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Downy mildew of impatiens, basil widespread

Impatiens are usually among the easiest bedding and container plants to grow in the Northeast. Give them some shade, some water, and they look like the photo above, rewarding you with colorful flowers all summer long. But, according to my mailbag, these workhorses aren't doing so well this year. 

After publishing a column recently that addressed a reader's difficulty getting her impatiens to grow this year (they were healthy, just small, and the problem likely was too much sun), about a dozen readers sent me-too emails, but their sympoms seemed more severe.

For starters, readers are reporting that leaves are turning yellow and then falling off their plants. Then, there's the presence of a white substance on foliage, and the bizarre "disappearance" of plants altogether. 

What they're all describing is downy mildew, a disease that only recently has begun to affect impatiens. And it's pretty widespread around here this year.

So, what to do? Sorry to be the bearer of bad news, but you absolutely must pull up those plants; there's no saving them. Bag them tightly in plastic (to contain the spores) and place in the trash. Leaving them in the ground may allow the spores to overwinter in the soil and infect new plants next year.

Downy mildew of basil also is making the rounds this year. It's a serious disease, and if your plants are infected, do not eat the leaves. Rinsing them is not a solution; they must be disposed of. The most noticible symptom is yellow leaves, which could easily be mistaken for a problem with nutrients or watering.

The pathogen can be transmitted from infected seeds, on leaves or via airborne spores. If you're growing basil, go outside, right now, and check your plants, comparing them to the photos below. While you're at it, check in on your coleus, sage, salvia and mint, which also are in the Lamiaceae family and are susceptible, too, as are most curcubits and, of course, impatiens.

I've lost all my potatoes and zucchini this year to other diseases, and I'm not about to risk my basil. Tonight, I'm cutting it all down and making pesto.


The first symptom you'll likely notice is yellowing on the upper side of this leaf.

 

Flipping the leaf over will reveal the pathogen.

For more information and photos of downy mildew of basil, visit Vegetable MD Online

All photos by Cornell University plant pathologist Dr. Meg McGrath.

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