Causes of Yellowing Top Leaves on Tomatoes and How to Prevent and Treat Them
AbstractYellowing top leaves on tomatoes is a sign of tomato yellow leaf curl virus disease. It requires timely field sanitation, crop rotation, flooding the greenhouse and sealing it for more than 15 days, and appropriately delaying the sowing date. Seedling stage: heart leaves crinkle, leaf color is slightly yellow, and plants are stunted. Flowering stage: plants are noticeably stunted and grow slowly. Fruiting stage: symptoms worsen, leaf edges curl upward severely, leaf texture becomes hard and the edges shrink, and the fruit's market quality is poor. Late growth stage: leaves curl upward and turn yellow and crinkle, but yield is not affected.
I. Symptoms of yellowing top leaves on tomatoes
1. Seedling stage
(1) Yellowing top leaves on tomatoes can show mild symptoms of infection 25 to 30 days after sowing, specifically as crinkled heart leaves, slightly yellow leaf color, and plants that are shorter than normal seedlings.
(2) In hot seasons, seedling-stage symptoms are relatively obvious and easy to identify, while in low-temperature seasons the seedling-stage symptoms are slightly milder.
2. Flowering stage
(1) Obvious symptoms generally begin to appear 40 to 50 days after tomato transplanting, and the flowering stage is generally the peak period for yellowing top leaves on tomatoes.
(2) The main signs are obvious stunting, slow growth, yellowing, crinkling and shrinking of new top leaves, and thickening of the veins on the underside of the leaves.
(3) Leaf edges curl upward, and some leaves also thicken, but the leaves still remain green. Severely infected plants become severely stunted and cannot set fruit normally.
3. Fruiting stage
(1) After plants with yellowing top leaves on tomatoes enter the fruiting stage, symptoms generally worsen, mostly showing obvious yellowing of the leaves.
(2) Some leaves also remain green without yellowing, with severe upward curling of the leaf edges, obvious thickening of the leaves, harder and smaller leaf texture, and the veins on the underside of the leaves gradually turning purple.
(3) Some leaves become increasingly narrow, and the internode spacing shortens significantly, showing a stunted appearance.
(4) Compared with normal plants, diseased plants are noticeably shorter, generally usually 50cm to 80cm tall. Some plants can also grow to a certain height, but they set fewer fruits and the fruits are smaller.
(5) At maturity, the fruit colors unevenly and is hard, with patches of yellow-green mixed in, resulting in poor market quality.
4. Late growth stage
(1) Tomato plants infected by the virus are stunted in the late growth stage, and the fruit quality is poor with no market value.
(2) Tomatoes infected by the virus show upward curling, yellowing and crinkling of the leaves in the late growth stage, but this has little effect on yield.
II. How to prevent yellowing top leaves on tomatoes
1. Carry out field sanitation promptly
After harvesting the crops grown before planting tomatoes, thoroughly remove residual branches, fallen leaves and field weeds to reduce the population of tobacco whiteflies.
2. Crop rotation
When growing tomatoes, promote paddy-upland rotation and rice-vegetable rotation, or switch to vegetables that tobacco whiteflies do not like to feed on, such as celery, lettuce, Chinese chives, or onions and garlic, etc.
3. Flood the greenhouse and seal it
The high-temperature season from July to August is a period of high incidence of pests and diseases. During this time, level the soil in the greenhouse plot in a timely manner, build soil ridges around the perimeter, cover it with old plastic film, and fill the entire greenhouse with water and seal it for more than 15 days to eliminate tobacco whiteflies and reduce the occurrence of soil-borne diseases.
4. Appropriately delay the sowing date
If tobacco whiteflies are difficult to control, sowing can be delayed until mid-to-late September, which can reduce the occurrence of tomato yellow leaf curl virus disease.