leaf rust

Compared to root and stem rusts, leaf rusts are more likely to cause damage to susceptible species, but in most seasons, conditions are favourable for the disease to occur. In Victoria, severe leaf rust diseases can curtail grain yield by also 20 per cent in affected diversity and alleviate grain quality. Leaf rust is effectively monitored when resistant varieties are grown, but fungicide protection may also be necessary when susceptible varieties are grown.

The recent discovery of new species of leaf rust means that discovery of a new species of leaf rust in Victoria in 2014 increased the importance of the disease, as many important species have low levels. of leaf rust resistance. They are now more susceptible to this new pathotype than the old types.

What can you ask for

Leaf rust is a relatively simple disease to analyze as it forms brownish-orange bumps raised on the leaves' surface. These bumps can be removed from the leaf, leaving an orange-brown mark on the finger.

Scattered pustules on the leaf are circular to oval in shape and are confined mainly to the upper part of the leaf. Later in the season, black teliospores appear on mature plants, usually on the underside of a leaf or leaf blade. These black spores are harmless.

Disease cycle

Leaf rust is involved by the fungus Puccinia triticina.

Like other grain rusts, leaf rusts require an organism to survive from one season to the next. The most important rusts in Australia are volunteer wheat plants that grow in summer and autumn.

Rust cannot be transmitted from one season to another in seed, straw or soil.

Wheat varieties susceptible to leaf rust allow inoculum levels to build on volunteers during summer and fall. This can be a problem in seasons following rainy summers that favour the growth of self-cultivated wheat. Plants heavily infested with rust in the fall provide a source of rust for the new season's wheat crop. If these conditions are followed by a mild winter and a warm spring, the chances of a leaf rust outbreak are high. Therefore, the potential for rust outbreaks is greater after a wet summer.

In Australia, leaf rust reproduces abiotically due to the absence of another species. This reduces the evolution of rust in the field and increases the likelihood that resistant varieties will be effective for a long time.

Rust is wind-blown and can spread over large areas in a short time. The formation of rust epidemics in the crop is favoured by moisture conditions and a temperature of 15-22 ° C.

Administration

Opposite types

The best way to control leaf rust is to avoid susceptible species. When planting resistant varieties and when many varieties of wheat are resistant long-term control can be achieved.

However, leaf rusts sometimes produce new races that can attack resistant species when they are first released. These new races occur when an opportunistic mutation occurs in this fungus that reproduces abnormally. Widespread cultivation of resistant species reduces the environment's rust levels and the emergence of new races.

Growers need to be aware of their variety's resistance to leaf rust.

Traditional methods

Heavy grazing or using herbicides in the fall to remove established wheat will reduce the rust in the following crops. However, if spring conditions are favourable for the development of leaf rust, then even small rusts that survive the fall can spread and cause significant yield losses in the spring.

Seed treatment

There are seed treatments that will prevent early leaf rust infection. Seed treatment is important for susceptible species, especially if sown early or after a wet summer, which promotes volunteer growth.

Foliar fungicides

Several types of fungicides are registered to control leaf rust in wheat. Fungicides should not be considered as a substitute for resistant strains. They have support for when the new rust race is changed and used in places where there is not enough resistance.

Fungicide response is not easy on resistant or moderately resistant species. Earlier in the year, when the rust epidemic began, production was significantly lost. Crops need to be monitored for rust early, as time is critical for effectively controlling rust diseases with fungicides.

Epidemics can explode, and once they get out of control, they can be difficult to contain.

As with other rusts, it is important to apply fungicides early in the outbreak. If severe disease occurs early in the season on susceptible varieties, then two fungicide applications may be necessary.

Rusts that develop after pod emergence are unlikely to impact grain yield significantly.