Page-Dumroese, Deborah S.; Harvey, Alan E.; Jurgensen, Martin F.; Larsen, Michael J. 1996. Ponderosa pine seedling response to planting-site soil fumigation and fungicide application. Northwest Science. 70(2): 139-146.
Ponderosa pine (Pinus ponderosa Laws.) was used as a biological model to determine the effects of planting site soil fumigation and fungicide applications on stock planted in moderately-fertile soils of the Intermountain West of the United States. Five soil fumigation (Vapam) treatments, singularly and in combination with fungicide (triadimefon) applications, were compared to a control. Growth characteristics, nutrition, and ectomycorrhizal colonization were evaluated. Seedlings were significantly taller in the spring fumigation treatment at the end of four growing seasons. Greatest ectomycorrhizal colonization occurred in the non-fumigated treatment with fungicide applied before planting. Generally, spring or fall fumigation treatments, without fungicide applications, produced the tallest seedlings. These results suggest that soil fumigation applications before outplanting could improve early performance of ponderosa pine when reforesting sites with abundant, native ectomycorrhizal inoculum. It also suggests that if fumigation is impractical, reduction of vegetative competition may give similar growth gains. Elimination of non-native ectomycorrhizae in the nursery may improve colonization after outplanting.