Effect of site and silvicultural treatment on insect pests and diseases of young ponderosa pine

Graduation date: 2009Ponderosa pine is an important species both commercially and ecologically in\ud western North America. This study considers the incidence of insect and disease pests\ud on a series of replicated ponderosa pine research plantations in northern California.\ud The studies, on an environmental gradient, contain a series of silvicultural treatments\ud including vegetation control, fertilization application and insecticide application/\ud thinning. The mean annual temperature and total precipitation were used as climatic\ud variables and the site index was considered as an environmental site variable. Needle\ud retention was negatively correlated to the site productivity, with no treatment affects.\ud Estimates of mean needle retention were in-line with those found in the literature.\ud Total foliar herbivory was the lowest at the highest productivity site, again there were\ud no treatment effects. The gouty pitch midge had the highest level of infestation on the\ud branches of the trees at the site with the lowest productivity. The environmental\ud variables support this with drier, warmer and higher sites being more susceptible.\ud Sequoia pitch moth attacks were highest at the more drier and warmer sites while\ud treatments with vegetation control appear to experience higher levels of attack. Total\ud foliar pathogen infection was the lowest at the highest site index. There was no\ud statistically significant difference between the other five sites and no treatment effect\ud was established. Western gall rust was the highest that the most productive sites and\ud treatments that were fertilized had higher levels of infection. The year of gall infection\ud was associated with the occurrence of El Niño events in the study time period