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Become Proactive with Downy Mildew Issues

Proven Profits


Learn about several
great alternative plant ideas here.

Become Proactive
with Downy Mildew Issues

By Ken Dushane, Integrated Pest Management Coordinator

Most growers are well aware of the emergence of Downy Mildew as a threat to Impatiens walleriana varieties, especially since the outbreak has now been documented in more than 30 states. This popular species has been a landscape staple for years.

White spores on the underside of leaves is a key symptom of Downy Mildew.


Our growers are concerned about it as much as we all are at Four Star, because we grow quite a bit of the Rockapulco® Impatiens in our greenhouses. Lately, when growers ask me what my thoughts are about the problem, I say my thoughts haven't changed much from previous years. I feel that Downy Mildew has always been a big concern in general and with recent mass publications regarding it affecting Impatiens in the landscape like it is, we're even more focused on it.

Growing 'clean' plants at Four Star

Because Impatiens is such a popular plant, we still expect consumer demand for 2013, but at a slower rate. We will produce slightly fewer of these plants and increase production of alternatives for Impatiens walleriana in the landscape (see accompanying article "Impatiens Alternatives offer Advantages").

Four Star follows strict cultural practices to ensure clean, healthy plants, including using fungicides preventatively during propagation.

Our growing team continues to take preventative measures to ensure that plants arrive clean and healthy for our customers. During propagation, we take it one step further than many others and apply fungicides preventatively to minimize crop losses and make sure the plants are healthy, vigorous and easy to grow for growers, retailers, landscapers or homeowners.

Loss of foliage is one of symptoms consumers notice first.

Proven Winners® has its own cultural procedures to maintain cleanliness, consistency, and health of all those varieties, which are then supplemented by individual propagators like us. We strictly follow both the Proven Winners and Four Star guidelines.

Growers can be Proactive

Once Impatiens walleriana leave our greenhouse and are in the hands of the grower, it's always a good idea for growers to educate themselves as much as possible about Downy Mildew and have a fungicide rotation planned ahead of time. One of the key factors in disease management is taking preventative measures in terms of cultural practices and chemical control, if needed. By using better watering practices and other cultural practices, growers can help prevent the disease significantly. Want to learn more about these practices? We welcome your inquiries to the contact numbers below.

Downy Mildew Rotation*

1.  Compass O, Heritage, Pageant (Group 11 — strobilurins)
2.  Subdue Maxx (Group 4) — use in a tank mix for better control
3.  Aliette, Alude (Group 33 — phosphonate)
4.  Micora (Group 40 — mandipropamid) — new, effective fungicide from Syngenta

* Rotate modes of action and chemical classes to prevent resistance

An ounce of prevention goes a long way in terms of treating for Downy Mildew. It can easily spread via water and wind, and can affect nearby susceptible cultivars. Proper identification and early detection are crucial to manage an outbreak in the landscape or greenhouse. Other cultural practices that can help include:

  • Minimize watering later in the day
  • Maintain proper air movement
  • Avoid leaving the plants wet for extended periods of time.
  • Know what to look for: Yellowing, curling of leaves, stunted growth, white spores on the underside of leaves, loss of foliage.

Alternative Treatments
for Landscape Beds*

1.  Cease (use preventatively)
2.  Truban (use preventatively on beds)

* Rotate modes of action and chemical classes to prevent resistance

Here's what we recommend if you find Downy Mildew:

  • If you find infected material, discard immediately.
  • Treat with a rotation of products after discarding the material (see below) in the area where you found infected material (if in a landscape). I recommend continuing the treatment into the next season as spores can overwinter and re-establish themselves.
  • Do not plant this variety in the same landscape areas.

Ken Dushane welcomes questions about IPM practices and processes at Four Star. He can be reached at or 734-654-7483.

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