Leaf Diseases Reduce Nutritional Quality Of Grasses

The long growing season, moderate temperatures, high humidity and mild winters support the growth and survival of pathogenic organisms in coastal BC and the Pacific Northwest. The most important leaf disease in the region is stripe rust in orchardgrass. As the name suggests, stripe rust pustules are arranged in characteristic stripes on the leaves. Outbreaks of stripe rust strike south coastal BC in late summer and fall.

Stripe rust overwinters in BC only in the very mild years. More commonly, it blows in from southern Oregon and northern California on southerly summer winds. Once established, the pathogen prefers warm dry days with 2-3 hours of morning dew on the leaves. Under these favourable conditions the stripe rust fungi can double in number every 4-5 days.

Stripe rust reduces digestibility of orchardgrass and increases both acid (ADF) and neutral detergent fibre (NDF) values. There is a direct correlation between visual severity of the disease and increase in ADF concentration (Fig. 5). Effect on protein content is less pronounced.

Fig 6. Variety differences in resistance to stripe rust.

Farmers can minimize the impact of stripe rust by planting resistant varieties of orchardgrass (contact supplier), planting some land to tall fescue, providing ample fertilizer and water and harvesting soon after the disease appears.

Other fungal diseases are thought to have a similar effect on quality although there is less direct evidence. Tall fescue and perennial ryegrass are resistant to stripe rust but both grasses are susceptible to crown rust and stem rust. These diseases tend to proliferate earlier in the season than stripe rust.

Leaf scald overwinters locally and is favoured by cool humid conditions in spring and early summer. The disease starts with scald-like lesions on leaves that spread and kill off large segments turning them brown