Identification and Control Methods for Vegetable Fusarium Wilt and Bacterial Wilt
Identification and Management of Vegetable Fusarium Wilt and Bacterial Wilt
Many kinds of vegetables can be affected by Fusarium wilt and bacterial wilt. For example, watermelon, melon, cucumber, winter melon, broad bean, cowpea, pepper, tomato, potato and others can develop Fusarium wilt; pepper, tomato, potato, eggplant and some leguminous vegetables can develop both Fusarium wilt and bacterial wilt. These two diseases are very common on vegetables, and their occurrence is also severe, often causing 30% to 50% loss of vegetables, or even total crop failure. Therefore, correctly distinguishing and identifying these two diseases and taking targeted corresponding measures for prevention and control is particularly important.
1 Identification of the Two Diseases
These two diseases often occur simultaneously on vegetables, and their external symptoms are in some ways extremely similar. The common notable characteristic of both diseases is that they both belong to vascular bundle diseases, manifesting as plant wilting and blighting. In the early stage of disease, both show drooping and wilting of leaves and shoot tips, especially more obvious at noon or under strong light, while they can recover to normal in the early morning and evening; in the middle stage of disease, when diseased plants are pulled up and the stems are dissected, the vascular bundles have already turned brown; in the late stage of disease, the diseased plants wither and die. Although the symptoms are very similar, as long as field diagnosis is carefully carried out and the entire disease development process is monitored, they can be distinguished.
1) The types of pathogenic bacteria causing the diseases are different. Fusarium wilt is a fungal disease caused by Fusarium oxysporum of the genus Fusarium in the subdivision Deuteromycotina, while bacterial wilt is a bacterial disease caused by the rod-shaped bacterium Pseudomonas solanacearum.
2) The speed of plant wilting differs. Bacterial wilt develops rapidly; from the appearance of symptoms, it takes only 4-6 d for the plant to wither and die, showing acute wilting of the whole plant, while Fusarium wilt plants begin with leaf drooping and withering until death, requiring 12-15 d; the speed and time of withering are 8-9 d slower than the former.
3) The location and order of leaf wilting on diseased plants differ. Fusarium wilt diseased plants start from the lower leaves and wilt progressively from bottom to top. Leaf color gradually changes from green to pale, from yellow to withered yellow, and then to brown. The leaves basically do not fall off, and the whole plant dies. The plant is stunted, and the tender stems droop and bend. For example, melon Fusarium wilt can occur throughout the entire growth period, with the heaviest occurrence from flowering to fruit-setting stage. When seedlings are affected, roots are few, leaves shrink, and then the whole plant lodges and dies. In the flowering and fruit-setting stage of adult plants, leaves wilt successively from bottom to top; at the initial stage of disease, they wilt during the day and recover to normal in the morning and at night, and after 10 d they appear withered and are easy to pull up. Another example is watermelon Fusarium wilt, which mostly occurs after fruit setting in adult plants. Diseased plants grow slowly, and the lower leaves first wither and turn yellow, developing progressively upward. At first they wilt during the day and recover in the morning and evening, and after several days the whole plant wilts and dies. Bacterial wilt diseased plants differ from Fusarium wilt in that the young leaves at the upper tips, tender shoots and newly unfolded tender leaves wilt. Without waiting for leaves to wither, turn yellow and change color, the whole plant quickly loses water, becomes green-wilted and withers. For example, bacterial wilt of pepper, tomato and potato all manifest as wilting of green leaves and green branches.
4) The symptoms and signs shown by diseased plants differ. On Fusarium wilt diseased plants when humid, yellow-white or pink mold-like substances can be seen at the base of the stem (vine or tendril); these are the fungal conidiophores and conidia. For example, on the base of melon Fusarium wilt vines, brown streaks or longitudinal cracking of the epidermal layer are common. When humid, resinous gum exudes, the vascular bundles in the stem turn brown, the vine becomes water-soaked and rots, and white cornmeal-pink mold-like substances appear on the surface. In contrast, bacterial wilt only shows disease symptoms on the external stem, leaves, branches and other parts, and does not produce signs (pathogens). Only after cutting the diseased stem crosswise and squeezing the discolored vascular bundles by hand does white bacterial fluid overflow; this is its pathogenic bacterium. If the cross-cut diseased stem is immersed in a glass bottle containing light salt water, a milky white mist-like substance can also be seen spraying out from the cut, which of course is also the pathogenic bacterium.
2 Control Methods
Vegetable Fusarium wilt and bacterial wilt are two stubborn diseases that are very difficult to cure. They can be transmitted by soil, seeds, fertilizers, manure, water flow and wounds caused during agricultural operations. The pathogens invade from root wounds and root hair tips, secrete toxins in the crop vascular conduits, block the conduits, affect the normal transport of water and nutrients, and cause crop wilting and death. The conditions for their occurrence are high temperature and high humidity (20-25°C, relative humidity above 80% is suitable for disease occurrence), continuous cropping, excessive application of nitrogen fertilizer, poor drainage and irrigation, unrotted fertilizer, phosphorus deficiency and potassium deficiency, etc., all of which can lead to the occurrence of Fusarium wilt and bacterial wilt. At present, there is no effective pesticide to completely cure these two diseases, and comprehensive integrated control techniques must be adopted to be effective.
1) Rational crop rotation, staying away from pathogen sources. The pathogens of Fusarium wilt and bacterial wilt are both "soil inhabitant fungi." Fusarium wilt pathogens overwinter in the soil as fungal mycelium, thick-walled spores or sclerotia, and can live saprophytically in diseased residues for 5-7 years; bacterial wilt pathogens can also overwinter in the soil with diseased residues, surviving from 14 months to 7 years. Therefore, as long as these two pathogens remain in the soil, once the land is infected in 1 year, the disease will occur every year. Therefore, on land where the disease has occurred, 2-5 years of rotation and crop replacement should be implemented, or water-dryland rotation is even more effective. At the same time, before planting, diseased residues must be thoroughly removed and burned, diseased plants must not be used for composting, unrotted organic fertilizer must not be applied, agricultural operations should minimize wounds on vegetable plants, drainage and irrigation conditions should be improved, and pathogen sources should be avoided in many ways.
2) Select, breed and promote disease-resistant cultivars for cultivation. The pathogens of Fusarium wilt and bacterial wilt have physiological race differentiation, and different physiological races have different pathogenic abilities and host ranges. Therefore, selecting and promoting disease-resistant vegetable varieties is possible, and this is an effective way and necessary measure to resist and reduce disease. Generally, early-maturing tomato varieties are all resistant to bacterial wilt; those already promoted include Kangqing 19, Hongkang No. 1 and No. 2, 28A, Shuzzao No. 3, Xiang Tomato No. 1, Qiuxing, Xiangyin; those bred in Guangdong include Zaokang No. 1, Kangqing No. 1, Yuehongyu, Yuexing, Xiaxing, Fengshun, Hybrid No. 1 and No. 2 and other varieties. Varieties resistant to tomato Fusarium wilt include Xi'an Dahong, Qiangli Mishou, Mansi, Sukang No. 3, Shuzzao No. 3, Yukang No. 4, Qiangfeng, Folomide and others. Varieties resistant to watermelon Fusarium wilt include Jingxin No. 1, Bianliang No. 1, Hongdouren, Dafengxin, Jinzhong Guanlong, Duoli, Xindeng, Longhua, Longbao, Jingkang No. 2 and No. 3, Zhengkang No. 1 and No. 2, Zhengzhou 8902 and 8903. Those resistant to cucumber Fusarium wilt include Jingyan No. 5 and No. 7, Jinza No. 1, No. 2, No. 3 and No. 4, Jinchun No. 4, Zaofeng No. 2, Zhongnong No. 5 and others; varieties resistant to common bean Fusarium wilt include Fengshou No. 1, Jinzhou Shuangjidou, Jiuli, Qingdao Dou, Chunfeng No. 1 and No. 2, Qiukang 19 and others; varieties resistant to cowpea Fusarium wilt include Guangdong Zhuchangdou, Zhuyan, Xiyuan, Jietu No. 1, Changde Doujiao and others. Varieties resistant to pepper bacterial wilt include Zaoza No. 2, Tongjiao No. 1 and other varieties. In addition, Zhejiang used CHZ-26 as a disease-resistant rootstock to graft eggplant, and Hainan used pumpkin as a rootstock to graft watermelon against Fusarium wilt, and large-area cultivation achieved success.
3) Disinfect seeds and vegetable seedbeds to eliminate pathogen sources. ① Seed treatment. Soak seeds in warm water or hot water. This method is effective against both Fusarium wilt and bacterial wilt. The specific method is to soak seeds in warm water at 53-55°C using 3-4 times the seed weight for 15 min, stirring while soaking, and stop stirring when the water temperature drops to about 36°C, then continue soaking for 4-5 h before promoting germination and sowing; for melon and vegetable seeds, which take a long time to germinate, hot water scalding can be used: use the same amount of water as above at 70-75°C, pour the melon seeds into it, then repeatedly pour back and forth with another small bucket, and when the hot water cools to slightly hot to the touch, stir for 10 min. ② Chemical disinfection. For bacterial wilt, seeds can be soaked in 600-fold trichloroisocyanuric acid solution for 6-8 h. For the control of both Fusarium wilt and bacterial wilt, seeds can be soaked in 100-fold 40% formaldehyde solution for 15 min. For Fusarium wilt, 50% thiram WP can be used to dress seeds at 0.3%-0.4% of seed weight. Vegetable seedbeds can be replaced with disease-free bed soil, and sprayed for disinfection with 70% thiophanate-methyl WP or 50% carbendazim WP, 75% disulfoton sodium SP at 400-fold solution.
4) Suppress pathogen reproduction and spread. Fusarium wilt is prone to occur in clayey soil, acidic soil and plots where acidic chemical fertilizers are excessively applied. Soil pH 5-5.6 is most prone to disease. Therefore, lime can be applied to adjust soil pH and inhibit disease development, and the soil additive S-H developed in Taiwan Province, China (main components urea, mineral ash and organic matter) can also be applied. Fusarium wilt and bacterial wilt are extremely prone to outbreak after long rain followed by sudden high temperature, or after long clear high temperature and drought followed by continuous rain and muggy weather, causing patchy wilting and death. Therefore, throughout the entire cultivation process, field temperature and humidity should be regulated, soil should be kept dry, moisture should be removed and waterlogging eliminated, deep furrows and high ridges should be used, appropriate dense planting should be adopted, timely pruning should be done, fruit retention and fruit protection should be moderate, field ventilation and light transmission should be maintained, a good ecological environment should be created, nitrogen fertilizer should be applied appropriately, phosphorus and potassium fertilizers should be increased, soil testing and formula fertilization should be implemented, balanced growth should be promoted, and during the flowering and fruiting period, 1-3 sprays of potassium dihydrogen phosphate (KH2PO4) and other fertilizer-pesticide mixed solutions should be applied. These health-promoting cultivation management measures can achieve immediate results in suppressing disease spread and increasing plant disease resistance and immunity. Spraying 2% pyrimidine nucleoside antibiotic AC at 500-fold solution in the initial stage of disease has a certain effect on resisting disease, protecting plants, and preventing and resisting disease outbreaks.
5) Chemical control. Apply some high-efficiency, low-toxicity, low-residue pesticides to kill and control pathogens. For Fusarium wilt control, spray 70% thiophanate-methyl WP at 500-600-fold solution or 50% carbendazim WP at 400-fold solution, 40% fosetyl-aluminum WP at 500-fold solution; for bacterial wilt control, spray 72% agricultural streptomycin sulfate WP at 4000-fold solution. Spraying 14% copper ammonia complex AS at 400-fold solution or 50% copper succinate-glutamate WP at 400-fold solution, 77% copper hydroxide WP at 400-fold solution is effective against both Fusarium wilt and bacterial wilt.
1 Identification of the Two Diseases
These two diseases often occur simultaneously on vegetables, and their external symptoms are in some ways extremely similar. The common notable characteristic of both diseases is that they both belong to vascular bundle diseases, manifesting as plant wilting and blighting. In the early stage of disease, both show drooping and wilting of leaves and shoot tips, especially more obvious at noon or under strong light, while they can recover to normal in the early morning and evening; in the middle stage of disease, when diseased plants are pulled up and the stems are dissected, the vascular bundles have already turned brown; in the late stage of disease, the diseased plants wither and die. Although the symptoms are very similar, as long as field diagnosis is carefully carried out and the entire disease development process is monitored, they can be distinguished.
1) The types of pathogenic bacteria causing the diseases are different. Fusarium wilt is a fungal disease caused by Fusarium oxysporum of the genus Fusarium in the subdivision Deuteromycotina, while bacterial wilt is a bacterial disease caused by the rod-shaped bacterium Pseudomonas solanacearum.
2) The speed of plant wilting differs. Bacterial wilt develops rapidly; from the appearance of symptoms, it takes only 4-6 d for the plant to wither and die, showing acute wilting of the whole plant, while Fusarium wilt plants begin with leaf drooping and withering until death, requiring 12-15 d; the speed and time of withering are 8-9 d slower than the former.
3) The location and order of leaf wilting on diseased plants differ. Fusarium wilt diseased plants start from the lower leaves and wilt progressively from bottom to top. Leaf color gradually changes from green to pale, from yellow to withered yellow, and then to brown. The leaves basically do not fall off, and the whole plant dies. The plant is stunted, and the tender stems droop and bend. For example, melon Fusarium wilt can occur throughout the entire growth period, with the heaviest occurrence from flowering to fruit-setting stage. When seedlings are affected, roots are few, leaves shrink, and then the whole plant lodges and dies. In the flowering and fruit-setting stage of adult plants, leaves wilt successively from bottom to top; at the initial stage of disease, they wilt during the day and recover to normal in the morning and at night, and after 10 d they appear withered and are easy to pull up. Another example is watermelon Fusarium wilt, which mostly occurs after fruit setting in adult plants. Diseased plants grow slowly, and the lower leaves first wither and turn yellow, developing progressively upward. At first they wilt during the day and recover in the morning and evening, and after several days the whole plant wilts and dies. Bacterial wilt diseased plants differ from Fusarium wilt in that the young leaves at the upper tips, tender shoots and newly unfolded tender leaves wilt. Without waiting for leaves to wither, turn yellow and change color, the whole plant quickly loses water, becomes green-wilted and withers. For example, bacterial wilt of pepper, tomato and potato all manifest as wilting of green leaves and green branches.
4) The symptoms and signs shown by diseased plants differ. On Fusarium wilt diseased plants when humid, yellow-white or pink mold-like substances can be seen at the base of the stem (vine or tendril); these are the fungal conidiophores and conidia. For example, on the base of melon Fusarium wilt vines, brown streaks or longitudinal cracking of the epidermal layer are common. When humid, resinous gum exudes, the vascular bundles in the stem turn brown, the vine becomes water-soaked and rots, and white cornmeal-pink mold-like substances appear on the surface. In contrast, bacterial wilt only shows disease symptoms on the external stem, leaves, branches and other parts, and does not produce signs (pathogens). Only after cutting the diseased stem crosswise and squeezing the discolored vascular bundles by hand does white bacterial fluid overflow; this is its pathogenic bacterium. If the cross-cut diseased stem is immersed in a glass bottle containing light salt water, a milky white mist-like substance can also be seen spraying out from the cut, which of course is also the pathogenic bacterium.
2 Control Methods
Vegetable Fusarium wilt and bacterial wilt are two stubborn diseases that are very difficult to cure. They can be transmitted by soil, seeds, fertilizers, manure, water flow and wounds caused during agricultural operations. The pathogens invade from root wounds and root hair tips, secrete toxins in the crop vascular conduits, block the conduits, affect the normal transport of water and nutrients, and cause crop wilting and death. The conditions for their occurrence are high temperature and high humidity (20-25°C, relative humidity above 80% is suitable for disease occurrence), continuous cropping, excessive application of nitrogen fertilizer, poor drainage and irrigation, unrotted fertilizer, phosphorus deficiency and potassium deficiency, etc., all of which can lead to the occurrence of Fusarium wilt and bacterial wilt. At present, there is no effective pesticide to completely cure these two diseases, and comprehensive integrated control techniques must be adopted to be effective.
1) Rational crop rotation, staying away from pathogen sources. The pathogens of Fusarium wilt and bacterial wilt are both "soil inhabitant fungi." Fusarium wilt pathogens overwinter in the soil as fungal mycelium, thick-walled spores or sclerotia, and can live saprophytically in diseased residues for 5-7 years; bacterial wilt pathogens can also overwinter in the soil with diseased residues, surviving from 14 months to 7 years. Therefore, as long as these two pathogens remain in the soil, once the land is infected in 1 year, the disease will occur every year. Therefore, on land where the disease has occurred, 2-5 years of rotation and crop replacement should be implemented, or water-dryland rotation is even more effective. At the same time, before planting, diseased residues must be thoroughly removed and burned, diseased plants must not be used for composting, unrotted organic fertilizer must not be applied, agricultural operations should minimize wounds on vegetable plants, drainage and irrigation conditions should be improved, and pathogen sources should be avoided in many ways.
2) Select, breed and promote disease-resistant cultivars for cultivation. The pathogens of Fusarium wilt and bacterial wilt have physiological race differentiation, and different physiological races have different pathogenic abilities and host ranges. Therefore, selecting and promoting disease-resistant vegetable varieties is possible, and this is an effective way and necessary measure to resist and reduce disease. Generally, early-maturing tomato varieties are all resistant to bacterial wilt; those already promoted include Kangqing 19, Hongkang No. 1 and No. 2, 28A, Shuzzao No. 3, Xiang Tomato No. 1, Qiuxing, Xiangyin; those bred in Guangdong include Zaokang No. 1, Kangqing No. 1, Yuehongyu, Yuexing, Xiaxing, Fengshun, Hybrid No. 1 and No. 2 and other varieties. Varieties resistant to tomato Fusarium wilt include Xi'an Dahong, Qiangli Mishou, Mansi, Sukang No. 3, Shuzzao No. 3, Yukang No. 4, Qiangfeng, Folomide and others. Varieties resistant to watermelon Fusarium wilt include Jingxin No. 1, Bianliang No. 1, Hongdouren, Dafengxin, Jinzhong Guanlong, Duoli, Xindeng, Longhua, Longbao, Jingkang No. 2 and No. 3, Zhengkang No. 1 and No. 2, Zhengzhou 8902 and 8903. Those resistant to cucumber Fusarium wilt include Jingyan No. 5 and No. 7, Jinza No. 1, No. 2, No. 3 and No. 4, Jinchun No. 4, Zaofeng No. 2, Zhongnong No. 5 and others; varieties resistant to common bean Fusarium wilt include Fengshou No. 1, Jinzhou Shuangjidou, Jiuli, Qingdao Dou, Chunfeng No. 1 and No. 2, Qiukang 19 and others; varieties resistant to cowpea Fusarium wilt include Guangdong Zhuchangdou, Zhuyan, Xiyuan, Jietu No. 1, Changde Doujiao and others. Varieties resistant to pepper bacterial wilt include Zaoza No. 2, Tongjiao No. 1 and other varieties. In addition, Zhejiang used CHZ-26 as a disease-resistant rootstock to graft eggplant, and Hainan used pumpkin as a rootstock to graft watermelon against Fusarium wilt, and large-area cultivation achieved success.
3) Disinfect seeds and vegetable seedbeds to eliminate pathogen sources. ① Seed treatment. Soak seeds in warm water or hot water. This method is effective against both Fusarium wilt and bacterial wilt. The specific method is to soak seeds in warm water at 53-55°C using 3-4 times the seed weight for 15 min, stirring while soaking, and stop stirring when the water temperature drops to about 36°C, then continue soaking for 4-5 h before promoting germination and sowing; for melon and vegetable seeds, which take a long time to germinate, hot water scalding can be used: use the same amount of water as above at 70-75°C, pour the melon seeds into it, then repeatedly pour back and forth with another small bucket, and when the hot water cools to slightly hot to the touch, stir for 10 min. ② Chemical disinfection. For bacterial wilt, seeds can be soaked in 600-fold trichloroisocyanuric acid solution for 6-8 h. For the control of both Fusarium wilt and bacterial wilt, seeds can be soaked in 100-fold 40% formaldehyde solution for 15 min. For Fusarium wilt, 50% thiram WP can be used to dress seeds at 0.3%-0.4% of seed weight. Vegetable seedbeds can be replaced with disease-free bed soil, and sprayed for disinfection with 70% thiophanate-methyl WP or 50% carbendazim WP, 75% disulfoton sodium SP at 400-fold solution.
4) Suppress pathogen reproduction and spread. Fusarium wilt is prone to occur in clayey soil, acidic soil and plots where acidic chemical fertilizers are excessively applied. Soil pH 5-5.6 is most prone to disease. Therefore, lime can be applied to adjust soil pH and inhibit disease development, and the soil additive S-H developed in Taiwan Province, China (main components urea, mineral ash and organic matter) can also be applied. Fusarium wilt and bacterial wilt are extremely prone to outbreak after long rain followed by sudden high temperature, or after long clear high temperature and drought followed by continuous rain and muggy weather, causing patchy wilting and death. Therefore, throughout the entire cultivation process, field temperature and humidity should be regulated, soil should be kept dry, moisture should be removed and waterlogging eliminated, deep furrows and high ridges should be used, appropriate dense planting should be adopted, timely pruning should be done, fruit retention and fruit protection should be moderate, field ventilation and light transmission should be maintained, a good ecological environment should be created, nitrogen fertilizer should be applied appropriately, phosphorus and potassium fertilizers should be increased, soil testing and formula fertilization should be implemented, balanced growth should be promoted, and during the flowering and fruiting period, 1-3 sprays of potassium dihydrogen phosphate (KH2PO4) and other fertilizer-pesticide mixed solutions should be applied. These health-promoting cultivation management measures can achieve immediate results in suppressing disease spread and increasing plant disease resistance and immunity. Spraying 2% pyrimidine nucleoside antibiotic AC at 500-fold solution in the initial stage of disease has a certain effect on resisting disease, protecting plants, and preventing and resisting disease outbreaks.
5) Chemical control. Apply some high-efficiency, low-toxicity, low-residue pesticides to kill and control pathogens. For Fusarium wilt control, spray 70% thiophanate-methyl WP at 500-600-fold solution or 50% carbendazim WP at 400-fold solution, 40% fosetyl-aluminum WP at 500-fold solution; for bacterial wilt control, spray 72% agricultural streptomycin sulfate WP at 4000-fold solution. Spraying 14% copper ammonia complex AS at 400-fold solution or 50% copper succinate-glutamate WP at 400-fold solution, 77% copper hydroxide WP at 400-fold solution is effective against both Fusarium wilt and bacterial wilt.