Understanding Black Rot In Cole Crops

Black rot is a significant disease of cabbage and other crucifer crops worldwide. The pathogen spreads through infected seeds or plant-to-plant through water droplets. It can be distributed rapidly among greenhouse transplants and in seed beds.

The black rot pathogen spreads through infected seeds or plant-to-plant through water droplets. It can be distributed rapidly among greenhouse transplants, as shown here.
The black rot pathogen spreads through infected seeds or plant-to-plant through water droplets. It can be distributed rapidly among greenhouse transplants, as shown here.

The disease can also spread from weeds and debris in the soil. The role of weeds and soil debris as a source of the pathogen was previously unknown.

The goal of a project at Cornell University using DNA fingerprinting to identify strains of the black rot pathogen was to gain a better understanding of the potential sources of inoculum in New York and the severity of disease from different sources. The information gleaned will allow the development of management strategies to control the disease.

Since 2004, Cornell researchers have annually surveyed black rot pathogen isolates from transplants and symptomatic plants in commercial fields using selective media, ELISA (enzyme-linked immunosorbent assay), pathogenicity, and DNA fingerprinting. The studies have shown that while it is possible for the pathogen to overwinter in New York, this has not been the most common source of inoculum.

Fingerprinting results identified new strains of black rot that have been in New York each year of the study (2004-2013), and the new strains are the predominant strains each season.

The Role Of Weeds
To better understand the role of weeds as a source of inoculum, in the spring, weed samples were collected from five fields that had severe black rot the previous fall. From each field, 15 to 20 weed samples were collected, and attempts were made to isolate the pathogen. The pathogen was isolated (based on molecular data) only from cruciferous weeds; however, none of the bacteria isolated produced symptoms on cabbage plants when inoculated in a greenhouse assay.

Additionally, the DNA fingerprint patterns of the isolates obtained from weeds did not match any of the DNA fingerprint patterns from isolates acquired from cole crops. This means the isolates collected from weeds did not come from the severely infected cabbage plants that were in the same field the previous year.

In two or three instances, researchers isolated the pathogen from weeds in fields during a black rot epidemic, with the symptomatic cruciferous weeds growing next to the infected cabbage. In these cases, the isolates in the weeds were identical to those in the cabbage plants, based on DNA fingerprinting.

It is impossible to know if the pathogen moved from the cabbage to the weed, or from the weed to the cabbage. The researchers’ hypothesis is that the pathogen moved from the cabbage to the weed.

They reached that hypothesis because in each case the isolate had not been observed in New York, and they identified the identical isolate from cabbage in other geographically separated fields. Thus, while strains of black rot that cause disease in cole crops can be harbored and detected in weeds in New York, this is not the predominant source of inoculum.

Photo Credit: Chris Smart
Photo Credit: Chris Smart

New Pathogen Strains
Based on the fingerprint studies, it is known that new strains of black rot arrive each year. The pathogen then spreads during transplant production and in the field. With this information, researchers began studies with the goal of determining the efficacy of available control strategies.

Experiments have been conducted to determine if applications of copper during transplant production will reduce the spread of the pathogen in the greenhouse and lead to less disease in the field. The treatments were continued into the field to determine if there was an impact on yield.

Results of a three-year study indicate that application of copper during transplant production does reduce the spread of black rot. Application of Actigard (Syngenta Crop Protection), a plant activator, also reduced spread of black rot, but some cupping of leaves was observed.

Control With Copper
A trial in 2013 compared copper-based control products for efficacy against black rot under field conditions. Healthy transplants were planted in a randomized complete block design. Treatments were sprayed on a seven-day schedule until just prior to harvest, and plants were inoculated with the pathogen 24 hours after the first spray.

Disease incidence and severity were rated four times. No phytotoxicity was noted with any of the treatments. Black rot symptoms were first observed in early July and by the first rating on July 10, 100% of the untreated plants showed black rot symptoms.

The wet and cool environmental conditions during June and early July of last year were not optimal for the spread of black rot, and while the number of plants with black rot symptoms was high, the severity was fairly low.

At the last rating, black rot lesions covered 39% of the inoculated but untreated (no copper) plants. The un-inoculated plants with no treatment had a severity rating of only 4% by late July, but 100% of them had symptoms of black rot. All of the treatments (Kocide 3000, DuPont Crop Protection; Champ WG, Nufarm Agricultural Products; Cueva, Certis U.S.A.; and Cuprofix Ultra 40 Disperss, United Phosphorus, Inc.) on the inoculated plants significantly reduced the severity of the black rot at the final rating.

Additionally, the Kocide and Cuprofix treatments had significantly less black rot than the Cueva treatment; however, this was a lower rate of Cueva than had been tested in 2012 when no significant differences were seen between Cueva and Kocide. 

Topics: , , , ,

Leave a Reply

Disease Control Stories
Biocontrols Conference
September 11, 2017
The Grower’s Take: Citrus, HLB, and Biological Control
Uncle Matt’s Organic orange juice brand has enjoyed steady growth since its 2002 inception. The brand’s success is due to Read More
Biocontrols Conference
September 1, 2017
Dispelling the Rumors: Using Biologicals and Biochemicals in IPM Programs
Whether you’re a grower, packer, processor, or retailer, you have experienced the dramatic shift in consumer preference for sustainable practices Read More
Biocontrols Conference
September 1, 2017
Silicon: a Biocontrol Agent that Boosts Plant Immunity
Quality and profitability are two important factors that drive our agricultural markets. We have fine-tuned our cultivation processes over centuries Read More
Crop Protection
August 9, 2017
Why Some of the Most Dangerous Potato Diseases are Successful
If you understand the role oxygen, and its lack, plays in potato diseases, you'll be better equipped to battle them. Read More
a freshly picked avocado cradled in hand
Crop Protection
August 3, 2017
Can Avocados Be Saved from Deadly Laurel Wilt Disease?
Scientists from Florida and California are on the case and collaborating. Read More
sprayer nozzles
Biocontrols Conference
July 31, 2017
11 New Biocontrol Products You Need to Know
One of the highlights of the Biocontrols Conference & Expo Series is getting an early look at some of the Read More
Disease Control
July 25, 2017
Brown Rot Sinks its Teeth into Michigan Cherries
Unseasonably wet weather causes outbreak, and growers are warned it can spread to peaches. Read More
Disease Control
July 24, 2017
Researchers Find Detection Method for Crown Gall Disease
Oregon State University researchers developed molecular tools to work with commercially available kits that allow the user to quickly and effectively test plants for the disease, using a dipstick that reveals the presence of the pathogen within minutes. Read More
Cucurbit leaf crumple virus
Cucurbits
June 20, 2017
Take Caution to Curb Cucurbit Leaf Crumple Virus
Learn how to identify, the survival and spread, as well as management methods for this disease. Read More
Illustration of CRISPR-Cas9
Citrus
June 15, 2017
Make Way for Life-Saving Science on Your Farm [opinion]
While nature always finds a way to adapt, science continues to find other ways to cope. Read More
Berries
June 10, 2017
Orange Rust Management Tips for Brambles
Disease is on the rise this season and can affect any propagated plant material. Read More
Crop Protection
June 7, 2017
Field Scouting Guide for Squash Powdery Mildew
Learn how to spot and treat a pest that impacts all cucurbits. Read More
Bee Vectoring Technologies experimental hives
Citrus
May 23, 2017
Insects (Bad and Good) Make for Interesting Field Trips
Disease-fighting bees and the deadly citrus psyllid were at the center of two recent, research-fueled out-of-office adventures. Read More
UF/IFAS scientist Jonathan Crane inspects avocado trees in South Florida
Crop Protection
April 20, 2017
Beetle Battle Burgeoning for South Florida Avocado Growers
Scientists identify more species of pests that vector deadly fungus. Read More
Alternaria Leaf Spot of Cucurbits
Cucurbits
April 19, 2017
Alternaria Leaf Spot Awareness Can Save Your Cucurbit Crops
Learn how to identify, the survival and spread, as well as management methods for this malady. Read More
The Latest
Berries
September 20, 2017
Getting to the Bottom of Bacterial Wilt …
Prolific plant pathogen now presenting a new challenge for Florida producers and researchers. Read More
Disease Control
September 15, 2017
Scientist Uncovers Chilling Side of Dead…
Lab tests indicate laurel wilt pathogen grows faster in the fall and winter. Read More
Biocontrols Conference
September 13, 2017
Get Better Results From Your Biopesticid…
Softer crop protection programs are becoming a must in specialty crop production. Growers who aren’t learning more about their options Read More
Biocontrols Conference
September 11, 2017
The Grower’s Take: Citrus, HLB, and Biol…
Uncle Matt’s Organic orange juice brand has enjoyed steady growth since its 2002 inception. The brand’s success is due to Read More
Biocontrols Conference
September 1, 2017
Dispelling the Rumors: Using Biologicals…
Whether you’re a grower, packer, processor, or retailer, you have experienced the dramatic shift in consumer preference for sustainable practices Read More
Biocontrols Conference
September 1, 2017
Silicon: a Biocontrol Agent that Boosts …
Quality and profitability are two important factors that drive our agricultural markets. We have fine-tuned our cultivation processes over centuries Read More
Crop Protection
August 9, 2017
Why Some of the Most Dangerous Potato Di…
If you understand the role oxygen, and its lack, plays in potato diseases, you'll be better equipped to battle them. Read More
Crop Protection
August 3, 2017
Can Avocados Be Saved from Deadly Laurel…
Scientists from Florida and California are on the case and collaborating. Read More
Biocontrols Conference
July 31, 2017
11 New Biocontrol Products You Need to K…
One of the highlights of the Biocontrols Conference & Expo Series is getting an early look at some of the Read More
Disease Control
July 25, 2017
Brown Rot Sinks its Teeth into Michigan …
Unseasonably wet weather causes outbreak, and growers are warned it can spread to peaches. Read More
Disease Control
July 24, 2017
Researchers Find Detection Method for Cr…
Oregon State University researchers developed molecular tools to work with commercially available kits that allow the user to quickly and effectively test plants for the disease, using a dipstick that reveals the presence of the pathogen within minutes. Read More
Cucurbits
June 20, 2017
Take Caution to Curb Cucurbit Leaf Crump…
Learn how to identify, the survival and spread, as well as management methods for this disease. Read More
Citrus
June 15, 2017
Make Way for Life-Saving Science on Your…
While nature always finds a way to adapt, science continues to find other ways to cope. Read More
Berries
June 10, 2017
Orange Rust Management Tips for Brambles
Disease is on the rise this season and can affect any propagated plant material. Read More
Crop Protection
June 7, 2017
Field Scouting Guide for Squash Powdery …
Learn how to spot and treat a pest that impacts all cucurbits. Read More
Citrus
May 23, 2017
Insects (Bad and Good) Make for Interest…
Disease-fighting bees and the deadly citrus psyllid were at the center of two recent, research-fueled out-of-office adventures. Read More
Crop Protection
April 20, 2017
Beetle Battle Burgeoning for South Flori…
Scientists identify more species of pests that vector deadly fungus. Read More
Cucurbits
April 19, 2017
Alternaria Leaf Spot Awareness Can Save …
Learn how to identify, the survival and spread, as well as management methods for this malady. Read More