Infections detected in a timely manner can be quickly treated, so gardeners need to regularly inspect fruit crops. One of the reliable signs of grape disease is red spots on the leaves. An accurate diagnosis can be established by examining the damaged bushes in detail.
Causes of redness of leaves
There are several reasons for the appearance of red spots on grape leaves:
- infectious diseases;
- pest infestation;
- lack or excess of certain nutrients;
- uneven distribution of load on the vines.
Important. Reddening of the leaves occurs in colored grape varieties. With the same diseases, spots on white grape bushes usually take on a yellow and brown color.
The nature of redness can be judged by some signs:
- Focal redness of the leaves indicates the infectious nature of the disease (rubella).
- Uniform redness of the green mass may be a symptom of a lack of potassium and phosphorus. And also about an excess of fluorine-containing mineral fertilizers.
- Red spots with the presence of pinpoint bites, cobwebs, and larvae on the reverse side of the leaf are caused by the large distribution of certain insects (leafhoppers, spider mites) that feed on the sap of the plant.
Infectious rubella
A common fungal disease caused by the marsupial fungus Pseudopeziza tracheiphila Muller-Thurgau. It affects the leaves of the plant, very rarely the clusters and stems. The vines and crops suffer due to the death of a large number of leaves in the lower part of the shoots in early spring. Grape bunches on infected bushes are severely delayed in development. The widespread spread of this disease can lead to loss and spoilage of up to 70% of fruits.
The fungus overwinters in fallen grape leaves and on some other plants. In a warm, humid spring, the fungus quickly germinates and begins to spread. The first signs can be noticed already at the end of May; light spots appear on young leaves, which turn red over time (in colored grape varieties).
Usually the first 4-8 leaves are at risk; at the initial stage, the infection looks like mildew. Red spots come from the edge of the leaf, limited by large and small veins.
The optimal temperature for development is considered to be 18-20 °C.In summer, when it is dry and hot, the fungus stops its active spread. At the end of August, in September, with increasing humidity, re-infection occurs, but without serious consequences.
Spider mite
One of the reasons why grape leaves turn red is infection of the plantings by spider mites (Tetranychidae). They feed on the internal pulp through punctures in large veins on the back side. Soon the affected leaves become covered with raised spots, turn red (in white varieties they turn brown) and dry out. Under favorable conditions for life, spider mites multiply quickly (6-10 generations during the warm period) and can cause significant damage to the future harvest. The berries become more sour and smaller, about 20-30% may fall off before picking.
Spider threads can be seen on infected plants. Spider webs make it difficult for chemicals to penetrate, making pest control more difficult. Adults are about 0.5 mm long and require binoculars to see and count them. More than five pieces per leaf are a signal for urgent processing of plants.
Non-infectious rubella
Grapes are very demanding on the composition of the soil and mineral fertilizers. An excess or deficiency of certain elements can lead to a general weakening of the plant and reddening of the leaves. The most common case is potassium starvation of the vineyard. In this case, the green mass turns red evenly over the entire planting area. The second reason may be excess fluorine due to incorrect calculation of the dosage of fluoride-containing fertilizers.
Important. Overloaded vines, with an illiterate calculation of the number of clusters for ripening and uneven garter can also give a signal of weakening reddening of the leaves.
Leaf damage by cicadas
Small insects that resemble grasshoppers can cause significant damage to the grape harvest and are one of the reasons why grape leaves begin to turn red. Grape leafhoppers feed on plant sap at all phases of their development. Adult insects are easy to spot by shaking the bush. Cicadas jump together in different directions.
Dots and yellowish spots appear on damaged leaves, which turn red over time in colored grape varieties. The leaf curls and dries out. In hot, dry weather, the number of cicadas increases rapidly, which can cause significant damage to the crop. In addition to direct damage to plants, cicadas are carriers of infections.
Important. Cicadas do not like the smell of garlic and onions and try to stay away from them. Sowing onions between the rows of grapes will keep pests away.
Consequences
Red spots, regardless of the cause of their occurrence, lead to wilting of leaves and early denudation of shoots. A large loss of green mass affects the quality of the fruit. The sugar content decreases sharply, the grapes crumble before ripening and lose their profitable appearance. Disease of the first leaves in early spring stops the development of shoots and prevents full flowering.
A weakened plant subsequently struggles well with other diseases. Mechanical damage to leaves by pests is an “open gate” for serious fungal and viral infections.
Ways to fight infection
Before deciding what to do about the redness, you need to find out exactly the cause. The different nature of leaf damage requires the use of certain chemicals.
Treatment of rubella
Against infectious rubella, bushes are treated with fungicides in the 3-4 leaf phase. After 7-10 days, the procedure is repeated. Then the treatment is combined with sprays against mildew after another 7-10 days. Medicines for rubella usually provide for the simultaneous fight against mildew: “Ridomil Gold”, “Delan”, “Switch”, “Skor” and others. The bushes are sprayed on both sides early in the morning in dry, windless weather.
Treatment of non-infectious rubella
The fastest way to saturate grapes with potassium is to foliar spray with a complex mineral fertilizer containing potassium sulfate or its other compounds. The first feeding is planned two weeks before flowering.
The second spraying is done a week after flowering. Grapes do not react so quickly to root fertilizing with potassium, but when selecting the composition of a complex fertilizer, you need to add potassium compounds. In autumn and spring, humus is added in large quantities to each bush.
Fighting spider mites
Treatment of red spots on grapes due to the spread of spider mites is carried out by treating the vines in early spring with a 5% lime-sulfur decoction. It is important to do it before the buds swell. During the growing season, ticks are exterminated by spraying with a 1% solution of colloidal sulfur. The drugs Fufanon, Talstar, Omite, and Karbofos have shown themselves to be effective in the fight against spider mites.
The treatment is carried out only on the reverse side, carefully spraying each leaf. The web prevents the penetration of drugs to pests. After 10 days, the treatment is repeated.
Means for combating leafhoppers
Cicadas are controlled with chemicals only when the insects spread uncontrollably.Usually their numbers are controlled by insect predators; sticky traps can be placed. Treating bushes with garlic infusion will help repel leafhoppers. A glass of ground garlic per 10 liters of water. The insects will not die, but will try to move to another place. If the damage from leafhoppers exceeds the norm, the bushes are treated with pesticides.
Well proven:
- “Benzophosphate” (60 g/10 l of water, valid for 2-3 weeks);
- “Confidor” (1.5-2 g per 10 liters of water, valid for 2-4 weeks);
- "Zolon" (valid for 2-3 weeks).
Before cultivating the vineyard, the plantings are thoroughly weeded and heavily damaged shoots are removed.
Important. Cicada larvae are able to feed on the sap of only living plants; after pruning, they quickly die.
Treatment is carried out in spring and summer 2-3 times with a break of 10-14 days. Spraying begins from the lower branches, spraying the solution with fine dust on both sides. Neighboring fruit crops and grass are also treated with an insecticide. A month before the grapes begin to ripen, it is prohibited to treat the bushes with drugs.
Prevention means
All residues after pruning the grapes, as well as fallen leaves, are removed from the site. It is on them that most pests and fungi overwinter. The area occupied by grapes should be kept free of weeds. It also provides shelter and food for pests and fungi.
Bushes weakened due to lack of nutrients react sharply to infection with other infections. Therefore, you need to follow the feeding schedule. In the fall, rotted manure is added for digging. During the growing season, do not forget about foliar potassium fertilizing. Proper pruning and staking of vines will protect the bushes from dampness and poor ventilation. This is the key to success in the fight against fungal diseases.The beds with garlic and onions next to the vineyard are protected from the invasion of leafhoppers.
