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Green Speak

Horticulture topics from gardens to lawns and then some.

Impatiens Got You Down?

It sure seems like it has been awhile since I posted an entry. Oh wait, it has been awhile! I must keep this up for my following of 2. Hi mom & dad!

I received an email earlier this month regarding downy mildew on impatiens (Impatiens walleriana), which spurred the idea for this article. Impatiens downy mildew has been appearing sporadically throughout the Midwest for the past several years and has been confirmed in most of the Eastern US including Texas and Oregon.

Downy Mildew may be a disease you've never seen before or might be all too familiar with. If this is disease is news to you, let's go over some basic scouting tips for downy mildew on your impatiens. Officially known to plant pathologists as Plasmopara obducens, Impatiens Downy Mildew is a fungus-like pathogen that causes symptoms of yellowish or pale-green foliage, downward curled leaves, leaf distortion, white to light-gray fuzz on leaf undersides, new leaves are small and discolored, flower buds fail to form and defoliation can occur. (Stephanie Porter, U of I Plant Clinic) In other words this disease will leave behind bare stems and no blooms. The perfect environment for impatiens downy mildew is rainy days coupled with cool night temperatures.

For those that have given up on this popular annual, Michigan State University Floriculture has created a great website listing alternatives for impatiens. Click HERE to access their webpage. This is also a great resource for selecting colorful shade tolerant annuals.

For those who have yet to experience impatiens downy mildew or you other dire holdouts, Stephanie Porter with the U of I plant clinic has seven recommendations for protecting your impatiens.

  1. When purchasing all garden impatiens (including double impatiens and mini impatiens), balsam impatiens, garden balsam, or rose balsam (New Guinea impatiens are resistant), be sure that they are in good health and inspect them for disease. Native wild impatiens (jewelweed) is also susceptible to impatiens downy mildew.
  2. Don't plant impatiens too closely together or in heavy shade.
  3. Do not water impatiens via overhead sprinklers (especially at night) and avoid any other conditions that may promote leaf wetness.
  4. Scout for this disease often, especially when the temperatures become cooler (spring or fall). Sporulation and infection will not occur during hot or dry conditions. EARLY DETECTION IS THE KEY!
  5. Remove all diseased plants AS SOON AS POSSIBLE! All infected plants, fallen debris, and roots should be removed and destroyed! DO NOT PLACE DISEASED PLANTS IN THE COMPOST PILE!
  6. Once plants are infected with this disease, there is NO chance of saving them!
  7. There are some fungicides available; however they are used for protection only! They will not "cure" this disease. In addition, the fungicides need to be applied often, so they usually are not an economical or a feasible choice for homeowners. Remember to rotate chemistry to avoid fungicide resistance.

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