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Pathogen transfer rates between postharvest surfaces and broccoli

Compared with other types of fresh produce, broccoli has not often been the focus of food safety-related research, despite the fact that it is commonly served raw in salads, salad mixes, and crudités platters. So, when Cornell M. Eng. student Yuezhi Wu consulted with Produce Safety Alliance Director Betsy Bihn about possible food science-related topics for his Masters in Engineering thesis, Bihn (who had recently signed on as a collaborator with the Eastern Broccoli Project) naturally thought of broccoli. The resulting study is the first to examine transfer rates of E. coli between broccoli and two surfaces commonly encountered in small packing operations. Though preliminary, the results will inform future risk assessments of the broccoli postharvest environment and help identify measures to prevent contamination events.

Wu’s co-authors on the study are his advisor, Cornell Biological and Environmental Engineering Professor Ashim Datta; Bihn; and Extension Specialist Lindsay Springer, a recent Food Science PhD who at the time was working with Bihn. After considering the postharvest surfaces that broccoli typically encounters in a small farm operation, the authors decided that gloved hands and conveyor belts pose the most risk. In a series of experiments with a nonpathogenic strain of E. coli, the team then measured bacterial transfer rates from contaminated broccoli to previously clean glove and conveyor belt material, and from contaminated conveyor belts and gloves to broccoli crowns and stems. To mimic contact between gloved hands and broccoli, small disks cut from nitrile gloves were pressed against broccoli stems or crowns for 5 seconds; to mimic contact with the conveyor belt, broccoli was dropped onto squares of belt material and kept there for 20 seconds.

The researchers found that the transfer rate from contaminated conveyor belt material to broccoli was much higher than the rate of transfer from contaminated broccoli to the conveyor belt. Contaminated glove disks transferred more bacteria to broccoli crowns and stems than contaminated crowns and stems transferred to glove material. Broccoli crowns in particular picked up more bacteria from contaminated gloves than did broccoli stems, which was attributed to the more porous structure of the crown. The authors noted that these results are consistent with studies using other fresh produce, which have found that transfer rates from non-organic surface (like the gloves and conveyor belt) to organic surfaces (broccoli and other vegetables) is typically higher than the reverse. The results emphasize the importance of cleaning and sterilizing conveyors and of sterilizing or replacing gloves frequently. Ultimately, this type of data can be used to construct models that will help growers understand contamination risks and determine the ideal cleaning schedule for their operation.

Reference

Wu, Y., L. Springer, E. Bihn, and A. Datta.  Quantifying Escherichia coli Cross-Contamination Rates among Broccoli, Conveyer Belt and Glove. https://hdl.handle.net/1813/57072

A new resource for plant research

The plant research community has a valuable and practical new resource available: a rapid-cycling Brassica oleracea population that can be used to map the genetics of many traits simply by phenotyping. The population and related resources are described in a recent publication led by Zach Stansell in Thomas Björkman’s lab at Cornell University.

  • The map and reference genome are complete
  • Bioinformatic-analysis pipeline is available
  • Seed is available for free
  • Researchers only need to phenotype and analyze


The BolTBDH population is derived from a from a cross of rapid-cycling Chinese kale with broccoli. It is particularly valuable for studying reproductive development because progeny lines have inflorescences that range from non-heading to fully heading broccoli. Variation is documented for many other traits, such as architecture and glucosinolate content, and variation in many others remains to be explored and documented.

To1000 is a small plant with long inflorescences, Early Big is a normal broccoli
Parents of BolTBDH: the rapid-cycling Chinese kale, TO1000 and the broccoli ‘Early Big’.

Continue reading A new resource for plant research

Selecting subjective traits in multiple sites.

Zach Stansell has adapted his tool for breeders so that it is usable for any crop that has a highly subjective breeding goal.

Stansell with computer code
Zach Stansell has developed an R package that helps breeders assess their criteria for subjective traits like beauty in many locations.

We are sharing the information with various media outlets. The first pass is a publication in the Cornell Chronicle.

Many horticultural crops need to meet the quality criteria of a particular market or of the main breeder. They need to meet those criteria in many environments. How can you test for   quality  in many locations at the same time. This technique is good at predicting the reference person’s quality score by having trained raters make objective measurements.

The package is posted on GitHub so that anyone can use it for free. It is annotated and revised to work with just about any trait of interest or any crop. The revision was done with Deniz Akdemir, Cornell statistician. The development of the method is published in HortScience (Stansell, Zachary, Thomas Björkman, Sandra Branham, David Couillard, and Mark W. Farnham. 2017. Use of a Quality Trait Index to Increase the Reliability of Phenotypic Evaluations in Broccoli HortScience 32:1490-1495. doi: 10.21273/HORTSCI12202-17 )

 

New Eastern Broccoli Buyer Listing

Small to mid-size growers in the eastern US have trouble finding reliable buyers for their broccoli, even as distributors, wholesalers, restaurants, and others say they cannot source enough regional broccoli to meet demand.  While matching specific buyers with specific sellers is beyond the scope of the Eastern Broccoli Project, we recently added a buyer listing webpage that may help the two groups connect. Growers can use the information to discover and introduce themselves to buyers with a declared interest in sourcing eastern-grown broccoli.  Buyers who agree to be listed have the opportunity to engage with local and regional suppliers of this popular produce item.

The Eastern Broccoli Project has developed numerous resources to help growers produce high quality broccoli and understand the expectations and challenges of the eastern broccoli supply chain (click on the ‘Resources’ tab of the menu to see some). However, it is up to growers and buyers to forge the good relationships that are critical to sustaining the eastern broccoli industry.  The buyer list is intended to help that process by fostering contacts and discussions between entities with complementary interests. Growers are generally advised to secure a buyer early, preferably before they have a crop in the ground.  Many buyers (not just the ones on our list) have specific expectations with respect to certifications, seasonal availability, minimum load size, and delivery.

All of the listings have been approved by their respective buyers. Each includes a brief description of the enterprise and the region they serve, along with a contact email address and logo with website link.  We expect the list to expand as more companies and food hubs find out about this opportunity to connect with eastern broccoli growers.

Hygienic Design for Post-harvest Facilities and Equipment

Preventing post-harvest contamination of broccoli and other fresh produce is easier when equipment and packing sheds are built with food safety in mind. A new resource developed with support from the Eastern Broccoli project brings the principles of hygienic design to the post-harvest environment to show how incorporating the right features and materials can simplify cleaning and eliminate common hiding spots for pathogens.

Hygienic design is the norm for food processing environments, but surprisingly little attention has been given to applying the principles to post-harvest equipment and facilities that handle raw agricultural commodities. That omission caught the attention of Produce Safety Alliance Director and Eastern Broccoli collaborator Betsy Bihn, who engaged University of Vermont Agricultural Engineer Chris Callahan to develop guidelines that would make it easier for cooling and packing environments to be in compliance with food safety standards. The result is Hygienic Design for Produce Farms, which is available for download from Callahan’s blog and via a link on the Eastern Broccoli Production resource page.

The publication explains the five key principles of hygienic design (visible and reachable surfaces; smooth and cleanable surfaces; no collection points; compatible materials; and preventing contamination) and discusses some of the tools and materials that can be used  to implement them in post-harvest operations.  The main goals are to eliminate “harborage points” (places where contaminants and pathogens can settle) and to ensure that all surfaces are accessible and suited to regular cleaning and sanitizing.  An “On-Farm Hygienic Design Checklist” is included in the publication and is also available in downloadable, stand-alone pdf and Excel formats.

The publication is intended for growers who are constructing or renovating their washing and packing operation. Agricultural equipment manufacturers will also find the publication useful, as it provides insights about the types of equipment improvements their customers need.

Managing nitrogen timing in summer-harvested broccoli

Picture of tight and loose heads, with cross-section of the heads
Late nitrogen application can cause early side-branch elongation, making the heads less desirable on the market. The top image shows a tight head with solid side branches. The lower image has a head that has begun to loosen at the sides. This effect can be reduced by having the last nitrogen application at least four weeks before harvest so that the growth rate is slowing down a bit just as harvest begins.

One of the challenges with raising broccoli in the East is getting heads to stay dense. In the warmth of summer, the outer branches of broccoli tend to start elongating a little before harvest maturity. They “blow up” in the words of many producers. The result is a head that doesn’t pack tightly in the box and has soft edges that are prone to damage in handling.

The solution is to let growth slow a little during the week before harvest. Growth is promoted by the combination of warmth, water, nitrogen, and sunlight. Warmth is a given for harvests in July and early August, sunlight we have no control over, and abundant water sometimes comes whether we want it or not. The main management tool is nitrogen.

Slowing growth by reducing nitrogen is a considerable challenge because abundant nitrogen is needed during the vegetative growth to get strong, healthy, fast-growing plants. The best approach is to supply nitrogen relatively early in the growing period, and not add nitrogen in the last four weeks.

Many popular broccoli varieties are harvested starting only eight weeks after transplanting. Therefore, the last nitrogen application should be only four weeks after transplanting. At that time, the foliage is near full cover, which a good time for a traditional side-dress application as well as cultivation to get escaped or newly germinated weeds. Fertigation through a trickle-irrigation system would be during the fourth week. At that time, the plants are large enough to take up the nitrogen but not so far along that excess growth at harvest will cause loose heads.

Applying all of the nitrogen before planting is a possibility. Ordinarily, applying 120 to 150 pounds per acre of nitrogen preplant is ill-advised because of the high likelihood of leaching before the crop takes it all up. However, because broccoli is only in the ground for about nine weeks through the end of harvest, and reaches its maximum uptake five weeks after transplanting, the risk of leaching loss is relatively low compared to the typical situation. Pre-plant application of the fertilizer opens up production options that don’t allow side-dressing or liquid fertilization.

This early-nitrogen approach is also helpful in reducing hollow stem. Hollow stem is likewise a symptom of excessive late vegetative growth. The main tool for managing hollow stem is adjusting the plant population. If hollow stem is a problem, it’s likely that both yield and quality will be improved by spacing the plants closer together. In New York we have found an in-row spacing of 8 inches to work quite well. But limiting late nitrogen also tempers the growth rate at the right time.

This article was published in VegEdge on June 5, 2019. A publication of the CCE Cornell Vegetable Program.

More Eastern farms are raising broccoli according to 2017 Census of Agriculture

We have eagerly awaited the 2017 Census of Agriculture to see whether the Eastern Broccoli Project is having an effect. Today, the results were released, allowing us to compare our early effect (2017) with the pre-project baseline. We are happy to see so many more Eastern farms finding a place for broccoli in their crop mix.

State
2012
2017
Gain
Maine 145 273 88%
Vermont 87 111 28%
New Hampshire 61 116 90%
Massachusetts 135 243 80%
Rhode Island 25 27 8%
Connecticut 51 132 159%
New York 290 535 84%
Michigan 158 443 180%
Pennsylvania 245 522 113%
New Jersey 64 136 113%
Delaware 5 19 280%
West Virginia 23 95 313%
Maryland 44 76 73%
Virginia 105 221 110%
North Carolina 140 317 126%
Tennessee 28 142 407%
South Carolina 34 100 194%
Georgia 44 138 214%
Florida 76 168 121%

Fertilizing the broccoli orchard

We have good fertility recommendations for various areas in the East on the resources tab.

A recent Bizarro comic has a great reference to broccoli’s ability to use fertilizer.

Fertilizer makes broccoli grow big
(c) Dan Piraro Used by permission.

We are not in cahoots with the “National Board of Broccoli Producers,” so broccolini is a fair stand-in at the Eastern Broccoli Project.

Waist high broccoli in a field with black soil.
Broccoli on muck soil gets a lot of nitrogen and water, and can grow very tall. Retired Cornell broccoli researcher Joe Shail provides the scale.

One consideration is that broccoli can get too big, and get hollow stem. Growers harvesting in the heat of summer find that making the last nitrogen fertilization four weeks before harvest helps avoid the excessive burst.

Some early varieties are maturing in 50 days in the summer. If you do the math, that means the last nitrogen side dress or fertigation is just three weeks after transplanting. Putting on ~150 lb/ac of nitrogen without burning the plants takes some planning.

Alternaria strikes in 2018, overwhelms Quadris

Alternaria was widespread in the East this year. Unrelenting rain after mid-August created conditions in the Northeast that were conducive to this normally secondary disease. More important, the strain going around was not controlled by the most commonly used fungicide.

Alternaria lesions on head are deep. Even one renders the head unmarketable.

 

Christy Hoepting conducted a fungicide trial to test both our current fungicide program and new materials. Azoxystrobin (Quadris) is widely used, and a 2014 survey in New York showed no resistance. (Cornell pathologists Meg McGrath and Chris Smart are checking for known and novel resistance in 2018 isolates.)

This year, Tim Coolong reported in August that a Quadris-resistant strain was showing up in Georgia. Christy’s trial showed Quadris failing to control in New York. The good news is that the Alternaria was susceptible to fluxapyroxad and pyraclostrobin, the active ingredients in Priaxor. Priaxor is already labeled for use in New York, except Long Island.

The hot and humid weather with heavy rainfall from remnants of hurricanes during August was the perfect storm for Alternaria leaf spot (ALS) to rage out of control in brassica crops across Western New York in 2018. Cornell Vegetable Program fresh market specialists received several complaints about a disease that caused unsightly lesions on both leaves and marketable portions of brassica plants. When ALS attacks the head of broccoli or cauliflower, it renders them unmarketable. Hoepting visited with a grower who was planning to cut broccoli production by one-third, because he had just lost over 85% of his most-recent 5-acre planting to ALS head rot, a loss of $7,500. She immediately set up an ad hoc small-plot replicated trial on his farm in hopes of finding a fungicide that could control this devastating disease.

By the time the broccoli was ready to harvest, differences among treatments in side-by-side plots were striking. In the untreated check, 98% of the heads were unmarketable due to severe ALS, while the best fungicide in the trial, Merivon (fluxapyroxad and pyraclostrobin) had only 5% unmarketable heads.  The fungicides that the grower had been using, Bravo and Quadris (azoxystrobin), resulted in 98% and 49% unmarketable heads, respectively. Commercially available fungicides Switch, Quadris Top and Endura had significantly lower unmarketable heads than Quadris with only 10 to 33%.

Priaxor can be applied at most 2 times sequentially and 3 times total. The only targeted fungicide that can be used with it in a program is Switch (cyprodinil and fludioxonil) because its active ingredients are in different chemical groups (FRAC groups 9 and 12) from those of Priaxor (7 and 11).

If the grower were to adopt a 4-week fungicide program with top-performing fungicides, he could expect to get at least 75% marketable heads. Compared to his Bravo/Quadris program, which only yielded 1470 pounds and net $1,323 per acre, the new program could increase both yield and net profit 5-fold by 5881 pounds and $5,562 per acre, despite a 5-fold increase in cost of fungicides from $44 to $223 per acre. After viewing the fungicide trial on his farm, the grower immediately adjusted his fungicide program to include the most effective fungicides in all of his remaining brassica plantings. He is planning to resume full broccoli production next year with the new fungicide program, which has potential to increase profit by $166,860 in his 30 acres of broccoli. Trial results will be shared with CVP growers over the winter, so all conventional growers can benefit from improved ALS control in their brassicas.

Alternaria leaf lesions with other diseases three weeks after one heavy rainfall event and regular showers afterwards

 

The Alternaria pattern can give false hope. There are lesions on older leaf, then clean younger leaves that grew after the big rain. However, the infection also affects the head.

For a 2014 survey showing all 47 isolates being susceptible to Quadris, see Kreis, Dillard and Smart. Plant Disease. http://dx.doi.org/10.1094/PDIS-03-16-0414-RE

 

Note added January 11: Today at the Southeast Vegetable Conference, Dr. Bhabesh Dutta of the University of Georgia at Tifton showed that the pathogen present in Georgia this year is a different (new) species of fungus that it is not controlled by azoxystrobin. Pathologists around the East are testing isolates from their regions to determine whether this species is the one that cause unusually high losses in the region.

This result is useful in that Dr. Dutta has already identified a fungicide program that should be effective in 2019. If the other azoxystrobin-resistant isolates turn out to be the new species, it mean that there has not been a change in the usual Alternaria.

Produce Safety Webinar for Broccoli Producers

Are you wondering what the implications of new food safety regulations are for broccoli production?  Join Eastern Broccoli Food Safety specialists Chris Callahan, Betsy Bihn, and their colleagues on Monday, May 14 at 2 p.m. EDT  for a webinar on “Produce Safety for Broccoli Producers”.

Topics will include:

  1.  An overview of produce safety
    1. Coverage thresholds and compliance dates
    2. The Food Safety Modernization Act and Produce Safety Rule
  2. Broccoli-specific produce safety considerations
  3. Overview and feedback on educational material development.

You can register for the webinar using the form below.  Registration is not mandatory, but it will help us with planning and make it easier for you to get a direct link to the webinar via email.  The form also has room for you to list specific questions that you would like to see addressed during the presentation.

The webinar is geared towards growers, but the information will also be useful to buyers, extension specialists, researchers, and others.  Registrants will be emailed instructions for joining the webinar by the day of the event.

(This event has passed.  You can view a recording of the webinar, and download the slides, from Chris Callahan’s blog page here http://blog.uvm.edu/cwcallah/2018/06/18/produce-safety-in-broccoli/ .)