Now through the spring is the time to take a close look at crops that are susceptible to downy mildew so that the disease can be detected early. This post follows the previous one that describes the general identification and biology of downy mildew diseases. Here are some more images illustrating the symptoms on various ornamental crops. 

Downy mildew on impatiens caused by Plasmopara obducens affects all Impatiens walleriana hybrids, but does not affect New Guinea impatiens. (LEFT) Symptoms of impatiens downy mildew often first occur on leaves

Downy mildew sporulation on undersides of leaves and buds (circled)

near the tips of branches.  At first, the top of leaves can develop an irregular yellow-green or purple discoloration.  Affected leaves often curl downwards. Infected plants are often stunted. Leaves and flowers can eventually drop off, leaving a bare stem. The pathogen in wet and cool

Downy mildew on impatiens can lead to severe defoliation and death

conditions can sporulate profusely producing a  fuzzy white mass on the under sides of leaves, stems and flower buds.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Downy mildew on statice ( species) caused by Peronospora statices. (BELOW)  Bluish gray sporulation occurs on undersides of leaves. On upper surface of leaves, infections appear as light green areas that turn yellow, then coalesce, and eventually the leaf dies.

 

Downy mildew on hebe (Hebe species) caused by Peronospora grisea. (BELOW). The disease is usually noticed first by a yellowish discoloration often with purple halos on the lower leaves of the plants. Leaves become curled and distorted. A grayish- brown sporulation may develop on the underside of the leaves. Eventually the affected parts of leaves turn brown and shrivel. Plants can be entirely defoliated and killed.

 

Downy mildew on snapdragon (Antirrhinum majus) caused by Peronospora antirrhini. (BELOW) Young tip leaves are dull green, severely stunted, and roll downward. Gray-purple fungus grows on undersides of leaves. Disease is common on seedling phase; large plants are less frequently attacked. Infected plants fail to produce flowers.