​What should winegrowers do for their vineyard after the recent heavy rains that fell in Rio Grande do Sul?

The various vine cultivars planted in Rio Grande do Sul are in the phase before flowering; In some warmer regions and in early cultivars, the presence of open flowers is already observed. In general, continued rain during flowering favors climate change, that is, the fall of unpollinated flowers. Rain, by preventing the expulsion of the “hood” of the flower, ends up preventing pollination. Likewise, physiological disease, which results from the low photosynthesis carried out by the vine leaves, also contributes to the loss of flower buds. The fall of baguinhas results from any factor that reduces the germination of the pollen grain or the fertilization of the ovule. Another factor that can cause flower buds to fall or cause damage to the inflorescence is the mixture of products such as fungicides and foliar fertilizers. Before applying the mixture or new products, the producer must carry out a test on a plant to verify that no phytotoxicity will occur in the inflorescence.

In the current phase of plant development, some fungal diseases become important and, if they are not adequately controlled, serious damage could occur. A anthracnose (smallpox) and excoriosis These are early-cycle diseases that appear on leaves, branches, inflorescences and clusters. The damage caused by these fungi to the leaves causes a reduction in the photosynthetic area, reducing the synthesis of sugars and other substances, as well as their translocation to other organs of the plant. The attack on the inflorescence and the bunch also causes a reduction in production. At this stage, the products recommended for prevention and control are based on the following active ingredients: dithianone, difeconazole, imibeconazole, metconazole or mancozeb.

Other diseases of great importance, especially during periods of leaf wetness, as currently observed, are mildew and gray rot (Botrytis). Downy mildew, also known as mold, can appear on all plant organs, except the trunk and roots. In the aerial part, it causes defoliation, while in the inflorescence and cluster it impairs fruit set and causes the flowers to fall, and can also cause the appearance of black grain and the fall of berries, in addition to making the end of the inflorescence curved, in the shape of a hook. . The phase of greatest susceptibility of the vine to mildew is the flowering phase, however the producer must not neglect other stages of plant development, in order not to compromise production, the final quality of the product and the vigor of the plants for the following harvest. . It is recommended, after the rain stops, as soon as possible, to apply fungicides for prevention and control. Among the suggested products, those based on: cymoxanil + mancozeb, metalaxyl + mancozeb, dimethomorph, famoxadone + mancozeb, fosetyl aluminum, pyraclostrobin + metiram and capitan stand out. Potassium phosphites can also be used alone or in a mixture. In the case of gray rot, caused by the fungus Botrytis, the attack on the flower bud causes it to fall, as the fungus, by infecting the ovary, prevents the cap from being detached from the flower, damaging pollination. Temperatures above 20°C and high humidity are favorable conditions for the attack of the Botrytis. During this flowering phase, spraying with Bacillus subtilis, boscalid + cresoximmethyl, iprodione, pyrimethanil or promicidone.

In vineyards with a history of ripe grape rot (Glomerella), the fungus can infect and colonize the flowers, causing them to fall, or remain in a latent state until the grape matures. For prevention and control, the producer must carry out the first application at the full flowering stage and the recommended products are based on: pyraclostrobin + metiran or tebuconazole, among others.

It is worth mentioning that any pesticide that the producer uses must be applied correctly, that is, the sprayer must have undergone periodic maintenance; nozzles must be in good condition; there should be no leaks in hoses; the pressure gauge must be working properly; the jet must be directed towards the target and the pressure and speed of the tractor must be consistent for uniform coverage, without drift and without environmental contamination. It should also be noted that the application must not be carried out with the aerial part of the plant wet and, above all, the producer must use PPE in good conditions, in order to protect their health and not expose themselves to contamination by the products applied. .