(reprinted)
The following information appeared in the February 2010, Cornell Cooperative Extension, Veg Edge Publication. This publication serves the counties of Western New York.
Without a doubt, with the amount of late blight (LB) inoculum likely around we’re going to have to manage the disease on potatoes and tomatoes in 2010 unless the season is very dry from beginning to end. While some LB strains are more virulent on potatoes than tomatoes, and vice versa, growers of both crops should be planning to take preventive action. LB is a community disease since the spores can move on the air considerable distances. Potato and tomato growers, and home gardeners, all need to be vigilant and share information if LB shows up. Once the disease is detected it is often very difficult, if not impossible, to control. It can develop very rapidly, especially in wet weather. Info below incorporates revised recommendations of Steve Johnson, University of Maine. There is info on LB and other potato concerns here. See also the Cornell Veg Guidelines.
Eliminate Inoculum! As soon as the snow melts scour your property and destroy potato cull piles, potatoes in rock piles, and volunteers. Go back in a few weeks and do it again, unless you’ve buried the potatoes under 2 ft. of soil. Potatoes often survive in the middle of large cull piles, to emerge and sprout later. Culls can be spread in open fields until early March to ensure that they freeze, eliminating the pathogen. Stay away from wells and streams as considerable nutrients are released from rotting tubers. Potatoes can be composted, in combination with sawdust but it must be done correctly to ensure that all the tubers break down. Cull potatoes can be fed to livestock and is a common practice in some areas.
Check Your Potato Seed and Tomato Transplants! Buy only from reputable dealers. Commercial potato growers should call for a NYS Dept. of Ag & Markets Farm Products Inspection, offered at a nominal cost, as soon as seed is delivered. Tomato growers should thoroughly inspect their plants and isolate anything suspicious. Upon arrival, look materials over for decay and dark areas. LB infected potato tubers are firm and mottled reddish-brown under the skin as deep as an inch. Warming tubers for 2 – 3 weeks may make any infection present more visible. Infected tomato transplants may have darkened areas on the leaves or stems. Bagging suspicious plants overnight may result in sporulation. Any fine, white sporulation on the edge of the dark areas should make you suspect LB. Take suspicious material to an Extension Vegetable Specialist for identification. The Ontario and Monroe CCE offices can make a positive ID through microscopic examination of spores, difficult for potato tubers, however.
Use Whole Seed if You Can – Use of whole potato seed reduces the risk of spreading what might be a minimal amount of LB to many more tubers during cutting. Keep seed lots separate to avoid potential spread of LB and to more accurately track any infection that does develop in the field. Discard suspicious looking seed throughout the seed handling phase. Conventional growers should plan on using a mancozeb containing seed treatment at a minimum, preferably one with cymoxanil in addition.
Buy Crop Insurance – At least the minimum, as a risk management practice.
Plan to Use Less Nitrogen – Many growers use higher amounts of nitrogen, and apply it later in the season, than is recommended. Review the recommended rates and timings in the Cornell Vegetable Guidelines. Very lush foliage is more susceptible to infection by LB and other diseases. In addition, excess N in potato plants keeps them green and susceptible to LB infection for a longer period late in the season. N rates vary with variety and soil type.
Get the Word Out in the Spring to neighboring home gardeners, and encourage your local Cooperative Extension office to get the word out more widely to gardeners as well. Garden store tomatoes and potatoes must be considered as possible sources of LB. Big Box Store tomatoes were a major cause of the LB epidemic last year.
LB Questions? – Growers in WNY, contact Carol MacNeil at 585-394- 3977 x406 or crm6@cornell.edu. In the Eastern region, contact Chuck Bornt at 518-272-4210 x125 or cdb13@cornell.edu. Growers in other areas of the U.S. should contact their local cooperative extension service for information on LB in their area.
All weevils are insects but not all insects are weevil… some are actually helpful (ugh). And to be clear with that last pun – weevils are NOT helpful…
