Grower Research

Free testing of virus diseases of watermelon by Dr. Ali

Please advise all growers that we will be willing to test watermelon samples (from field or greenhouse showing virus-like symptoms) free of charge during the whole 2012 season as well beyond the project duration.

I would encourage the growers to collect and send to us even few infected plants they find in their fields rather waiting for epidemic infection etc.

Dear Watermelon Producer,
We appreciate your support for our research project entitled “Frequency and Distribution of Old and Possible New Viruses in Watermelon” during the 2010 growing season. A copy of the research progress report is enclosed for your information. In brief, we have analyzed more than 650 samples collected from 9 different southern states and identified the frequency of seven viruses in these samples. Further work is needed to complete the characterization of 200 unknown samples that could potentially represent new viruses. A tremendous amount of time will be required for complete characterization. Although each sample may require two days work, we are committed to the challenge. As we get additional information, we will keep you updated.

Viruses are important pathogens of watermelon and have caused sporadic epidemics in watermelon industry for years all over the US that often go undetected. The recent example of vine decline disease of watermelon is one example which is caused by a virus and has damaged watermelon crops specifically in Florida. Very little information is available about the number and frequency of viruses that occur regularly in watermelon across the US. In addition, no study has been conducted before this work which reported the large scale documentation of these viruses in multiple states of the US. We intend to document the occurrence, distribution and complete characterization of these viruses that infect watermelon crops. The main objective of our work is to identify all these viruses before they reach epidemic levels that threaten watermelon crops. With this information, we should be able to develop durable and long lasting control strategies for these viruses. Therefore, we look forward to your continued support for our research project in 2011 as well.

We have photographed more than 600 samples with various symptoms during our survey in 2010. We intend to compile a symptom manual of all the viruses detected in this work that will be helpful for watermelon growers and extension personnel in identifying virus disease in the field. We have 200 samples that are unique and need further characterization. We expect that we will find some new viruses from these samples.

We would also like to test greenhouse transplants if anyone suspects virus infection. We will appreciate your cooperation in this matter. Finally, we encourage more people to participate in the study to obtain a thorough representation of viruses affecting watermelons from all major production states. If you are interested in participating, get in touch with us prior to next watermelon season.

Sincerely,
Akhtar
Project Principal Investigator
Dr. Akhtar Ali
Assistant Professor of Plant Virology
Department of Biological Science
The University of Tulsa
Tulsa, Oklahoma 74104
Tel: 918-631-2018
Fax: 918-631-2762
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.


Project collaborators
Dr. Benny D. Bruton and Dr. Wayne W. Fish (USDA-ARS, Lane Oklahoma)
Dr. Edward Sikora, (University of Auburn), Alabama
Dr. David B. Langston (University of Georgia)
Dr. Shouan Zhang, (University of Florida)

 

 


Cucurbit Downy Mildew Found in South Carolina

By Anthony Keinath, Vegetable Pathologist, Clemson University, Coastal REC, Charleston, SC
Cucurbit downy mildew has been found on yellow summer squash and zucchini plants at a “big box" store in Charleston, SC. Some plants were likely sold between the dates of first discovery (Wed. 4/6/11) and confirmation (Sun. 4/10/11). Remaining plants were pulled on 4/10/11. Plants were at bloom stage in one-gallon pots with 5-10% severity of downy mildew on about 25% of the leaves. Several spots had begun to sporulate. The plants were grown in Miami, FL, which is the only area in which cucurbit downy mildew has been reported so far this season.

All cucumber, muskmelon, and squash fields in Charleston, Berkeley, and Dorchester counties of South Carolina should be sprayed now using the preventative schedule below. Cucurbit growers in other parts of South Carolina should spray with chlorothalonil or mancozeb and be ready to spray if infected plants are found in their location or if a field outbreak of cucurbit downy mildew develops in South Carolina.

Downy_MildewSymptoms and Signs

Leaf spots on cucumber and cantaloupe start as pale green to yellow angular spots that turn brown and spread. Leaf spots on squash are small, bright yellow flecks across the leaf surface. Slight yellowing may be seen around the edges of the spots or on other parts of the leaf that are already infected. Brownish-purple spores are found on the bottom of infected leaves in the early morning. They give the under-side of the leaf a “dirty” appearance as seen in the photo from cucumber.

How Downy Mildew Spreads
Downy mildews do not survive on dead tissue or in soil. They can only grow on live plants. Cucurbit downy mildew is spread by air as wind blows spores northward from the south in the spring. Spores spread the farthest and fastest during windy, cloudy periods. Outbreaks are most likely during wet, warm weather.

Currently, cucurbit downy mildew is only found in the field in south Florida and Puerto Rico. See the Cucurbit Downy Mildew Forecast at http://cdm.ipmpipe.org/. Growers, scouts, home owners, and other interested people can sign up to receive e-mail or text message alerts when new outbreaks of downy mildew are reported to the system.

Fungicides
Fungicides are necessary to manage cucurbit downy mildew. Two different fungicide programs are recommended in 2011. The first program is for prevention and should be used before downy mildew is found in a field. The fungicide choices are Gavel (Dow), Tanos (DuPont), and Previcur Flex (Bayer). Tanos and Previcur Flex must be tank-mixed with chlorothalonil or mancozeb.

Once downy mildew hits, two different fungicides need to be used. Apply Ranman (FMC) and Presidio (Valent) mixed with with chlorothalonil or mancozeb alternated weekly. See page 196 of the Southeastern U. S. 2011 Vegetable Crop Handbook or http://www.thegrower.com/south-east-vegetableguide. Organic growers should use copper products but also should expect yield loss in cucumber and muskmelon, because copper is not completely effective against downy mildew. Summer squash has some tolerance to downy mildew. Home gardeners should spray with chlorothalonil or copper.

Cucurbit downy mildew in most parts of the U.S. is resistant to Ridomil, all strobilurin fungicides (Cabrio, Quadris, Flint, Pristine, and Reason), and Revus. These fungicides are not recommended against cucurbit downy mildew.

Clemson Public Activities- April 2011

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