Symptoms of Tomato (Lycopersicon esculentum) Leaf Curl Disease and Its Treatment Methods

Whether greenhouse tomatoes or open-field tomatoes, especially under high temperature and drought conditions, are prone to leaf curling with different symptoms. So what are the symptoms of tomato leaf curl disease? What pesticide to spray? How to prevent and control it?

Tomato leaf curl can be divided into two types: upward leaf curl and downward leaf curl. Whether tomato leaves curl upward or downward, both are physiological disorders, and the causes are mainly as follows:

Causes of upward leaf curl in tomatoes:

1. After entering the peak fruiting stage, if tomatoes encounter high temperature and drought weather and cannot be supplemented with water in time, the leaf area is large at this time, and high temperature and strong light intensify leaf transpiration, making the lower leaves of the plant prone to curling upward. Especially at ventilation openings, tomato leaf curl tends to be more severe.

2. In summer, temperatures are high, and some vegetable growers do not pay attention to reducing the pesticide concentration. Once the pesticide concentration is too high and phytotoxicity occurs, the leaf surface will become discolored or develop spots, and the leaves will also curl upward.

3. Applying too much nitrogen fertilizer increases the concentration of the soil solution, causing tomato leaflets to flip and curl upward; in saline-alkali areas, the high soil solution concentration can also cause leaves to curl upward.

4. Pinching too early easily causes axillary buds to sprout, and the phosphate in the leaves has nowhere to be transported, leading to leaf aging and leaf curling.

5. Viral diseases are generally spread by virus-transmitting insects such as aphids and whiteflies. Affected tomato leaves will show symptoms such as chlorosis, shrinking, wrinkling, and curling. Leaf curling mostly appears on the heart leaves and upper leaves, and is prone to occur under high temperature and strong light.

Prevention and control methods for upward leaf curl in tomatoes:

1. After tomato planting until fruit set, carry out drought-hardening training; after fruit set, water and fertilize in a timely manner; in midsummer, cover with a shade net to prevent high temperature and drought.

2. In the high-temperature summer season, reduce the pesticide concentration as much as possible. Once phytotoxicity occurs, promptly spray water or spray a foliar fertilizer that alleviates phytotoxicity.

3. During the tomato growing period, nitrogen fertilizer should not be used excessively; increase the application of phosphorus and potassium fertilizers. Especially in summer, to prevent tomato plants from excessive vegetative growth, nitrogen fertilizer use should be controlled even more. Also, try to choose non-saline-alkali areas for planting tomatoes; in saline-alkali land, soilless cultivation or soil improvement measures can be implemented.

4. Removing tomato side branches is also called pruning. Generally, it should be done when they grow to more than 7 cm. If pruning is done too early, the leaf assimilation area decreases, too many branches and leaves are removed, the aboveground growth of the plant is poor, and root development is also affected, weakening the ability to absorb water and fertilizer, thereby inducing leaf curl. A common case is that when tomatoes have too many branches removed, pruned, and leaves picked at one time, leaf curl occurs afterward; this is the reason.

Causes of downward leaf curl in tomatoes:

1. In summer, the temperature difference between day and night is small. To prevent tomato flower and fruit drop caused by excessive vegetative growth, it is correct for some vegetable growers to spray naphthalene acetic acid, but when the concentration is too high, tomato leaves will show reverse curling on the first and second days after spraying, and the leaves will return to normal on the third day. The usual concentration for naphthalene acetic acid is 20-30 PPM, but if the concentration exceeds 50 PPM, the reverse curling time may be longer, and some flowers and fruits may drop.

2. If the soil is excessively dry in the early stage and then suddenly watered too heavily in the later stage, leaf transpiration will be inhibited, and reverse curling will occur when the leaves show a self-protective state.

3. When using 2,4-D for flower dipping during the flowering period, if the concentration is too high or it splashes onto the leaves, the leaves will become thicker, wrinkled, or curl downward. In addition, when cultivated in open fields in spring, if nearby wheat fields are sprayed with 2,4-D butyl ester to control weeds in wheat fields, the drifting liquid can also easily cause phytotoxicity, leading to deformed and upward-curling leaves.

Prevention and control methods for downward leaf curl in tomatoes:

1. When reverse curling is severe, spray Yeshuo tomato-specific disease-resistant liquid fertilizer to relieve it.

2. Avoid excessive drought, but do not water too heavily after drought; especially avoid watering heavily at noon during high temperatures.

3. When using 2,4-D for flower dipping, the concentration must not be too high, and the amount used should not be too large. Be careful not to drip the solution onto the leaves, and it is also not suitable for spraying. When using 2,4-D butyl ester for weed control, stay as far away from the vegetable greenhouse area as possible, or apply it when the greenhouse is closed.

According to the above description, whether tomato leaves curl upward or downward, it is largely related to pesticide use. Therefore, it is recommended that growers, starting from the seedling stage, use tomato-specific disease-resistant liquid fertilizer (foliar spray) + tomato-specific seaweed long-acting water-soluble fertilizer (drenching) to promote well-developed roots, good growth, fewer yellow leaves, a longer harvest period, disease resistance, increased yield, and fertilizer savings.