One of the highlights for me this past summer was the four days that I spent at Bob Marshall 4-H Camp in the Black Hills. The hiking, the noisy dining hall, and the talent show all made for great memories. I even had a few minutes to myself to go fly fishing at the Lake Bismarck and caught a perch, which I released, on a grasshopper dry fly.
As we drove away, we were saddened by the sight of the brown and dying Ponderosa pine trees. The Black Hills has experienced landscape level outbreaks of mountain pine beetles beginning in the late 1990s with the losses now totaling into millions of trees, according to John Ball, Extension Forestry Specialist. Many landowners are concerned that their Ponderosa pine trees have been, or may become, attacked.
The mountain pine beetle is a small insect that lives most of its life just beneath the bark of living pine trees. The adult beetles are black to rusty brown and about one-fifth to one-third inch long, about the size of the lead point of a pencil. Their emergence reaches its peak near mid-August, though some beetles continue to fly into mid- to late September. The adults burrow into living pines and construct tunnels, known as galleries, just beneath the bark in which to lay eggs.
The beetles attack individual trees in large numbers, often in the hundreds. This mass attack allows them to overwhelm the defense of the tree which consists of producing vast quantities of resin. If the beetles are successful in penetrating the bark, the tunneling activity by the adult beetles and their larvae injures the tree by disrupting the movement of food from the needles to the trunk and roots. If the attacks were successful, the following spring the needles on these infested trees begin to turn yellow to a bright red, and become gray the following year.
A different pathogen, Dothistroma needle blight continues to show up in parts of South Dakota. This disease is becoming more common in the state and several of the surrounding states as well. While Dothistroma does occur in our state, it is also a disease that can be easily misdiagnosed. There are a number of stressors that can cause pine needle discoloration and banding, and it is best to send a sample in, rather than just a picture, to confirm the presence of the disease. Management at the present time involves applications of a copper-containing fungicide as the new growth expands in the spring.
Diplodia tip blight is probably the most common disease reported on Austrian and Ponderosa pines in our state. It is commonly associated with hail or other stresses. The symptoms commonly seen or reported are yellowing and wilting new needles on the shoot tips. The shoot tips are also stunted and often covered with sticky white resin and the older needles are missing or have turned an ash-gray and are hanging.
The control for the disease is an application of a copper fungicide or a fungicide containing chlorothalonil just as the buds are beginning to open and then repeat the application once the new needles completely emerge and finally a third application ten days later. Control is probably not the best choice to describe the treatments for this disease. Management may be better, as our treatments do not cure the tree, just reduce the severity and often annual treatments are necessary to maintain an attractive tree.