This is the season of citrus harvest, but it has been found that many orchards are seriously yellowed, and the yield and quality are affected. When visiting orchards in Nanning, Laibin, Liuzhou, Guilin, Hunan, Guangdong and other places, I found that many orchards had yellowing phenomenon to varying degrees, why is the problem of yellowing so prominent this year?
Picture taken in Besercillin
During this time, there were large areas of yellowing fruit trees everywhere, which were very serious, and some orchards accounted for one of the yellowing trees
Half, even to seventy or eighty percent, is unbearable.
Image taken in Shaoguan, Guangdong
Yellowing trees are particularly serious, it is expected that this year's yellowed fruit trees may account for 1/5 of the total, that is, 20%, then whether it will continue to yellow next year, then another 20%, then nearly half of the orchards will be destroyed! If we do not pay attention to prevention at this time, the consequences will be unimaginable.
What causes yellowing? How can it be prevented?
1. Yellowing caused by root damage
The veins of the damaged roots first yellow and then extend throughout the leaves, causing the fruit tree to be severely yellowed. Root damage is caused by these factors: (1) water accumulation, reduced oxygen content in the soil, root system can not breathe, affecting nutrient absorption, resulting in root and rotten roots; (2) water shortage and drought, reduced transpiration of trees, hindering water and fertilizer absorption; (3) soil salinization is serious, the concentration of ions in the soil is too high, the root system cannot absorb water and fertilizer, and the root system is damaged; (4) excessive fertilization or too close to the root when fertilizing, burning roots.
Solution: Yellow leaves are serious, first retract, cut off the branches with severe yellowing, and reduce nutrient consumption. Then apply some fertilizer to promote root growth to restore the robust growth of the root system.
2. Yellowing caused by lack of hormones
When there is insufficient nutrients in the soil, citrus usually shows symptoms of deficiency of nutrients, which can also cause yellowing of fruit trees.
Solutions: For the lack of yellowing, nitrogen, phosphorus and potassium, calcium, magnesium, boron, zinc, iron, copper and manganese caused by citrus deficiency, it is generally recommended that root fertilization and foliar topdressing be carried out simultaneously, when the nutrients are replenished, the symptoms of deficiency will slowly disappear, and we must do a good job in citrus water and fertilizer management.
3, too many hanging fruit caused by yellowing
Hanging fruit too much, beyond the range of the tree itself can bear, the tree will absorb all the nutrients to the fruit, there is no excess nutrient supply to the leaves, easy to lead to yellowing of the leaf veins, tree decline, so that the fruit will become smaller, the quality is affected.
Usually, small fruit varieties need 20 to 40 leaves to raise 1 fruit, extra-early-ripening, early-ripening Wenzhou mandarin orange 30 to 35 leaves to raise 1 fruit, medium and late ripening Wenzhou mandarin 20 to 25 leaves to raise 1 fruit; medium fruit varieties need 40 to 60 leaves to raise 1 fruit; large fruit varieties, such as grapefruit need 150 ~ 200 leaves to raise 1 fruit.
There are too many hanging fruits, and the trees are weak
Solutions: There are too many fruit hanging from fruit trees, and it is necessary to thin the fruit, and pick some small fruits, diseases and insects, top fruits and so on in a timely manner. For example, this kind of variety can properly remove some bunches of fruit, which is conducive to the expansion of the fruit and the improvement of quality.
4. Infection with yellow dragon disease can also cause yellowing of fruit trees
Last year, when visiting Liuzhou, Laibin, Guilin and other places, it was found that many orchards had outbreaks of psyllids, which became the vector for spreading huanglongbing.
(1) Yellow dragon disease identification: (1) red nose fruit, the disease-induced fruit to the ripening stage near the stalk yellow, most of the other places are still green, basically can be judged to have been infected with yellow dragon disease; (2) mottled yellowing leaves, the base and edge of the old leaves begin to yellow, the leaves as a whole yellow-green, mottled;
(3) Uniform yellowing or yellow shoots is another feature of citrus yellow dragon disease: all leaves turn green in the spring, and the spring shoots drawn out are also green; in the summer and autumn shoots, the leaves begin to turn yellow; in the winter, the new shoots do not turn green, showing obvious symptoms of yellow dragon disease; (4) The yellowed leaves and branches can also be sent to professional institutions for testing, which can quickly detect whether they are infected.
Solutions need to be prevented in advance of huanglongbing disease:
(1) Select robust, non-toxic detoxification seedlings.
(2) Strengthen the nutrient and strong tree potential: the bottom is fat, the fertilizer is timely, and the organic and inorganic are used together to enhance the tree potential and improve the stress resistance of fruit trees.
(3) You must prevent pyllids: Pyllids are the transmission medium of yellow dragon disease, and you need to prevent psyllids. Citrus wood lice generally overwinter as adults, and do not lay eggs without young shoots. Spring arrives, and overwintering adults migrate to the buds of the first spring of citrus to suck up sap and lay eggs. Therefore, the winter qingyuan is a key period of the year to control psyllids. The second is the initial stage of new shoots, and each new shoot stage, spraying at least 2 times, the first spray in the first bud about 1 to 3 cm, 7 to 10 days apart spray the second agent. The available agents are: imidacloprid, thiamethoxam, chlorpyrifos, cypermethrin, perchloropyridine and other agents.
(4) Regularly visit the garden and find huanglong disease disease trees, be sure to spray the psyllids first, and then dig up the diseased trees after 3-7 days. If only the tree is cut down, glyphosate should be used to suppress the stump to prevent the diseased tree from pulling out the diseased shoots again.
Here's a reminder: be sure to pay attention to the yellowing of fruit trees and don't let yellowing ruin your orchard. In the next issue, we will continue to share some precautions for citrus celebrities.