Disease Late Blight Tomatoes

Late blight update

On Thursday, June 17, two tomato samples from southwest Pennsylvania were confirmed to have late blight.  One was a transplant purchased from a nursery and one from a home garden.

Note: Late blight has not been found yet in Indiana.  Reports of findings last week in Indiana were not accurate.


I have confirmed with Michigan specialists that no late blight has been reported in Michigan yet (as of June 14).

Other reports of late blight have included findings on tomato transplants being sold to gardeners in the Winnipeg and Brandon areas, and confirmations in Kentucky, Maryland, and areas of the southern US.  In Michigan, they have found that volunteer potato plants are emerging from fields that had late blight last year.  These plants would present a risk and should be killed or removed immediately.

Should growers be implementing a late blight control program for their tomato fields at this point?  In some areas, TOMcast would indicate that the first fungicide spray is imminent, anyway.  Growers who have included fungicide (chlorothalonil or mancozeb) with their copper program for bacterial disease have some protection on the plant already.  Other growers may want to take a cautious approach and start their fungicide program a bit early.

Growers should know the symptoms of late blight and monitor their crop carefully.

If hot, dry weather returns, late blight infection should not be a concern.  This disease prefers cooler, wet conditions.

Recommended protectant fungicides for tomato late blight in Ontario:

chlorothalonil (Bravo 500)

mancozeb (eg. Dithane DG, Manzate Pro-Stick, Penncozeb 80 WP)

metiram (Polyram DF)

famoxadone + cymoxanil (Tanos 50 DF) – has some kickback activity

mandipropamid (Revus) – has some translaminar movement

pyraclostrobin (Cabrio) – use high rate for late blight

Note:  Organic producers may be interested in an article by Meg McGrath (Cornell University) on managing late blight in organically-produced tomato.

Keep in mind that at this point in the season, managing bacterial disease is also important, especially in areas that have seen storm activity recently.

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