What Happened to All the Basil We Were Getting?

By Nina Berryman

Another casualty of the wet summer we have been having: the basil. Okay, “casualty” might be too strong a word...it’s not dead, at least not yet. At first glance the basil still looks fine. But upon closer inspection many of the leaves are starting to yellow. Upon further inspection, there is a white fuzzy layer on the underside of most of the leaves. All signs point to… Basil Downy Mildew!

Just like the late blight, which is affecting our tomatoes, downy mildew thrives in wet, cloudy conditions which have been so common this summer. Basil downy mildew was first reported in the US in October of 2007. It reached the Northeast for the first time last year. It has been reported in various countries in Europe, Africa and Asia over the last 10 years or so. Prior to the turn of the millennium though, it had only been reported in Uganda and that was in 1933.

UV-rays can kill the spores of this fungus, but we haven’t had too many sunny days in the last few months. The spores travel by wind and then get deposited on plants by rain. I found one source that said there are no fungicides that can be used against it, and one source that said there are only a few.

One of the other Weavers Way Farm sites (at the Awbury Arboretum) also has the fungus. It was noticed there about one week before it was noticed at Saul. Late blight on the tomatoes also showed up at the other site about one week before it did at Saul. Perhaps because of our higher elevation, or because our site has fewer trees and more wind, there seems to be about a one week delay in disease outbreaks. The farmers at the other site stopped harvesting basil for a couple of weeks and have reported that it seems to be coming back. We will try the same tactic at Saul and hopefully the basil will bounce back. Keep your fingers crossed! Hopefully you all made some pesto and put it in the freezer already!

Sources:
Cornell University, Cornell Horticulture:
http://www.hort.cornell.edu/department/Facilities/lihrec/vegpath/photos/downymildew_basil.htm

Cornell Univeristy, Vegetable MD On line: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html