Propagation and Pest and Disease Control Cultivation Techniques for Purple-leaf Plum in Northern Jiangsu

Propagation and Pest and Disease Control Cultivation Techniques for Purple-leaf Plum in Northern Jiangsu

Cultivation

Planting Environment Purple-leaf plum is light-loving and should be planted in a spot with ample sunlight. It must never be planted in shade or under large trees; insufficient light not only causes poor plant growth but also makes the leaves turn green. Purple-leaf plum is drought-tolerant and moisture-loving, but it does not tolerate waterlogging. Planted in a high, dry spot it can grow normally, while in a low-lying spot it grows poorly. Purple-leaf plum is not demanding about soil; it prefers fertile, moist neutral or acidic sandy loam and also tolerates mildly saline-alkaline soil, growing normally in mildly saline-alkaline soil with a pH of 8.8 and a salt content of 0.2%. It is relatively cold-tolerant, but it should still be planted as much as possible in a spot sheltered from the wind and facing the sun, not in a wind gap. The leaves of purple-leaf plum are purplish-red, so when planting, care should be taken not to match it with similar colors; only when the colors differ can the beauty of the leaf color be shown.

Water and Fertilizer Purple-leaf plum likes a moist environment. For newly planted seedlings, in addition to watering thoroughly three times, water thoroughly 1 to 2 times each in April, May, June and September. In July and August rainfall is plentiful, so if it is not excessively dry, watering may be omitted, and when there is a lot of rain it should be drained promptly to prevent root rot from excessive water. In early to mid-November, the freezing water should also be watered sufficiently and thoroughly. In the management of the second year, water once each in early March, April, May, June, September and early to mid-November. From the third year on, it is only necessary to water thoroughly the thawing water and freezing water each year in early spring and early winter, and it can rely on natural rainfall to grow. It should be noted that in autumn, watering must be controlled to prevent excessive water from causing leggy shoot growth and frost damage in winter.

Purple-leaf plum likes fertilizer. In addition to applying an appropriate amount of rotted and fermented barnyard manure at the bottom of the pit when planting, some farmyard manure may be applied each year before watering the freezing water, so that the plant grows vigorously and the leaves are bright. It should be explained that although purple-leaf plum likes fertilizer, it only needs to be fertilized once each year in late autumn, and in an appropriate amount. If fertilized too many times or in too large an amount, the leaf color will become dull rather than bright, reducing its ornamental value. In addition, when fertilizing, be careful not to apply too much nitrogen fertilizer. If the amount of nitrogen fertilizer is too large, not only will the seedlings grow excessively lush and leggy and become prone to pests and diseases, but it will also affect the leaf color of the plant, making the leaves turn green and giving a poor ornamental effect.

Pruning and Shaping In northern Jiangsu, the best tree form for purple-leaf plum is the open-center scaffold form. This tree form has a crown that is open yet still compact, with an obvious trunk and well-arranged main branches. The shaping of purple-leaf plum is generally carried out over 4 years. The first year's pruning is done after planting, cutting back at a trunk height of about 0.8 to 1.2 m. The first bud below the cut is used as the leader of the main branch, and 3 to 4 robust new shoots are selected below the first bud as main branches. The branches should be evenly distributed and may not be on the same line, but the difference between top and bottom should not exceed 5 cm, and they should spread upward at a 45° angle. After the main branches are selected, they should be properly pinched during the growing season to promote their thickness. In the second year's winter pruning, the trunk leader should be properly cut back, selecting a strong bud and cutting 1 cm above it; the direction of the bud should be opposite to that of the previous year's trunk leader. The main branches should also be cut back, leaving strong outward-facing buds. In the third year's winter pruning, the trunk leader should again be opposite in direction to the second year's trunk leader, and the second tier of main branches should be selected and retained, likewise keeping outward-facing buds, so that once grown they are staggered with the second year's main branches. In the fourth year, the third tier of main branches is selected and retained in the same way.

In actual work, the natural open-center form is also used quite a lot. The pruning method is: after the seedling is planted, cut it back at a trunk height of 0.5 to 1 m, without letting it grow a trunk leader, and select only 3 to 5 new shoots as main branches. The retained main branches should be roughly evenly distributed, with an opening angle of 45°, and then the main branches are pruned year by year according to the method for pruning main branches in the open-center scaffold form. Although this tree form is not as attractive as the open-center scaffold form, its crown has better ventilation than the open-center scaffold form, and its ornamental effect is also good.

It is worth mentioning that no matter which tree form is used, when pruning the main branches at each tier, an appropriate number of lateral branches should be retained so that the crown is full and not hollow. After the tree form is basically formed, it is only necessary each year to remove excessively dense branches, drooping branches, overlapping branches, crossing branches and dead branches.

Pest and Disease Control

The main insect pests of purple-leaf plum include red spider mite, stinging caterpillar, bagworm moth, leafhopper, aphid, scale insect, etc. If they occur, 40% dicofol emulsifiable concentrate at 1000 times solution can be sprayed to kill red spider mite, Bt emulsion at 1000 times solution to kill stinging caterpillar and bagworm moth, 10% imidacloprid at 1500 times solution to kill scale insect and leafhopper, and Chansha at 500 times solution to kill aphid.

Purple-leaf plum has relatively strong disease resistance. Its common disease is bacterial shot hole, which occurs widely and causes serious damage. After onset, it not only affects the plant's normal growth and ornamental effect, but in severe cases can also cause the diseased plant to die. Control methods: prune rationally to facilitate ventilation and light penetration for the plant. Pay attention to controlling piercing-sucking pests such as aphids and scale insects. Strengthen water and fertilizer management; the planting hole must never accumulate water; when fertilizing, pay attention to nutrient balance, and especially to the application of phosphorus and potassium fertilizers. Before bud break in spring, spray 5 degrees Baume lime-sulfur mixture or 1:1:100 Bordeaux mixture to eliminate the source of infection. In the early stage of disease, spray 95% carbendazim or 15% streptomycin wettable powder at 500 times solution, spraying once every 10 days; 3 to 4 consecutive sprays can effectively bring the disease under control.

Propagation

Seedlings of purple-leaf plum grown from seed mostly have leaves that turn green, so asexual propagation is generally adopted. The commonly used propagation methods include bud grafting, air layering and cutting.

Bud Grafting The rootstock can be peach, plum, plum (Japanese apricot), apricot, mountain peach, mountain apricot, wild peach and seedlings of purple-leaf plum. Comparatively speaking, peach rootstock has strong growth vigor and purple-green leaf color, but it fears waterlogging. Plum as rootstock is more tolerant of waterlogging, while apricot and Japanese apricot have longer lifespans but also fear waterlogging. In northern Jiangsu, wild peach is most commonly used.

For grafting, the rootstock is generally a two-year-old seedling, preferably one specially cultivated as a rootstock. Before grafting, it should first be cut back, retaining only a 5 to 7 cm stump above the ground. In mid to late June, fix the bud position on the branch previously selected as the scion; the graft bud should be plump and full, without dried tips or pests and diseases. Use a sterilized budding knife to make a 30° angled cut upward into the xylem from 2 cm below the bud position, up to 1 cm above the bud position, then make a horizontal cut 1 cm above the bud position, gently remove the graft bud, and then at 3 cm above the ground on the rootstock use the knife to cut a "T" shaped incision in the bark, so that the graft bud and rootstock are tightly combined, then bind well with plastic tape. After grafting, if the graft bud has not wilted after about 7 days, it indicates that it has survived; after about 25 days the plastic tape can be removed.

Air Layering

① Branch selection. The branch should be selected from a plant with relatively strong tree vigor and no pests or diseases. The branch diameter is generally 1 to 2 cm, and 2- to 4-year-old branches are best.

② Layering operation. Layering is carried out from mid-April to mid-May in spring. On the layer, select a suitable position and use a grafting knife to score two cuts, with a spacing of about 1.5 cm, then ring-bark the epidermis between the cuts. Immediately after ring-barking, put on a plastic bag, tie the plastic bag tightly shut below the lower cut, then put the prepared sandy loam mud slurry into the plastic bag and knead it into a ball. The mud ball should wrap around the ring-barked area and keep it in the middle of the mud ball, then tie the upper opening of the plastic bag tightly shut.

③ Later management. After the plastic bag is sealed, check it frequently to see whether the mud ball is dry and hard. If the soil ball is soft, it indicates that the wrapping effect is good and the soil moisture content is relatively high. After about 45 days the wound can heal and begin to take root. After leaf fall in late autumn, cut the layer off below the mud ball, cut open the plastic bag, and transplant. If it is dry and hard, it indicates that there is a place where the plastic bag is leaking air; immediately inject water with a syringe and put another plastic bag over the original one.

Cutting

Preparatory Work Before Cutting Cutting can be carried out from mid to late October to early to mid-November, but it must be completed before the soil freezes. The seedbed should be set up in a sunlight greenhouse with straw mats or thermal insulation quilts [Jishan Huayao].

The seedbed should be prepared half a month before cutting; generally a flat bed is sufficient. The soil should be sandy loam. Before making the bed, apply rotted and fermented cow and horse manure at 600 to 800 kg per mu. The soil and fertilizer must be mixed evenly. After raking level, thoroughly mix 40% quintozene granules with the soil for disinfection at 7 to 8 g/sq m. After disinfection, cover with plastic sheeting to seal it.

The cuttings should be free of pests and diseases, 0.5 to 1 cm in diameter, and highly lignified. The cuttings are generally cut to 12 to 15 cm, with the lower cut made into a horseshoe shape and the upper cut smooth, 1 to 1.5 cm from a bud. Bind 100 to 150 cuttings into 1 bundle, soak in a 50 ppm indolebutyric acid solution for 24 hours, then remove and set aside.

Cutting First make holes in the seedbed with bamboo sticks, with a plant and row spacing of 10 cm x 10 cm. After making the holes, cutting can be carried out. The cutting depth is such that 3 to 4 buds are exposed. Immediately after cutting, water thoroughly once.

Management After Cutting After cutting, the temperature in the greenhouse should not be lower than 5°C. On sunny days, the thermal insulation quilt or straw mat should be uncovered at around 9:30 in the morning to raise the temperature and increase light, and after 4 p.m. the covering should be put back in place for insulation.

In mid-March, water thoroughly once again, and at noon when the greenhouse temperature is relatively high, ventilate appropriately to harden the seedlings. In mid-April, remove the greenhouse film and spray the leaves once with 0.5% urea solution to enhance growth. After that, apply a nitrogen, phosphorus and potassium compound fertilizer once about every 45 days, and water according to soil moisture conditions to keep the soil at more than half moisture. Stop fertilizing before the end of August. In the spring of the second year, they can be transplanted into the nursery for cultivation.