By far, the
most popular flowering plants we sell at The Dees' are impatiens. Because of
this, I need to warn you of a deadly disease that is attacking them this year
called downy mildew. Downy mildew is a very destructive disease leading to the
eventual defoliation and failure of impatiens in the landscape. IT IS NOT A PROBLEM
ON NEW GUINEA IMPATIENS, just the common bedding impatiens, double impatiens,
and fusion impatiens (walleriana varieties).
Downy mildew has been around for a few years but has
hit Long Island hard this year, because we have had a lot of moisture and cool
weather (especially at night), which has made ideal conditions for the disease
• Leaves turn yellow and chlorotic and look like they need to be fertilized
• Infected leaves may be spotted and curl downward
• A white powdery substance may develop on the underside of leaves. These are the spores that go airborne a great distance in a neighborhood and infect other impatiens plants.
• Pre-mature leaf and flower drop, resulting in bare, leafless
Downy mildew is a water mold and requires moisture
to duplicate itself and cause new infections. Impatiens in heavily shaded areas
where leaves stay wet for extended periods of time will tend to have a higher
and more severe rate of infection. Plants in slightly sunnier areas will tend
to have less chance of getting the disease because the leaves dry quicker. It
also helps to have good air circulation around the plants.
As of right now, there isn’t a fungicide to cure
impatiens that have downy mildew--there is only a preventative. If you have any
of the symptoms above, my advice would be to pull all infected plants from your
flower beds or planters and dispose of them completely, making sure not to leave
any portion of the plant in the soil.
The best way to prevent downy mildew is to do the following:
• When you first plant your impatiens, do not overcrowd
them. Leave ample room for growth of the individual
plants, as this allows for better air circulation.
• When watering, try not to wet the foliage. Use a soaker
hose to line the bed, or if you have a sprinkler
system; install bubblers in your beds instead of mister heads.
(Bubblers flood the bed instead of spraying water over the top of the plants.)
• Spray your impatiens with Bonide Copper Fungicide and Ortho Disease-B-Gon (daconil) as a preventative every 2-4 weeks during the growing season. Alternate the use of these products for more effective control.
• Water in the morning to allow the leaves to dry off during the day.
Alternative plants you can use in shaded areas in place
of impatiens include begonias, new guinea impatiens, coleus, lobelia, torenia,
and caladiums. In partial sun, you can use salvia, caliente geraniums, nicotiana,
and new guinea impatiens.
My last few articles have not been very positive as
I have been writing about insect and disease problems you may encounter in your
garden. This is only an attempt to educate our customers so they can protect
the investment they have made in their home landscape. We want you to continue
to have success in your garden. I promise after this "downer" on downy
mildew, I will soon get back to writing about more exciting garden ideas. Many
of my topics come from you, so keep your ideas coming. I really appreciate the
Dees' Nursery & Florist