春甘蓝外叶和球叶损失对产量的影响及主要食叶害虫防治行动阈值

Study on the Influence of Artificial Defoliation on the Yield of Common Cabbage and the Action Thresholds for Main Leaf-Mass Consuming Insect

为得出几种主要菜虫的防治指标 ,测定了春甘蓝京丰 1号不同生育期的绿叶数及全株叶面积和菜青虫、甜菜夜蛾、斜纹夜蛾的食叶面积并进行了田间剪叶试验 .结果表明 :甘蓝莲座期对外叶损失有相当强的补偿力 ,每株有菜青虫 3.5头 (即每 35 7cm2 叶面积有 1头 )时产量比对照约增 10 % ,据此认为每株春甘蓝上的菜青虫或甜菜夜蛾多于或等于 5头时应防治 ,甜菜夜蛾与菜青虫、斜纹夜蛾多于或等于 1.5头时应进行防治 ;菜球充实初期次之 ,每 30 0 cm2 叶面积有菜青虫 1头 (合每株 2 6 .7头 )时比对照约增产 3.6 % ;结球始期对虫害敏感 ,每 315 cm2 叶面积有菜青虫 1头 (合每株 12 .7头 )时减产 4 .1% .心叶及球叶受害对产量的影响表现与外叶受损相似的趋势 ,莲座期剪去心叶面积多达 3/ 4 ,约合 0 .91头菜青虫取食心叶 ,比对照增产 6 .3% ;菜球充实初期各层绿叶剪去 1/ 3面积 ,约合每株 4 .2头菜青虫取食球叶 ,增产 6 .1% ,但剪去 1/ 2即约合 8.4头菜青虫取食球叶则减产 6 .82 % ;结球始期不同剪心叶量均导致减产 ,例如每株剪心叶 1/ 3,约合 0 .73头菜青虫取食心叶 ,减产 2 .4 % .菜球充实初期 ,球叶损伤减产程度虽然不如结球始期剪心叶的严重 ,但成熟菜球外观畸形 ,未达上市标准 ,若加工腌菜则无妨 ;

Leaves of 'Jingfen No.1' cabbage at different growth stages were counted.The leaf areas of plant and the feed consumption by the larvae of Pieris rapae (CWB), Spodoptera exigua and Spodoptera litura were measured in laboratory.The results of the experiment of artificial defoliation in field are as follows:A) The cabbage plant at rosette stage has considerable compensation for the leaf area reduction.Compared with untreated plant, the yield increases by 10% when outer growing leaves are cut off by leaf area equivalent to consumption of 3.5 CWB(per 357 cm 2 leaf area inoculated one larvae).Therefore,the action thresholds for the CWB, S.exgiua and S.litura on the sping cabbage can be calculated to be 5,1.5,5 larvae per plant respectively at precupping stage.At precupping growth stage,the cabbage plant is susceptive to the leaf damaged.The yield reduces by 4.1% for the one larvae per 315 cm 2 leaf area(or equivalent to the consumption of 12.7 larvae of CWB/plant).B)The influence of inner leaves damaged on the cabbage yield is similar to that of outer leaves damaged.At precupping growth stage,the yield increases by 6.3%,even though 3/4 of the leaf area is defoliated(or equivalent to the consumption fed by 0.91 larvae of CWB per plant,compared with the untreated plant;at early heading stage,the yield increases by 6.1% for the 1/3 of inner leaf area defoliated(equivalent to the consumption of 4.2 larvae per plant).However,the defoliation of 1/2 of inner leaf area result in yield loss of 6.8%(equivalent to consumption fed by 8.4 larvae/plant).Several defolia ted amount of wrapped leaf area can result in yield loss at cupping stage . For example , defoliation of 1/3 of inner leaf area(equivalent to consumption of 0.73 CWB/plant) causes yield loss of 2.4%.Although the yield reduction caused by the wrapped leaves injured at early heading stage is not significant as the inner leaves defoliated at cupping growth stage,but the cabbage looks like abnormal,not accorded with the demand of market.