Small pinyons 1 to 2 m (3 to 6 ft) tall are  readily killed by fire, but larger trees appear more resistant. Fire is  generally not a serious problem, however, because stands are open and  understory fuels are sparse. Where vegetation is dense and weather  conditions favorable, fire has been effective as a treatment for  converting woodlands to grasslands (3,18,40).

    Among insects most commonly attacking the vegetative portion of trees  are pinyon pitch nodule moth (Petrova albicapitana arizonensis), tiger  moth (Halisidota ingens), mountain pine beetle (Dendroctonus  ponderosae), pinyon sawfly (Neodiprion edulicolus), adelgid  (Pineus coloradensis), pinyon needle scale (Matsucoccus  acalyptus), pine needle scale (Chionaspis pinifoliae), Arizona  fivespined ips (Ips lecontei), pinyon ips (Ips confusus), pinyon  needle miner (Coleotechnites edulicola), pinyon tip moth (Dioryctria  albovittella), and gallmidges (Pinyonia spp., Janetiella  spp., and Contarinia spp.) (22,24,27,28,63,67). The  most damaging cone and seed insects include cone moths (Eucosma  bobana) and the pinyon cone beetle (Conophthorus edulis). Many  species of nematodes, especially in the Helocotylenchus, Tylenchus,  and Xiphinema genera, are parasitic on pinyon roots, but their  effect on growth in natural stands is unknown (53).

    A number of foliage diseases have been reported on pinyon, including  needle casts (Elytroderma deformans and Bifusella saccata)  and needle rusts (Coleosporium jonesii and C. crowellii)  (36,67). Pinyon blister rust (Cronartium occidentale) and  pinyon dwarf mistletoe (Arceuthobium divaricatum) cause stem  diseases, the latter being considered the major pathogen of pinyon. Verticicladiella  wagenerii, a root rot, is also ranked high as a damaging agent;  principal heart rots are red-ring rot (Phellinus pini) and brown  cubical rot (Fomitopsis pinicola). Armillaria mellea and Phaeolus  schweinitzii are not particularly important diseases, but both cause  root rot and butt rot.