 Commercial Vegetable Production Recommendations Guide).

How do you know if copper resistance is present on your farm? 

Growers who have used copper applications for controlling bacterial leaf spot in crops such tomato or pepper for many years should always monitor for efficacy. If you notice or have noticed a loss in copper efficacy over time, then there is a good chance copper resistance is present. Once copper resistance is detected, further applications will be unwarranted and ineffective. The only method to truly determine if copper resistance is present is through laboratory testing, however growers who pay close attention to efficacy should have a good idea if copper is still effective.

What can you do to mitigate bacterial leaf spot development on your farm?

In crops such as bell pepper, it comes down to growing cultivars with resistance to BLS and knowing what races are present on your farm. Many of the recommend commercial cultivars have varying resistance packages to the different races of the pathogen. Some cultivars, such as Paladin which has Phytophthora resistance has no resistance to BLS. Other “older” cultivars such as Aristotle X3R has resistance to races 1-3; newer cultivars such as Turnpike has resistance to races 0-5,7-9; while cultivars such as Playmaker and 9325 have resistance to 0-10 (also known as X10R cultivars). Unfortunately, BLS resistance in commercial tomato varieties are lacking, but efforts from around the world are making progress.

Moving forward in 2021.

More sampling and surveying are planned for the 2021 production season in New Jersey. Growers who are interested having tomato or pepper samples collected from their farm for species determination and copper resistance testing are encouraged to contact their county agent so arrangements can be made.

 

 

 

Filed Under: Vegetable Crops Tagged With: ,