Grapevine diseasespose a great threat to crops due to the low amount of registered protection measures for grapevine spraying. Using the wrong type of preservative may contaminate the fruit. For this reasoncombating grapevine diseasesis all about prevention. Systematic protective measures (sanitary pruning, spraying) allow to effectively stop the development of diseases even before the fruit appears. Here are the most importantdiseases of grapevines and fighting themin amateur crops.
Grapevine diseases - downy mildew
Fig. Folini, CC BY 2.5, Wikimedia Commons
1. Grapevine downy mildew
Downy mildewis the most dangerous and most common grapevine disease caused by the fungus Plasmopara viticola. The development of the disease is favored by warm (20 ° C) and humid weather. Thisgrapevine diseaseposes the greatest threat in rainy weather in late June and early July.
Grapevine downy mildewattacks primarily leaves. Less frequently it develops on branches, flowers and fruits.
Symptoms of this grapevine diseaseare young leaves covered with round, olive-brown, translucent, greasy spots. After a few weeks, the stains turn reddish brown. On the underside of the leaf, a white-purple coating is visible on the spots. On older leaflets, the spots form a mosaic image. Infected flowers turn yellow and dry, and berries turn brown and fall off. The disease weakens whole shrubs that cannot hold fruit and becomes less frost-resistant.
Grapevine downy mildew is combatedwith Dithane NeoTec 75 WG or natural Limocide.
Spraying with Dithane NeoTec 75 WG(20g in 8 liters of water / 100m²) is preventive - the first treatment before flowering. In the case of growing sensitive grapevines, especially in rainy summers, the treatments should be repeated 4 times (at 7-10 day intervals).
Spray the grapevine with Limocidepreventively or at the first symptoms of the disease, from the second leaf phase to the end of the inflorescence phase, at intervals of 10 - 14 days. The preparation is dosed in the amount of 2 ml per 1 liter of water. A maximum of 6 sprayings per season can be done.
Grapevine diseases - powdery mildew
Fig. Maccheek, CC BY 3.0, Wikimedia Commons
2. Grapevine powdery mildew
Grapevine powdery mildew , caused by the fungus Oidium tuckeri, is especially dangerous for grapevines grown under cover. However, global warming makes it a greater and greater threat also for vines grown in the field.
The symptoms of powdery mildew in grapevinescan be observed in inflorescences, non-lignified shoots and fruits. A powdery coating appears on the affected parts of the plant. Shoots and flowers darken and die. On the youngest leaves, on heavily infected shoots, they are slightly curly and their edges curl upwards. Yellow-green spots appear on the upper side of the leaf blade, covered with a powdery coating. Older leaves have a silver-gray coating on their entire surface.
Grapevine diseases - powdery mildew
Fig. depositphotos.com
The most dangerousin this grapevine disease , however, is the infestation of young fruit. On their skin there are small, dark spots and cobweb-shaped discoloration. The skin dries up and stops growing, while the flesh continues to grow. As a result, the fruits crack and rot. The cracks in the fruit are very deep, reaching down to the seeds.Infected leaves and clusters give off the characteristic mushroom odor.
Ascombating powdery mildew of grapevines , prophylactic spraying of bushes with sulfur preparations, eg Siarkol 800 SC (27.4-40 ml in 10 l / 100m²) is recommended. We spray the grapevines in May, before the flowering of the vines and repeat them every 7 days throughout the growing season.From 2018, we can also use 2 new ecological preparations to combat powdery mildew in grapevines, which perfectly protect the grapevine against this disease. They are:
- Lecitec - a preparation based on natural lecithin
- Evasiol - horsetail preparation
3. White rot of grapes
White grape rot , caused by the fungus Metasphaeria diplodiella, usually occurs in areas where there is a risk of hail. The disease develops in humid weather at 20-30 ° C on fruit damaged by hail.
Thisgrapevine disease mainly affects berries damagedby hail, birds and wasps. The fruit changes color to a light brown color, wrinkles and dries up. The infected shoots are covered with small, brown spots that spread over its entire surface. Sick shoots dry up and become covered with a brown coating.
Fighting white rot of grapesis to protect the ripening fruit against mechanical damage (eg caused by hail, birds, wasps). Proper agricultural technology is also of great importance, i.e. regular removal of all mechanically damaged parts of the plant. When the first symptoms of this grapevine disease appear, we use preparations recommended for the fight against downy mildew.
Grapevine diseases - gray mold
Fig. Tom Maack, CC BY 3.0, Wikimedia Commons
4. Grapevine Gray Mold
The symptoms of gray mold on grapevinesare most common on ripening fruit, where the disease causes the greatest damage.Berries turn brown and rot. The skin is covered with a gray dusting coating, characteristic of gray mold. Under very favorable conditions for the fungus (i.e. high air humidity)the symptoms of this grapevine diseasemay also appear on the leaves. Large spots appear on the surface of the leaf blade, surrounded by a yellow-green border. The tissue on the stains dries out and turns brown, and a dusty mold bloom appears on its surface.
Fighting gray mold on grapevinesis difficult. The basis of protection is to maintain low air humidity between the grapevines, through the correct cutting of the vines.
In regions with high rainfall (e.g. Małopolska) it is recommendedselection of grapevines with low susceptibility to this disease For both preventive and emergency spraying (after noticing symptoms of gray mold infection), non-professional users can use Switch 62.5 WG. The recommended dose is 12g per 100m² (this amount should be dissolved in 4-10 liters of water).A maximum of two sprays per season can be performed, with an interval of at least 21 days.
5. Physiological diseases of grapevines
Grapevines may also suffer from non-infectious diseases related to improper fertilizationIf the pH is not correct, it can be difficult to get some nutrients from the soil. The pH of the soil recommended for grapevines is 6.5 - 7.2 (slightly acidic to neutral soil). If the pH is right, just apply proper fertilization. In amateur cultivation, it is worth reaching for fertilizers with a rich composition of macro- and microelements, such as Target fertilizer for grapevines with micronutrients.
Yellowing of young vine leaves(leaf blade turns yellow but veins remain green) may indicate chlorosis, a non-infectious disease caused by iron deficiency. Iron chelate or ferrous sulfate are used to supplement this element.Ifolder leaves are yellow and the nerve area is green , magnesium deficiency will be more likely.
Grapevine chlorosis
Yellowing of the leaves with the simultaneous reddening of the petioles and the beginnings of the veins , and causes a lack of nitrogen. In turn, the discoloration of the leaves to a brown-brown color and the accompanying deformation and curling of the leaf edges may indicate a phosphorus deficiency. A brownish-purple discoloration of the leaf edges, followed by their drying out, indicates a potassium deficiency (often accompanied by an excess of calcium in the soil).
Grapevines are very sensitive to inadequate boron content in the soil With its shortage, the edges of the upper, youngest leaves curl up. A mosaic of yellow-green spots is formed on the leaf blade. In turn, with an excess of boron, the edges of the leaf blades turn yellow and become covered with black necrotic spots.
MSc Eng. Agnieszka Lach
