In recent years, grasses in Manitoba have fallen victim to various stripe and streak diseases, according to Philip Northover, a plant pathologist with Manitoba Agriculture.
Brown stripe and brown leaf streak are caused by the fungus Cercosporidium graminis. The symptoms have been reported on timothy and orchardgrass. Fescues, bluegrasses, bentgrasses and meadow foxtail also could suffer serious damage from brown stripe outbreaks. However, this disease is not of concern on cereal crops.
Brown stripe can develop throughout the growing season, but cool, wet conditions in spring and fall can result in the premature loss of leaves as they die from the tips downward.
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This loss of leaves can cause highly susceptible grasses to mature early, reducing forage quantity and quality. Seed yield and quality are also affected.
In hot and dry years, development of the disease can be reduced or halted until suitable conditions reappear. Cool, wet autumns increase the likelihood the problem will develop should the fungus be present in the field.
The fungus Cercosporidium graminis overwinters in diseased leaves and crop debris. Conidia develop in early spring and are splashed and blown onto healthy leaves.
Initially, the lesions on the leaf blade may be small, rounded brown spots that take on an oval or more elongated appearance as they increase in size.
As the spots extend along the leaf blade, they appear largely brown in colour with a greyish white to light brown centre. In severe cases, the streaks extend to the leaf sheath.
Depending on the species of grass affected and the growth stage, the streaks may appear as narrow bands or wide patches on the leaf surface.
Rows of olive grey to black dots, which are masses of spore structures, appear in parallel rows in the lighter centres of the older lesions. This is characteristic of Cercosporidium infection.
No chemicals are registered to control brown stripe.
The following management practices will vary depending on whether a field is grown for forage or for seed production:
- Plant certified seed of species adapted for local conditions.
- Careful, controlled burning of dead grass in early spring may be warranted if pastures are severely affected. In seed crops, destroying sources of the fungus by burning the field after harvest reduces disease severity in the next crop.
- Heavy grazing in the fall will reduce the leaf tissue available for attack and cut fungus populations for next season.
- Rotate at least two years with non-grass crops, if possible.
- Control weed grasses that could act as a reservoir of the fungus.
Producers should avoid the following:
- Don’t use excessive rates of fertilizers high in quickly available nitrogen. Maintain adequate soil fertility, especially of potassium and phosphorus, based on a soil test.
- Don’t have pure dense stands of a single grass variety. Where practical, seed a mixture of forages. In seed production, this is not practical.
- Do close grazing and clipping. Follow recommended mowing and grazing practices.
- Do not leave a heavy mat of hay on the grass during damp weather.
- Where feasible, plow under cover crops and plant debris cleanly.
