杭州地区油菜病毒病的发病规律及防治研究

油菜苗期病毒病的发生,决定于带毒有翅蚜从毒源寄主上迁入的时间与虫口数;本田期病毒病的流行为害,在很大程度上与苗床后期和本田初期有翅若蚜的长成和扩散有关。杭州地区的传毒蚜虫主要为菜缢管岈,其有翅蚜的发生及迁飞高峯期约在9月下旬至10月下旬,油菜病毒病发病率的高峯与有翅蚜发生高峯成正相关。本研究进一步证实了带病的十字花科杂蔊菜的蓿根,越夏后萌发的植株是秋菜及油菜的重要毒源之一。在7月中旬正8月上旬的炎热夏天仅看到火白菜是菜缢管蚜的寄主,但未检查到病株,另一试验火白菜感病后无隐蔽现象。杭州地区10月份的降水量、降雨天数以及相对湿度对当年病毒病流行与否影响最大,天气干旱病毒病相当严重。暴雨或连续降雨两天以上能影响有翅蚜,发生量与迁飞量显著下降,因而在一定程度上抑制了病毒病的蔓延。播种时用6%可湿性六六六粉每亩3斤撒施畦面,苗床期两片真叶开始,连续用乐果及二二三、六六六混合液治蚜4次,与加强肥水管理,效果达84.7%。

SOME FACTORS RELATING TO DISEASE PREVALENCE OF THE RAPE MOSAIC DISEASE IN HANGCHOW,CHEKIANG AND NOTES ON THE PRELIMINARY CONTRO

1.In the field,the prevalence and severence of the rape mosaic disease depend-ed,to a large extent,on the dispersal of the winged aphid vectors during the lateseedbed stage and the early field planting stage.Rhopalosiphum pseudobrassicae Davis was the principal form of aphid vectors found in the vicinity of Hang-chow.The peak of flight of its winged form(occuring from the last part ofSeptember to the last part of October)correlated closely with the extensivenessof the disease prevalence.2.New growths(during the late summer and early fall)from the natural-ly infected dormant root of a cruciferous weed,Rorippa montana(Wall)Small played a significant part as one of the primary sources for the new infection of the fall-sown crucifers.Only the summer sown Brassica sinensis had so far been identified as the host of R.pseudobrassicae during the hot weather of middleJuly to the first part of August.However,no mosaic symptoms appeared in the seplants.The absence of diseased plant was not due to masking effect.3.Studies of several-years meteorological data revealed that rainy days inOctober,days of precipitation and relative humidity were generally the most influencing factors in checking the disease.Heavy showers or rains extending longerthan 2 days had a profound depressing effect on the activity of the winged aphids and consequently a check on disease spread.On the other hand,the occurrenceof a drought in October was closely correlated with an outbreak of the rapemosaic disease.4.Results of the preliminary control experiment with the Chinese rapevariety Ai-da-gan showed that controlling aphids with insecticides in the seed-bed,in connection with light application of liquid nitrogenous fertilizer,had abeneficial effect in reducing the disease.By surface dressing of the seed-bedwith 6% of wettable benzene hexachloride(BHC)followed by spraying the seed-lings with Rogor and a mixture of DDT and BHC 4 times,beginning from the 2-leaf stage,together with three applications of liquid fertilizer reduced the dis-ease by 84% over the plot which received only one spray of DDT+BHC and twoapplications of liquid fertilizer.