Apple anthracnose leaf blight: control methods and symptoms from June to August, and specific effective fungicides

When it comes to apple anthracnose leaf blight, many fruit growers get a headache. Because of its short incubation period and rapid spread, once infected and not controlled in time, it takes only three days from infection to leaf drop, causing early and massive defoliation of the trees, reducing fruit quality, and even destroying the orchard. So how do you control apple anthracnose leaf blight? What specific effective fungicides are there?

Recently, apple anthracnose leaf blight has shown a trend of large-scale outbreaks, and it has presented several new characteristics: first, it is spreading from early-maturing varieties to mid-maturing varieties (including the Delicious apple lines); second, it is developing from disease on leaves to disease on both leaves and fruit; third, once it occurs it causes severe defoliation, and it is very difficult to cure with chemicals.

Why is anthracnose leaf blight so hard to control

1. Severe damage

It mainly damages leaves and fruit, causing early and massive defoliation, reducing fruit quality, and even destroying the orchard;

2. Short incubation period

Once infected and not controlled in time, it takes only three days from infection to leaf drop;

3. Long transmission distance

The pathogen spores spread through the air, expanding outward at a rate of 200 kilometers per year;

4. Big differences among varieties

Disease resistance varies greatly among different apples. Gala, Qinguan, and Golden Delicious are susceptible varieties, while Fuji and others are very hard to infect.

Symptoms of apple anthracnose leaf blight

When anthracnose leaf blight first appears, multiple dried lesions are distributed on the leaves. The lesions are initially brown. Under conditions of high temperature and high humidity, the lesions expand rapidly, and in about 2 days they can spread across the entire leaf. In 2-3 days, the leaves of the whole tree can dry up and fall off. The withered leaves are dark in color, mostly dark brown, as if scorched by fire or scalded by water. When environmental conditions are unsuitable, dead spots of varying sizes form on the leaves, the healthy tissue around the lesions then turns yellow, and severely affected leaves soon fall off. When the lesions are relatively small and numerous, the symptoms of the diseased leaves closely resemble those of brown spot disease. On affected fruit, multiple round, brown, sunken lesions 1-2 mm in diameter appear on the fruit surface. Around the lesions, the fruit surface shows a red halo, and the flesh beneath the lesions is brown and spongy, about 2 mm deep. The number of lesions is large, with up to hundreds of lesions on a single fruit. Affected fruit become “pitted fruit”, and the lesions no longer expand. Under natural conditions, spores are rarely produced on fruit lesions, which is clearly different from the symptoms of common apple anthracnose.

When apple anthracnose leaf blight occurs

June to August is the most suitable period for apple anthracnose leaf blight to occur. At this time the temperature is around 30°C, and rainfall is abundant, fully meeting the conditions for the spread, infection, and onset of the apple leaf blight anthracnose pathogen, making it the peak period of disease occurrence. Compared with brown spot disease, anthracnose leaf blight has the characteristics of a short incubation period, a large amount of spore production, rapid onset, fast speed, and a fierce course. There are no small black dots on the lesions. In most cases, the leaves at the base of new shoots on the outer periphery or upper part of the canopy yellow and fall first, gradually developing upward and inward, and in severe cases all the leaves on the tree fall off, leaving only the fruit.

Causes of apple anthracnose leaf blight

1. This year, a large area of the country suffered frost damage and reduced production. Combined with above-average early rainfall, the fruit trees carried a relatively light load and grew vigorously quite commonly, resulting in extremely poor ventilation and light penetration in the tree canopy;

2. Orchards where anthracnose leaf blight occurred in previous years were not completely cured, so the pathogen population is large;

3. Heavy rainfall in spring and summer increases orchard humidity, favoring pathogen reproduction, spread, and infection;

4. Reduced production in frost-damaged orchards led fruit growers to give up management, resulting in inadequate prevention;

5. The earlier frost damage caused some leaves to rot, making them extremely susceptible to infection by various pathogens.

Apple anthracnose leaf blight control recommendations

1. Strengthen agricultural control. Before the rainy season arrives, repair the drainage facilities well to ensure that accumulated water in the orchard can be drained promptly. For densely planted orchards, strengthen summer pruning to improve ventilation and light penetration. After the disease occurs, promptly remove fallen leaves and take them out of the orchard for sterilization treatment, and spray the trees to kill pathogens. Remove diseased fruit early to avoid excessive consumption of tree nutrients. Strengthen cultivation and fertilizer management to improve flower bud quality and strive for a still relatively high yield next year.

2. Spray regularly for protection. Change the mistaken idea that you do not spray until you see disease. Starting in early May, spray pyrazole-type fungicides and complexed mancozeb plus prochloraz, once every 10-15 days, ensuring that before every period of continuous cloudy and rainy weather lasting more than 2 days, both leaf surfaces and branches are under the protection of the fungicide.

3. Pay attention to the quality of the chemicals and the spraying. At present, the agents effective against anthracnose leaf blight mainly include: pyraclostrobin, prochloraz, dithianon (note: there is risk for early-maturing varieties such as Gala), bromothalonil, and other chemical agents, as well as biological preparations such as polyoxin, kasugamycin, and ethylicin (biological preparations are not effective when used alone and need to be used in combination with the chemical preparations above). Some copper preparations, such as nonylphenol copper, quinolinone, copper abietate, and thiodiazole-copper, also have a certain preventive effect when used in advance. In addition, spraying must be meticulous and thorough, not missing a single branch, especially spraying the inner branches and trunk of the canopy, and it should ensure that the front and back of the leaves and the fruit are all evenly covered with the fungicide. At the same time, the higher the degree of atomization of the spray liquid, the better the control effect.