When crops are attacked by adversity, the leaves will first show up, often with yellowing, spots, curling and other phenomena. There are two types of leaf curling: curling up and curling down. Only by understanding the reasons for them can we solve them in a targeted manner.
Reasons for leaf curling
1. High temperature, drought and water shortage
If crops encounter high temperature (temperature continues to exceed 35 degrees) and drought weather during growth and cannot replenish water in time, the leaves will curl up.
During the growth process, due to the large leaf area, the dual effects of high temperature and strong light enhance the transpiration of the leaves of crops. The speed of leaf transpiration is greater than the speed of water absorption and transportation of the root system, which can easily cause the plants to be in a state of water shortage, so that the stomata of the leaves are forced to close, the surface of the leaves is dehydrated, and the lower leaves of the plants are prone to curling up.
2. Ventilation problem
When the temperature difference between the inside and outside of the shed is large, if the air is suddenly released, the exchange of cold and warm air inside and outside the shed is relatively strong, which will cause the leaves of vegetables in the shed to curl up. What is particularly obvious during the seedling period is that the ventilation in the greenhouse is too fast, and the exchange of outdoor cold air and indoor warm air is strong, which can easily cause the leaves of vegetables near the vents to curl. This upward curling of leaves caused by ventilation usually starts from the tip of the leaf, and the leaves are in the shape of chicken claws. In severe cases, the dry tip has white edges.
3. Pesticide damage
As the temperature rises, especially in summer, the temperature is relatively high. If you don't pay attention when spraying pesticides, pesticide damage will occur. Once the concentration of the drug is too high, the surface of the leaves will change color or grow spots, and the leaves will also curl upward. For example, pesticide damage caused by improper use of hormone 2,4-D will cause the leaves or growth points to bend, the new leaves cannot unfold normally, the edges of the leaves are twisted and deformed, the stems and vines are raised, and the color becomes lighter.
4. Excessive fertilization
If the crop uses too much fertilizer, the concentration of the root soil solution will increase, which will hinder the root system's absorption of water, so that the leaves will show water shortage, causing the leaflets to turn over and curl up.
If too much ammonium nitrogen fertilizer is applied to the soil, the ribs of the leaflets on the mature leaves will bulge, the leaflets will present an inverted boat bottom shape, and the leaves will turn up and curl up.
Especially in saline-alkali areas, when the salt concentration of the soil solution is high, it is also easy for the leaves to curl up.
5. Element deficiency
When the plant is severely deficient in phosphorus, potassium, sulfur, calcium, copper, and some trace elements, it can cause leaf curling symptoms. These are physiological leaf curling, which is often distributed on the leaves of the entire plant, without the symptoms of bright vein mosaic, and often occurs on the leaves of the entire plant.
6. Improper field management
When vegetables are pinched too early or crops are pruned too early and too heavily. If vegetables are pinched too early, it is easy for axillary buds to grow, resulting in no place for the phosphoric acid in the vegetable leaves to be transported, causing the lower leaves to age first and the leaves to curl up. If the crop is pruned too early or too heavily, it will not only affect the development of the underground root system, limit the number and quality of the root system, but also cause poor growth of the aboveground part, affect the normal growth and development of the leaves, and induce leaf curling.
7. Diseases
Viral diseases can generally be spread by aphids, whiteflies, etc. When a plant has a viral disease, all or part of the leaves will bend upward from top to bottom, and the leaves will fade, become smaller, shrink, and grow in clusters. In severe cases, there will be only veins but no mesophyll, which is mostly manifested on the heart leaves and upper leaves.
In the late stage of leaf mold disease, the leaves will gradually curl from bottom to top. The leaves at the bottom of the diseased plant will first become ill, and then gradually spread upward, making the leaves of the plant yellow-brown and dry. In severe cases, the leaves of the whole plant may curl.
Reasons for leaf curling
1. Watering during long droughts
If the soil is too dry in the early stage and the amount of water is suddenly too large in the later stage, the transpiration of the crop leaves will be severely inhibited. When the leaves show a self-protection state, they will curl back and the leaves will curl downward.
2. Impact of low temperature and freezing damage
When the temperature is continuously below 10℃, the mesophyll cells of crops will be damaged by cold, and the leaves will begin to wilt. In severe cases, the leaves will dry up and bend downward, and the mesophyll cells will freeze and whiten. Late spring cold will also cause the leaves of new shoots to curl downward!
3. Improper use of hormones
When the concentration of naphthaleneacetic acid is too high, the leaves will curl up after spraying. When 2,4-D is dipped in flowers, the concentration is too high or it is sprinkled on the leaves, causing the leaves to thicken, shrink or curl downward.
4. Pest damage
Tea yellow mites are very small and are usually difficult to identify with the naked eye. The main symptoms of plants being damaged by mites are narrowing of the leaves, stiff uprightness, downward wrinkling or twisting, and finally bald tips. The leaves will become smaller, harder and thicker, and the most important thing is that the back of the leaves are oily and have tea rust color. Aphid damage can also cause severe curling of the leaves, because aphids usually feed on the back of the leaves and young tissues, so aphid damage can also cause the leaves to curl downward to varying degrees.
5. Nematode damage
Nematode infection can cause the roots to fail to absorb nutrients, resulting in serious root lesions and causing the leaves to flip downward.
