| The incidence and severity of major fungal and nematode pathogens of commercial forest trees in Delaware were evaluated from 1979 to 1982. This survey was the first of its kind in Delaware, and employed aerial photography with conventional techniques in the detection of forest tree diseases. A survey of urban decline of Acer platanoides also was conducted in Newark, Delaware.; Soil-borne nematodes and soil fertility were not factors in diseases of forest trees. The most prevalent fungal pathogens on hardwoods in survey plots were: Armillariella mellea, Clitocybe tabescens, Dibotryon morbosum, Ganoderma spp., Gnomonia spp., Nectria galligena and Phyllactinia corylea. Nectria galligena caused the greatest damage, infecting 10% of the standing hardwood timber growing in plots. The predominant fungal pathogens on coniferous species growing in survey plots were Cronartium quercuum f. sp. quercuum and Heterobasidion annosum. Incidence of the latter pathogen was as high as 88% in thinned stands of Pinus taeda. Fusarium spp. were consistently isolated from declining maples in Newark, Delaware, and several Basidiomycetes were fruiting on diseased trees.; Several lignicolus Basidiomycetes were associated with decay of living and dead hardwoods and softwoods growing in survey plots, including Laetiporus sulphureus, Polyporus squamosus, Spongipellis pachyodon, and Schizophyllum commune. Color and false-color infrared aerial photography were ineffective in detection of diseased trees, with the exception of certain hardwood plots in New Castle Co., and pinewood nematode-infested pines at Cape Henlopen State Park, Lewes, Delaware.; The pinewood nematode, Bursaphelenchus xylophilus, was found in Delaware in 1981 and subsequently identified on Pinus species, including P. resinosa, P. rigida, P. strobus, P. sylvestris, P. taeda, P. thunbergii and P. virginiana. Distribution, population dynamics, and chemical control of B. xylophilus were examined, and a modification in axenic myoculture of the nematode was successful. |
