How to prevent and control clubroot in rapeseed? A detailed guide to scientific control methods
Rapeseed, also called oil bok choy or bitter greens, Latin name: Brassica campestris L., a plant of the Brassicaceae family and Brassica genus; the tender stems and leaves of rapeseed originated in our country. Its stems are dark green, and its stalks are like those of bok choy. It is a variety of Brassicaceae bok choy, and its flowers are yellow. In agronomy, multiple species of plants whose seeds contain oil are collectively called rapeseed. At present, the main cultivated (variety) types of rapeseed are: bok choy type rapeseed (Brassica rapa (campestris) L.), mustard type rapeseed (Brassica juncea L.), and cabbage type rapeseed (Brassica napus L.). They are mainly distributed in Anhui, Henan, Sichuan and other places. Rapeseed is rich in nutrients, among which the vitamin C content is very high. Rapeseed generally grows in relatively humid climates, such as southern China. Rapeseed also has many uses; for example, rapeseed flowers can be eaten when the buds are unopened; when rapeseed flowers are in full bloom, they are also a beautiful scenic line (Hanzhong City in Shaanxi, China has a rapeseed flower sightseeing tourism area); after the flowers fade, rapeseed seeds can be pressed for oil.
Variety classification of rapeseed
Rapeseed cultivated in China can be divided into three major types: bok choy type, mustard type, and cabbage type.
Bok choy type
Rapeseed is further divided into northern China small rapeseed and southern China oil bok choy. Northern China small rapeseed has a short plant type, few branches, thin stems, poorly developed basal leaves, prostrate growth, elliptical leaf shape, obvious lyre-shaped lobes, and many bristles, covered with a thin layer of waxy bloom. Menyuan rapeseed in Qinghai belongs to this type. Southern China oil bok choy looks very much like ordinary bok choy. Compared with northern small rapeseed, it has a larger plant type, thicker and sturdier stems, loose leaf mesophyll tissue, well-developed basal leaves, wide petioles, and in most cases no waxy bloom. Suzhou cangcai and Xinghua rapeseed belong to this type. Bok choy type rapeseed has medium-sized petals that overlap each other, a shorter growth period, and a somatic chromosome number of 10.
Mustard type
The plant type is tall, with slender branches located high up, basal leaves have obvious petioles, the leaf surface is wrinkled, and it has bristles and waxy bloom. The flowers are small, the petals are smooth and do not overlap, and it has a pungent taste. The somatic chromosome number is 18. Fine-leaf rapeseed and large-leaf rapeseed both belong to this type. Rapeseed planted in the Anshun area of Guizhou is mostly mustard type.
Cabbage type
The plant is medium in size, the leaves are relatively thick and have waxy bloom, the leaf margins are deeply notched, and the leaves are semi-clasping. The leaves on the upper part of the stem are sessile, the flowers are relatively large, the petals overlap, the seeds are relatively large, and it does not have a pungent taste. The somatic chromosome number is 19. Shengli rapeseed, Oro rapeseed and European rapeseed all belong to this type.
Scientific control methods for rapeseed clubroot
Damage symptoms of rapeseed clubroot
The symptoms of rapeseed clubroot appear on the roots. These “tumors” are spindle-shaped or irregularly deformed and mainly occur on the main root, with fewer on the lateral roots. In the early stage, the surface of the “tumors” is smooth and white, and later the color gradually turns brown, the surface becomes rough, and over time cracking also appears. These cracked “tumors” are easily infected by other pathogens and then rot and smell bad. In the early stage of the disease, at noon, because the temperature is high, the transpiration of rapeseed increases, losing a lot of water, and at this time because the roots have been damaged by the “tumors”, the root's ability to absorb water and fertilizer has already decreased. Therefore, under water deficiency, the aboveground part of the diseased plant is prone to wilting; in the morning and evening when the temperature is lower, the transpiration of rapeseed is small, less water is lost, so wilting does not occur. As the condition continues to worsen, the diseased plant will completely wilt and even die.
Scientific control methods for rapeseed clubroot
1. Prevention. For the control of rapeseed clubroot, start first with cultivation management, eliminate or reduce the number of pathogens in rapeseed fields from the source, and create an environment favorable for rapeseed growth and unfavorable for pathogen growth.
Methods: Do not transfer rapeseed seeds from diseased areas; rotate with other non-cruciferous crops, preferably rice; carry out 4~5 years of rotation in heavily diseased fields, which can effectively reduce the disease; build good drainage facilities in rapeseed fields, use deep furrows and narrow beds, clean ditches to prevent waterlogging, and reduce soil moisture; avoid planting rapeseed in low-lying waterlogged plots or acidic soil; fly ash compound fertilizer can be used to improve the soil. Choose fields without this disease for raising seedlings to prevent the spread of pathogens. After rapeseed harvest, diseased and residual plants should be burned or composted. Note: compost must be fully decomposed before it can be used in rapeseed fields. Taking the above measures can reduce many opportunities for disease occurrence, but it does not mean the disease will no longer occur.
2. Treatment. When a small number of clubroot-infected plants appear in the field, the diseased plants need to be pulled out in time, and quicklime should be scattered into the diseased holes for soil disinfection. If there are many diseased plants, 50% carbendazim wettable powder 500-fold solution can also be used to drench the roots, 250 milliliters per plant; or 40% quintozene powder 500-fold solution can be used to drench the roots, 400~500 milliliters per plant, which can also effectively control the condition.