DISEASES OF BARLEY
1. Stem rust — Puccinia graminis f.sp. secalis
The disease is recognized by pustules, (blister-like spots), that break through the surface of stems, leaves, and leaf sheaths, and often of the chaff and beards. In severe attacks, the kernels are badly shrivelled. Rusted stems turn brown, become dry and brittle, and soon break over.
Mode of spread and survival
The Pathogen is airborne conidia. Rust survives on the stubble and straw of barley, wheat, and rye as black, thick-walled, cold-resistant spores.
The disease is favoured by the spring and summer and may produce successive crops of red spores every 10 to 14 days until growing conditions become favourable.
- To adopt cultural practices.
- Avoid heavy applications of Farmyard manure or nitrogen fertilizer.
- Four sprays of zinab @ 0.2% at fourth night interval.
2. Covered smut — Ustilago hordei
This disease first becomes noticeable at heading time. Hard, black masses of smut spores, each covered with a greyish membrane, are found in the place of kernels in affected heads. Each smutted head contains millions of tiny spores which are spread to healthy seeds while the grain is harvested or in storage. The barley seedling becomes infected between germination and emergence from the soil
Mode of spread and survival
- The Pathogen is seed-borne and through airborne conidia.
- They survive in soil in dormant for many years.
The highest percentage of infection occurs at soil temperatures of 22 to 25o C during pre emergence. More smut develops in plants grown in acid soil than in those grown in neutral or alkaline soil.
Covered smut may be controlled by treating the seed with an appropriate systemic seed protectant fungicide.
3. Powdery mildew —Erysiphe graminis f.sp. hordei
The first infection is small, white or light-gray spots of cottony threads on the upper surface of leaves. The spots enlarge, darken, and become powdery with age as they produce millions of spores. Eventually, the spots may cover large areas of the leaf. A yellowing, followed by browning and gradual drying of the leaf usually accompanies this process. Severe attacks may be found on stems, glumes, and awns. As the plant approaches maturity, tiny, black reproductive bodies of the fungus develop in infected areas.
Mode of spread and survival:
The pathogen is soil and air-borne and survives in infected leaves.
- Dusting sulphur at 25 kg/ha
- Growing resistant varieties.
4. Barley stripe mosaic — Barley stripe mosaic virus (BSMV)
The symptoms of stripe mosaic vary with the barley variety, the strain of the virus, and seasonal conditions. The virus may cause brown stripes in the leaves but the most frequent symptoms are bleached, yellow or light green stripes, light green to yellow mottling and sometimes an almost complete yellowing of the leaves. Plants become severely stunted. Sometimes symptoms do not appear in the upper three or four leaves, although the virus is present in them.
Mode of Spread &Survival
- Infection is spread from the grass reservoirs to oats and aphids.
- The virus survives between growing seasons in grasses which persist through the summer.
BYDV is always more severe following wet summers when aphid survival and build-up has occurred, because of the role of aphids in establishing infection.
Roughing and vector control helps to reduce the incidence. Also volunteer plants/weeds should be eradicated to reduce the inoculums.