Analysis of the Causes of Low Fruit Set in Apricot Trees and Solutions

Apricot tree (scientific name: Armeniaca vulgaris Lam.) is a deciduous tree, terrestrial, with hairless plants. Leaves alternate, broadly ovate or round-ovate, with rounded blunt serrations on the margins; flowers solitary, white or slightly red; fruit nearly spherical, mostly white, yellow to yellow-red, often with a red blush; seed kernels mostly bitter or sweet. Flowering period March-April, fruiting period June-July. It is widely cultivated throughout China.

Factors Affecting Fruit Set in Apricot Trees

1. Pollinator tree configuration factor. At present, most apricot varieties in China are self-unfruitful, and some farmers happen to overlook this important phenomenon when developing apricot trees. When establishing an orchard, planting a single variety or improperly configuring pollinator trees often results in flowers but no fruit, low yield, or no harvest year after year. Surveys have found that quite a number of farmers, when establishing apricot orchards, only pay attention to the introduction and development of new varieties, and do not understand or pay enough attention to the configuration of pollinator trees. Some do configure pollinator trees, but the number of pollinator trees is too small, accounting for only 1%-3% of the total, and the planting method is also unscientific, so pollination cannot be well achieved, directly leading to apricot trees flowering abundantly but setting few fruit and yielding poorly.

2. Fertilizer and water factor. An adequate supply of inorganic and organic fertilizers is the foundation for high yield in apricot trees. At present, most apricot orchards are not only seriously deficient in phosphorus, potassium and other trace elements, but nitrogen fertilizer is also far from meeting the needs of apricot tree growth and fruiting. Some apricot trees are not fertilized for even many years, resulting in nutrient deficiency, weak growth, extremely low organic matter content in the plant, and low physiological function, so they cannot flower and fruit normally, showing a condition of many flower buds, a large number of flowers, and few fruit set. Apricot trees are relatively drought-tolerant and generally do not need watering, but in drought conditions, failure to water in time will cause serious flower drop and physiological fruit drop.

3. Pruning factor. Apricot trees are light-loving tree species, and only under conditions of sufficient light can they grow and fruit well. Some apricot trees are left unpruned in a neglected state, and some are pruned improperly, causing branches to grow excessively, the canopy to become closed, and degenerated flowers to increase, which affects fruit set. In some apricot trees, branch retention during pruning is unreasonable, and improper branch spacing and pruning length also cause flower and fruit drop.

4. Climate factor. Although the apricot tree body is cold-tolerant, its flowers and young fruit often suffer yield reduction or even total crop failure due to late frost damage. This is the most important reason for “apricot trees full of flowers, but fruit scattered and sparse.” The degree of freezing damage is related to the intensity and duration of low temperature. The critical temperatures for frost damage to apricot flowers and young fruit are -3.9°C at the initial flowering stage, -2.2°C at the full flowering stage, and -0.6°C at the young fruit stage. Therefore, avoiding and preventing freezing during the flowering period is already an important measure that must be taken in some areas to develop apricot production, increase yield, and increase income.

Technical Measures to Improve Fruit Set Rate in Apricot Trees 

1. Select excellent varieties. Selecting varieties with a high proportion of complete flowers, strong self-fruiting ability, frost resistance, relatively late flowering, and early fruiting and high yield as the main planted varieties is the key to improving fruit set rate. For example, Jintaiyang, Kaite apricot, etc. In addition, varieties with early, middle and late ripening can also be selected in combination to reduce losses caused by early spring frost.

2. Configure pollinator trees. Varieties should not be too uniform. Some varieties are self-sterile and need 2-3 varieties configured for pollination. The suitable configuration ratio of pollinator trees to main planted varieties should be 1:3-4.

3. Strengthen soil, fertilizer and water management, enhance tree vigor, increase nutrient accumulation in the tree body, and improve flower bud quality. This is an effective measure to reduce flower organ abortion, improve fruit set rate, and increase yield.

Base fertilizer is best applied in autumn, generally in September-October combined with expanded hole deep digging and applied as early as possible. During the young tree period, the whole orchard should be deeply dug once over 3-4 years. During deep digging, root damage should be minimized, especially to the skeletal roots. Base fertilizer is mainly barnyard manure, compost, and human excrement and urine. The amount of fertilizer applied should be flexibly controlled according to tree age, tree vigor, fruiting amount, and fertilizer type.

On the basis of autumn application of base fertilizer, topdressing should also be applied in a timely manner: (1) Before sprouting (late March-early April), use urea 15 kg/mu + N, P, K compound fertilizer 450 kg/mu, applied in holes or furrows; (2) In mid-to-late May, the new shoot vigorous growth period and flower bud differentiation period are the critical fertilizer demand period for apricot trees. For fruiting trees, apply urea 100-1205 kg/mu as topdressing, broadcast in rings or applied in furrows; (3) After fruit harvest, apply compound fertilizer mainly based on nitrogen fertilizer as topdressing, and for fruiting trees apply N, P, K compound fertilizer 0.5 kg/tree.

In order to timely supplement the nutrient consumption of the tree body, foliar topdressing is needed for apricot. (1) Before flowering, spray dry branches with 0.5-1% urea solution. (2) At full flowering stage, spray 0.3% borax + 0.3% urea solution to improve fruit set rate. (3) After flower fall, spray 0.3% urea + 0.3% potassium dihydrogen phosphate solution. (4) 40 days after flower fall, spray 10×10-4B9, which can increase the proportion of first-class flowers and fruit set rate. (5) Half a month before fruit maturity, spray 0.3-0.4% potassium dihydrogen phosphate to promote fruit coloring.

4. Place bees in the orchard during flowering and conduct artificial supplementary pollination. Apricot trees are insect-pollinated flowers, and bees and other insects can help pollination. Placing bees in apricot orchards can significantly improve fruit set rate. Because the apricot flowering period is short, if adverse weather such as low temperature, cloudy days, rainfall or strong wind occurs, insect activity is hindered and pollination is affected, so artificial pollination of apricot trees is needed. Artificial pollination uses pollen from wild apricot (large pollen amount, strong pollen vitality). After mixing pollen and starch at 1:2, use a writing brush or the rubber tip of a pencil to dip the pollen and apply it to the stigma of the flowers.

5. Delay flowering and avoid frost. Because the apricot flowering period is susceptible to late frost damage, the fruit set rate is low. For this reason we adopt: (1) Whitewashing the trunk and spraying 8% limewater inside the canopy, or irrigating multiple times in early spring to lower soil temperature, delay germination, and irrigating heavily before full flowering to postpone the flowering period. (2) Before frost arrives at full flowering stage, spray 350 times anti-freezing fruit-setting agent, or spray water at flowering stage (water forming ice releases heat), or use the smoke method to prevent frost. When frost weather is forecast, at 2 o'clock at night, light the smoke piles so that the temperature in the apricot orchard does not drop below zero degrees. (3) Heavy pruning. Some varieties (such as Honghebao) can promote secondary shoots by heavy pruning in summer. After the secondary shoots grow to 30 cm and are pinched, they can promote tertiary shoots, or even quaternary shoots. In this way, the flowering period of primary, secondary, tertiary, and quaternary shoots is extended by 5-7 days. Even if the first batch of fruit freezes, the flowers on the secondary, tertiary, and quaternary shoots can avoid the late frost, greatly improving the fruit set rate.

6. Girdling of young trees. The suitable time for girdling is mid-May. The width of the trunk girdling cut is 1/25-1/30 of the trunk diameter. Apply 25% carbendazim 100-fold solution to the wound for disinfection, and wrap it with plastic film (which can effectively reduce gum flow and promote wound healing). One week after girdling, begin spraying 0.3% urea solution 2 times, once a week, then spray 0.3% potassium dihydrogen phosphate solution 2 times, with one week between each spraying. Through girdling, young trees can effectively increase the number of flowers and fruit set rate in the following year.