Ph.D. Nguyen Minh Tuyen

Curly and yellowing disease of tomato leaves is fairly common for tomato plants around the world, especially in areas with warm, arid climates. In Vietnam, tomato yellow leaf curl disease is quite common in areas that have grown tomatoes for many years, especially in areas where many shallow crops are grown such as melons, eggplants, cucurbits, potatoes, peppers, etc.

* Pathogens: Tomato yellow leaf curl disease is caused by a number of viruses. For example, tobacco virus (TMV), squash virus (CMV), potato virus (PVX, PVY), tomato virus (ToMV, TYLCV, TRSV)... Depending on the virus species, the transmission route is different.

* How the disease is spread: The pathogen is caused by a virus, so there must be intermediate animals that carry and transmit the disease, then the disease can be spread. The intermediate animals such as aphids (Aphid), whiteflies (Bemisia tabaci), thrips (Thrips), some chewing worms, beetles and even humans... Insects and insects carry viruses from diseased plants. then sow to healthy plants. Humans cause mechanical wounds on plants during planting and tending, allowing the virus to penetrate the plant, or the virus can be spread through garden tools, cuttings and rootstocks. In addition, some viruses have the ability to survive for a long time in the dried debris of diseased plants (for example, TMV species can survive up to 50 years, some authors say it can survive up to 100 years). Viruses always exist on other host plants such as weeds, wild plants... and this is the source of the disease to persist and spread.

* Symptoms: Depending on the virus species, tomato varieties, light intensity and temperature, depending on the stage of plants infected with the virus, the time of disease onset and symptoms will be different. Usually, when infected with a virus, the plant is often dwarfed, growth and development are poor. Leaves may be small, wrinkled, deformed, and often mosaic (on the same leaf with mixed yellow-green areas), or the leaves may be darker than normal. When a plant is infected with more than one virus species, the symptoms are mixed and complex. Many times the symptoms on the Leaves are like being stuck with herbicides or micronutrient deficiencies.

* Harms: The earlier the plant is infected with the virus (since the  plant has just grown), the shorter the incubation period, and the sooner the plant develops the disease. When grown plants are infected with the virus, due to their higher resistance, the disease develops later, or does not develop the disease. The sooner the plant develops the disease, the greater the damage, even if it does not yield. Diseased plants are often dwarfed and the leaves are curled, yellow, mosaic, so the photosynthetic capacity is reduced, thus reducing the yield. On the fruit can show disease symptoms or not depending on the virus species and tomato variety, but certainly when the plant is diseased, the number and size of the fruit will be reduced, the fruit will be slightly crunchy On resistant varieties, if the plant has been infected with the virus, even though it does not show symptoms of the disease, the plant still silently carries the virus and is still capable of transmitting the virus to other plants when conditions permit.

Prevention: The disease is caused by a virus, so there is currently no specific treatment. However, we can effectively manage the disease by managing the way it is spread. To manage the disease, we must apply many measures simultaneously to get the desired results. Those measures are:

- Sanitize the remnants of previous crops, especially those that are host to viruses such as tomatoes, tobacco, cucurbits, potatoes and some vegetables. Avoid planting near fields where the above crops are grown. Sanitize weeds around the borders (including in nurseries).

- Sanitize garden tools after pruning diseased plants.

- Use varieties resistant to sucking pests and diseases.

- Use clean water for irrigation.

- Uproot and destroy diseased plants, do not throw diseased plants on the borders of the fields or into rivers and streams.

- Limit damage to plants when planting and caring.

- Avoid over-fertilizing nitrogen fertilizers, enhance micronutrients by using foliar fertilizer Poly Feed 19-19-19 to increase resistance to pests and diseases.

- Monitor closely the density of sucking pests, especially aphids and whiteflies, to prevent them from growing until 25- 30 days later. This is the stage that determines the rate of diseased plants, determines the severity or mildness of the disease. Currently, a popular and effective product for sucking insects is SK Enspray 99EC mineral oil. This product is completely non-toxic to humans and animals. SK mineral oil kills worms through the mechanism of causing worms to suffocate and die. To increase effectiveness and kill some types of chewing worms and other beetles, farmers often combine SK mineral oil with biological products like Comda Gold 5WG to prevent.