A Detailed Guide to Common Grape Diseases and Their Control Methods

Grape is a common fruit that is well loved by many people. The common diseases of grapes are mainly downy mildew, white rot, anthracnose, brown spot, and so on. Let us take a look below at the control methods for these common grape diseases.

I. Downy mildew

On affected leaves, small semi-transparent, water-soaked spots with indistinct edges first appear on the leaf surface, then gradually expand into pale yellow to yellowish-brown angular lesions of varying size and shape. Sometimes several lesions join together to form large, yellowish-brown, dried-up patches. When the air is humid, a white mold-like growth (the pathogen's sporangiophores and sporangia) appears on the underside of the lesions. Later the lesions dry up and turn brown, and diseased leaves tend to drop early.

When young shoots, tendrils, petioles, and flower-cluster stalks are infected, the lesions are initially semi-transparent, water-soaked spots, then gradually enlarge and become yellowish-brown to brown and slightly sunken. When air humidity is high, a relatively sparse white mold-like growth appears on the lesions. The growth of diseased shoots stops, they become distorted, and in severe cases they die.

When young berries are infected, the lesions are nearly round and grayish-green, with a white mold-like growth on the surface; later they shrivel and drop off. When berries are infected after they have grown larger, mold-like growth generally does not form. When the rachis is infected, it can cause part of the cluster or the entire cluster to drop.

The pathogen overwinters in diseased plant residues or in the soil with fallen leaves. The disease is severe in humid, cool, rainy, foggy, and dewy weather.

Control methods:

Adhere to the principle of prevention being more important than cure: before the disease occurs, especially before the rainy season arrives, pay attention to using protective agents for prevention, such as propineb, dimethomorph, and fluoro-manganese-zinc. When the disease is relatively severe, spray with fluopicolide and propamocarb hydrochloride at an interval of about 10 days, spraying continuously 2 times.

II. White rot

White rot is the most damaging disease and causes the heaviest losses. It mainly affects fruit, new shoots, leaves, and so on, and occurs almost every year. In ordinary years it reduces yield by 15%-20%, and in epidemic years by more than 60%, or even causes total crop failure.

The timing and severity of white rot are closely related to rainfall: if the rainy season comes early, the disease occurs early; if the amount of rain is large, the disease is severe; if the rainy season is long, the disease lasts a long time. After each rain, a peak in disease occurrence appears. In particular, storms or hail often cause major epidemics. The timing and severity of the disease are closely related to cultivation methods: the closer the cluster is to the ground, the more severe the disease. The timing and severity of the disease are closely related to tissue maturity: it cannot occur on young fruit, only when the fruit begins to color and ripen, and the closer to maturity, the more severe the disease. The pathogen overwinters on the soil surface and in diseased plant residues.

Characteristics of white rot:

Brown, irregular, water-soaked lesions appear on the fruit stalk and pedicel and gradually spread to the berries, causing the fruit to turn brown and rot, with small grayish-white granules on the fruit surface. When shaken, diseased berries and even diseased clusters drop very easily. Under humid conditions, the diseased tissue has an earthy, fishy smell.

This disease is a high-temperature, high-humidity disease and spreads by wind and rain. In the rainy seasons of July and August, especially after hail or storms, it very easily causes major epidemics.

Key control points:

Before budding: spray the plants once with 3-5 degrees Baume lime sulfur mixture.

Before flowering: spray propineb.

After flower drop: spray propineb + tebuconazole.

Before the disease occurs, spray protective agents regularly for prevention: tebuconazole, thiram.

When scattered lesions are found, promptly spray curative agents to eradicate them: tebuconazole, thiram + Guomeifeng.

III. Anthracnose

Anthracnose mainly affects the fruit. In epidemic years it easily causes large-scale fruit rot, so that a bumper harvest cannot be gathered. The pathogen overwinters on diseased fruit, cluster stalks, and one-year-old canes. Infection begins at the young fruit stage, but no symptoms are shown. It mainly damages the fruit, causing the fruit to become soft, rot, and drop. Characteristics of the disease: with early infection, the incubation period is as long as more than 20 days, and the disease begins near maturity, entering its peak period at fruit ripening; with infection at maturity, the incubation period is about 4 days; the disease is severe under high temperature, high humidity, and rainy, foggy, or dewy conditions.

Key control points:

Before budding: 5 degrees Baume lime sulfur mixture.

After flower drop: spray propineb or thiram.

Before bagging: spray the fruit clusters separately with propineb + prochloraz, then bag them.

After the young fruit swells: spray propineb and thiram alternately. In dry weather, apply once every 20 days; with heavy rainfall, once every 10-12 days.

After coloring: spray the fruit clusters separately with tebuconazole. Spray the leaves with 70% thiophanate-methyl 1000-fold solution. Once every 10-15 days, spraying continuously 2-3 times. After removing the bags, spray the fruit clusters separately with tebuconazole.

IV. Brown spot

Brown spot mainly affects leaves and causes early defoliation. It generally begins after fruit set, mostly occurring on leaves near the ground and gradually spreading upward. Under suitable conditions, multiple reinfections can occur. The disease is severe when management is extensive, fertility is insufficient, and plants are weak. It mainly spreads by rain splash, generally starting on the lower leaves and gradually spreading upward, causing early defoliation. The disease occurs easily in hot, humid, rainy seasons.

Key control points:

Before the disease occurs: spray general protective agents for prevention, such as mancozeb.

When scattered lesions are found: spray propiconazole for treatment.

When the disease is severe: spray tebuconazole continuously 2 times at an interval of 7 days.