impatiens downy mildew forecast: too soon to tell

I PRE-ORDER CERTAIN ANNUALS—reserving whole flats of favorites with my local garden center to make sure I won’t get shut out. Normally that early commitment includes a favorite peachy-colored impatiens, but this year, I’m not so sure. Impatiens downy mildew ravaged the popular bedding plant in many parts of the country last year, so I asked Margery Daughtrey, a plant pathologist and senior Extension associate with Cornell University, what the early line is from where she sits in her Suffolk County, Long Island, lab–and some substitutes I might consider for that annual order of mine.

First, a recap of what Impatiens downy mildew (the fungus-like Plasmopara obducens) looks like:

Did your impatiens seem to collapse in 2012? Early signs of infection may have been leaves that looked yellowish, as if the plant needed feeding, or foliage that curled under or seemed to wilt. Sometimes, a white material (the downy mildew) is visible on the undersides of leaves. Eventually, plants may defoliate, drop their flowers, and basically collapse. The fungus loves moist conditions and cool nights in particular. Particularly disturbing: symptoms happened earlier last year than before—as early as June.

The disease, which attacks Impatiens walleriana (the species our common shade-garden choice is bred from) showed up in 2012 first in Florida and later in the Mid-Atlantic, the Northeast, and even Utah and the West Coast. By Daughtrey’s count, 35 states had at least one case of the disease in 2012, and some Canadian provinces as well.

my q&a with cornell’s margery daughtrey

Q. I’ve been watching the trade publication “Greenhouse Grower” for news on impatiens downy mildew, and in a December article, you said that growers are of course well aware of

how-to ornamental plants annuals & perennials pests & diseases state Florida state Utah