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
Symptomless plum tree infected with plum pox virus.  (Photo credit: William Shane)
Disease Control
November 28, 2016
Tips To Keep Your Stone Fruit Orchard Clean
Managing serious plant diseases of peach and plums requires a cooperative approach. Read More
potato field
Crop Protection
November 21, 2016
Syngenta Announces New Fungicide Product Line
The Miravis brand contains a new active ingredient that is currently pending EPA approval. Read More
Rhizoctonia Root Rot
Disease Control
November 20, 2016
Rhizoctonia Pathogen A Major Bane To Beans
Learn how to identify, the survival and spread, as well as management methods for this vegetable disease. Read More
Bacterial wilt symptoms in Florida blueberries
Berries
November 16, 2016
Florida Blueberry Growers Warned To Watch For New Deadly Disease
Pathogen has been confirmed on three farms so far. Read More
This watermelon seedling is showing Fusarium wilt symptoms. The first symptom that appears on infected plants is wilt in a single leaf or a single vine.
Photo credit: Kathryne Everts
Crop Protection
November 8, 2016
The Effect Of Soil Fertility On Fusarium Wilt In Watermelon
Ongoing research sheds light on the role soil health plays in the severity of the deadly pathogen in watermelon crops. Read More
Even with powerful electron microscopes, viruses cannot be identified based on particle shape. 
Pictured here are particles of tomato apex 
necrosis virus. Photo credit: B. W. Falk
Crop Protection
October 31, 2016
Zika And Zucchini Yellow Mosaic: Analogies Between Human- And Plant-Infecting Viruses
While we certainly do not equate the seriousness of Zika with agricultural problems, the Zika virus can serve as a reminder about aspects of the many plant-infecting viruses, from alfalfa mosaic to zucchini yellow mosaic, that affect vegetables. Read More
Photo credit:  Scott Bauer
Disease Control
September 9, 2016
Arizona Iceberg Lettuce Research Council Awards Grant To Focus On Lettuce Diseases
A recent survey indicates disease control and management were identified as the highest priority. Read More
The Latest
Crop Protection
December 6, 2016
Orondis Opti Fungicide Receives Registra…
The product provides control of Oomycete diseases in vegetables and other specialty crops. Read More
Crop Protection
November 30, 2016
The Effect Of Soil Fertility On Fusarium…
Ongoing research sheds light on the role soil health plays in the severity of the deadly pathogen. Read More
Crop Protection
November 28, 2016
Stave Off Sweet Potato Disease
Management can be made easier through variety selection and improved sanitation practices. Read More
Disease Control
November 28, 2016
Tips To Keep Your Stone Fruit Orchard Cl…
Managing serious plant diseases of peach and plums requires a cooperative approach. Read More
Crop Protection
November 21, 2016
Syngenta Announces New Fungicide Product…
The Miravis brand contains a new active ingredient that is currently pending EPA approval. Read More
Disease Control
November 20, 2016
Rhizoctonia Pathogen A Major Bane To Bea…
Learn how to identify, the survival and spread, as well as management methods for this vegetable disease. Read More
Berries
November 16, 2016
Florida Blueberry Growers Warned To Watc…
Pathogen has been confirmed on three farms so far. Read More
Crop Protection
November 8, 2016
The Effect Of Soil Fertility On Fusarium…
Ongoing research sheds light on the role soil health plays in the severity of the deadly pathogen in watermelon crops. Read More
Crop Protection
October 31, 2016
Zika And Zucchini Yellow Mosaic: Analog…
While we certainly do not equate the seriousness of Zika with agricultural problems, the Zika virus can serve as a reminder about aspects of the many plant-infecting viruses, from alfalfa mosaic to zucchini yellow mosaic, that affect vegetables. Read More
Disease Control
September 9, 2016
Arizona Iceberg Lettuce Research Council…
A recent survey indicates disease control and management were identified as the highest priority. Read More
Crop Protection
September 3, 2016
Dickeya dianthicola: A New Threat To Po…
The disease, identified in Maine in 2014, has caused significant losses in potatoes on the Eastern Seaboard. Read More
Citrus
August 30, 2016
Scientists Fervent To Find Cure For Dead…
Now spreading to sorghum, yellow leaf malady could infect crops from Florida to Texas. Read More
Disease Control
August 23, 2016
Florida Sweet Corn Has New Deadly Stalke…
Learn how to identify, the survival and spread, as well as management methods for this disease. Read More
Berries
August 4, 2016
Genetics Key To Keeping Strawberry Growe…
Savings to the tune of $30 million a year would come with a solution to angular leaf spot. Read More
Disease Control
July 19, 2016
Open Your Eyes To Common Smut In Sweet C…
Learn how to identify, the survival and spread, as well as management methods for this formidable fungus. Read More
Crop Protection
July 18, 2016
Early Infection Of Downy Mildew Confirme…
The pathogen has been confirmed in Michigan cucumbers in Bay County for the 2016 season. Read More
Crop Protection
July 18, 2016
Potato Growers: Be On The Lookout For Ne…
Standard measures have been typically less effective against new strains. Read More
Crop Protection
July 13, 2016
Dickeya: A New Potato Disease
The disease caused big losses last year; growers need to check fields for symptoms. Read More