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.
 
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January 21, 2020

Understanding Protectant Fungicides
(FRAC groups M01 – M11)

Protectant (contact) fungicides, such as the inorganics (copper, FRAC group M01) and sulfur (FRAC code M02); the dithiocarbamates (mancozeb, M03), phthalimides (Captan, M04), and chloronitriles (chlorothalonil, M05) are fungicides which have a low chance for fungicide resistance to develop. Protectant fungicides typically offer broad spectrum control for many different pathogens.

Why wouldn’t fungi develop resistance to protectant fungicides? Protectant fungicides are used all the time, often in a weekly manner throughout much of the growing season.

[Read more…]

Filed Under: Vegetable Crops Tagged With:
January 21, 2020

Got humidity in the greenhouse? Get rid of it!

Unfortunately, closed greenhouses retain heat and unwanted humidity which can spell problems if left unchecked, especially during prolonged periods of overcast days and cooler weather.

Remember, high relative humidity equals wet leaves which can favor the development of diseases such as Botrytis or bacterial diseases such as bacterial leaf spot. To avoid potential problems, do your best to vent out as much humidity as possible on a daily basis in the early morning or late afternoon. Turn on circular fans to promote air movement and finish watering earlier enough in the day so leaves have enough time to dry out before nightfall. Any flats with transplants with suspect leaf spots should be pulled out of the production facility and isolated until a proper diagnosis can be made.

As a side note, stressed transplants where water and/or fertility have been withheld are also more prone to disease development. A light fertilizer application may go a long way in improving transplant health before setting in the field.

Please see Table E-14 in the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations guide for a list of control options for important diseases in greenhouses.

Filed Under: Vegetable Crops
January 20, 2020

Understanding The Differences Between FRAC Group 11 and FRAC Group 3 Fungicides

FRAC Group 11 Fungicides

The strobilurin, or QoI fungicides (FRAC group 11) are extremely useful in controlling a broad spectrum of common vegetable pathogens.

You may know some of strobilurins as azoxystrobin (Quadris), trifloxystrobin (Flint), pyraclostrobin (Cabrio), or Pristine (pyraclostrobin + boscalid, 11 + 7). For example, FRAC group 11 active ingredients such as azoxystrobin are also now available generics or in combination products as Quadris Top (azoxystrobin + difenoconazole, 11 + 3), Quilt (azoxystrobin + propiconazole, 11 + 3), or Quadris Opti (azoxystrobin + chlorothalonil, 11 + M5).

All strobilurin fungicides inhibit fungal respiration by binding to the cytochrome b complex III at the Q0 site in mitochondrial respiration. Simply said, the fungicide works by inhibiting the fungi’s ability undergo normal respiration. The strobilurin chemistries have a very specific target site, or mode-of-action (MOA).

Although highly effective, fungicide chemistries like those in FRAC group 11, with a very specific MOA, are susceptible to fungicide resistance development by some fungi. Why is that? In the strobilurin’s, a single nucleotide polymorphism of the cytochrome b gene leads to an amino acid substitution of glycine with alanine at position 143 of the cytochrome b protein.

For us, knowing the specifics on the technical jargon isn’t so important, it’s understanding what is at stake. So, if we hear someone speak about G143A resistance development to the QoI fungicides (where resistance is already known in cucurbit Powdery mildew and Downy mildew), we know what they are talking about and how important it is! So much so, if cucurbit powdery mildew develops resistance to one strobilurin compound it may develop what is known as cross resistance and become resistant to all chemistries in FRAC group 11, even if only one chemistry has been used!

[Read more…]

Filed Under: Commercial Ag Updates, Vegetable Crops Tagged With: , ,
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: , ,