The reasons for the early yellow leaves of pear trees are as follows:
1. The nutrient supply structure is unreasonable.
2. The tree structure is unreasonable
3. Unreasonable water regulation
4. Improper use of chemical pesticides.
Prevention and control measures mainly include:
1. Improve tree nutrition and enhance tree vitality.
First of all, we should pay attention to the application of organic fertilizer, especially those orchards with organic matter content below 1% or even below 0.5%. Specifically, after harvesting fruits in autumn, organic fertilizer can be applied through ditches or holes, and about 2-3 kilograms of coarse fertilizer can be applied per kilogram of fruits, with appropriate amounts of nitrogen, phosphorus and trace element fertilizers. Secondly, pay attention to the application of topdressing, such as topdressing before flowering, topdressing after fruit expansion and topdressing before harvest. Among them, sufficient potassium fertilizer can be applied during the fruit expansion period, and fertilizers such as urea and potassium dihydrogen phosphate can also be applied in combination to properly supplement the nutrition of branches and leaves.
2. Strengthen pruning to create a ventilated tree.
For pear trees whose crown is too high and upright, they can be retracted, trimmed and reshaped in stages to reduce the fruiting parts and increase the fruiting area. For closed and unventilated orchards, according to the characteristics of trees, some lateral branches can be selectively cut off, and internal branches, peripheral transverse branches, dead branches and pest branches can be thinned out, so as to improve the ventilation and light transmission conditions within and between trees, improve the utilization rate of light energy and reduce the phenomenon of early defoliation.
3. Rationally control water and pursue water balance.
In the process of watering the pear orchard, the principle of "small water will not dry up for a long time, and flood irrigation should not be used as much as possible" to meet the water demand of plants. At the same time, for areas where floods often occur, it is necessary to trim a reasonable drainage system in the orchard to avoid large-scale water accumulation in the orchard. For orchards that are often dry, the method of planting grass in orchards can be used to increase soil water-holding capacity and improve water use efficiency.
4. Adjust the use structure of chemical pesticides
First of all, strictly control the frequency and concentration of organophosphorus pesticides. If other pesticides can be used instead, it is best to use biological pesticides or pyrethroid pesticides. When it is needed, pay attention to the concentration and spraying time, and avoid the high temperature period at noon. Secondly, spraying bordeaux mixture during fruit expansion to prevent diseases. This operation can not only prevent rain erosion, but also supplement copper and calcium elements for pear leaves, so that pear trees grow vigorously, the leaves are dark green and thick, and the early leaves are reduced. However, it should be noted that it should not be used when there is a danger of pear psylla.