Powdery Mildew

Gail Ruhl, Sr. Plant Disease Diagnostician, Botany & Plant Pathology Department, Purdue University

Powdery mildew diseases are prominent this time of year, on many different hosts (Fig 1, 2 Tulip tree) (Fig 3 Maple leaves). Heavy infestations of powdery mildew fungi on foliage can inhibit growth due to limiting the photosynthetic ability of plant leaves and may cause dieback, such as seen on this heavily infected Ninebark (Physocarpus sp) (Figs 4 and 5)).

Fortunately, at this late date in the growing season, plants have already produced the majority of food for the year and late infection by powdery mildew will cause little damage to long-term plant health.

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Figure 1. Tuliptree

Figure 2. Tuliptree

Figure 3. Maple

Figure 4. Ninebark (Physocarpus sp)

Photo courtesy of Ardie Roth

Figure 5. Ninebark (Physocarpus sp)