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Managing Leyland cypress problems

Tips for preventing disease in Leyland cypress trees.
Tips for preventing disease in Leyland cypress trees. Getty Images/iStockphoto

As expected, many Middle Georgia trees are experiencing problems this spring. These trees were already weakened when faced with the drought last fall. Problems are prevalent in Southern magnolias, pines, ornamental cherries and Leyland cypress trees.

Leyland cypress are fast-growing, evergreen trees, reaching 50 feet tall by 25 feet wide. They are favorites for homeowners to use as hedges. Although Leylands may provide a nice green border, problems are typically just around the corner, and for many, this spring is no exception.

The predominant factor contributing to disease problems in Leyland cypress trees are cultural or environmental issues. Often, trees are installed much too closely. As they grow and mature, the close, dense canopies prevent good air flow, which increases the opportunity for disease. They should be spaced at least 8 feet apart.

It is also important to plant them in a sunny, well-drained location. These trees will eventually decline in shady environments. They are also not tolerant of “wet feet,” or water-logged roots, due to overwatering. Equally important, however, is that they cannot survive extended periods with no rain or irrigation.

Consider using a soaker hose under the trees. Run it once a week, just long enough to wet the soil 12-18 inches deep. Let the soil dry out between watering. Add 3-5 inches of mulch after planting.

Leyland cypress problems usually manifest themselves as one of two fungal diseases. Browning and dieback is largely due to Seiridium and Botryosphaeria (Bot). The easiest way to distinguish between Seiridium and Bot is to run your hands across recently browned branches. If the needles fall off upon touching, then it is likely Seiridium. If they stay attached, then it is Bot.

Bot canker expands to girdle the branch, leading to a quick kill and leaving the needles intact. It tends to affect one or two branches in a localized area. Seiridium cankers enlarge longitudinally, with multiple cankers developing around the branch. These cankers interfere with water flow and the branch dies back (resembling drought stress).

Seiridium cankers often appear randomly distributed across the tree canopy, with some appearing yellow, some light tan, some brown. Both diseases often produce oozing cankers on the trunk and stems of Leyland cypress trees.

Unfortunately, there are no fungicide sprays effective in controlling Seiridium or Bot cankers. For many homeowners, spraying a large Leyland every seven days is not a viable,economical control option anyway. Therefore, the best course of action is to keep the plant in good health so it can resist these disease pressures.

On trees already infected, prune the brown (dead) branches from the tree. Cut back to healthy tissue and clean shears periodically with a 10-percent alcohol or bleach solution. Not only will this make the tree look better, it will decrease disease spread by reducing the fungal inoculum.

Once this is done, then irrigation is the best remedy to prevent any smaller cankers from expanding to kill more of the plant.

Here are the important keys to prevent Leyland cypress diseases:

▪ Avoid injuring trees when planting or working around them.

▪ Avoid stressing Leylands by planting them too close together

▪ Irrigate Leylands during periods of drought or in summer when rains cannot be counted on.

In cases of severe dieback, removal and replanting is the only option. There are also other alternatives to Leyland cypress hedges. Consider hollies, junipers, osmanthus or others.

Contact county Extension agent Karol Kelly at karolk@uga.edu.

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