Red spots on grape leaves: why, causes and what to do for treatment

Timely detected infections can be quickly treated, so gardeners need to regularly inspect fruit crops. One of the reliable signs of grape disease are red spots on the leaves. An accurate diagnosis can be established by examining the damaged bushes in detail.

Causes of leaves turning red

There are several causes 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 varieties of colored grapes. 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:

1. Focal redness of the leaves indicates the infectious nature of the disease (rubella).
2. Uniform reddening of the green mass can be a symptom of a lack of potassium and phosphorus. And also about the excess of fluorine-containing mineral fertilizers.
3. Red spots with punctate bites, cobwebs, larvae on the back of the leaf are caused by the large spread of some insects (leafhoppers, spider mites) that feed on plant sap.

Infectious rubella

A common fungal disease caused by the marsupial Pseudopeziza tracheiphila Muller-Thurgau. It affects the leaves of the plant, very rarely 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 already in early spring. Grape clusters on infected bushes are far behind in development. A large 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 warm, humid spring, the fungus germinates quickly 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 sheet, limited to large and small veins.

The optimal temperature for development is considered to be 18-20 °C. In summer, in dry and hot times, the fungus stops its active spread. At the end of August, in September, with an increase in humidity, re-infection occurs, but without serious consequences.

Spider mite

One of the reasons why the leaves of the grapes turn red is the infection of plantings with spider mites (Tetranychidae). They feed on the inner pulp through punctures on large veins on the back side. Soon, the affected leaves become covered with convex spots, turn red (turn brown in white varieties) and dry out. Under favorable conditions for life, the spider mite multiplies rapidly (6-10 generations during the warm period) and can cause significant damage to the future crop. The berries become more acidic and smaller, about 20-30% may fall off before picking.

Spider webs can be seen on infected plants.The web makes it difficult for chemicals to penetrate, making pest control more difficult. Adults are about 0.5 mm long, using 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. The green mass in this case turns red evenly over the entire planting area. The second reason may be an excess of fluorine due to incorrect calculation of the dosage of fluorine-containing fertilizers.

Important. Overloaded vines, with an illiterate calculation of the number of clusters per ripening and uneven tying, can also signal weakening by reddening of the leaves.

Cicada leaf damage

Small insects resembling grasshoppers can cause significant damage to the grape harvest and are one of the reasons why the leaves of the grapes 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. The leafhoppers jump together in different directions.

Dots and yellowish spots appear on damaged leaves, which eventually turn red in colored grapes. The leaf curls and dries up. In hot, dry weather, the number of cicadas grows rapidly, which can cause significant damage to the crop. In addition to direct damage to plants, cicadas are carriers of infections.

Important. Leafhoppers do not like the smell of garlic and onions and try to stay away from them. Planting 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 exposure of shoots. A large loss of green mass affects the quality of the fruit. The sugar content is sharply reduced, the grapes crumble before ripening, and lose their profitable appearance. The disease of the first leaves in early spring stops the development of shoots and prevents full flowering.

A weakened plant does not fight other diseases in the future. Mechanical damage to leaves by pests is an "open gate" for serious fungal and viral infections.

Ways to fight infection

Before you decide what to do with redness, you need to find out exactly the cause. The different nature of leaf damage requires the use of certain chemicals.

Treating rubella

Against infectious rubella, bushes are treated with fungicides in the 3-4th leaf phase.After 7-10 days, the procedure is repeated. Then the treatment is combined with mildew spraying after another 7-10 days. Rubella preparations usually provide for the simultaneous fight against mildew: "Ridomil Gold", "Delan", "Switch", "Skor" and others. Bushes are sprayed on both sides early in the morning in dry, calm weather.

Treatment of non-infectious rubella

The fastest way to saturate grapes with potassium is to carry out foliar spraying with a complex mineral fertilizer containing potassium sulphate or other compounds thereof. 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, potassium compounds must be added. In autumn and spring, humus is applied in large quantities under each bush.

Fight against 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 have time before the swelling of the kidneys. During the growing season, ticks are exterminated by spraying with a 1% solution of colloidal sulfur. The drugs "Fufanon", "Talstar", "Omayt", "Karbofos" showed themselves well in the fight against spider mites.

Processing is carried out only on the reverse side, carefully spraying each sheet. The web prevents the penetration of drugs to pests. After 10 days, the treatment is repeated.

Means for the fight against leafhoppers

The fight against leafhoppers with the help of chemicals is carried out only with the uncontrolled spread of insects. Usually their numbers are controlled by insect predators, sticky traps can be set. Processing the bushes with an infusion of garlic will help scare away the leafhoppers. A glass of ground garlic in 10 liters of water.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.

Performed well:

• "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);
• Zolone (valid for 2-3 weeks).

Before cultivating the vineyard, the planting is carefully weeded from weeds and heavily damaged shoots are removed.

Important. Leafhopper larvae are able to feed on the juice 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 starts from the lower branches, spraying the solution with fine dust from both sides. Neighboring fruit crops and grass are also treated with insecticide.A month before the start of grape ripening, it is forbidden to treat the bushes with drugs.

Means of prevention

All residues after pruning grapes, as well as fallen leaves, are removed from the site. It is on them that most pests and fungi hibernate. The area occupied by grapes should be kept clean from weeds. It also provides shelter and food for pests and fungi.

Weakened due to lack of nutrients, bushes react sharply to infection with other infections. Therefore, you need to follow the feeding schedule. In autumn, rotted manure is brought in for digging. During the growing season, do not forget about foliar potash top dressing. Proper pruning and garter vines will protect the bushes from dampness and poor ventilation. This is the key to success in the fight against fungal diseases. Beds with garlic and onions next to the vineyard are protected from the invasion of leafhoppers.

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