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PEST OF THE MONTH Seiridium Canker By Jodi Zirbel What does it look like? One of the most significant diseases to affect Leyland cypress, Seiridium canker is caused by the fungus Seiridium unicorne. These cankers form on branches and stems, as well as branch axils, enlarging longitudinally rather than girdling branches. Cankers appear as dry, dark-brown or purple patches on the bark, often appearing sunken with a raised edge, and usually associated with increased resin flow. Host material and range A fast-growing evergreen, Leyland cypress works well as a screening plant, which has helped to bolster its popularity throughout many areas of the United States. However, as the species becomes more prevalent, so do diseases affecting it. The most damaging of these diseases is Seiridium canker, which affects Leyland cypress trees wherever they grow. Photos courtesy of Dr. Jean L. Williams-Woodward, University of Georgia environmental stress caused by drought. Studies have shown that Seiridium cankers form at a rate three times faster on drought-impacted trees than on those properly hydrated. In addition, the fungus appears to spread by rain and overhead irrigation, as well as infected pruning tools. Be sure to prune infected trees at least one inch (3 to 4 inches is recommended) below the canker and routinely sterilize trimmers to avoid further infestation. Long-distance transport of the disease occurs through infected trimmings, so avoid moving dis- eased branches and be sure to dispose of them properly. Treatment tips Examine trees for signs of infection Current threat Unlike other types of canker that single-handedly enlarge to gir- dle the branch, Seiridium cankers form in longitudinal clusters, multiplying around a branch, which collectively reduces water flow. As a result, the branch wilts and yellows, and ultimately turns red- dish brown. Similar to drought stress, needles will easily fall off, and braches affected by the canker will dieback. If the fungus spreads through the tree and infects the trunk, the disease can be fatal. Most often, branch dieback is the first symptom of Seiridium canker, and in many instances years pass before the initial infection results in a visible canker. For an infection to occur, the tree needs an open wound. With this point of entry, fungal spores appear on the canker as black dots barely visible to the human eye. These spores continue to spread —often transported via water or infected prun- ing tools — into open wounds and cracks of new and existing trees. Another common symptom, although not defining, of Seiridium canker is an abundant flow of resin. While resin is a sign of a healthy tree, a small cut at the site of the canker typically reveals unhealthy reddish-brown tissue underneath the bark that is unusually sticky. Prevention tips One of the most noticeable ways to limit the effects of the Seiridium canker fungus is to properly irrigate trees to reduce 8 Arbor Age / March 2011 and immediately prune diseased branches. This will make the tree more aesthetically pleasing and also help to reduce the spread of the fungus. Eliminating the threat coupled with effec- tive irrigation has been shown to be the best cure for the fungal disease. Currently, there are no fungicide treatments proven to be com- pletely effective against Seiridium canker. However, diseased trees that have been treated with a fungicide and properly irrigated have been shown to heal around the canker, so that within two years the canker was no longer visible. If pursuing a fungicide treatment, consider using a potassium-phosphite soil drench or trunk injection such as ArborFos containing Phosphorous acid. The potassium-phosphate materials have recently shown activity with other sap-limited cankers, such as Botryosphaeria on Madrone, and may help in suppressing canker development over time. What can you do? Monitor trees often, looking for early signs of infestation. If detected, quickly prune infected areas to reduce further damage, and be sure to sterilize pruning equipment between each cut. Also, increase the amount of mulch used whenever possible to reduce drought damage, and investigate soil surfactants that promote consistent soil moisture throughout the soil profile to avoid channeling. Jodi Zirbel is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit www.Mauget.com to learn more about Seiridium canker. www.arborage.com