Impatience a No-no for 2013

[lavender]

A number of gardeners lost impatience last year to downy mildew (Plasmopara obducens) . The problem wasn't recognized early enough to deal with it because this mildew is not common in northern gardens. It came in on impatience grown in the south. Although the spores shouldn't overwinter in northern climates there is a type of encapsulated spore that may winter over in garden debris. The various county extension services in affected areas are warning against growing impatience in the same soil in which they were planted last growing season if they were lost to downy mildew. 

 

Most other plants can be safely planted in the soil although other plants may be susceptible to this type of mildew. Pansies and sunflowers are two that are commonly mentioned.  There doesn't seem to have been much research done to identify the downy mildew that affects other plants as being the identical strain that so devastated impatience. There are a lot of "expert" opinions. There is no anecdotal evidence that it spread to other garden plants that I have heard.

 

The new Guinea impatience are resistant to downy mildew as are SunPatiens

[Petee]

This fungus has been around for years but never attacked with the deathly results of 2012.  It's here folks, and it's not going away.  Fungicidal sprays are labor intensive and may not work.

 

People are being urged NOT to grow IMPATIENS this summer.  Nurseries are also being asked not to grow or stock it but my guess is that some won't listen because they want the money.  Some will resist because they want to preserve their good reputations as not selling plants that quickly die.  It's a close situation to Late Blight and it's incidence was increased by bringing plant starts up out of the south.  Grow your own plants to begin with.  Fewer diseases will be brought into your garden.

 

There are substitutes such as New Guinea Hybrid Impatiens for that same form and color.  Hybrids are being developed to resist this fungus but as in Late Blight, till more resistant plants are actually grown and tested you will have to risk infecting your soil by buying Impatiens or spray regularly to try to protect them.  Once your potting soil is infected then don't use it again in pots.  Several cold winters will have to occur before you can be fairly sure that it had died out of your soil.

 

Remember that if it does develop in your garden, you'll be blessing the downwind neighbors with it too.

 

Late Blight can travel many miles before it lights in a garden.  I'm guessing this fungus will be able to do it as well.  Just don't grow Impatiens till more research is done to find out how to fight it. Stop it at the source.

 

Here's a Penn State link with more information:  http://extension.psu.edu/plants/green-industry/news/2012/alert-whats-up-with-the-impatiens-this-year

 

Another one from Cornell:  http://www.gardensalive.com/article.asp?ai=1211

 

The really bad news is that it can travel to a few other plants but they're not sure of how many yet.   

[lavender]

Don't dump soil from pots that contained infected plants in your yard or compost heap. Bag it in plastic and put it out in the sun. Better still, if you can, send it to a landfill where it will be buried deep. Do the same with all infected plant debris and use good garden hygiene. 

Since it is being suggested that this particular strain of downy mildew can live more than 5 years in the soil in its encapsulated form anyone who has only a small patch of ground might try solar sterilization of the soil. This is a technique that works quite well on weeds and weed seeds. I've tried it and been pleased with the results. It also works on nematodes and other bugs that live in the soil. How effective it might be with downy mildew is anyone's guess at this point but research has proven it to be effective on fusarium and verticillium wilt.

Dampen the soil if it is very dry. Cover it with clear plastic. A double layer or bubble wrap works best. The soil temperature should reach a  temperature near 100 degrees F  fir from 3-8 weeks.

In our area this is probably most effective in the middle of summer.  So if you are having soil based problems year after year it might be worth the time and trouble to try this. We certainly have been plagued by plant and windborne diseases in the last few years. Probably some of it is because of our warmer winters. Our climate is becoming more hospitable to pests from the south.