Despite all the efforts of breeders, it has not yet been possible to defeat plant diseases and they remain a deadly threat to the vine. The most delicious and beautiful varieties are most affected by diseases.
The most dangerous disease of grapes is mildew, or pernosporosis, downy mildew. It is common wherever there are vineyards, as the pathogen is a fungus that lives on living tissues. It hibernates on fallen leaves and directly in the soil with spores, easily tolerates heat and frost. Germinates at 10 ° C, is transferred to the reverse side of the leaf with wind or rain. There can be up to 20 generations of the fungus per season, and reproduction will stop only with the death of the plant or with a decrease in temperature. The external manifestation of the disease is numerous yellowish spots. The reverse side of the leaf, due to the active reproduction of the fungus, is covered with a bloom of mold, this does not happen in dry weather. On resistant varieties, the spots are smaller, dry quickly and look like punctures with a needle with a dried edge, the leaf has an oily sheen. On the shoots, spots also appear, yellowish and then brown, which tend to become moldy.
The varieties with mediocre taste and high acidity have genes for resistance to mildew, the most serious disease in grapes. The Isabella variety is resistant to this disease, which has a sharp taste, high content of tartaric acid and uncolored, slimy berry pulp. When bad taste is diluted by crossing with good varieties, disease resistance is also diluted.
Therefore, the treatments have to be done constantly, according to the developed scheme and changing the drugs for better efficiency.
Particularly strong lesions are at the tops of the shoots on unstable varieties, then the disease affects both the inflorescences and the newly appeared ovaries of berries. On more mature berries, the infestation appears as bluish-gray, depressed spots under the peduncle. The berries turn brown, shrivel and fall off. This disease can only be prevented by systemic preventive treatments.
For successful use, you need to know the classification of chemicals and remember the timing of their use.
Insecticides are used against caterpillars, aphids, beetles and butterflies, and against ticks, individual preparations are acaricides. Fungicides help against fungal diseases, and herbicides are used against weeds. Contact ones are those that need to get to a harmful object for action. Quasi-systemic drugs accumulate on the surface of the treated plants and are released gradually. Systemic ones penetrate into the cell sap of the plant.
A popular insecticide and at the same time an acaricide is karbofos. It is effective against leaf rollers and other pests, has a continuous toxic effect and is compatible with Bordeaux liquid and acaricides. Application should take place no later than 20 days before harvest.
Bordeaux liquid is a chemical agent based on copper sulfate and quicklime, a contact agent against many fungal diseases and bacteriosis. It is used in the fight against mildew, anthracnose, black rot, rubella, cercosporosis and melanosis. It needs to be prepared just before use, and any grower needs to know how to prepare it. Substitutes for Bordeaux mixture are less effective and often counterfeited, and when stored in improper conditions, they lose their chemical properties and do not work. The treatments must be repeated, since after precipitation the protective properties decrease and come to naught.
