多效唑对杨梅枯枝病的影响及防治

Effect of paclobutrazol(PP333)on twig dieback of Myrica rubra and control

检测分析不同剂量多效唑施用后在杨梅叶片、根部、果实的残留情况,以及对叶片色泽、根系、果实品质的影响；综合分析多效唑与杨梅枯枝病发生的因果关系.并针对枯枝病发生特点,利用自主研发的混配药物进行综合防治试验,并对治愈植株果实的农药残留进行随机检测.结果表明,重度、中度、轻度发病树叶片、根部多效唑含量差异显著,分别为叶片439.00,25.60,13.20μg/kg ,根部266.00,3.38,1.20μg/kg ,发病程度越高残留量越大；果实中均未检测到多效唑残留；500 mg/kg 高质量分数的多效唑处理使杨梅叶片气孔密度增大,气孔面积减小；T1（200 mg/kg）,T2（300 mg/kg）,T3（500 mg/kg）3个质量分数的多效唑连续施用与植株枯枝病轻度、中度、重度发生相对应,呈正相关；利用自主研发的混配药物对枯枝病发病植株进行防治效果显著.轻度发病树经3年连续治理后基本恢复正常生长,死树率为0,而作为对照的发病率为74.7％、死树率为21.6％；中度发病树治愈率均分别达90％以上,对照发病率为100％；严重发病树治愈率均在50％以上,对照在4年后全部死亡.经综合防治后恢复正常生长的植株果实的农药残留显著降低,克百威、甲胺磷、氧乐果和溴氰菊酯4个农药残留指标低于国家无公害标准的1～5倍,重金属铅的含量低于国家无公害标准的8倍.总之,多效唑施用后对杨梅可产生不可逆的影响,即多效唑（中高浓度多次施用）—树势早衰—拟盘多毛孢菌寄生侵染—枯枝病出现—枯枝死树—病菌扩大繁殖并加速传播,形成恶性循环,导致枯枝死树连续发生.而利用笔者的专利技术尽早采取综合防治效果明显.

Summary Red bayberry （ Myrica rubra （ Lour .） Zucc） is one of the major fruits planted in Zhejiang Province , China . It provides an important financial support for the farmers in this area . However , the fungal disease twig dieback severely threats the growth of red bayberry . Once one plant is infected by this disease , it would spread and destroy the whole orchard in three years . Controlling technology on this disease is urgently needed at this area .Paclobutrazol （ PP333 ） is a chemical widely used for plant growth regulation . It causes plant growth shorter , stronger , more branches and better fruiting . It has been widely used on the red bayberry for higher production . However , over‐dosage use of the chemical PP333 is suspected to connect with the epidemic of twig dieback in Zhejiang , China . The causal agent of the twig dieback disease was proved to be Pestalotiopsis species . It is postulated that the application of PP333 inhibits some bacteria growth and breaks microbial community balance in the soil , so that the causal agent of twig dieback is predominant .In order to test the hypothesis , we investigated the correlation between application amount of PP 333 and disease severity in eight farms in Zhejiang in four years . In the eight farms , we investigated the connection of application dosage of PP333 with the residues of the chemical in leaves , roots and fruits respectively . In different treatments of PP333 , leaf colour , root architecture and fruit quality were also investigated . Application of three concentrations of PP333 , T1 （200 mg/kg） , T2 （300 mg/kg） and T 3 （ 500 mg/kg） , resulted in light , moderate and heavy twig dieback disease , respectively . The results showed that over‐dosage application of PP333 in successive years caused fruit tree early senility and server diseases infection .In order to cure the infected fruit trees , we applied a new home‐made chemical to the infected trees . The results showed that the home‐made chemical is quite effective to control the disease . After three years of treatment on the light infected orchard , all the disease infected trees were recovered to be healthy . However , the control orchard without treatment was more seriously infected . The infected trees occupied 74 .7% and 21 .6% trees died . In the moderate infected orchard , three years of treatment recovered over 90% of infected trees . The untreated control trees get infected to be 100% . In the heavy infected orchard , three years of treatment recovered over 50%of infected trees . As the control , all the untreated trees died in the fourth year . The results showed that the new home‐made chemical was very effective to cure the infected trees .Physiological effects of PP333 on Dongkui red bayberry were also investigated . The higher concentration of PP333 （500 mg/kg） caused higher stomatal density and smaller stomatal size . Twig dieback severity was correlated with the amount of PP333 chemical residues in leaves and roots . Application of different amounts of PP333 to the trees had significant different residues of PP333 in leaves and roots . On the light , moderate and heavy infected fruit trees , the content of PP333 in leaves was 13 .20 , 25 .60 and 439 .00 μg/kg respectively and the content of PP 333 in roots was 1 .20 , 3 .38 and 266 .00 μg/kg respectively , but the chemical residuals in fruits were very low .We concluded that over‐dosage application of PP333 is the major cause of twig dieback disease predominance on red bayberry . The over‐dosage application of PP333 promotes fruit tree early senility , then promotes Pestalotiopsis species infection , then causes twig dieback symptoms and tree dies , and then more Pestalotiopsis species are spread and more trees are infected . It forms a vicious cycle . To control the disease , our patented home‐made chemical is effective .