Your impatiens bed seems to be melting away and it could be that it is being taken away by a disease called downy mildew. What was once a lush bed of flowers and foliage is now absent of petals and leaves and just bare stems. Impatiens downy mildew symptoms begin as a light-green yellowing or stippling of infected leaves. Very subtle gray lines or markings are sometimes observed on the top of the leaf. Infected leaves may curl downward at the edges, but generally this is a more advanced symptom of infection. Young plants and immature plant tissues are especially susceptible to infection. As such, leaf symptoms are often first observed on the younger or terminal growth. Seedling cotyledons are also highly susceptible to infection. Plants infected at an early stage of development may be stunted in both height and leaf size, yet may show no visible signs of sporulation if environmental conditions are not favorable for disease expression.
To scout for this disease turn the leaves over and look for a light dusting or coating of white. Severely affected leaves will shrivel and fall off just loaded with disease and spores to keep the infection going. So what happened that impatiens can just seem to die overnight? Well, classic plant pathology teaches us about the disease triangle. In this situation we had masses of susceptible host, the impatiens which is a common bedding plant. Secondly we had a new pathogen, a water mold, a very aggressive water mold, and thirdly and most importantly is the correct environment to favor this disease, which is cool nights and moisture. We had these components come together perfectly for the perfect downy mildew storm. Once you have the disease it’s too late.
Sanitation is key, this disease is highly aggressive and can spread very rapidly, so be sure to remove and destroy infected plants as soon as you find them. Because you can’t control downy mildew in the landscape, you have to look at alternative plants that will do well in the landscape such as begonias and alyssum, petunias and geraniums are also a good choice. Another substitute for color is the New Guinea impatiens which are a tad more expensive, and have a more upright than spreading form; but, they do not get the downy mildew disease. Because we can’t control downy mildew disease, don’t plan on using impatiens in infected beds for a number of years. Research is being done to determine how this disease can best be managed.
I have planted impatiens in the same flowerbed for a number of years. The last couple of years, I have had problems with parts of some plants suddenly wilting and dying. They appear to have been cut at the stem. Sometimes the whole plant dies.
This is probably cutworm activity. By now, the larvae probably have morphed into the adult moth and laid eggs for next year’s feeding. You can place a granular insecticide, such as Sevin, into the soil at planting time to take care of this pest. It is a good idea to alternate your plant species each year to prevent insect and disease problems from developing. Window box plantings, and container plantings almost always use pasteurized, fresh soil each year, which eliminates this problem.
I have several potted impatiens. They were growing great in large pots and cascading over the sides. Lately, they have been getting leggy. The branches are growing straight up, with flowers at the top only. I also have a problem with a pink double impatien. The base of the stems appears to be rotting. The plants are kept in moderate shade, good dirt and not overwatered. What am I doing wrong? (e-mail reference)
A: Impatiens can be cut back to force them to bush out. The plant that is rotting at the base most likely has a soil-borne pathogen. It isn’t anything you are necessarily doing wrong. It just happens sometimes. Consider using a soil drench fungicide, such as Funginex, in the future before replanting.
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Brenda Larson is the Horticulture Agent for North Carolina Cooperative Extension in Lee County.