What are the control methods for downy mildew in mustard?

Mustard (Brassica juncea) is an annual or biennial herbaceous plant of the genus Brassica in the family Cruciferae (crucifers). It is a famous specialty vegetable of China, native to China, and a commonly cultivated vegetable throughout the country, mostly distributed in the provinces south of the Yangtze River. The main and lateral roots of mustard are distributed within about 30 cm of the soil layer; the stem is a shortened stem, and the leaves are borne on the shortened stem. They come in elliptical, ovate, obovate, lanceolate and other shapes, and the leaf color is green, dark green, light green, yellow-green, green with stripes, or purplish red. It is rarely cultivated in European and American countries and originated in Asia.

Morphological characteristics of mustard

Mustard (the original variety) is an annual herb, 30-150 cm tall, usually hairless, sometimes with bristles on young stems and leaves, covered with a waxy bloom, and with a pungent taste; the stem is erect and branched. The basal leaves are broadly ovate to obovate, 15-35 cm long, with a rounded-obtuse apex and a wedge-shaped base, lyrately pinnatifid, with 2-3 pairs of lobes, or not lobed, and the margins all have incisions or teeth; the petiole is 3-9 cm long and bears small lobes; the lower stem leaves are smaller, with incisions or teeth on the margins, sometimes with rounded-obtuse serrations, and do not clasp the stem; the upper stem leaves are narrowly lanceolate, 2.5-5 cm long and 4-9 mm wide, with inconspicuous sparse teeth or entire margins.

The raceme is terminal and elongates after flowering; the flowers are yellow, 7-10 mm in diameter; the pedicel is 4-9 mm long; the sepals are pale yellow, oblong-elliptic, 4-5 mm long, erect and spreading; the petals are obovate, 8-10 mm long and 4-5 mm wide. The silique is linear, 3-5.5 cm long and 2-3.5 mm wide, and the valves have 1 prominent midvein; the beak is 6-12 mm long; the fruiting pedicel is 5-15 mm long. The seeds are spherical, about 1 mm in diameter, and purplish brown. The flowering period is March-May, and the fruiting period is May-June.

Control of downy mildew, a disease of mustard

What is downy mildew?

Downy mildew is also called "baking disease" and "galloping horse dryness", etc. It mainly harms cruciferous vegetables such as mustard, Chinese cabbage, bok choy, cabbage and radish. It occurs commonly in all parts of the country and causes very serious damage. Symptoms of downy mildew, a disease of mustard:

It mainly harms the leaves, followed by the stems, pedicels and seed pods. The disease starts from the outer leaves. Light green to light yellow small spots appear on the upper surface of the leaves, and after expanding they become yellowish brown and form polygonal spots due to the restriction by the leaf veins. When humid, white mold is produced on the underside of the lesions. In severe cases, a large number of outer leaves die. When seed plants are affected, white mold and deformities grow on the stems, pedicels, floral organs and seed pods. The seed pods are light yellow, with dark brown long round streaks, small and curved, and bear few seeds. Conditions for the onset of downy mildew, a disease of mustard:

This disease is a fungal disease. The pathogen overwinters in the soil with the diseased plant residues, and can also overwinter on the mother plant. The following year it spreads and infects via wind and rain. The disease develops rapidly at 16-20 degrees C, and epidemics are severe when there is much rain, much dew and insufficient sunlight. In addition, the disease is severe under continuous cropping, repeated cropping, low-lying land, poor ventilation, excessive density, poor nutrition and weak growth. When viral disease occurs severely in the field, downy mildew also occurs severely. Disease resistance also differs among different varieties. Control methods for downy mildew, a disease of mustard:

(1) Select disease-resistant varieties.

(2) Seed disinfection: before sowing, dress the seeds with 0.3% of the seed weight of 50% thiram, or 25% metalaxyl, or 75% chlorothalonil, to eliminate the pathogens on the seed surface.

(3) Reasonable crop rotation and timely sowing: rotate with cruciferous crops every other year, and avoid cruciferous crops as adjacent crops, to reduce sources of infection. Appropriately delay the sowing date for autumn and winter cultivation to avoid high temperature and rainy seasons.

(4) Field management: remove diseased and weak seedlings in time at the seedling stage; clean the field in time after harvest and plow the soil deeply to reduce sources of the disease. Apply sufficient organic fertilizer and increase the application of phosphorus and potassium fertilizers; water in time during the growing period, apply sufficient topdressing, and ensure robust plant growth to enhance disease resistance.

(5) Chemical control: at the early stage of the disease, use 40% phosethyl-Al at 300 times dilution, 25% metalaxyl at 800 times dilution, 64% oxadixyl M8 at 500 times dilution, 72.2% propamocarb at 600-1000 times dilution, or Daconil M-45 at 400-600 times dilution. Use one of the above chemicals, or apply them alternately in rotation, once every 7-10 days, for 3-4 consecutive sprays.