Andy Wyenandt

This is an archive of Dr. Wyenandt's posts on the Plant and Pest Advisory.

March 11, 2021

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: ,
March 10, 2021

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:
March 10, 2021

Damping-off: Identifying and Controlling Pathogens in Transplant Production in 2022

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: Vegetable Crops Tagged With: ,
February 8, 2021

An update on the potato pathogen, Dickeya dianthicola

It has been nearly six years since Dickeya dianthicola was first reported in potato in New Jersey in 2015 and many other states up and down the East Coast in the spring and summer of 2016. Before then, this seed-borne pathogen had not been detected in potato fields in the mid-Atlantic region and elsewhere. Unfortunately, some potato growers suffered substantial economic losses during the 2015 and 2016 growing seasons. Organic potato producers who grew very small acreage were also affected by Dickeya dianthicola. Most of the commercial potato acreage in New Jersey and elsewhere was being planted with seed purchased from Maine or Canada. When a disease such as this is so widespread when it first occurs it suggests that contaminated seed is the likely inoculum source. Extension personnel from the region learned from visiting farms and talking with growers that occurrences were associated with specific seed lots. With knowledge of the probable origin of the pathogen, Extension personnel from the region developed best management guidelines for Dickeya dianthicola to help potato growers in the region minimize the potential for a Dickeya outbreak in their operation.

Since that time, along with Dickeya dianthicola, other seed-borne tuber rotting pathogens (Pectobacterium spp.) have routinely been found causing significant problems for potato growers in the region. Research on Dickeya and Pectobacterium has been ongoing in the US and other parts of the world where these pathogens occur with data and results related to the most recent outbreaks being published most recently. In a survey of soft rot bacteria collected from potato fields in New York state during the 2016 growing season, a majority of isolates collected were designated as D. dianthicola or P. parmentieri. Based on their dnaX sequence analysis, the authors determined that the D. dianthicola isolated from potato plants in New York formed a single clade, being genetically identical to each other and to D. dianthicola ME23 isolated in Maine in 2015 (Ma et al., 2018). More recent research by Ge et al (2020, Plant Dis. First Look) surveyed commercial potato fields in Maine as well as suspect Dickeya samples collected from potato seed pieces, tubers, or plants from potato fields in 11 other states from 2015 to 2019. A total of 1183 samples were collected. A total of 256 Dickeya dianthicola isolates were used to identify pathogen genotype (I, II, or III) and the “inoculum geography”.  Of these, 231 (~90%) were Type I, 14 (~5%) were Type II, and 11 (~4%) were Type III. In Maine alone, 95% of the total isolates collected from commercial potato fields were Type I. “As such, it was suspected that the original contamination in other states initiated from Maine” since “Maine is the primary seed potato supplier to states in the Northeastern U.S.”. The only consistent genotype found in each year of the study from all states sampled from was Type I for which the authors hypothesized was “likely associated with Maine seed origination”. Not finding Dickeya dianthicola Type II and III in Maine in each year of the study may reflect the fact these types were rare compared to Type I thus a larger sample size was needed to confirm they likely were not present those years. Additionally, while most occurrences of Dickeya dianthicola in potato production fields were associated with seed originated from Maine, there were occurrences associated with seed from Wisconsin and Canada. It is possible Type II and III are principally associated with those seed. Seed source was not determined for the samples.

 

Filed Under: Vegetable Crops Tagged With: , ,
February 4, 2021

Greenhouse Sanitation Important for Disease Management

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 and weeds which may harbor insect pests and disease. Efforts need to be taken throughout the transplant production season to minimize potential problems.

  • All equipment, benches, flats, plug trays and floors should be properly cleaned and then disinfested prior to use.
  • Any weeds in or around the greenhouse structure should be removed prior to 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.

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.

 

Filed Under: Vegetable Crops
January 28, 2021

A survey for all basil growers in the US.

As a follow-up to the virtual Basil Workshop held by UMASS, Rutgers University, and the University of Florida in December 2020, UMASS has created a short survey for any US basil grower to participate in. Below is a link to the survey and additional information that basil growers might find useful.

The link to the survey is:

https://forms.gle/NyNz9MuwubFMnHnh8

The slides for the workshop presentations will be posted shortly on a new website. We will have more information in February!

Below are some useful basil links:

Maps & reports for basil downy mildew (BDM) and other basil monitoring: https://basil.agpestmonitor.org/

Note that you can submit reports to this site and help us map the annual spread of BDM.

Anyone can follow the Rutgers basil breeding program on Instagram: @rutgersbasil

Filed Under: Vegetable Crops Tagged With: