Embrapa Trigo warns of the time to monitor diseases in wheat crops

The wheat crop is in vegetative development in most crops in the South Region. The time is to monitor the crops to better control diseases, especially leaf spots and powdery mildew. The alert is from Embrapa Trigo.

“Look up and look down”, in short, this is the recommendation of Cheila Sbalcheiro, phytopathologist at Embrapa Trigo. Above, to assess weather conditions based on the weather forecast, and below, are the wheat plants that require daily visits to monitor the crop. “Climate is a determining factor in the incidence of diseases. Dry weather will favor powdery mildew and viruses, while humidity will favor fungi and bacteria”, explains Cheila.

According to the phytopathologist (a branch of agricultural science that studies plant diseases), the success of the crop depends on assertive decisions by the producer. Choosing the right pesticide is not enough, you also need to get the right time to apply it and have favorable weather conditions to apply it. “Care for powdery mildew in drier periods and leaf spots after consecutive days of rain requires greater attention from the producer in this initial phase of wheat, as these diseases evolve very quickly and, if not controlled, will certainly impact the final yield. of farming”, says Cheila. She explains that plants need green tissue to ensure productivity, but as fungi cause lesions on the leaves, they tend to compromise the photosynthesis area, limiting the plant's growth and reproduction potential.

Under wheat growing conditions in the Southern Region, the main diseases are leaf spots, powdery mildew, rust and Fusarium head blight. The best alternative to minimizing disease problems starts with choosing the cultivar. “It is necessary to choose cultivars with the greatest set of resistance to different diseases. If this is not possible, try to check the climate forecast to anticipate the risk of certain diseases that year and, also, invest in the diversity of cultivars, considering the greatest possible number of resistances to reduce widespread losses”, advises Cheila.

Fertilizing

Maintaining a balance in nitrogen fertilization can help with crop health. Low fertilization leaves the plant weakened, with little energy to react to the entry of necrotrophic pathogens, which cause the death of leaf tissue, such as leaf spots and bacterioses. On the other hand, excessive nitrogen fertilization accelerates the formation of green tissue, leaving a “full plate” for biotrophic fungi, which parasitize the living tissue of plants, such as powdery mildew and rusts. Excess also increases tillering and can close the plant canopy more quickly, creating a humid microclimate that will favor the survival of fungi and making it difficult for fungicides to reach the leaves in the middle and lower third.

Defensive

The entry of new products into the pesticide market, the improvement of application technology and more resistant cultivars, combined with better producer training and technical assistance have shown better control of diseases during wheat management. However, some problems are still associated with the incorrect use of pesticides, such as phytotoxicity and underdosing.

Mixing pesticides in the tank to save fuel or even using products that are about to expire are still common practices in the field. Formulas, which are often chemically incompatible, are the main cause of phytotoxicity in plants. Even when phytotoxicity does not cause the death of plants, the lesions are entry points for fungi and bacteria that, until then, would not be a problem in that crop: “It is common to find cases of bacteriosis that result from phytotoxicity. The bacteria were in the soil or on the surface of the leaves waiting for an opportunity to enter the tissue. The phytotoxicity caused the lesion and favored the bacteria”, warns phytopathologist Cheila Sbalcheiro.

Underdosing pesticides, in addition to not guaranteeing efficient control, also brings the risk of fungi adapting to the product, meaning that the pesticide will no longer be as efficient in the next harvest.

Gibberella

Fusarium head blight, a disease caused by the fungus Gibberella zeae (Fusarium graminearum), continues to be the main problem affecting ears in crops in Rio Grande do Sul, Santa Catarina and the central-southern region of Paraná. In these regions, the environment with frequent periods of high humidity, rain on consecutive days and temperatures between 24 and 30ºC, increase the occurrence of epidemics.

The fungus that causes Fusarium head blight attacks the ears, compromising the yield and quality of the grains. The period of susceptibility of ears is long, from earing to the final stage of grain filling. When the ear is affected in the early stages, the grain is not formed and most of those that form are lost in the harvesting process because they are lighter. In addition to impacting yield, grain with Fusarium head blight may be contaminated with mycotoxins, which compromise human health and cause digestive complications in animals.

Damage reduction lies in the adoption of less susceptible cultivars, associated with staggering sowing, diversification of cultivars with different earing cycles and use of fungicides that must be applied before climatic conditions favorable to ear infection occur.

Embrapa Trigo coordinates the Cooperative Testing Network, which brings together several research institutions, universities and chemical product manufacturers, aiming to evaluate the efficiency of fungicides (registered or in the registration phase) in controlling diseases in the field, under natural infection, in main wheat producing regions in Brazil. Currently, the tests include powdery mildew, leaf spots, Fusarium head blight and blast.

At the end of each wheat harvest, the results of the research trials are published and made available on the website http://www.ensaioscooperativos.net and serve as guidance for better management of diseases in wheat.