Downy Mildew of Grapes
Downy mildew of grapes is a profoundly serious disease of grapes, caused by a fungus that can cause severe damage to the grape crop. The disease is caused by a special type of fungus in grapes called Plasmopara viticola. The disease is found everywhere in the world where grapes grow. This disease of grapes is found especially in those areas, where temperatures are above 11ºC, and rain in the spring-summer session.
Mildew of Grapes Symptoms
Symptoms of Downy Mildew Disease The fungus attacks all green parts of the plant, especially the grape leaves. Harmful spots on the leaves are in two pieces, one yellow color and found between the veins of the leaves. So as the disease progresses, heavy white spots may appear on the underside of the leaves which are the second piece of the disease. Because symptoms of Downy mildew are most likely to appear on the leaves 6 to 8 days after infection. So severely affected leaves fall off the disease. Because young berries of grapes are extremely sensitive, they are also affected by the disease, and eventually, infected grapes berries fall off.
Biology of Downy Mildew of Grapes Pathogen
Plasmopara viticola causes disease by creating both asexual biflagellate zoospores and sexual oospores. The mycelium is aseptate. It belongs to the oomycete family Peronosporales. Related genera like as Bremia, Peronospora, and Sclerospora also contain several important downy mildew diseases. Most taxonomists now place oomycetes in the kingdom Chromista, rather than in phylogenetic groups with ascomycetes or basidiomycetes. In spite of their distinct evolutionary position, oomycetes share many ecological, biological, and epidemiological features with fungal plant diseases.
This obligatory parasite, Plasmopara viticola, has globose haustoria that it uses to draw nutrients out of its living host. Hyphae are often found within the host organism. To reproduce sexually, antheridia and oogonia fuse within the host tissue. It was only recently discovered that Plasmopara viticola is heterothallic. The oospore, the sexual spore produced, serves as the pathogen’s dormant and survival stage. The major inoculum consists of oospores, which can survive the winter in decomposing leaves or be released into the soil when detritivores bury them.
They often begin germinating in large numbers not long after grape buds break, and in some growing zones, oospore populations may continue germinating throughout the whole growing season. The sporangium at the end of an oospore’s solitary germ tube. After developing inside the sporangia, zoospores are then discharged. In order to germinate and invade the plant, zoospores require living, green host tissue with open stomata. Desiccating sporangia or zoospores is a simple task. They can’t survive in dry air or bright light for more than a few hours, so most infections happen right after they’re released. However, under cool humid conditions, they may live on leaf surfaces for more than 24 hours.
Downy Mildew of Grapes Disease Cycle
The fungus survives easily on sick leaves on the ground, with herbs. So in the spring season, when the right environment for the disease is available, it spreads to the leaves and fruits through rain and wind. Because fungi have two types of germs, both of which live on seeds. These germs enter the plant’s respiratory tract and start an infection. Wet weather spreads the disease. Therefore, the spread of the disease begins with the duration of the wet season.
Mildew Treatment Disease Management
- Keep up plant vigor. Make sure the soils have good drainage. Fertilize at least every other year in accordance with the results of a soil test.
- Sanitation. Take out the fallen leaves that contain overwintering inoculum.
- Pruning. Remove the ends of diseased shoots by pruning.
- Fungicides are a crucial control method, especially for cultivars that are vulnerable. Before bloom, at the end of bloom, seven to ten days later, then again ten to fourteen days later, and lastly three weeks after the third treatment. An additional spray is recommended around two weeks before the first bloom opens for cultivars that are more vulnerable to downy mildew or in areas where the disease was problematic the previous season. Pesticides such as captan, copper, fetal-Al, mancozeb, maneb, and ziram have been registered for use.
- Cultivars. Choose resistant varieties and plant them.
Downy Mildew of Grapes Chemical Control
A chemical control method for Downy Mildew of Grapes, both pre-infection and post-infection fungicides is widely used to control downy mildew. If the mildew control spray is used according to the schedule, then shows the best result. The use of fungicide sprays in humid and rainy seasons reduces the potential incidence of the disease. Downy Mildew Disease control through the chemical use of fungicides includes copper-based fungicide spray, Bordeaux mixture is the other solution to control Downy Mildew Disease.
Downy Mildew of Grapes Organic Treatment
To reduce the risk of disease when planting vineyards, choose a place that has not been attacked by mildew before. Have proper drainage arrangements. So the drip irrigation system should be chosen for irrigation. Because the fungus spreads more in moisture. Therefore, the proper arrangements should be made for the movement of air between the vines. To do this, grapevines should be planted in rows where air can pass easily, and the leaves are not wet.
Mildew Cultural Control Practice Method
When planting vineyards the location, drainage, type of irrigation and trellising method should all be considered to minimize the danger of disease. Grapevines should be planted in dry, sunny locations with enough air circulation to prevent the onset of downy mildew. Grapevines should be placed in rows that make use of natural patterns of air movement to assist in decreasing leaf moisture. Few cultural management techniques are available to control downy mildew in existing vineyards.
Trellising methods and pruning can be utilized to regulate the leaf canopy to minimize leaf wetness. Avoid increased humidity and leaf wetness at night to reduce subsequent infection. Where possible, the use of overhead irrigation should be avoided or scheduled such that leaves will dry fast. Reducing leaf litter and trimming may minimize the amount of overwintering inoculum.
Mildew of Grapes Control Genetic Resistance
All Vitis vinifera varieties are at risk from downy mildew, but some are more vulnerable than others. Although the Niagara and Catawba cultivars of V. labrusca are very sensitive to downy mildew of grapes, other North American species demonstrate resistance to the disease. Grapes with improved resistance to downy mildew have been developed through interspecific hybridization between V. vinifera and the North American species. However, wine drinkers tend to choose varietals over hybrids, despite the fact that the latter is sometimes more fruity. The genetic modification of V. vinifera cultivars to increase their resistance to disease is the subject of multiple ongoing scientific investigations.