Apologize for the long silence, but been spending many days answering emails and phone calls. Things have been busy at the clinic with many different issues. Unfortunately, there is one that prompted me to write this blog entry.
Several weeks ago, I received a couple of photos of bad looking impatiens. One of those leaves show symptoms which was suspicious of downy mildew. So I requested that a physical sample be sent to the Plant Clinic. Sure enough, we were able to find the water mold (Plasmopara obducens) and the spores on the underside of the leaves. Since then, the Plant Clinic has received at least one other physical sample and several reports of plants with suspicious symptoms. In some email communication this week, I found out from some colleagues that they have notice similar symptoms on landscapes around their areas (an area covering the Dallas-Fort Worth metroplex to parts of East Texas).
So what’s the big deal? – This disease can easily wipe out an impatiens planting or at the very least make it look really bad. And if you find white fuzzies on the underside, you know you got a bad infection. It was kind of surprising to me to find this problem this late in Texas because downy mildews,in general, are associated with mild to cool temperatures. In fact, parts of the US Northeast have reported this problem as early as April of this year. But I guess we are pretty mild in some parts of Texas and night time temperatures are still around 60-75˚F in the Northcentral/northeast Texas area.
So folks, be on the look out for this problem. If you do find them, consider roguing (remove and destroy) the infected plants and clean it up as best you can. This pathogen can survive on plant debris for a considerable period of time. If you need to have it confirmed, you can submit a sample to the Texas Plant Disease Diagnostic Lab (fill out Form D1178).
Good resource link: American Floral Endowment website (http://www.endowment.org ) – there is an article about controlling impatiens downy mildew and a compilation of various online resource about impatiens downy mildew.