Sclerotinia sclerotiorum
1. Symptoms
Oil Sunflower can infect any part of the plant during the whole growth period. Because of the different infected position and the different infected period, there are four types of root rot, root rot, root rot, stem rot and disc rot in the field.
1 after infection in seedling stage, the young roots, cotyledons and base of stem could rot, and white villous mould layer appeared on the infected part.
2 root and rhizome rot usually occurred from 6-8 leaves to mature stage. The pathogen could infect the main root, lateral root and rhizome, spread to the base of stem, and cause the infected part to brown and rot gradually, causing the plant to wither and die. The diseased plants, often in the soil or near the ground in the rhizomes there are some black-brown, different size, shape of the sclerotia.
(3) in the stage of adult stem rot, the infected stem usually started from the base of the stem, and after the brown watery spots appeared at the base of the stem, the layer of white villous mould appeared, which continuously expanded upward, making the stem easy to break or break. The hyphae can expand on the surface of the stem when wet, and when dry, a large number of white hyphae and black sclerotia can be seen on the pith of the stem.
4 at the late stage of flowering, the infected disc was infected by the pathogen. At the beginning of the disease, some brown watery spots appeared on the back of the disc, the seeds had musty and bitter taste, and the empty seeds and blighted grains on the diseased disc were 15-20 times of the healthy ones.
2. Prevention and control
1 agricultural control of Sclerotinia sclerotiorum did not infect gramineous crops, but should be done in rotation with gramineous crops. The disease remains are deeply buried in the soil to reduce the source of bacteria.
2 physical control of artificial removal of seed sclerotia, but also the use of warm water. The seeds were immersed in 40-45 ° C water, every 100 kg of seeds with 200 kg of water, stirring for 10-15 minutes, sclerotia water sink, the seeds floating on top, fishing out to dry for seed. When clearing the nucleus in warm water, the bottom of the container is cone-shaped, so that the expanded sclerotium is not easy to float.
3 seed treatment seeds can carry bacteria both inside and outside, more bacteria can be carried by seed coat, and better control effect can be obtained by dressing seeds with medicament. Seed dressing with 0.3% -0.5% of seed weight of dimethachlor, verapamil and Benomyl was effective to control rhizoctonia solani and root rot of seedlings. Seed dressing with Thiram could reduce the incidence of the disease by more than 85% .
4 the resistance of oil sunflower to sclerotinia sclerotiorum is weak, the time of infection is long, and the lack of accurate forecasting method increases the difficulty of chemical control, and Oil Sunflower is a high-stalk crop, the field canopy degree is large, the later control is more difficult. According to research, the best fungicides for controlling Sclerotinia sclerotiorum are 500 times the amount of dimethachlon, 3-(3,5-dichlorophenyl)-5-ethenyl-5-methyl-2,4-oxazolidinedione and sukailing, the second is a mixture of thiophanate-methyl, carbendazim or thiophanate-methyl plus Carbendazim 1∶1,500 times, sprayed at the end of flowering and again 10 days later, it has good effect on the control of Sclerotinia sclerotiorum.
Black spot of oil sunflower
1. Symptoms
The disease can damage the leaves, petioles, stems and disk of oil sunflower. At the beginning of the disease, brown spots 1-3 cm in diameter appeared on the leaves, and when enlarged, they appeared as round, oval or irregular brown spots with light central color and grayish white, with or without concentric rings, sometimes several disease spot fusion, produces the massive blight spot, causes the leaf local scorch, the rupture or forms the perforation. In the case of continuous high humidity, the lesion on both sides of the black mold layer. After the petiole is infected, the petiole dies with the leaf. When infected, the stem produces spindle-shaped or irregular brown spots up to 1-5 cm in length. After infection, many small brown spots appeared at the back edge of the disk, and if the environment was favorable, it would cause local or total decay of the disk, resulting in severe yield loss. In humid climate, the appearance of dark brown fine-velvety or olive-colored mold layer in the disease area is an important feature of the disease.
2. Prevention and control
1 there is no high resistant cultivar of oil sunflower in agricultural control, but the hybrid cultivar is more resistant than the general cultivar, after harvest, oil sunflower should be turned over in late autumn, and the diseased remains should be turned into the soil to reduce the infection source; Crop rotation with gramineous crops is practiced. 2 seed treatment before sowing with 0.3% Thiram, Mancozeb, carbendazim, Benomyl and other fungicides to prevent the seeds from carrying bacteria. In addition, boron, manganese, zinc and other micronutrient were added to seed dressing. 3 the spraying of Carbendazim, Mancozeb and Chlorothalonil 500 times on the leaves had good effect. Thiram and dichlorfon can also be used foliar spray.
Oil sunflower downy mildew
1. Symptoms
The symptoms can be divided into 4 types according to the occurrence period and the characteristics of the symptoms.
1 the dwarfing plants were severely stunted, the internodes were shortened, the root system was poorly developed, the leaves were chlorotic or the mosaic lesions along the main veins or side veins appeared on the leaves, if there was rainfall or high humidity, on the back of the infected leaves, a dense layer of white mold appears. The infected plants often can not form a disk, and even if they do, the disk is very small and the seed-setting rate is very low.
2 the leaf spot type plants grew well, but the large multi-angle chlorotic spot appeared on the leaf front or near the main vein, and the white dense mold layer appeared on the back of the diseased part of the leaf.
3 the flower and fruit victimization type mainly occurred in the late stage of oil sunflower growth and development. The flowers of the infected plants were withered, the seeds were not solid, the seeds were blighted and thin, and the disc was not bent or drooping, and there was no positive reaction.
4 the latent type had no obvious external symptoms, the pathogen was confined in the underground part of the plant, and sometimes infected 25-30 cm above the ground, making the stem pale green and the cells around the pith pale brown. This symptom is the manifestation of the resistance of the plant to the pathogen.
2. Prevention and control
1. Planting disease-resistant varieties for agricultural control, such as Xinkuiza No. 3 and No. 4 were more resistant to downy mildew. Downy mildew can survive in soil for 7-8 years, and its damage can be completely eliminated by 8-10 years of rotation. The disease condition can be obviously reduced by 4-5 years of rotation, the disease could be reduced by using gramineous crops as the preceding crops. It is strictly forbidden to introduce or retain seeds from the diseased areas. The diseased plants are pulled out three times in the reserved fields. The first time, the diseased plants are pulled out at the stage of 2,3 leaves to 4,5 true leaves. The second time, the diseased plants are pulled out before flowering, before the third harvest, the diseased sunflower flower disc was removed, and the diseased plant and flower disc were taken out of the field and buried deeply to ensure that the seeds were disease-free. The spent oil sunflower disc after threshing, if not economically significant, must be burned to reduce the source of primary infection. The control effect of 0.3% metalaxyl WP was still over 93% at the 5th week after emergence, and it was also effective to use metalaxyl Mancozeb or metalaxyl copper for seed dressing, and 0.3% Thiram for seed dressing, or add 0.05% zinc sulfate or magnesium sulfate powder seed dressing also effective. Deep ploughing of soil can reduce the source of primary infection, increase the application of phosphorus fertilizer and apply nitrogen fertilizer rationally. Suitable sowing, suitable depth and shortening the time of seedling emergence can reduce the disease.
(2) metalaxyl, metalaxyl copper, metalaxyl Mancozeb and so on could be sprayed on the leaves at the initial stage of chemical control.
These are the prevention and control techniques of common diseases of oil sunflower introduced in this article. I hope it will be helpful for you to plant oil sunflower.