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Continued reports of late blight in PA and across the Northeast.

Posted: September 27, 2011

As we head into fall, the cool and wet conditions favor the continued development of late blight on both tomato and potato.
Characteristic symptoms of late blight on tomato fruit. The white fuzzy growth on the surface of the fruit is the actual pathogen, Phytophthora infestans. (Photo credit: Beth K. Gugino)

Characteristic symptoms of late blight on tomato fruit. The white fuzzy growth on the surface of the fruit is the actual pathogen, Phytophthora infestans. (Photo credit: Beth K. Gugino)

Additional outbreaks of late blight continue to be confirmed in PA. The latest was on tomato in a commercial field in Berks Co. This season late blight has also been confirmed on tomato in Northumberland, Mercer, Snyder, Montour and Venango Counties as well as on potato in Cambria and Erie Counties. The most common genotype identified this year in PA and the Northeast has been US23. It is considered aggressive on both tomato and potato and is mefenoxam sensitive therefore, Ridomil is another management option. Mefenoxam is systemic and inhibits both fungal growth and sporulation. Keep in mind that in PA high tunnels are considered greenhouses when the sides are down which would prohibit the use of any pesticides containing mefenoxam which are prohibited in greenhouses. However, when the sides are up products labeled for use in the field are permissible in a high tunnel. Be sure to thoroughly read the label before using any pesticide.

Remember that late blight is a community disease! If you suspect late blight please contact your local Penn State Cooperative Extension Office, the Penn State Plant Disease Clinic or Beth Gugino at bkgugino@psu.edu or 814-865-7328. For the most current map of confirmed late blight outbreaks please visit http://usablight.org.