Caused by plant toxicity
First of all, young leaves are tender plant tissues, which are more sensitive to phytotoxicity than old leaves. Maybe the old leaves are still green and the young leaves are curly.
The main pesticide causing phytotoxicity is stone sulfur mixture. The main component of sulfur mixture is calcium polysulfide, which has the ability to penetrate and corrode pathogenic cells and pest walls. It is a bactericide commonly used in kiwi fruit tree during hibernation. However, if the application concentration is too high or the application time is wrong, it is easy to cause phytotoxicity, and if the application concentration is too high in spring, it will cause new leaf deformity.
Curling of young leaves caused by phytotoxicity (real shot)
Characteristic difference:
The leaves are shriveled, the leaves are curled, the leaves are deformed, and some leaves have brown patches similar to sunburn on the front. There is an illusion of "veinlets extending" at the edge of leaves.
The young leaves can't spread out due to drug damage (real shot)
How to avoid:
1. Choose the appropriate medication time, and start using the stone sulfur mixture after defoliation pruning. The concentration can reach 4~5 Baume degrees.
2. Reduce the concentration. When using stone sulfur mixture in the growing season, the concentration should be below 0.3 Baume degree.
—— Excerpted from the Atlas of Primary Colors of Kiwifruit Diseases and Pests.
Ulcer caused by
Ulcer also likes to join in the fun. When kiwifruit New Ye Gang was infected with canker, green spots and water stains appeared, and the leaves were scorched and curled. When young leaves are infected with canker, the weather has just warmed up, and irregular polygonal brown spots will appear in the later stage of infection.
Canker disease causes young leaves to curl.
Characteristic difference:
The edge is burnt, and you can see the edge that is obviously green and soaked in water.
Late frost causes leaves to curl.
The harm of late frost mostly occurs in northern planting areas, usually from late March to mid-April. When the temperature rises in early spring, trees will begin to sprout. At this time, the temperature rises rapidly, but from late March to mid-April, the temperature often drops suddenly. It will cause late freezing damage to new shoots, buds and new leaves.
The late frost curled the young leaves.
Feature recognition:
Judging from the time of occurrence, it usually occurs in April. In addition, it is different from the curl of young leaves caused by canker, which can cause the leaf edge to scorch, with obvious boundary and relatively small area.
How to prevent:
1, early spring irrigation. According to the weather forecast, if there is cold current or frost, you can water it in advance to reduce freezing damage. Reduce soil temperature and delay tree germination.
2. Spray antifreeze. Before the late frost, the whole garden should be sprayed with brassinolide 10000 times or tiburon 1000 times to reduce the freezing damage.
3. Take emergency measures. Pay attention to the weather forecast. Before the arrival of the cold current, a pile of smoke was set every 15 meters in the wind direction on the orchard. Or spray 0.3% ~ 0.5% sucrose aqueous solution on the trees in the afternoon or evening the day before the cold current comes. When the cold current strikes at night, the water sprayed on the fruit trees will release latent heat when it is cold and frozen, so that the temperature of the trees will not drop suddenly, and the harm of late frost will be alleviated or prevented.
Leaf Curling Caused by Calcium Deficiency
Calcium mainly exists in the middle layer of cell wall and supports cells. Calcium nutrition will form insoluble calcium salt in plants, which is difficult to move, and calcium deficiency symptoms will show up at the growing point.
Calcium is a trace element, which can't be reused in plants like nitrogen. When calcium is deficient, the young parts of plants can't use the calcium stored in the old leaves.
However, when nitrogen is deficient, because nitrogen can move in the plant, when the nutrients absorbed by the root system are insufficient, the young part can absorb and utilize the nitrogen in the old leaves, so the symptoms of nitrogen deficiency are manifested in the old leaves.
Calcium deficiency causes young leaves to curl.
Leaf Curling Caused by Calcium Deficiency
Characteristic difference:
When calcium is deficient, young leaves are curled and deformed, mostly showing gaps or turning yellow and necrotic from the leaf edge. In addition, the leaves of plants will be scorched, because calcium deficiency may lead to the accumulation of nitric acid in young leaves, which will shrink the growing points and burn the edges of young leaves. When calcium deficiency is serious, the veins at the base of leaves will be necrotic and black.
Correction method of calcium deficiency:
Generally, kiwifruit orchards generally use lime or fertilizer with high calcium content (calcium phosphate and calcium nitrate, containing 20% calcium). ), little calcium deficiency. Once calcium deficiency occurs, 0. 1% calcium chloride water-soluble fertilizer can be sprayed on the leaves at the early stage of growth.
—— Excerpted from Efficient Cultivation of Kiwifruit
Leaf curling caused by boron deficiency
Boron is also an immobile element in plants. Boron is not a structural component of plants, but it is essential for the formation of new organs. When kiwifruit lacks boron, immature young leaves (more tender than tender leaves) become thicker, deformed and twisted, and the tissues between branches and veins usually swell up. When boron is seriously deficient, the elongation of plant internodes is limited and plants become shorter.
Boron deficiency causes young leaves to curl (source: kiwifruit efficient cultivation)
Characteristic difference:
Boron deficiency in kiwifruit is characterized by small and irregular black spots near the center of tender leaves, and then spread to both sides of veins to form large black spots, while veins usually remain green. Boron deficiency mostly occurs in sandy soil and soil with low organic matter content.
Boron deficiency correction:
Apply boron fertilizer in advance in boron-deficient soil and water it in time to prevent soil drought; Don't use too much lime fertilizer, use compost and manure to improve soil fertility. In addition, borax can be applied or boric acid aqueous solution can be sprayed on the leaves.