What are the control methods for apple tree root rot?

Apple trees often suffer from root rot. Because the root system is buried in the soil, when the disease is initially contracted or mild, it is either not discovered or, once discovered, not accurately diagnosed, so the right treatment is not applied. In mild cases this leads to weak tree vigor and reduced yield and quality; in severe cases it causes the death of the plant, or even the loss of the entire orchard. Apple tree root rot occurs mostly when there is too much rain during the growing season, excessive water content in the soil, poor drainage, compacted soil and little organic matter; orchards with acidic and slightly acidic soil are affected most severely. Planting too deep or piling soil too thickly, damage to the root system during cultivation, or biting by underground pests such as white grubs can easily trigger and worsen the disease. The control methods are:

1. Strengthen cultivation management and identify unfavorable disease conditions

(1) Ensure good drainage. Before the rainy season arrives, dig drainage ditches well, promptly eliminate standing water and excess moisture, lower the groundwater level and soil moisture content, and by no means allow waterlogging to damage the roots.

(2) Turn the orchard soil and apply fertilizer. In September—October after fruit harvest, deep-plow the orchard and heavily apply base fertilizer. Use mostly farmyard manure and green manure that are complete in elements and rich in organic matter, so that compacted, barren soil is improved into loose, fertile soil as quickly as possible, thereby improving the water, fertilizer, air and heat conditions of the rhizosphere soil and creating good growing conditions for the root system.

(3) Apply more lime. In orchards with rather acidic soil, during the growing season, in conjunction with intertillage and weeding, apply an appropriate amount of lime to adjust the pH value to above 6.5, so as to improve the physical and chemical properties of the soil and create an environment unfavorable to the occurrence of the above diseases.

(4) Maintain a reasonable load. Trees with too many flowers and fruits should be thinned properly, and cultivation should be done carefully to protect the root system and root crown from as much damage as possible, so as to reduce entry routes for pathogens and strengthen disease resistance. Do not plant black locust around the orchard; those already planted should be cut down.

2. Deal with diseased plants in time to prevent the spread of the disease

(1) Dig trenches. When diseased plants first appear or only a few are affected, immediately dig deep trenches in a ring around the diseased plant at the drip line, and pour in 5 degrees Beaume lime sulfur mixture, so as to prevent the diseased roots from contacting the healthy roots of neighboring fruit trees and to prevent the disease from spreading.

(2) Clear the roots and disinfect. Dig open the soil of the tree plate and inspect. For severe cases, saw off the completely rotted large roots, scrape clean the rotted cortex and wood of the diseased parts, pick them all up and destroy them in a concentrated manner. After scraping, pour 5 degrees Beaume lime sulfur mixture on the diseased parts and the surrounding soil; after it dries, brush the diseased parts with 2—4 times diluted Fubiqing for disinfection and treatment. If it happens to be the rainy season, take the opportunity to air the roots for 15—20 days, then cover and restore them with pathogen-free soil.

(3) Approach grafting to replace roots. For trees with many rotted large roots, after clearing the roots and disinfecting well, plant three robust rootstocks with well-developed root systems in a triangle along the trunk base. After they survive, graft them onto the trunk by “approach grafting”, using the root systems of the new rootstocks to replace the function of the old rootstock, so as to save critically endangered plants and promote recovery of tree vigor.

(4) Topdress in time. For trees with many rotted large roots, during the disease period, because nutrient absorption, transport and exchange between above and below ground are seriously affected, the tree body suffers from insufficient nutrients. Therefore, after completing the above treatments, promptly spray once with 300 times diluted compound fertilizer solution, and when new roots grow, apply once a topdressing of decomposed human and animal manure and urine water plus an appropriate amount of superphosphate, so as to make up for nutrients and promote new root growth.

These diseases also damage fruit trees such as pear, peach, plum, cherry and Chinese chestnut. The disease period, symptoms and occurrence patterns are much the same as those of apple, and the same methods can be used for control. In orchards with many underground pests such as white grubs, during the occurrence period sprinkle cartap powder into the soil and turn it under to kill them by toxicity, or drench the roots with 2.5% deltamethrin diluted 1000 times with water.