The climate with humid nights and temperatures above normal requires attention to fungal diseases in wheat. Monitoring crops until the end of grain maturation is essential to manage diseases such as leaf rust and Fusarium head blight.
the fungus Puccinia triticina, which causes wheat leaf rust, can attack the green parts of plants from emergence to the final stage of grain maturation. The name is due to the rusty visual appearance, especially on the leaves, due to the appearance of orange pustules. Damage can be greater than 60% in susceptible cultivars.
The rust inoculum (fungal spores) is present in wheat crops every year, as the fungus survives on volunteer plants and the spores can be transported by the wind, bringing the disease from several wheat-producing regions in South America. However, leaf rust becomes a problem when climatic conditions are favorable for the reproduction of the fungus.
The ideal climate for the fungus is 20°C with 3 hours of continuous wetness on the leaves. However, the disease can develop quickly even at temperatures between 10°C and 30°C. High relative humidity also favors the disease, especially if there is dew formation, as the fungus spores need a film of free water on the leaves to germinate and invade the leaf tissues.
Reports of epidemics in Rio Grande do Sul and Santa Catarina are more frequent between the months of August and September. This year, the winter climate (Aug2020), with higher temperatures, interspersed with short periods of cold, show an insufficient scenario for natural control of inoculums in the field.
The best form of control is the use of resistant cultivars, with adult plant resistance (RPA) characteristics. According to Cheila Sbalcheiro, a phytopathologist at Embrapa Trigo, more than 60 races of the fungus that cause wheat leaf rust have been identified, but a cultivar can be resistant to most races and susceptible to just one of them which, under favorable conditions, disease will occur: “Even if there is infection, disease progress will be slow in cultivars with adult plant resistance. The photosynthetic area is little affected and energy expenditure on defense against the pathogen is reduced; This way, the plants’ yield potential is not greatly impaired,” explains Cheila.
In general, the use of fungicides is efficient for the chemical control of leaf rust, as long as they are used at the dose recommended by the product manufacturer. The recommendation is to use the combination of strobilurins and triazoles when the intensity of the disease reaches the economic damage threshold (LDE), as advised in the publication Technical Information for Wheat and Triticale - 2020 Harvest.
The number of applications will occur depending on the susceptibility of the cultivar and the climatic conditions favorable to the occurrence and progress of the disease in the harvest. The interval for reapplication of fungicides must respect the persistence period of the active ingredients used, observing the maximum period of protection to keep the incidence of diseases below the LDE. The last application of fungicides should not go beyond the milky grain phenological stage, as the probability of financial return with application after this stage is very low.
Fusarium head blight is another disease that requires attention in wheat from now on, from heading to grain filling. Caused by the fungus Gibberella zeae, the disease can cause damage to the yield and quality of the grains, since when the ear is affected in the early stages, the grain is not formed, and most of those that are formed are lost in the harvesting process. . In food, grains with FHB can be contaminated with mycotoxins, which compromise human health and cause digestive complications in animals.
To minimize damage from FHB, Embrapa Trigo researcher Maria Imaculada Pontes Moreira Lima recommends monitoring climate forecasts daily: “The occurrence of FHB depends on high rainfall, that is, consecutive days of rain. The temperature between 20 and 25ºC, typical of spring, is an open door for the disease”, warns the researcher, remembering that control with the use of fungicides is not completely efficient, resolving 50 to 70% in combating the fungus. “If it rains right after application, the rain washes away the pesticide and leaves the wheat unprotected again,” says Imaculada.
The research recommendation is to apply fungicide only when there is a favorable environment for infection (see the risk prediction system of SISALERT). In this sense, the application must be carried out before the expected rainfall occurs, so when the rain occurs, the ears must already be protected. The protection period with fungicides (combination of triazoles and strovirulins) is estimated at a maximum of 15 days, when, in the event of new rain forecast, a second application is necessary.
Receive the latest agriculture news by email
Receive the latest agriculture news by email
