North Carolina Pest News – September 20, 2013 (Fruits & Vegetables)

NORTH  CAROLINA  PEST  NEWS
North Carolina State University * College of Agriculture & Life Sciences
Departments of Entomology and Plant Pathology * Raleigh, NC 27695
Volume 28, Number 24, September 20, 2013

CAUTION: The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.

ANNOUNCEMENTS AND GENERAL INFORMATION

Final Issue of North Carolina Pest News for 2013

This will be the final issue of the North Carolina Pest News for 2013. The editor would like to thank all of the Extension specialists and county agents and directors that contributed articles and/or insect trap data for the newsletter this season.

Thank you for your interest in the North Carolina Pest News. Meanwhile, individual articles on insect and disease pests in North Carolina will be provided as Pest Alerts via electronic mail and the Internet at http://ipm.ncsu.edu/current_ipm/palert99.html.

FRUIT AND VEGETABLES

From: Lina Quesada-Ocampo, Extension Plant Pathologist

Vegetable Disease Diagnostics Report

The Vegetable Pathology laboratory (http://projects.cals.ncsu.edu/veggiepathology/) at North Carolina State University has been working in collaboration with the Plant Disease and Insect Clinic (http://www.cals.ncsu.edu/plantpath/extension/clinic/) to diagnose vegetable diseases. We have compiled a report to provide our stakeholders with information of some of the trends we have observed so far this year.

The clinic has received approximately 330 vegetable samples this year, and our laboratory has independently provided diagnostics for 53 additional samples as part of our collaborator role with the cucurbit downy mildew IPM pipe (http://cdm.ipmpipe.org/). The following figure shows the percentages of vegetables grouped by type/family, and indicates that the vast majority of samples we diagnose are cucurbit and solanaceous crops, followed by brassica crops, sweetpotatoes, lettuce, beans and spinach.

On the vegetable samples we cover at the clinic with the vegetable diagnostician, Shawn Butler, (http://www.cals.ncsu.edu/plantpath/extension/clinic/about.html) (all vegetables except for tomatoes and peppers) and our independently-diagnosed samples, we found that the most frequent diagnosis have been oomycete diseases (in order downy mildew, Phytophthora and Pythium), an abiotic cause (fertilization, soils, salts, water stress, injury, chemical burns, etc), and fungal diseases (in order Fusarium, gummy stem blight, and anthracnose). It is important to note that cucurbit downy mildew is highly represented in the oomycete disease group due to our work with this pathogen, but diagnostics of other downy mildews, Phytophthora and Pythium were still significant. We also indentified some bacterial diseases such as bacterial leaf spots and fruit blotch and a few virus and nematode-affected samples. Several samples submitted were affected by insect damage and no pathogens were found and other samples could not be processed due to poor quality of the sample.

When we look more closely at the diagnostics by vegetable type of the crops we collaboratively diagnose with the clinic (all vegetables except tomatoes and peppers), we see differences in the most common diagnosis for these vegetables. The following figure shows the crops with more samples submitted (cucurbits, brassicas, sweetpotatoes and alliums). For allium crops, the most common diagnosis was insect damage, followed by fungal diseases. For brassica crops abiotic causes were the most frequent diagnosis, followed by insect damage and fungal diseases. For sweetpotato more than half of the samples were affected by fungal diseases and others by abiotic causes. In cucurbits, oomycete diseases were the most common cause of crop damage, and if we remove the cucurbit downy mildew samples, fungi are the main cause of cucurbit disease.

Vegetable crops are most susceptible to disease when there is an underlying abiotic stress or injury, thus, having good soil, fertilizing and insect control strategies will results in a healthier crop.

Oomycete and fungal diseases that frequently affected crops this year include pathogens that are dispersed via air currents, and contaminated seed, soil, water or plant material.

For the airborne pathogens such as downy mildew, is important to use host resistance when available and a preventive spray program since there is little one can do to avoid exposing the crop to the pathogen.

For pathogens potentially being introduced into the field through contaminated seed or transplants such as gummy stem blight, is important to start with pathogen-free material, destroy any seedlings showing symptoms of disease and all neighboring seedlings, and protect the seed and transplants with fungicides if possible.

For pathogens potentially being introduced into fields through infested soil or irrigation water such as Phytophthora and Pythium, it’s important to take steps to determine if you have the pathogen present or not since they can survive in your soil for many years and have a broad host range, which limits the efficacy of crop rotation. If the pathogens are not present, do what you can to avoid introducing them by cleaning your equipment after visiting a field. If you have the pathogen in your field take steps to determine if your irrigation water may be contaminated, if it is, consider using deep well water for irrigation or incorporating a filtering system. If your water is clean, but the pathogen is in your soil, crop rotation to non-hosts will help, as well as cultural practices (use of plastic mulch and drip irrigation), and preventative spray programs. Some growers have used fumigation in cases were inoculum levels of soilborne pathogens are high.

We will continue to publish news and alerts about diseases affecting North Carolina vegetable crops through the Extension Plant Pathology Portal

(http://www.cals.ncsu.edu/plantpath/extension/clinic/about.html).

Further information about disease control strategies for specific pathogens can be found in the North Carolina Agricultural Chemical Manual (http://ipm.ncsu.edu/agchem/10-toc.pdf).

Follow us on Twitter (https://twitter.com/QuesadaLabNCSU) and Facebook for more veggie disease alerts (https://www.facebook.com/QuesadaLabNCSU).

Written By

Amie NewsomeExtension Agent, Agriculture - Commercial Horticulture (919) 989-5380 (Office) Johnston County, North Carolina

Posted on Sep 24, 2013

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