Embrapa researcher points out precautions for wheat sowing in the South Region

The frequency of rain has hindered wheat sowing in southern Brazil. Soil waterlogging, in addition to making it difficult for machines to enter the field, also increases the risk of incidence of common wheat mosaic. The forecast of La Niña in the coming months may favor the development of winter cereals, but raises awareness about the risk of late frosts.

The wheat sowing window in the Southern Region runs from May to July, considering regional differences in climate, soil and cultivar cycle. The dates are defined by the Agricultural Climate Risk Zoning (Zarc) with the aim of reducing the risk of crop losses caused by the climate.

In general, producers are in a hurry to implement winter crops with a view to sowing soybeans afterwards. However, sowing wheat in waterlogged areas can cause problems with common wheat mosaic, a disease that depends on free water in the soil so that the vector (a microorganism) can reach the plant's root system and transmit the virus. In most cases, the mosaic occurs in areas with a history of the disease, as both the vector and the virus can remain in the soil for a long time. The incidence and severity of the disease are usually greater in poorly drained fields with water, compacted soils and wheat monocultures. However, in moist soil and with forecast rainfall after sowing, the risk of large areas of crops being affected increases.

According to researcher Douglas Lau, from Embrapa Trigo, mosaic damage is associated with rainfall close to or greater than 200 mm in the sowing month. “The most critical phase is in the days following sowing, when early infection has the potential to cause greater damage to the plants, affecting the development of the forming tissues”, explains Lau. Damage can reach a 50% reduction in grain yield in susceptible cultivars, compromising ear formation in crops such as wheat and triticale. The safest recommendation for producers is to invest in mosaic-resistant cultivars.

Risks with late frosts

Delaying wheat sowing can reduce the risk of losses due to late frosts, since the greatest damage caused by frost occurs during wheat ears and flowering, when, in addition to failures in graining, complete death of the ear may occur. The incidence of late frost can cause damage at the end of July in wheat in the north of PR, in August in crops in the Northwest region of RS, or from mid-September in the Planalto do RS. According to researcher Gilberto Cunha, from Embrapa Trigo, the strategies to avoid the risk of frost are staggering planting, using cultivars with different maturation cycles and following agricultural zoning that guides the best time to implement crops in different regions. from the south of the country.

The CPTEC/Inmet/Funceme forecast for the winter months of 2024 for the South Region indicates favorable conditions for above-average rainfall in the central and eastern part of Rio Grande do Sul, Santa Catarina and southeastern Paraná. In other areas, the forecast is for rain close to and below average, mainly in the north of Paraná. Above-average temperatures are forecast for most of the winter, especially in Paraná. In the center-south of Rio Grande do Sul, temperatures close to average are predicted. The arrival of air masses of polar origin could cause a decline in temperatures in a few days, making it possible for frosts to occur in some locations, especially in areas at higher altitudes.