Studies On Key Links Of Epidemic Process And Control Technique On Purle Leaf Blotch

at suitable temperature, the spores of Alternaria porri can germinate over 90%and begin to produce appressoriums after three hours in the fresh water, the quantity ofappresorium was most after six hours. The rate of spore invasion was positive related to rateof appresorium; Temperure of spore germination was between 23℃to 25℃,the best suitabletemperature was 25℃; The germinated spores were dehydrated more than 6 days.Chemical fertilizers could reduce the spore infection, and Nitrogen and potassium werebetter than phosphate.The incubation period of Alternaria porri was 3 days under natural condition, and there islittle difference among varieties. The relation curve was "invert J" shape between the rate ofaccomulated symptomatic appearance and time.Symptomatic appearance will last 10days.Temperature has obvious effect on incubation period. The size of lesion changes with thegrowth stage of onion.The least is 0.5cm,the biggest is 3.0cm.There are severl factors influencing spore production capacity of the lesion.The first isquantity of water penetrating into leaf. The second is whether there is water on lesion. Ifthere is much water penetrating leaf, the lesion and green part or dead part can produce manyspores when RH is 81%～85%.If there is no water penetrating into leaf, the lesion mayproduce spores when having water on lesion and RH is around 100%,otherwise, they onlyproduce few spores even if RH is around 100%. Temperature effect on production also,thelesion have the best production capacity at 25℃-28℃,and at30℃-35℃,the productioncapacity is less.Juvile lesion(6-9 days) can produce more spore than other periodlesion.Lesion can produce spores under either direct light or black light,but under blacklight can produce more spore than under direct light.The number of spore produced is relatedto the growth stage of onion,but not to the size of lesion.The most of onion varieties in northeast area of China are susceptible to the disease.Butsome varieties are lightly susceptible,and these varieties have less lesion.The spores scatter mostly in the evening and the distance of the disease is more than43m.The spores on onion residue in field can survive in winter and is the preliminaryinfection source in spring. The distribution model is aggregation.Several effective pesticides were chosen out such as Daconil, Manzate, DithaneM-45,Sandofan-M8,Kocide,Iprodione,Thiram,Triadimefon,Carbendazo,Score,Topsin Mthrough experiments. According to the results, integrated control measure was put forward.