Purple eyespot, or purple spot, is caused by Cladosporium phlei and is the most common foliar disease of timothy (Phleum pratense) in Manitoba.
 

Symptoms

As the name suggests, the main symptoms are circular purple spots resembling eyes. Small, circular purple and later brown spots on the leaves with white to gray-brown centers (See Figure 1) are the most distinctive symptoms.

After a couple of weeks, the purple border fades to a light brown and the leaf tissue turns yellow between the spots. Growth may be reduced in severely affected plants and the leaves wither and dry out from the leaf tip. Death of the entire leaf may occur, in the event of extensive spotting of the leaf, lowering the value of the crop both in terms of seed production and the yield and quality of forage.

Generally, cool, moist, environmental conditions favour the development of the disease, such as Manitoba experienced in May and early June. The spores of the fungus can germinate under a wide range of temperatures, therefore under moist conditions, new infections may occur in the summer.

Purple eyespot is often the most damaging in soils where plants are short of nitrogen, phosphorus, and moisture.
 

Figure 1
Purple eyespot lesions on timothy; note the
purple border surrounding a white-gray centre; note tip is starting to yellow and wither

Figure 2
Range of symptoms
caused by purple eyespot, with leaf tip dying back (upper leaves) and almost death of the leaf (lower leaves)

Cultural Control

The best way to manage this disease is to use resistant varieties, and ones that are well suited to growth in Manitoba. Generally North American varieties perform better against purple eyespot than European cultivars.

For hay production, harvest as early as possible to stop the fungal infection thereby preventing crop loss.

Chemical Control

Chemical control is rather limited, but Tilt^® 250E (propiconazole, PCP#19346) is registered for use against purple eyespot on the Canadian Prairies. It is best applied to the disease at the very early stages of development, if conditions remain favourable for disease development an additional spray may be warranted.

Cladosporium phlei (the cause of purple eyespot) can survive on crop residues, and rotations away from timothy may be an option if this disease is causing significant economic loss. Burning after harvest is an option which will reduce disease severity through reduction of crop debris, however, damage to plant crowns may occur.