When the root system of the diseased plant is pulled out, the taproot turns black with white mold on it, and the fibrous roots are few and small, weak and curved. The color of fibrous roots changed from healthy white to morbid grayish brown, the epidermis at the base of stem began to turn into grayish brown with different shades, and vascular bundles also turned brown, and gradually extended to plants.
Second, to sum up the cause of the disease, this is that chrysanthemum suffers from Fusarium oxysporum, which is caused by a specialized fungus infection of chrysanthemum, which means that this fungus belongs to chrysanthemum patent and generally does not harm other crops.
The control of chrysanthemum wilt is more difficult because of the following reasons:
1, misjudged the disease. Because the symptoms of chrysanthemum wilt and root rot are similar, it is generally difficult for inexperienced growers to confirm from the plant performance. Although some fungicides for controlling root rot are also effective against Fusarium wilt, they are not targeted after all, and the control effect is not obvious.
2. Continuous cropping is a disaster. Continuous cropping is generally not recommended for chrysanthemum planting. Once continuous cropping for more than three years, soil-borne diseases will begin to increase, and chrysanthemum wilt is also a kind of soil-borne diseases.
Fusarium oxysporum spores can overwinter in soil. The longer the continuous cropping time, the more germs in the soil. The pathogen can occur between 17-37℃, and the optimum temperature is between 24-28℃. Germs can be spread through irrigation water, diseased soil and manual operation. Especially in acidic soil, if nitrogen fertilizer is applied too much, it will encounter high temperature and humidity, water accumulation after rain, or improper artificial watering.
3. Precautionary measures are not in place. For chrysanthemum planted in continuous cropping or transplanted in continuous cropping (even if it is a new crop, the chrysanthemum seedlings cultivated in continuous cropping will carry germs), the soil or seedlings must be disinfected before planting, and chrysanthemum wilt can be prevented in the bud through a series of treatment measures.
Three effective control techniques 1, avoiding continuous cropping for many years and maintaining soil organic matter content. If the planting space is limited and it needs to be replanted year after year, it is necessary to pay attention to the supplement of soil organic matter every year, so that the contents of organic matter and nutrient elements in the soil are not unbalanced and the soil pH is moderate. As the saying goes, rotten eyes attract dust and weak seedlings attract disease. Only by promoting plant health is the root of less illness.
2. It is very important to master watering skills. As potted plants are the main planting method for ornamental chrysanthemums, the planting steps are as follows: now transplant chrysanthemum seedlings to the ground, cover the flowerpot after the slow seedling period is over, and fill the flowerpot with soil while the chrysanthemum seedlings grow in the flowerpot until the flowerpot is filled with soil and the chrysanthemum basically begins to take shape.
Because of this planting method, ordinary advanced irrigation measures are not needed. The hot summer is the critical period of chrysanthemum growth, and a large amount of water transpiration needs continuous supplementary irrigation. If the irrigation measures are unscientific, when watering chrysanthemum pots, it will often cause excessive watering, resulting in water accumulation and root rot. Coupled with high temperature and humidity, it is most likely to induce Fusarium wilt, and at the same time aggravate root rot, and even develop into root rot.
Therefore, it is suggested that when watering chrysanthemums, you can sum up the rules and water requirements of watering chrysanthemums. Don't water them fiercely or frequently, and you can't just water them halfway because you are afraid of watering them.
3, the specific plan of chemical control. For continuous cropping chrysanthemum fields, while paying attention to organic matter supplement, it is suggested that 25% copper acetate 2000g or 50% captan 500g+ 100 billion spores /g Bacillus subtilis 100g should be applied per mu for soil consolidation. These two formulas have obvious effects on controlling Fusarium wilt, and of course, they should be used together in the case of continuous cropping of serious fields.
For example, there is an ideal preventive measure, which is dipping the roots. The commonly used formula is 62.5g/L metalaxyl fludioxonil and 1 1% metalaxyl fludioxonil azoxystrobin suspension seed coating agent 10 ml, which is mixed with 10 kg water and a little soil to make a thin paste (one acre dosage).
For chrysanthemum with Fusarium wilt, it is better to spray the healthy plants and irrigate the diseased plants at the same time. The suggested formula is: 32.5% benomyl 10ml+ 1000 billion spores/g Bacillus subtilis 10 g +80% captan 15.