Key Technical Points for High-Quality, High-Yield Cultivation of Sweet Cherry

Sweet cherry, also known as large cherry, was introduced to Yantai from Korea by sea and to Xinjiang from Russia by land between 1880 and 1890, and has a cultivation history of more than one hundred years. In Shandong, sweet cherry is concentrated in such cities as Yantai, Qingdao, Weihai, Tai'an and Linyi, with Napoleon, Big Purple, Red Cherry and Late Yellow being the more numerous varieties.

I. Development prospects and regional requirements for sweet cherry

Compared with Chinese cherry:

① Large fruit, bright color, good taste. The single fruit weight of Chinese cherry is generally 1-2 g; that of sweet cherry is generally 5-8 g, and it has a strong glossiness; sweet cherry comes in all three colors of purple, red and yellow, and its soluble solids content, dry matter and sugar content are all higher than those of Chinese cherry;

② Storage and transport tolerance. Chinese cherry turns brown first and then molds after 24 hours at room temperature, so it can only be sold as soon as it is picked and cannot be sold far away; it rots at the slightest pressure and breaks at the slightest shock, making it extremely difficult to pack and transport; sweet cherry can be stored at room temperature for 15 days without discoloration, pitting or molding, has thick and tough skin, does not break under light shock, and does not rot under slight piling, making long-distance sales convenient;

③ Chinese cherry has small fruit and is difficult to pick, and its ripening period is concentrated, making labor organization difficult. At the same time, the clump-shaped tree form brings many disadvantages to spraying and fruit picking; sweet cherry has large fruit, mostly with a multi-trunk layered form, is easy to manage for flowers and fruit, and has a long ripening period, with ripe fruit not easily dropping, thus extending the market supply cycle;

④ The flowering period of sweet cherry is about 15 days later than that of Chinese cherry, so it is less susceptible to late frost damage.

Compared with major northern fruits, sweet cherry:

① Has an early ripening period and early market launch, with remarkable market value;

② Has a short flower and fruit management period, low input and high benefit;

③ Ripens before the peak of pests and diseases, so few pesticides are used during the fruit period, and it is recognized as a safe fruit with no pesticide residues. The market price is 20-40 yuan/kg, and the benefit is significantly higher than that of major northern fruits.

The suitable growth conditions for sweet cherry are: an average annual temperature of 10-15°C, more than 1440 hours at low temperature of 7.2°C, more than 2000 hours of annual sunshine, more than 200 frost-free days, and more than 600 mm of precipitation. In China's Bohai, Yellow Sea and East China Sea coastal areas, and on loam and sandy loam soils in plains, river valleys, mountain hollows and gullies in the Yellow River and Yangtze River basins, sweet cherry can all be planted.

II. High-yield and high-quality cultivation techniques for sweet cherry

1. Cultivate on sandy loam or loam with deep soil, loose texture and good aeration; cultivation on poorly drained and heavy clay soil easily causes weak trees and shallow root systems. Sweet cherry is light-loving, so establishing a cherry orchard must be done on sunny slopes or semi-sunny slopes with good light conditions. In areas with strong winds, windbreak forests should also be established.

2. Variety arrangement must be appropriate; only with good varieties matched with good rootstocks can sweet cherry be high and stable yielding. Choose large-leaf Chinese cherry and Mopasu as rootstocks to strengthen the root system and improve wind resistance. The proportion of pollinizer trees should be 20%-30%; in mountainous areas they can be mixed with the main cultivars, planting 1 pollinizer for every 3 main cultivar trees, while in plain areas plant 1 row of pollinizers for every 3-4 rows of main cultivars.

3. The plant and row spacing should be 4-5 m × 5 m, 6 m or 7 m, with 18-33 plants per 667 sq m; density should be lower on fertile soil and higher on poor soil.

4. Dig holes or trenches at the predetermined plant and row spacing for planting and apply sufficient base fertilizer. Because winters in North China are cold, dry and windy, autumn-planted seedlings easily lose water and dry out, so planting should be done as early as possible in spring after the soil thaws, generally in early March. Hole planting standard: dig large holes 60-100 cm deep and 100 cm in diameter; if trench planting, dig trenches 100 cm deep and 100 cm wide. Be careful to place topsoil and subsoil separately, then backfill 20-30 cm of organic matter mixed with topsoil into the planting hole or trench, such as leaves, straw, weeds or manure, tread it firm with the feet, then fill in part of the topsoil until about 30 cm from the ground, making the middle slightly higher than the surroundings, place the seedling into the hole or trench, spread the roots out, shake the seedling while filling soil, and tread it firm with the feet so that the roots and soil are in close contact. To prevent the soil from sinking after watering or the seedling from being blown over by wind, after planting fix it with a wooden stick or bamboo pole, then water immediately; after the water seeps in, build a small mound of soil at the base of the trunk, or cover with 1 sq m of plastic film, which can protect against cold and drought and improve the survival rate of the seedlings.

5. Sweet cherry has strict requirements for fertilizer and water. When digging the orchard in spring, broadcast soil manure over the whole orchard and apply human excrement and urine in trenches as base fertilizer, and topdress with chemical fertilizer after fruit harvest in June-July. From flowering and fruit setting to before fruit harvest, sweet cherry should not be topdressed, otherwise the fruit will ripen unevenly and its economic value will be reduced. Attention should be paid to applying fertilizer mainly in early spring and after fruit harvest; spraying 0.5% urea and 0.5% borax on the leaves outside the roots at the initial flowering stage can increase the fruit-setting rate by 8%-14.6%. Sweet cherry also has very strict water requirements and is very sensitive to drought and waterlogging. Sweet cherry belongs to the European line and requires an ecological environment with abundant rainfall and humid air. Because it grows rapidly, has large leaves and a high transpiration coefficient, sufficient water supply should be maintained from flowering to harvest. After flowering in spring, water fully 3 times at the right time. The first time is after petal fall, when the fruit is the size of a sorghum grain; the second time is when the fruit is the size of a soybean. During this period the fruit cells divide vigorously, and timely watering can promote longitudinal growth of the fruit. The third watering is when the fruit begins to color. At this time the fruit is in the cell expansion stage and transverse growth of the fruit accelerates. Satisfying the water supply is conducive to improving yield and quality. Each watering must be thorough. If the weather is dry and watering is insufficient, serious fruit drop will be caused, reducing yield; if spring drought watering is insufficient and later rain occurs, fruit cracking is also likely, reducing the economic value of the fruit. Therefore, under drought conditions, it is essential to ensure "three full waterings" to achieve a bumper harvest.

6. Training and pruning of sweet cherry. Sweet cherry has strong trunk dominance, grows rapidly, has strong sprouting ability, and a tall canopy, generally above 4-6 m. During the young tree period, branches grow vigorously and branching ability is strong; after entering the fruiting period, branching ability gradually weakens, while the demand for light is high. According to these biological characteristics, the multi-trunk natural open-center form should be used for training and pruning. The method is: after 2-4 scions cleft-grafted at the base survive, in late March of the second year before sprouting, select and retain 3-5 similarly growing branches on each grafted seedling as trunks, and cut the trunk at 50-60 cm above the ground to determine the trunk height. In subsequent yearly pruning, treat the multiple trunks as multiple main branches extending outward at a 35-degree angle, with no obvious central leader in the inner canopy; each trunk retains 2 branches 50-60 cm long each year as extension branches. Because trunk dominance is strong and branches tend to grow upright, the extension branches should use inner bud outward training to increase the angle and open them up, while side branches extend outward at a 50-degree angle with a length of about 40-50 cm. For branches below the main branches, side branches and extension branches, weak branches should be left unpruned, moderate branches should be short-cut, and strong vigorous branches should be removed. When young trees grow rapidly and branches become excessively vigorous, the early-maturing nature of sweet cherry buds can be used for multiple pinching to promote faster branching, expand the canopy, and help early fruiting. Using the multi-trunk natural open-center form for sweet cherry can not only form the tree shape 2-3 years earlier than the single-trunk layered form, but also produce a larger canopy and earlier fruiting. Generally it begins to bear fruit in 4-5 years and can enter the initial full-fruiting period in 8-10 years; at the same time, multi-trunk training can also prevent large trees from lodging.

After sweet cherry enters the fruiting period, pruning may not be necessary; after harvest in June, pay attention to thinning excessively dense branches in the inner canopy to improve light conditions there, and remove 1/3 of the current-year new shoots on the outer periphery, which can promote flower bud formation and also prevent the fruiting from moving outward; before sprouting in spring, cut off dead and dried branches.

7. Pests and diseases of sweet cherry and their control methods. The main leaf diseases of sweet cherry are peach bacterial shot hole and circular leaf spot, which occur severely in the rainy months of July, August and September, damaging branches, leaves, young shoots and fruit; if not controlled in time, they can cause defoliation of the whole tree and have very adverse effects on flower bud formation, tree vigor development, and flowering and fruit setting the following year. Therefore, attention should be paid to timely spraying for control: before sprouting in spring, spray 5-degree lime sulfur mixture to eliminate overwintering pathogen spores and also control scale insects; after harvest in late June and late July, spray 200-fold double-strength Bordeaux mixture on the leaves to control the above diseases.

Gummosis on the branches and trunk of sweet cherry is a physiological disease. After the trunk is injured and stimulated, sap flows out; in large trees in the full-fruiting period, gummosis on branches and trunk is severe in July-August after fruit harvest, gummosis is heavy when red-necked longhorn beetle damage is severe, and gummosis can also occur when branches freeze due to too-early pruning. When gummosis is severe, the damage to the tree is great, so it must be controlled promptly according to the cause. Avoiding injury and stimulation to branches and trunk is the only way to prevent gummosis in large sweet cherry trees.

The main insect pest of sweet cherry is the red-necked longhorn beetle. This insect overwinters as larvae inside branches and trunk; the peak emergence period of adults is late June to mid-July, eggs are laid in cracks in the bark of the main trunk, and larvae bore and damage the xylem of the main trunk and large branches from top to bottom. This pest causes severe damage and is difficult to control; after the main trunk is bored, gummosis is caused, severely weakening tree vigor and possibly leading to death of the whole tree.

Control methods are:

① Manually capture adults during the adult emergence period in June-July.

② In early June, apply trichlorfon yellow mud slurry to the trunk and large branches to prevent egg laying.

③ Inject 200-fold dichlorvos solution into the bore holes to kill larvae inside the branches and trunk.

④ When insect frass is found on branches or trunk, promptly dig out and remove the newly hatched larvae damaging under the bark.

⑤ Adults have chemotaxis, so sugar-vinegar liquid can be used for trapping and killing in combination with control of the pear fruit moth.