Detailed Explanation of Key Techniques for Summer Management of Plum Trees
1 Summer pruning
1.1 Bud rubbing and shoot removal. Removing buds immediately after they sprout is called bud rubbing; when the sprouted buds develop into tender shoots, cutting or pinching them off is called shoot removal.
1.2 Pinching. Pinching can be done when new shoots grow to 10~15 cm. The number of pinchings depends on the tree's vigor and requirements.
1.3 Twisting shoots. The best time for twisting shoots is when new shoots have grown to 30 cm and have not yet become woody; gently twist the upward-growing branches, competing branches and inward-growing branches 180° at a point 5~10 cm from the base.
1.4 Bending branches. In July, bend one-year-old upright branches and competing branches by hand from the base of the branch, then bend them upward along the branch every 5 cm until the tip.
1.5 Girdling. Carry out when growth is about to stop; make a ring of bark removal on the trunk or large branches of vigorous trees, with the width of the removed bark about 1/10 of the diameter of the shoot being girdled, giving an obvious flower-promoting effect.
2 Flower and fruit management
2.1 Flower thinning. For fruit trees with weak growth vigor and a large number of flowers, thin more and keep fewer; for those with strong growth vigor, thin less and keep more.
2.2 Fruit thinning. Keep 1~2 fruits per flower-spur branch, keep 1 fruit on short fruit branches (short fruit branches with few leaves may keep no fruit), keep 2~3 fruits on medium fruit branches, and keep 4~5 fruits on long fruit branches;
3 Fertilizer and water management
3.1 Topdressing before flowering. About 10 days before plum trees sprout (early April), apply 0.5~1 kg of quick-acting nitrogen fertilizer or 25 kg of decomposed human manure per tree.
3.2 Topdressing after flowering. Quick-acting nitrogen and potassium fertilizer should be applied in time to reduce physiological fruit drop; from late May to mid-June, apply 0.5 kg per tree.
3.3 Topdressing during fruit enlargement and flower bud differentiation. From after physiological fruit drop until before the fruit enters the rapid enlargement stage (late June to mid-August), apply a quick-acting nitrogen, phosphorus and potassium compound fertilizer, 0.5~1 kg per tree.
3.4 Topdressing in the late fruit growth stage. Apply fertilizer from when the fruit begins to color until before the harvest period. This time, phosphorus and potassium fertilizers are the main ones; quick-acting nitrogen fertilizer is best applied as a foliar spray at a concentration of 0.2%~0.3%, together with pesticide spraying.
4 Pest and disease control
4.1 Plum red spot disease
4.1.1 Spray 1:2:200 Bordeaux mixture before the plum tree flowers and when the leaf buds unfold.
4.1.2 Remove diseased leaves and diseased fruits from the plum orchard and destroy them centrally.
4.2 Control of plum gummosis. Scrape off the gumming area, then apply 5 degrees Beaume lime sulfur mixture, and finally apply a white lead oil protective agent.
4.3 Plum fruit moth
4.3.1 In spring, turn over the tree to destroy the overwintering sites of larvae and reduce the number of overwintering insects.
4.3.2 During the peak hatching period of plum fruit moth larvae, spray with 5% fenvalerate EC at 2000~4000 times dilution or 40% triazophos EC at 1000 times dilution.
4.4 Aphids
4.4.1 In spring, before the damaged leaves curl, spray with 2.5% cyhalothrin EC at 4000 times dilution or 40% dimethoate EC at 2000 times dilution.
4.4.2 During the growing season, mix 7 parts 40% dimethoate EC stock solution with 3 parts water, brush the solution onto the trunk around the main trunk in a band about 6 cm wide, and wrap it well with paper strips.
4.5 Red spider mites
4.5.1 Spray 5 degrees Beaume lime sulfur mixture before sprouting.
4.5.2 During the growing season, spray 5 degrees Beaume lime sulfur mixture, or spray 20% hexythiazox wettable powder at 4000~5000 times dilution, or spray 50% phoxim EC at 2500 times dilution. Spray once every 10 days, for 3 consecutive sprays.