Urgent: Late Blight Alert for All Gardeners!

This just in from Starting Point Blog on Yahoo News:

Most-read stories overnight: Tomato plants have been pulled from stores in six states due to the widespread appearance of late blight. While not harmful to humans, late blight is extremely contagious and destructive to plants. It is also the same disease that caused the Irish Potato Famine in the 1840s.

Lynn Prior, a Master Gardener and friend of the blog from College Hill, sent me the alert below from Penn State's The Small Fruit and Vegetable Gazette warning of late blight found in the Lehigh Valley. Lynn says the blight affects tomato plants the most, is very serious and must be tackled comprehensively by everyone because the spores can spread very quickly through the Valley. Here is a note from Lynn, including what to look out for, and how to prevent late blight, followed by the article, which also covers what to do if you find blight (the plants must be destroyed so they don't spread spores):

To all tomato gardeners:

Late blight is a fungal disease of tomatoes and potatoes, and it is present
here this year. Take a look at photos at:

Link to Photos of Late Blight on Tomatoes

and be sure to monitor your tomatoes at least once a week for symptoms: 1. dark lesions on stems 2. tiny brown leaf spots that develop become large and expand to cover whole leaves (white fuzziness on underside); leaves will die 3. green to brown spots on fruit. If you see symptoms, you should remove the infected tissue and put it in a plastic bag, then leave it in the sun to cook. Non-organic growers can protect their crops by spraying with the fungicide chlorothalonil. Ortho Garden Disease Control contains 29.6%chlorothalonil. Organic growers can use copper-based fungicides, although they are not as effective. Either way, if you choose to spray, begin now and continue spraying every week throughout the season. Also, this wet weather will increase the likelihood of other fungal diseases. To control fungal diseases, keep the plants and fruit off the ground: cage or stake plants. Also, minimize the time that leaves are wet by applying water to the soil and not overhead, water early in the day, and don't plant tomatoes too closely together - they need good air circulation. Next year, rotate your tomato plants to a different part of your garden.
-------------------

The Small Fruit and Vegetable Gazette

Disease Alert:
Late Blight Confirmed in Lehigh County—June 29, 2009
Beth K. Gugino, Penn State University, Vegetable Pathologist
Emelie Swackhamer, Extension Educator, Lehigh and Northampton Counties
Robert Leiby, Extension Educator, Lehigh County
Tianna DuPont, Extension Educator, Northampton and Lehigh Counties

Late blight was confirmed today on a tomato sample from a "big box" retail store in Lehigh County. Late blight has been confirmed in at least six Pennsylvania counties. It is advised that growers scout daily for late blight symptoms. You should assume that late blight is present and maintain an aggressive fungicide spray program.

Conditions these past few days have been ideal for the development of late blight in many regions of the state. Daytime temperatures have been between 60-75ºF and nighttime temperatures between 50-60ºF, accompanied by fog and heavy dews or rain over the past four or five days. Extended periods of high relative humidity are also important for this disease.

Updates on the late blight situation will be posted on the Penn State Department of Plant Pathology Web site.

If late blight is found in a localized spot in a field, destroy those plants as well as several of the surrounding non-symptomatic plants. Pull out and drop the plants, then apply a herbicide or disk/bury the plants. If few plants, they could be covered by a plastic tarp. Both the sunlight and heat will kill the spores. If disking the crop, apply a fungicide first to reduce the potential movement of spores on the equipment. Thoroughly clean all equipment (and yourself) used to destroy the crop to avoid spreading the spores around.

Protectant fungicides are available; (chlorothalonil, Gavel and mancozeb are listed in the 2009 Penn State Commercial Vegetable Production Recommendations).

If you are using a conventional protectant spray program you should consider including late blight specific chemistries, especially if you are in a county where late blight has been confirmed. Late blight specific fungicides with translaminar activity are listed below. Make it a practice to alternate between fungicides with different FRAC codes for resistance management and tank mix with a protectant when needed (some products like Gavel already include a protectant). When conditions are cool and wet (conducive for late blight), use a shorter five to seven day spray interval. The spray interval can be extended to ten days under more hot, dry conditions. Hopefully then, the warmer, drier weather will persist. Always check with Commercial Vegetable Production Recommendations for specific rates and tank mixing recommendations and always check the label for chemical use restrictions before applying a fungicide.
(over)
College of Agricultural Sciences Penn State, U.S. Department of Agriculture, and Pennsylvania Counties Cooperating
An Equal Opportunity University
Check with the Penn State Commercial Vegetable Production Recommendations for specific rates and tank mixing recommendations. Remember to tank mix and alternate between different FRAC codes for fungicide resistance management. Also, always check the label for chemical use restrictions.

Fungicides specific for late blight on POTATO and TOMATO include:
• Propamocarb (Previcur Flex) – FRAC 28
• Cymoxanil (Curzate, Tanos) – some kickback activity – FRAC 27
• Dimethomorph [Acrobat (potato), Forum (tomato)] – FRAC 40
• Cyazofamid (Ranman) – FRAC 21
• Mandipropamid + Difenoconazole (Revus Top) – FRAC 40 +3

Addtionally, Syngenta obtained a supplemental label for Revus on tomato and potato due to the short supply of Revus Top. Contact your supplier or your county's Cooperative Extension office for a copy of the supplemental label.

For certified organic growers, there are few control options currently available with known efficacy against late blight on tomato and potato. Frequent copper applications may provide minimal control if applied preventatively. In Pennsylvania there are several OMRI approved copper formulations. Other potential products include Sonata and Sporatec, however, minimal efficacy data is available. A fact sheet on late blight management for certified organic growers is available or call your Cooperative Extension office for a copy.

If you hear of any reports of or suspect late blight on tomato or potato in Pennsylvania or in the region, please report it to your county's Penn State Cooperative Extension office or send a sample to the Penn State Plant Disease Clinic at 220 Buckhout Laboratory, University Park, PA 16802 for confirmation.

Emelie Swackhamer,
Extension Educator
Lehigh and Northampton Counties