How to prevent and control tomato bacterial scab? Introduction to integrated control methods

During tomato cultivation, it is very susceptible to diseases such as bacterial scab. Once this disease occurs, it causes great harm to tomato plants, fruits and so on, and losses for growers are inevitable. Let us learn about the integrated control methods for tomato bacterial scab.

1. Symptoms of tomato bacterial scab

Tomato bacterial scab mainly damages the leaves, stems and fruits of the plant. On the plant, the lower leaves near the ground are affected first. At the diseased sites, dark green water-soaked spots initially appear with distinct edges, then gradually expand into irregular dark brown necrotic spots with slightly sunken centers and yellow chlorotic halos around them. Lesion expansion is often restricted by leaf veins. The diseased leaves gradually turn yellow, wither and curl, and in the later stage the diseased parts dry out, become brittle and fall off. When the stem is affected, small water-soaked spots usually appear first in the stem grooves, then spread upward and downward along the plant. The lesions are elongated, slightly sunken in the center, brown, and in the later stage the diseased parts become suberized and raised, forming nearly round, rough dead spots. When the fruit is affected, raised round white dots mostly form on the fruit surface, and later the center of the lesion becomes sunken, forming dark brown or blackish-brown raised ring spots. In severe cases, the lesions join together into irregular scab-like large patches. The disease is more severe before fruit coloring and during the young fruit enlargement stage. If the junction between the fruit and the fruit stalk is affected, it easily causes fruit drop.

2. Introduction to integrated control methods for tomato bacterial scab

1. Prevention should start from seedling raising

In planting areas with factory seedling-raising conditions, growers should try to buy or order seedlings from capable seedling enterprises and cooperatives. If seeds are purchased through ordinary channels, seed soaking in medicinal solution should be done properly, and soil or substrate that has previously been used to grow solanaceous vegetables must not be used for seedling raising. If the seedling substrate is mixed with livestock manure, it must be fully decomposed before use.

2. Site selection and land preparation, high-bed cultivation

It is advisable to choose loam plots with good drainage as tomato seedling-raising land and cultivation land. For field planting, waist ditches and surrounding ditches should be dug well, and beds about 1.2 m wide should be made. Between adjacent planting beds, ditches 30 cm deep and 20 cm wide at the bottom should be opened to facilitate drainage and reduce humidity.

3. Strengthen field management and apply fertilizer reasonably

Strengthen field management. Loosening soil and weeding should be done shallowly rather than deeply to avoid damaging the root system and causing wounds, and prevent the plot from being overly short of water or too humid. Before rainwater and dew on tomato leaves have dried, farm operations such as fertilizing, weeding, pruning and removing side shoots should not be carried out to prevent disease transmission. During the growing period, central diseased plants, diseased branches and leaves, and diseased fruits should be removed in time. Because this disease generally starts from the lower part of the plant and spreads upward, timely clearing of diseased branches and leaves can not only increase ventilation and light penetration, but also reduce re-infection by pathogens. Operations such as hilling, removing lower leaves and topping should be done on healthy plants first and diseased plants afterward. When fertilizing, follow “apply sufficient base fertilizer, apply seedling fertilizer early, and apply heavy fertilizer at the bud stage”. Apply sufficient base fertilizer at one time, mainly decomposed barnyard manure or compost, use chemical fertilizers as little as possible, avoid partial application of nitrogen fertilizer, and apply sufficient phosphorus and potassium fertilizer to enhance disease resistance.

4. Irrigation under plastic film

In tomato planting areas with suitable conditions, drip irrigation under plastic film should be adopted. This can not only reasonably save water, reduce labor intensity and improve the field microclimate, but also reduce damage from diseases, pests and weeds. Generally, about 15 days before planting, open furrows and lay drip tubes according to the terrain. In plots with many weeds from the previous crop, herbicides such as paraquat can be sprayed according to the instructions, then black or silver-gray film can be covered, and the plastic film should be sealed and compacted with soil. By covering film in advance, combined with the high temperatures in summer and autumn in the hot areas of Yunnan, some pathogens and weeds can be killed. The use of drip irrigation under film can control water demand at different growth stages of tomato. In actual production, it has also been found that this measure greatly reduces the occurrence and spread of the disease, and is worth promoting and using on a large scale in production areas.