, with "LATE BLIGHT DIAGNOSIS REQUESTED"
in the subject line IN ALL CAPS.
If late blight is present in your garden, remove the plant, roots and
all, before the next rain to minimize the chances it will spread to
other gardens and farms. Immediately bag the plant tightly in plastic
and set in the sun for a few days until the plant dies off completely.
Then dispose of in the trash. Do not compost. Do not leave it lying on
the ground for later.
If you're not sure -- and chances are you won't be unless you get a
professional diagnosis -- place suspect leaves in a sealed zipper-top
plastic bag overnight. Late blight spores will develop into a fuzzy mass
on the underside of the affected foliage.
Here are 10 things McGrath recommends you do to minimize late blight in
1. Kill volunteer potatoes. Dig up, bag and trash any potato plants that
sprout from tubers left in the ground or compost pile last year. It may
take repeated efforts to get them all.
2. Buy healthy tomato plants. Learn what late blight looks like. (See
photo above) If you spot any infected plants while shopping, alert store
management and your local Cooperative Extension office, and buy your
plants somewhere else. Or you can grow your own plants. (Late blight isn’t
spread on tomato seeds.) Start seed about 6 to 8 weeks before your last
frost date. 3. Use certified seed potatoes. Don’t use leftovers from
last year’s garden or table stock from the grocery store. 4. Keep plants
dry. The late blight pathogen thrives in cool, wet weather. That’s
because it requires moisture to infect plants, grows best when it’s
cool, and clouds protect spores from lethal UV radiation when they are
dispersed by wind. Even in absence of rain, the pathogen can infect
plants if the relative humidity is 90 percent or more. If plants need
watering, water the soil – not the foliage.
5. Be vigilant. Inspect plants at least once a week – more often if
weather is cool and wet. Immediately remove and bag foliage you suspect
might be infected. While late blight symptoms are distinctive – dark
brown lesions on stems and leaves with white fungal-like growth
developing under moist conditions – it’s possible to confuse it with
other diseases. Your local Cooperative Extension office can help you
with identification. 6. Act quickly. If symptoms continue despite
removing infected foliage, consider removing plants entirely – sooner
rather than later. "It is rarely possible to control late blight just by
removing affected tissue," McGrath said. "The longer you wait to remove
plants, the more spores your garden sends to the wind to infect other
gardens and farm fields." 7. Sound the alert. If you find late blight in
your garden, let your gardening neighbors and local Cooperative
Extension staff know so they can warn others and be on the lookout for
additional infestations. Make sure your neighbors know how to spot late
blight in their own gardens. 8. Dispose of plants properly. To reduce
disease spread, remove infected plants during the middle of a sunny day
after leaves have dried, if possible. But don’t wait for these
conditions. Seal plants in garbage bags and leave them in the sun for a
few days to kill plants and the pathogen quickly before placing in the
trash or burying underground or deep in a compost pile. Don’t just leave
plants on the ground or on top of the compost pile where they will
continue to be a source of spores until the plant tissue dies. With a
large number of plants, you can build a pile on the ground and cover
securely with a tarp until the plants die. 9. Keep an eye on other
tomato-family plants . Some strains of late blight can infect other
tomato-family plants, including weeds such as hairy nightshade and
bittersweet nightshade. Control them early so that late blight on these
plants doesn’t go unnoticed. Petunias and tomatillos are also vulnerable
to attack. 10. Use fungicides with care. Fungicides can control late
blight. ( Chlorothalonil and copper-based products are both available to
home gardeners.) But if you wait until late blight symptoms appear, it
might be too late to rescue plants. For fungicides to work effectively
on late blight requires a regular preventive spray schedule and thorough
spray coverage. Follow all label directions, including use of
respirator, waterproof gloves and protective eyewear.
The video at the bottom of this page is from last year's outbreak.
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