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油菜主要病害防治方法
油菜对磷、氮、硼、钾等营养元素需求量较大，缺营养元素就会患各种病害，直接导致油菜正常生长发育。
1.1 缺磷的诊断及防治
缺磷症状表现为油菜植株矮小，叶片缩小，叶肉变厚，上部叶片深绿，无光泽，中下部叶片呈紫红色，茎枝细小，角果、种子小。中等肥力田块每公顷施用过磷酸钙450～600 kg作基肥，集中施在根系旁边；初花期喷施0.2%～0.3%磷酸二氢钾溶液1 500 kg或2%过磷酸钙浸出液750～1 125 kg。
1.2 缺氮的诊断及防治
缺氮症状表现为植株瘦小，叶色变黄，分枝较少，根特别细长，角果稀，种子不饱满。氮肥应集中于苗期早施为原则，分次施用并在初花以前施完。移栽油菜要重施基肥，及时追施苗肥和薹肥；直播油菜除部分作种肥外，重点在苗期和薹期施用。
1.3 缺硼的诊断及防治
缺硼症状表现为植株侧根少，无新根，根表皮变褐，根颈膨大，表皮龟裂；茎秆表皮纵裂，角果和茎秆表皮呈蓝紫或紫红色；新叶尖及边缘紫红色，叶畸形；花序变短，花蕾易脱落，花而不实，有的茎基部长出许多小分枝，到成熟期仍开花。采取基施为主、根外喷施为辅的原则，整地时每公顷施用硼砂7.5～11.25 kg作基肥；育苗移栽前2～3 d喷施0.2%硼砂溶液750 kg；蕾薹期或初花期宜用液体硼肥750 g对水750 kg再喷施1次。
1.4 缺钾的诊断及防治
缺钾症状表现为植株矮小，前期叶色变淡，出现白斑，叶缘变褐，茎细而柔弱，节间长，易倒状，易感染病虫害，抗旱、抗害能力下降。每公顷用氯化钾11.25 kg或草木灰1 125～1 500 kg作基肥集中施用。
2.1 菌核病又叫茎腐病，俗称“白秆”“搭叶烂”等，多在油菜盛花期开始发生，落花后盛发，花瓣、老叶先受害，茎秆受害最严重。茎秆感染后早期病斑呈条形淡褐色水渍状，略凹陷，湿度大时，病斑蔓延较快，整个茎秆变成灰白色，表面长出白色绵毛状菌丝，干燥后表皮易裂，后期菌丝在茎内形成大量的黑色鼠粪状颗粒即菌核。叶片受侵染后，病初呈现暗青色不规则水渍状的斑块，后逐渐扩大形成圆形或不规则形状的浅褐或灰褐色轮纹病斑，外围有淡黄色的晕斑，湿度大时，病斑易扩展，上面长有白色菌丝，干燥时，病斑易破裂。
2.2 防治方法
（1）农业防治。选用抗病品种，实行水旱轮作，根据菌核在水中浸泡1个月以上能致死原理，可采用稻-油轮作，麦-油轮作来降低菌核数量；选用无病植株的种子，播时可用10%氯化钠浸种消灭种子表面菌源；油菜田保持排水通畅利于降低田间湿度；播前深翻土地或中耕培土，深埋菌核切断感染源。合理密植、科学施肥。甘蓝型品种每公顷移栽12万～15万株，直播18万～30万株为宜，根据油菜长势合理施用氮、磷、钾及微量元素，培育健壮植株，增强抵抗力；初花期、盛花期摘除植株中下部老叶、病叶、黄叶，减少感染源及改善通风透光条件，降低发病率。
（2）化学防治。发病初期，尤其初花期、盛花期每公顷可用50%多菌灵可湿性粉剂1.5 kg对水750 kg喷雾；或70%甲基硫菌灵可湿性粉剂1.5 kg对水750 kg喷雾；或50%速克灵0.75 kg、40%菌核净1.125 kg对水1.125 kg喷施，选择无雨天气连喷1～3次，每次间隔7 d。
3.1 症 状
油菜病株出现系统性枯斑，老叶片病早，症状明显，后传至新叶。初发病时叶片产生针尖大小透明斑，后扩展成近圆形2～4 mm黄斑，中心呈黑色彩褐色枯死斑，坏死斑四周油渍状。菜薹出现紫黑色梭形至长条形病斑，且从中下部向分枝和果梗上扩展，后期茎上病斑多纵裂或横裂，花、角果易萎蔫或枯死。角果产生黑色枯死斑点，多畸形。
3.2 防治方法
（1）选用抗病品种。因地制宜选用抗病品种，如84001-A35、玉油系列、云油杂系列等。
（2）适期播种。通过调节播种期避开蚜虫迁飞高峰期，降低蚜虫吸毒传毒的机会，减轻发病。姚安县播期一般是10月中下旬，早播会加重病害，过迟不利于油菜生产。秋季干旱少雨，往往与蚜虫迁飞期相吻合，导致苗期发病严重。同时，也为成株期积累了大量毒源，增加病害流行机会，适当延迟播种期有明显减轻苗病发生的作用。
（3）加强栽培管理。培育壮苗，增强抗性。做到苗肥足施、早施，避免偏施、迟施氮肥；结合中耕除草、间苗、定苗时拔除弱苗、病苗。苗床土壤干燥时及时灌溉，控制蚜虫为害。苗床不宜设在毒源寄生较多的蔬菜地附近，避免蚜虫频繁迁飞吸毒传毒。
（4）治蚜防病。有效消灭蚜虫介体或切断毒源很关键。应统筹考虑，连片防治，早治、连续治。要注意防治油菜苗床或大田苗期的蚜虫和毒源寄主植物上的蚜虫，统筹安排，联防联治。苗期有翅蚜植株10%～20%，或平均每株有无翅蚜20头或有翅蚜5头即迅速施药防治。抽薹后有蚜花枝率5%～10%，个别花枝上出现3 cm左右的虫蜡棒时需进行防治。喷药时注意喷在嫩叶、嫩茎及心叶上，正反面都要喷到。如果虫口密度大、为害严重，间隔5～7 d再喷药1次。
（5）药剂防治。发病时每公顷用2%菌克毒克1 500～1 800 mL或10%稼泰1 350 mL对水675 kg均匀喷雾。
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