Common Tree Diseases in Oklahoma
Irregular dead areas on leaf margins,
between and across and/or along veins, often moving onto
the shoots and small twigs; sometimes whole leaves are
Dead spot on the leaf that is well defined
from healthy tissue.
Dead area on the leaf that often diffuses
into healthy tissues.
Loss of dead areas inside of spots that result
in a series of holes in the leaf.
Leaf spot or blotch that is swollen or raised, so
Common Diseases of Conifers
Dothistroma Needle Blight of Pines-
can cause the premature loss of needles of several varieties of pine. This disease, if uncontrolled for several years, can severely weaken and eventually kill these trees.
Diplodia Tip Blight-
previously known as Sphaeropsis tip blight, is a common fungal disease of stressed conifers, especially pines with needles in bunches of 2’s and 3’s. Diplodia kills needles at the tips of branches. Symptoms often start on the lower half of the tree and progress upwards. When the new needles are expanding, they become stunted, turn yellow, and then turn tan or brown.
Rhizosphaera needle cast is the most common disease on spruce trees. Disease symptoms include a browning or purpling of needles, which eventually drop from the tree leaving bare patches. Typically symptoms first appear on the lower branches of a tree and work from the inside of the tree out.
Phomopsis Blight of Junipers-
This is the most common disease of cedar, juniper, and arborvitae in Oklahoma. Phomopsis blight is a foliar disease caused by the fungal pathogen Phomopsis juniperovora. It is most aggressive during cool, moist weather. Continuously wet foliage is needed for infection to occur. Areas with heavy shade and poor drainage allow for moist, slow drying areas for the disease to thrive in.
Cedar apple rust-
This disease is very common on juniper or cedar trees in Oklahoma. The most striking feature of this disease is the gall that appears on the cedar in the spring.
Pinewood Nematode Disease of Pines a.k.a Pine wilt-
Pine wilt is caused by the pinewood nematode, Bursaphelenchus xylophilus, which kills conifers, especially pines, of many species. The nematode is transmitted by sawyer beetles, a wood-boring bark beetle, through their feeding wounds into the resin canals. Here, the nematode will reproduce and hinder the movement of water through water-conducting tissues, eventually causing the plant to wilt.
For more information, visit http://www.forestry.ok.gov/Websites/forestry/Images/F-7618.pdf
affects the leaves, shucks, and twigs of the infected plant and manifests as small (1 to 5 mm), circular, black or olive green lesions. Scab fungus (Cladosporium caryigenum) invades young, rapidly growing shoots and leaves and later the developing nuts. Pruning to open up the tree for better air circulation will help reduce scab occurrence by reducing the number of infection periods occurring during the year. Good sanitation practices may help prevent the disease. Removal and destruction of all fallen leaves, shucks, and nuts each winter or early spring helps reduce tissue that is often involved in the primary infection. Also, selective pruning of infected tissue during the dormant season may help reduce the level of scab disease.