The summer we just experienced has been one of the most extreme summers I can remember. We not only experienced extremely high temperatures, but also extreme drought. These extreme conditions were stressful not only to people and pets but to plants as well. I have received numerous calls and have seen many cases of plants affected by the summer we experienced.
Some of these problems are just now showing up. One of the most common plant problems I have received calls about are problems with Leyland cypress trees. Leyland cypress has become one of the most widely used plants in commercial and residential landscapes. They are primarily used as a formal hedge, screen, or wind barrier. Leyland cypress is often considered relatively pest free; however, due to its relatively shallow root system and because they are often planted too close together and in poorly drained soils, Leyland cypress is prone to root rot and other damaging canker diseases.
One of the most common symptoms I have seen and received calls about is the yellowing or browning of the foliage sort of randomly throughout the tree. This browning of the foliage can be due to several diseases. Two of the most common diseases of Leyland cypress are Seiridium canker and Botryosphaeria or Bot canker. Seiridium canker is probably the most important and destructive disease on Leyland cypress in the landscape. One of the most noticeable symptoms is the browning of one or more top or lateral branches. The disease often spreads until a significant portion of the tree is affected. If you look closely, cracked bark in infected areas is often seen with extensive resin flow down the diseased branches. Environmental stress, primarily drought stress, favors infection and canker development. Cankers develop on drought-stressed trees up to three times faster than on adequately irrigated trees. Spring freeze and ice damage can often predispose the trees to infection as well. One possible reason this disease may have been so prevalent this year may be due to fact we had one of the hottest and driest summers we have had for quite some time.
Proper establishment and care are the best defenses against Seiriidium canker. Due to its relatively shallow root system, plant Leyland cypress in properly tilled soil and avoid over-watering and heat stress to ensure establishment of a healthy Leyland cypress.
Another damaging disease of Leyland cypress is Bot canker. Symptoms are very similar to those caused by Seiridium canker. Rust colored branches are often the first observed symptoms, and just like Seiridium plants suffering from environmental stresses (freezing, drought, or heat) are susceptible to Bot canker.
So how do you tell which disease your Leylands might have? One way to tell is to run your hand over the branches on newly infected limbs of trees. If the needles fall off, then it is Seiridium. If they stay attachedm it is Bot canker.
So, what do you do about the disease? Prune out the infected branches from the tree. This accomplishes two things: first, the tree will look better, and this also will reduce disease spread by reducing the number of fungal spores. Be sure to disinfect any pruning tools between cuts. If the tree is severely infected, the best control may be a chainsaw and simply removing the infected tree. Fungicide applications are usually not practical for large trees as they would be very difficult to spray the entire tree at regular intervals, about every 7-14 days throughout the year.
The best prevention is to try to keep the trees from becoming stressed in the first place. Don’t plant the trees too close together and be sure to irrigate during periods of drought. These are just two of the more common diseases that Leylands can get. They can also get others as well, but most of the trees I have seen with problems tend to be one of these. If you need additional information please be sure to call your local Extension office.

Bill Starr is Sumter County Extension agent/coordinator, University of Georgia Cooperative Extension Service, Southwest District. Contact him at 229-924-4476.