Fourteen plots of 25 loblolly pines each were excavated in order to determine incidence and severity of <u>Heterobasidion annosus</u> in asymptomatic loblolly pine in Virginia. Each plot was established between 30 m and 100 m from an identified source of inoculum. A bulldozer was utilized to excavate root systems of the trees. The root systems of all trees visually estimated to have greater than 1% infection (this included 51% of the trees sampled) were measured with a tape and the root length measurements were categorized as resin soaked, stringy or healthy. Of the trees sampled, 85% were infected with <u>H. annosus</u>. Basidiocarps were found on 9% of the sampled trees. The average frequency of roots per tree infected with <u>H. annosus</u> for all measured trees (>1%) was 30% of the primary roots and 31% of the secondary roots. The average root length infected for all the measured trees (>1%) was 14% for primary roots and 15% for secondary roots. The sample trees were tested for a growth difference with the t-test for unpaired plots. The sampled trees were placed into one of two classes: those trees with >1% infection of the root systems (diseased) and those with ≤1% infection of the root system (healthy). The average annual increment for each of the last five years was tested, and all five tests were significantly different in growth at the 0.01 level. The difference in growth between healthy and diseased trees over the five year period was 19% or approximately 4% per year. Of all the disease parameters measured in the study: crown rating, percentage of infected primary roots and percentage of infected secondary roots were the most effective parameters in describing the effect of disease on annual increment growth over the last five years prior to sampling. / Master of Science