The reason why broccoli bulbs are purple

1.1 Downy mildew mostly occurs in the rosette stage, the lower leaves appear yellow-brown polygonal or irregular spots with inconspicuous edges and limited by leaf veins, and white mildew occurs on the back of the leaves when it is wet. Generally, the disease is serious when there is high temperature and rain, large temperature difference between day and night, lack of sunshine, stagnant water in soil and high plant density.

1.2 Brown spot mainly harms leaves, flower heads and pods. The lower old leaves fell ill first, and there were round brown disease spots on the front or back of the leaves, with concentric lines; when the humidity was high, the black mildew layer grew in the affected part. In general, in the middle and later stages of growth, the disease is serious in case of continuous rain or lack of fertility.

1.3 Botrytis cinerea is mainly harmful to inflorescences, but also to stems and leaves. The tissue of the disease showed a light brown water stain, and then soft rot, covered with gray mildew. Germs spread through airflow, Rain Water and agricultural operations, and invaded the body from the wound or aging site. Seedlings are easy to occur under the conditions of poor growth, high density and high air relative humidity.

1.4 Sclerotinia sclerotiorum mostly occurs in the heading stage, flowering and podding stage. Generally, the disease begins at the base of the stem and petiole near the ground, and the disease spot shows brown water stains at the beginning. After the petiole is damaged, the leaves wither and droop due to the cut-off of water supply. In the case of high humidity, the disease is covered with white cotton-like sclerotia. The disease is transmitted by soil and is easy to occur under warm and humid conditions.

1.5 Black rot is harmful to leaves and bulbs. The disease of adult plants usually begins from the lower leaves. Most of the disease spots began to form V-shaped withered spots inward from the leaf edge, and the bacteria spread downward along the leaf veins to form large necrotic areas or irregular yellow-brown spots, and the leaf tissue at the edge of the disease spot was light yellow. After entering the vascular bundle of the stem, the pathogen gradually spread to the bulb or leaf vein and petiole, causing vascular bundle necrosis, blackening, and finally withering, but odorless, and the bulb black heart under dry conditions. In the field, the pathogen is mainly transmitted through diseased plants, fertilizers, wind and rain or farm tools. The disease is easy to occur under the conditions of general seed carrying bacteria, high temperature and heavy rain, improper fertilizer and water management, continuous cropping with cruciferous crops, rampant pests and so on.

1.6 soft rot mostly occurs in the heading stage and podding stage. Most of the bacteria invaded from the wound, and water immersion spots appeared at the base of the outer leaf or bulb at the beginning; when the damage was serious, the whole plant rotted, exudated purulent mucus, and the diseased part gave off a bad smell. Germs spread through Rain Water, irrigation water, bacteria-carrying fertilizers, insects and so on. The disease is easy to occur in seeds with bacteria, high temperature and humidity, excessive watering, many underground pests and continuous cropping.

1.7 virus diseases can be damaged in both seedling stage and adult stage. When infected at seedling stage, chlorosis, near-round spots and 2~3mm in diameter appeared on the leaves, and then the color of the whole leaves became lighter or became dense and light mottled. When the adult plant is infected, in addition to the thick and uneven mottle of the young leaf, there are black necrotic spots on the back of the old leaf, and the ball of the diseased plant is late and loose. In production, the disease is serious when there are early sowing, many poison sources or aphids, coupled with improper management, low terrain, lack of ventilation, or lack of water and fertilizer.

2 comprehensive prevention and control

2.1 the slightly acidic soil with good drainage, loose and fertile soil should be selected reasonably.

2.2 the nutrient soil for bed soil disinfection and seedling breeding must be piled up for a long time and sealed with formalin.

2.3Seeds were disinfected and soaked in 50-55 ℃ lukewarm water for 20 minutes and stirred continuously.

2.4 crop rotation and non-cruciferous vegetable rotation can effectively reduce the occurrence of diseases and insect pests.

2.5 strengthen seedling management, time seedling and seedling division, timely ventilation, reduce air humidity, and remove diseased seedlings in time.

2.6 strengthening the management of water and fertilizer, broccoli likes fertilizing water, forcing fertilizer and watering by stages and timely is the key to high yield. It is advocated to apply fully mature organic fertilizer, and compound fertilizer can be used for topdressing. Timely trench drainage in the rainy season to prevent soil stagnant water, so as not to cause retting roots.

2.7 improve growth conditions and clean the countryside in time; remove diseased leaves and old leaves in time; remove residual plants and rotten leaves in the field in time after harvest; and disinfect disease holes in order to reduce the source of bacteria. High border cultivation is adopted to effectively regulate soil temperature and humidity and improve the conditions of light, ventilation and drainage. When ploughing and weeding, we should avoid injuring leaves and cutting roots, and destroy diseased plants in time so as to reduce the route of transmission.

5000 times of agricultural streptomycin or chloramphenicol can be used to control fungal diseases such as downy mildew, Sclerotinia sclerotiorum, etc. at the initial stage of the disease, 50% carbendazim or 75% chlorothalonil can be sprayed once every 7 to 10 days for 2 times in a row, which can effectively control the occurrence of the disease. Spray insecticides regularly to kill aphids and other pests and cut off the route of transmission.