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Video: Diseases Of Black Currant
How to identify diseases of black currant and fight them for the sake of high yields of this crop
In black currant, the most common and harmful are fungal diseases (mycoses) - spotting (anthracnose and septoria), rust (goblet and columnar) and mycoplasma - terry. They are a serious reason for the weakening of the fruiting and productivity of the bushes of this culture.
Brown spot of currant
Spots are found in almost every garden plot, but the time of their manifestation is largely related to the weather conditions of the growing season. Severe damage to plants by these diseases reduces the assimilation surface of leaves and leads to premature leaf fall in the middle of summer, to a deterioration in the quality (decrease in sugar content) of berries, to a weak growth of annual shoots and a strong weakening of plants. Affected bushes hibernate poorly, reduce immunity to damage by other pests and diseases, as well as to the effects of adverse weather conditions.
Anthracnose (brown spot) is noted on leaves, petioles, young shoots and berries. On the leaves, the fungus forms small rounded spots, on the surface of which black tubercles with sporulation appear: bursting, they take the form of white grains. Light brown dots with a red border are fixed on the berries. Anthracnose causes early leaf fall and the death of young shoots. The disease develops strongly in the second half of summer. Intensive development of the disease is characteristic of a rather humid summer with low temperatures; in seasons with hot and dry weather, the disease develops weakly.
In black currant, the varieties Belorusskaya Sweet, Golubka, Imandra-2 show the greatest resistance to brown spotting. It should be noted that all types of currants are also affected by this disease, and gooseberries are much weaker.
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By Septoria (white spot) affects the leaves, stems and berries. At the beginning of the disease, small rounded spots of a bright brown color appear on the leaves, which expand and merge with severe damage. Later, lightening of these spots is observed (but with the appearance of a dark brown border), in the center of which (on the upper side of the leaf) small black dots are clearly visible - fruit bodies with spores: with their help, the fungus propagates. On the shoots there are elongated spots of the same color; over time, they crack and deepen, resembling ulcers in appearance. Flying away, spores infect more and more new leaves and shoots. Fruits are affected by septoria shortly before ripening: small, depressed brown specks appear on the berries.
White spot is especially harmful in seasons characterized by high temperatures and humidity in the spring and summer, as well as in thickened plantings. If weather conditions favor the development of the disease, yield losses can exceed 50%.
There are no black currant varieties resistant to septoria blight, while Belorusskaya Sweet and Yunnat varieties are characterized by a lower susceptibility. There are varieties of currants showing complex resistance or low susceptibility to both mycoses: Pamyat Vavilov, Binar, Veloy, Poetziya, Heiress and Detskoselskaya … Red currant suffers from septoria weaker (less often gooseberries are affected).
Measures to combat currant spots are the same. To prevent them, it is required: to maintain the optimal distance between the plants, to prevent thickening of the bushes (to thin out and remove the affected and damaged shoots) and timely destroy the weeds that create high humidity in the bushes.
To increase the resistance of plants in the spring, it is recommended to apply complete mineral fertilizer together with microelements (0.6 g of zinc, copper, manganese sulfates per 1 m²) with incorporation into the soil. Plant immunity can also be increased by spraying the leaves in June (foliar dressing) with a solution of a mixture of fertilizers (1-2 g of copper sulfate, 2 g of boric acid, 5 g of manganese sulfate, 3 g of zinc sulfate, 3 g of ammonium molybdate per 10 liters of water) or already finished preparations containing trace elements (you need to carefully monitor the preparation of the solution concentration in order to prevent burns of young leaves). In the fall, to reduce the stock of wintering infection, fallen leaves are composted or, when digging the soil under the bushes, they are stratified with earth.
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Goblet currant rust
Goblet rust appears on the leaves, petioles, flowers and ovaries of currants, on which orange-yellow pads with goblet depressions are formed. This disease is interesting in that it develops on currants in the first half of summer, and then seems to disappear: it changes the owner and passes to sedge, which grows on swampy or highly moistened soils. Despite this "migration", goblet rust is very harmful to currants and in the years of epiphytoties causes a strong leaf fall and a large damage to the ovaries, which leads to the loss of a significant part of the berry harvest. The disease also affects red currants and gooseberries.
Columnar rust affects only currant leaves: chlorotic spots are visible on the upper side, orange pustules on the lower side, which can densely cover the leaf blade by the end of summer. Affected leaves turn brown, dry out and fall off prematurely. The massive development of the disease is noted during the period of flowering and the formation of ovaries (especially in warm and humid weather). The fungus is able to successfully winter on leaves under a 5-7 cm layer of earth.
To reduce the prevalence of these types of rust, the use of the same agricultural techniques as for the control of spots helps. In the summer, it is possible to use three times spraying of the bushes against the pathogens of anthracnose, rust and septoria - this is before flowering - the most important treatment; immediately after flowering, but no later than 20 days before harvesting the berries; after harvesting fruits with a 1% solution of Bordeaux mixture, the versatility of which also lies in reducing the harmfulness of pathogens of many other fungal and a number of bacterial diseases.
Terry black currant
Terry black currant is the most dangerous, very harmful disease. In the north-west of the country, it causes significant damage to black currant plantings, "mowing" almost all the most common high-yielding and good-tasting varieties.
The disease is easily recognized by diseased (modified) flowers. The affected flowers become, as it were, transparent (from white-yellow to purple), ugly, double and fall off before the formation of fruits. In diseased plants, the appearance of narrow, small leaves with few veins is also observed, which makes the leaf appear wrinkled.
Often, young leaves from five-lobed become three-lobed, acquiring a dark green color and losing a specific smell. Lateral buds do not form flower brushes, but vegetatively thickened shoots. Diseased bushes degenerate: they become sterile or are characterized by a significant decrease in the yield of berries.
The causative agent of the disease spreads with planting material; the carrier of mycoplasma is the kidney currant mite.
Sometimes terry is called "reversion"; this name is associated with two characteristics of the disease: firstly, it means a condition in which the distinctive features of the leaves change (the whole bush looks like it has returned to the appearance of its wild ancestors), and secondly, in some years the disease is, as it were, masked (not appears for a year or two), then returns again (“reversed”).
Currant varieties are characterized by unequal resistance to terry and fruit mites, but, in my opinion, it is advisable to select varieties on a personal plot mainly according to the first indicator. It is known that black currant varieties Odzhebin, Altai, Vystavochnaya, Leningrad giant, Izmailovskaya are affected by terry and mites to a strong or medium degree.
The black currant variety Doveka is resistant to terry, but is damaged by a tick. The varieties of black currant Pilot A. Mamkin and Belorusskaya Sweet are weakly susceptible to ticks (and to fungal diseases); varieties Vologda and Volodinka are not resistant to ticks.
Although the listed varieties are not bad varieties in terms of their basic qualities, gardeners should take these characteristics into account for their resistance to these harmful objects. To increase the resistance of plants to this mycoplasma disease (also to limit it), experts recommend adhering to the rules of high agricultural technology: apply potash fertilizers, observe the correct watering times, and treat the soil in a timely manner. You should purchase only healthy planting material, beware of buying it from random people. It is impossible to harvest cuttings from tops, basal shoots and bushes affected by a tick.
Sometimes the fight is carried out with the tick itself in early spring: by plucking out the swollen buds inhabited by this pest. Pruning plants under the root (under the "stump") before budding can give a positive effect in the fight against currant mites, but it does not allow saving an already infected bush from terry and thus getting away from the pathogen itself. Plants heavily affected by this mycoplasmosis must be uprooted and burned; at the same time, crop rotation should be observed: it is recommended not to plant new bushes in the same hole, but to retreat at least a meter or to occupy this area with another agricultural crop.
Candidate of Biological Sciences,
Senior Researcher, All-Russian Research Institute of Plant Protection,