tan spot

 Pathogen

Pyrenophora tritici-repents cause tan spots. The fungus can live and reproduce on wheatgrass. Early in the growing season, ascospores are released from the pseudothecia (small black, raised fruiting bodies that form on wheatgrass) and dispersed by wind or rain. It is the main source of infection of the lower leaves, which are riper during planting and early mixing. After the first infection, the fungus spreads in the field or neighbouring fields by another type of spore called conidium produced by the black spots.

Symptoms of Disease

Symptoms of Pseudothecia Tan usually appear in early April. The disease first appears on the leaves as a small, brown-to-brown lens or diamond-shaped spot. The shape marks are elliptical to long spots of yellow colour, with a dark brown spot near the centre and surrounded by a yellow border. As the lesions increase, they tend to fuse, producing larger, irregular areas of dead tissue. The spots are always small when the leaves are young and actively growing. Where the spots are numerous, the leaves may turn yellow and cause the field to turn yellow. The lower, more mature leaves are infected first, and the virus spreads to the upper leaves as the disease progresses. As the plants grow, the fungus attacks the grass, producing pseudothecia in the fall. In mid-August, pseudothecia appear on the stalks left after harvest, and it is found that it is a black spot. They feel like coarse sandpaper to the touch.

Good Environmental Conditions

Tan spot is favoured by humid weather. Frequent rain in May and June encourages wheat growth and disease development. Spores are spread by wind or rain. The disease progresses very quickly when many spores are present, and rainy, foggy or foggy weather takes more than 24 hours to allow spores to germinate and infect plants. New spores appear with each watering cycle. Symptoms appear five to seven days after infection. Free moisture on the leaf surface is the most important environmental factor related to infection.

Administration

Cultural Practices

A special three-year following method called eco-farming (eco fallow) can be used to reduce the risk of black spots. Eco-farming is a method of crop rotation to control weeds and conserve soil moisture with minimal disturbance of crop residues. In this system, corn or sorghum is sown directly on the stubble of winter wheat during the winter wheat or corn rotation. In the eco-farming system, crops are grown directly on the residues of a different crop rather than on the residues of the same crop. This tillage method effectively eliminates diseases affecting certain organisms, such as the tan spot fungus that lives on crop residues.

Chemical / Pest Control

Foliar insecticides can control spots if the disease becomes severe during the wheat-growing season. Crop inspection should begin at the beginning of the growing season and continue regularly until the disease is detected or a decision is made to spray. It is done according to the observed disease state.