Ramularia and Target Spot almost did not affect the 21/22 harvest in MT

For a disease to develop, the interaction of three factors is necessary: ​​the host, the pathogen and the environment. In the second cotton harvest in Mato Grosso, sown between the months of January and February, the environmental factor was not favorable for the occurrence of diseases such as Ramularia spot (Ramulariopsis spp.) and Target spot (Corynespora cassiicola), considered the most important aspects of culture.

The early reduction in rainfall in important cotton-producing regions, such as Sapezal, Nova Mutum, Sorriso, Campo Verde and Primavera do Leste, determined the low incidence of cotton diseases compared to past harvests. This brought more peace of mind to feather producers thinking about managing crop diseases. However, the condition did not occur generally in the State, and in some regions the rainy season lasted a little longer, resulting in a greater evolution of the aforementioned diseases.

The results of research carried out in the 21/22 harvest at the experimental stations of the Mato Grosso Agricultural Research Support Foundation (MT Foundation) regarding diseases, were presented during the XIV Cotton Technical Meeting this week, in Cuiabá-MT. The agronomist, doctor in phytopathology and researcher at the institution in the area of ​​Phytopathology and Biologicals, João Paulo Ascari, led the panel 'Cotton Crop Disease Management', with the participation of Fabiano Perina and Luiz Chitarra, researchers from Embrapa Algodão.

“Taking a look back at our research areas, in the 19/20 harvest there was plenty of water available during the cycle, with a favorable microclimate for the greater development of both diseases, reaching a 50% incidence of Target Spot and 32% of Ramularia ”, details the researcher.

According to him, in the 20/21 harvest the scenario was of lower target spot pressure (7%) and Ramulária had a severity of 40%. “But in 21/22 there was almost no occurrence of Target Spot (1%) and Ramularia remained at around 30% severity. We understand that the dynamics of incidence is variable and situations, favorable or not, are different in each region”, he adds.

Tests with site-specific fungicides

To carry out some studies on cotton, the institution participates in the Ramulária Network, which promotes experiments that evaluate the efficiency of fungicides used to control leaf spots and other phytopathogens of the crop.

The evaluation of site-specific fungicides, applied in isolation to control Ramularia, took place in a trial conducted in the Sapezal region, with a cotton cultivar sensitive to the disease, sown on February 2nd (period of heavy rain) and first application at 30 DAE (days after emergency).

“It is important to emphasize that this is not a recommendation for the management of fungicides, but rather a trial with the aim of testing the effectiveness of the products in isolation to find out how much they contribute to controlling the disease”, highlights the specialist.

The results showed that the use of fungicides delayed the evolution of the disease growth curve, which was lower compared to the control without fungicides, with increases only from 105 days after crop emergence. During this period, precipitation volumes were very concentrated in February and there was a sharp reduction from March onwards. In the last harvest, the disease progress curve increased 90 days after sowing with better distributed rainfall volumes until the month of April. Therefore, the lack of water in this harvest hindered the evolution and pressure of diseases.

Multisite fungicide trials

Also from Rede Ramulária, on the same sowing date and time of the first application, the results of experiments with the use of multisite fungicides demonstrated that these products have been a very important tool for controlling Ramularia Spot, with emphasis on the active ingredient chlorothalonil .

“However, the application of multisite fungicides based on chlorothalonil, mancozeb and copper oxychloride promoted increases in productivity when added to the management program”, defines the professional.

Conclusions

According to the researcher, even in harvests like the current one, with unfavorable climatic conditions for the occurrence of both Target Spot and Ramularia, the application of fungicides is essential and must be done preventively at safe intervals, as the pathogen is in the area.

“Our guidance to producers is that they integrate the management tactics we have available, including cultural, chemical, biological and genetic management”, says João Ascari.

Furthermore, the agronomist reinforces that the producer has the preparation, technology and tools at his disposal to manage cotton diseases, but it is necessary to pay attention to the positioning of the products within the application program, always observing the indication regarding diseases occurring in the area to be treated.

New search

During the 21/22 cotton harvest, Fundação MT received reports of the occurrence, in the Sapezal region, of Rhizoctonia solani, which causes seedlings to fall and blight. Researcher João Ascari says that a visit was made to the area, the material was collected and the fungus R. solani was identified, infecting the listed plants.

“This problem is associated with plant losses, can lead to reseeding and directly affect crop productivity. The MT Foundation is conducting field trials and under controlled conditions (greenhouse) to understand the situation and be able to provide management responses for the producer to use in the next harvest”, anticipates the researcher.