Tomato (Lycopersicon esculentum) Early Blight and Anthracnose: Symptoms, Treatments and Prevention

Tomato (Lycopersicon esculentum) early blight and anthracnose are relatively common tomato diseases, occurring widely in all regions, and are important diseases harming tomatoes. So what symptoms do these diseases have? What chemicals should be sprayed? How should they be prevented and controlled? Let's find out below.

Tomato (Lycopersicon esculentum) Early Blight

Symptoms:

1. Tomato early blight occurs in Northeast China, North China, East China, Southwest China and other regions. Its most prominent feature is that no matter whether the lesions occur on fruit, leaves or the main stem, they all have obvious concentric rings, so it is also called ring spot disease. Fruit lesions are often near the fruit stalk, stem lesions are often at the branching points, and leaf lesions occur on the leaf mesophyll.

2. It mainly harms leaves, but can also harm seedlings, stems and fruit. When seedlings are infected, dark brown lesions form at the base of the stem, slightly sunken with concentric rings. When leaves are damaged at the adult plant stage, the disease mostly develops from the lower leaves upward. Initially water-soaked dark green lesions appear, which after expanding become circular or irregular ring-patterned spots, with the edges mostly having a light green or yellow halo, and the center showing concentric rings. In humid conditions, black mold (conidia and conidiophores) grows on the lesions, and in severe cases the leaves drop off. When the stem is infected, the lesions are mostly at the branching points and the base of the petioles, appearing as brown to dark brown irregular circular or oval lesions, sunken, with concentric rings, sometimes cracking, and in severe cases causing branch breakage. When green fruit is infected, it mostly starts near the calyx, initially as oval or irregular brown or black spots, sunken, and later the fruit cracks, with the diseased part being relatively hard and densely covered with black mold. When petioles and fruit stalks are infected, the lesions are grayish brown, long oval, and slightly sunken.

Prevention and control measures:

1. Variety selection

Choose disease-resistant varieties. Varieties such as Diliya, Outil, and Kaixuan 158 are relatively resistant and can be used in severely affected areas. Generally, early-maturing varieties and narrow-leaf varieties are less affected, while tall plants, large seedlings and large-leaf varieties are more affected.

2. Pay attention to crop rotation

Since the pathogen can survive for more than one year, attention should be paid to crop rotation. Generally, rotate with non-solanaceous crops for more than two years. When choosing a seedling bed, sufficient attention should also be paid.

3. Seed treatment

On the basis of selecting and retaining seeds from disease-free plots and disease-free plants, in addition to combining with the prevention of other diseases, treat the harvested seeds with dry heat at 70°C for 72 hours (note that the seeds should be given a certain after-ripening transition period after harvest). Before sowing, the seeds can be treated with warm water at 52°C and allowed to cool naturally for 30 minutes, then soaked in cold water and sprouted.

4. Chemical control

(1) Agricultural control

(1) Cultivate strong seedlings: adjust the temperature and humidity of the seedling bed well, and separate the seedlings when they grow to the two-leaf-one-heart stage, being careful to prevent the seedlings from growing too tall and spindly. This can prevent disease during the seedling stage.

(2) Crop rotation and stubble change: tomatoes should be grown in a three-year rotation with non-solanaceous crops.

(3) Strengthen field management: adopt high-ridge cultivation, apply fertilizer reasonably, and after transplanting and seedling recovery, close the ridges in time to promote new root development. In greenhouses, control temperature and humidity well and strengthen ventilation and light transmission management. During the fruiting period, regularly remove lower diseased leaves and bury them deeply or burn them to reduce the chance of disease transmission.

(2) Chemical control

Focus on prevention. From the seedling stage onward, spray every 7-10 days, and transplant with the chemicals applied. The effect is remarkable.

Treatment chemicals:

1. In the early stage of the disease, promptly remove diseased leaves, diseased fruit and severely diseased branches, and begin spraying fungicides. To prevent the development of resistance and improve control efficacy, rotation, alternation or mixed formulation is recommended. Spray once every 7 days, for 2 to 3 consecutive sprays.

2. When the disease is relatively severe, remove the central diseased plants and diseased leaves, and promptly adopt a prevention and control method combining Chinese and Western approaches.

3. Strengthen management. Apply sufficient fully decomposed organic base fertilizer and plant at a reasonable density. When cultivating in sheds or greenhouses, pay attention to ventilation and light transmission and reduce humidity. When cultivating in the open field, pay attention to timely drainage after rain. Carry out a 2-3 year rotation with non-solanaceous crops. In the early stage, promptly remove diseased leaves and diseased fruit and take them out of the field for centralized destruction. After the tomato vines are pulled up, promptly clear residual plants, fallen flowers and fallen fruit from the field, and combine with ploughing the land to do a good job of field sanitation.

4. In greenhouses, pay attention to heat preservation and ventilation. After each watering, ventilation must be carried out to reduce the air humidity inside the greenhouse. Especially at the time of early spring transplanting, the temperature difference between day and night is large and the relative humidity is high, making condensation likely, which favors the occurrence and spread of this disease. Therefore, properly coordinating water, heat and air inside the greenhouse is an effective means of preventing early blight.

Tomato (Lycopersicon esculentum) Anthracnose

Symptoms:

1. The anthracnose pathogen infects fruit before coloring and remains latent until after coloring, when the disease develops. Initially transparent small spots appear, and then the lesions gradually expand and turn black, slightly sunken, with small black dots borne on them. Under humid conditions, the diseased part also secretes red sticky liquid, and finally the fruit rots and drops off. In the middle and late growth stages and during storage, transport and sales after harvest, it can also cause fruit rot and losses.

2. Anthracnose mainly harms nearly mature fruit. Any part of the fruit surface can be infected, generally with the middle part being more commonly affected. Infected fruit first shows moist, discolored small spots, which gradually expand into nearly circular or irregular lesions, 1~1.5 cm in diameter, with the central part slightly sunken and turning blackish brown, with concentric rings and small black grains growing on them. Under relatively high humidity, pink sticky small dots also grow in the later stage. The lesions often crack in a star shape, and there is a ring of orange-yellow halo around the lesion (Figure 1). When the disease is severe, diseased fruit can rot and drop off in the field. Many fruits that were infected but did not develop the disease can successively show symptoms during storage, transport and sales after harvest, causing the number of rotten fruits to continuously increase.

Prevention and control:

1. Strengthen cultivation and disease control management

(1) After harvest, do a good job of cleaning the garden and destroy diseased residues.

(2) Deeply plough and sun the soil, combine with land preparation to apply sufficient high-quality organic base fertilizer, and plant on high beds with deep furrows.

(3) Tomato is a crop with a relatively long growth period, so it must be carefully managed. Promptly prune branches, remove side shoots and tie vines, and weed frequently to facilitate field ventilation and reduce humidity. Harvest promptly when the fruit is ripe to improve harvest quality, and take diseased fruit out of the field for timely destruction.

2. For chemical control, a preventive spray can be applied once during the young fruit stage.

(1) Starting from the green fruit stage, spray 36% thiophanate-methyl suspension concentrate at 500 times dilution, 50% carbendazim·sulfur suspension concentrate at 500 times dilution, 50% thiophanate-methyl wettable powder at 500 times dilution, 50% carbendazim wettable powder at 800 times dilution, or 70% thiophanate-methyl wettable powder at 1000 times dilution plus 75% chlorothalonil wettable powder at 1000 times dilution. The control effect is better than using the above fungicides alone.