By PAUL HETZLER

Although the term ‘blight’ strikes fear into the hearts of gardeners, it can actually be used to mean any plant disease, from the innocuous to the truly pernicious. Of all the plant maladies, I think the one most deserving of the fearsome moniker ‘blight’ is Phytophthora infestans, a.k.a. late blight. Roughly translated, its Latin name means “highly contagious plant-destroyer.”

Infamous for its role in the mid-nineteenth century potato famine in which it exacerbated a planned genocide against the Irish, this disease can indeed destroy entire harvests of potatoes and tomatoes. Fortunately, we now have many good management tools to help keep losses to a minimum when late blight strikes.

Unfortunately, late blight has just been confirmed in St. Lawrence County. Organic growers can use a copper-based spray to protect their tomatoes and potatoes, and others can use products containing chlorothalonil. Late blight can only survive on living plant tissue, so home gardeners should destroy late-blight infected plants by placing them in garbage bags and either placing them in the trash or leaving them in the sun until no green plant material is left.

Chuck Bornt of Cornell’s Eastern NY Commercial Hort Program advises commercial growers:

“Once you see LB [late blight] on your farm or if you’re downwind of a farm that has LB, use the systemic or translaminar products such as Curzate + Previcur Flex (or other material) + a protectant. Tank-mix Curzate and Previcur Flex because Curzate has a short residual (especially in hot weather), but very good “burn out “activity. Adding Previcur Flex or another labeled translaminar material will greatly improve control. Because of resistance issues with Ridomil, I would wait until the strain has been identified before using it, although so far this year most of the LB strains identified have not been resistant to Ridomil.

Also, if late blight has been identified on your farm you should destroy the infected area including a border area by either mechanical means (mowing, disking, flaming or rouging by hand and putting the plants in a garage bag and disposing of them properly) or with a burndown herbicide to reduce the amount of inoculum being produced. Before doing any of that, be sure to apply a fungicide to the field first in order to reduce the chances of spores moving into uninfected areas. And as always, if you have questions or think you may have LB, please contact Cornell Cooperative Extension.”

This has been an extremely bad year for other tomato and potato diseases such as Alternaria (“early blight”) and Septoria, which can be mistaken for late blight. If you think you have late blight, please contact Cornell Cooperative Extension for a diagnosis. Cornell’s Plant Science Department would like late blight samples to determine the specific strain.

Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.