Abstract: Brown spot needle blight of pines is one of important pine diseases,which is caused by Lecanosticta acicola .It is confirmed that the fungi can produce toxic substances in its culture filtrate.The toxic substances ware called LA toxins.LA toxins could not only poison pine needles also the leaves of weeds.Various bioassay materials were treated with crude LA toxin to select sensitive material for the future study.The results indicated that seedlings and young needles of sensitive host(slash pine,lobollolly pine)were selected as bioassay materials for their sensitivities and reaction of the typical necrotic and yellow bands on needles.Such symptoms were similar to the symptoms of natural infection in the field and were different from other injuries.Old needles of pines and weed leaves were not sensitive to LA toxins.Compared with other two bioassay methods(soaking and smearing),the acupuncturing bioassay is the most suitable method because it just needs less toxin and can cause the evident symptom rapidly.