Investigation Of Eucalyptus Disease And Chamical Control Of Eucalyptus Ring Spot

Eucalyptus robusta Smith is one of fast-growing tree species in the world and an important timber resource in China.A survey on eucalyptus diseases in Guangxi was carried out,the biological characteristics of Coniella eucalyptorum and Pseudoplagiostoma eucalypti were determined;the conidia of Coniella eucalyptorum released in plantation was captured,the regularity of this disease occurrence was investigated and the results of chemical control of this disease in eucalypt plantation were tested.The results were as follows:1.Eucalyptus diseases in GuangxiThrough investigation,13 kinds of eucalyptus diseases were identified:eucalyptus ring spot(Coniella eucalyptorum),eucalyptus yellow brown spot(Pseudoplagiostoma eucalypti),eucalyptus bacterial wilt(Ralstonia solanacearum),eucalyptus foliar blight(Calonectria reteaudii),eucalyptus purple blotch(Phaeoseptoria eucalypti),eucalyptus yellow-purple blotch(Phleospora sp.),eucalyptus bacterial angular leaf spot(Bacteria),eucalyptus Neopestalotiopsis leaf spot(Neopestalotiopsis clavispora),eucalyptus Chaetomella leaf spot(Chaetomella raphigera),eucalyptus Apoharknessia leaf spot(Apoharknessia eucalyptorum),eucalyptus Coniella leaf spot(Coniella quercicola),eucalyptus leaf and shoot white blight(Quambalaria pitereka)and eucalyptus powerdery mildew(Oidium sp.).Among them,eucalyptus Apoharknessia leaf spot and eucalyptus Coniella leaf spot were new records in China,and eucalyptus powerdery mildew were new records in Guangxi.Eucalyptus ring spot was the most important disease in eucalyptus plantation.2.The biological characteristics of Coniella eucalyptorum and Pseudoplagiostoma eucalyptiThe optimum mycelium growth temperature of Coniella eucalyptorum was 25℃-27.5℃;the lethal temperature was 48℃ for 20 minutes;the optimum pH value was 4-7 in PDA medium;the optimum carbon source for myceliium growth was-lactose,and the optimum nitrogen source was peptone;the mycelium grew fastest under 24 hours continuous light and 12 hours light/12 hours dark cycle;SDA medium was the most suitable for mycelium growth,while OMA medium could promote sporulation of Coniella eucalyptorum.The optimum mycelium growth temperature of Pseudoplagiostoma eucalypti was 25℃-32.5℃;the lethal temperature was 48℃ for 20 minutes;the optimum pH value was 5-7 in PDA medium;the optimum carbon source for mycelium growth was-lactose and the optimum nitrogen source was peptone;the mycelium grew fastest under 24 hours continuous light;PSA,PDA,OMA and CMA medium were all beneficial to the the mycelium growth of Pseudoplagiostoma eucalypti.3.Relationship between number of conidia of Coniella eucalyptorum,eucalyptus ring spot disease incidence in plantation and meteorological factors.Eucalyptus ring spot was milder from January to March in plantation,and gradually aggravated from May to October.The incidence of eucalyptus ring spot was most severe in October.From November to December,with the decrease of weather temperature,the disease incidence of eucalyptus ring spot gradually reduced.By the following spring,as the disease slowed down,some new shoots sprouted,but then the disease began to re-infect and the cycle continued.It was found that the unventilated environment was more favorable for the occurrence of eucalyptus ring spot.Combining captured conidia amount of Coniella eucalyptorum released in plantation,monthly growth of disease index and meteorological data(temperature and air relative humidity).It was found that the released conidia number of Coniella eucalyptorum was positively correlated with temperature;the growth of disease index in the plantation was positively correlated with released conidia number and air relative humidity,which had a time lag,that is,released conidia number and air relative humidity increased to top in August to September,the growth of disease index of eucalyptus ring spot increased to top in October,and released conidia number and air relative humidity decreased in October and November,the growth of disease index decreased in November to December.4.Chemical control experiment of eucalyptus ring spotThe virulence evaluation of ten fungicides against Coniella eucalyptorum was determined.propiconazole,prochloraz and carbendazim had the better antifungal effect,with the lower EC50 values of 0.01,0.03 and 0.05 μg/mL,respectively.The results of chemical control experiment in plantation showed that 450 g/L of prochloraz(750 times)and 250 g/L of propiconazol(1000 times)had the better control effect,and the control effect could reach 66.86%and 60.27%,respectively.