Wednesday, August 5, 2015

A downy mildew resistant basil?

This is a guest post by Montgomery County MG Mary Anne Normile.


I've had basil crops devastated by downy mildew for the last few years, so I was excited when I saw seed catalogs offering the basil variety ‘Eleonora,’ which is purported to be partially resistant to basil downy mildew (BDM). I started a packet of Eleonora seeds in the spring and distributed the seedlings to several gardeners in the Derwood demonstration garden to get a sense of how this variety performs.

Until last week ‘Eleonora’ had appeared to live up to its billing. I had seen no evidence to date of basil downy mildew in the plants in the 100 Square Foot Garden, where they are closely planted, or in other garden locations, where they are more widely spaced.

Eleonora is a Genovese-type basil, described as “spicier” than other Genovese basils. I made one good-sized cutting of my own plants and made pesto, which I can report as tasty as any made with Genovese basil. Any spiciness, if it exists, doesn’t seem to be a bad thing in pesto. After the cutting, the plants had been growing back nicely, and were just about ready for a second (small) cutting.

However, last week I saw the beginnings of BDM on a few of the Eleonora plants on my deck at home. They are in planter box containers, and, while they were not very widely spaced, I tried to give them good air circulation, as the planting directions advised. Basil downy mildew begins as a slight yellowing of the leaves with fuzzy gray patches on the underside, which are the spores.



As the disease progresses, the undersides becomes covered with the gray spores and the leaves eventually turn brown and drop off. The BDM on my ‘Eleonora’ plants seems spotty, and does not appear to be devastating the plants, or at least not yet. I'll keep an eye on them to see if the disease progresses, or whether they can tolerate a little BDM.

Other gardeners at the Derwood demonstration garden report that the ‘Eleonora’ plants they have grown in the demonstration garden, their community garden plot, and at home show no BDM to date. One gardener reported that the plants seemed to bolt early, but attributed that to the extra heat on her full-sun front steps.


Meanwhile, we have already lost the Thai basil ‘Siam Queen’ in the 100 Square Foot Garden to BDM, while the purple basils ‘Purple Petra’ and ‘Purple Ruffles’ remain BDM-free.

Erica adds: Sweet Dani Lemon basil also succumbed to BDM this week. Read more about BDM on the GIEI website here.

Addendum: Mary Anne reports now that BDM is advancing on the plants on her deck. Photo:


She says:

Again, this is anecdotal, and the fact that others have not seen BDM yet may mean that it does a better job at resisting than what my experience shows. It could just be that the growing conditions on my deck are conducive to BDM flourishing.

Maybe the moral of the story is that, where basil downy mildew is concerned, there is no magic bullet--so far. (Sigh)

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