CREJ - Property Management Quarterly - April 2016
By now, many Colorado residents are familiar with the name emerald ash borer, more commonly known as EAB. In fact, it now is considered one of the most destructive forest pests ever seen in North America. To date, it’s held responsible for killing more than 50 million ash trees in over 20 states across the country. In the Denver metro area alone, there are 1.45 million ash trees at risk, as the pest shows no signs of slowing down. Currently EAB remains in Boulder County. But many experts agree that this destructive and unrelenting pest will soon be migrating past Boulder’s city limits, possibly as early as June. The EAB population is building rapidly in northern Boulder, and hundreds of trees are dying from the infestation. Many speculate that EAB has traveled outside of Boulder, but has yet to be detected. The Denver Parks and Recreation Forestry Division is rolling out a public education campaign about EAB. Officials now understand the severity of the situation and are being proactive in educating the public about the long-term effects. Ash trees are found throughout Denver in public parks, green spaces and rights-of-way, in addition to residential properties, said Rob Davis, with the Denver City Forester, in a recent local newspaper article. The trees perform important functions, including cooling the landscape and mitigating air pollution and storm water runoff. “It is critical we activate a public awareness campaign to help stop the infestation of emerald ash borer in our community,” he said. What does that mean for property managers? If you have ash trees, you need to plan ahead. Waiting to treat until after the borer is discovered on your property or an adjacent property is not a good strategy. Once the borers are found, it is likely they’ve already been there for two to three years, causing significant, if not irreversible, damage. Following are some commonly asked questions about treating and protecting against EAB. How effective are insecticide treatments against emerald ash borer? Under experimental conditions, most results indicate a 90 percent or higher success rate. In practical applications, success rates for insecticide treatments are at least 80 percent effective. The discrepancy is due to the condition of the tree. Trees treated early, and in good vigor, have the highest success rate. The insecticides used to combat EAB are nearly all systemic. That means the insecticide is placed in the soil or injected directly into the trunk of the tree. The insecticide is taken up into the tree via the vascular system. EAB and other ash borers feed in that vascular system. When the insects have compromised the vascular system, the insecticide is not able to disperse evenly throughout the tree. In addition to treating for EAB, trees should be pruned while following other good horticultural practices emphasizing tree health. Will I have to treat ash trees forever? The answer is yes and no. EAB infestations follow a definite curve. For the first three years, EAB goes undetected while it infests the trees. During the next two to three years, borer populations build. During this “cusp” period, preventive treatments are recommended. For the next 10 years, the borer goes through an exponential growth phase. Treatments for EAB are essential. The result for most of the treated trees is they live, while nearly all the untreated trees die. With few trees left for EAB to infest, the populations of EAB will decline rapidly. Researchers in the Midwest are looking at this post-mortality phase. It looks as if treatments may be scaled back after this period. If I treat my trees, what should I expect? If the trees are not treated, they will die. This is a known fact. But many wonder if a treated tree will look the same. The answer is maybe … and maybe not. While the success rate for insecticide treatment is very high, when EAB becomes prolific, they will challenge the tree – or begin feeding on the tree before the insecticide controls them. Thus ash trees, even when treated, will accumulate more dead branches than normal and have a more sparse appearance to the tree canopy. When the EAB mortality curve subsides, the ash should return to its normal vigor. Ash trees make up approximately 15 to 20 percent of Colorado’s urban forest. It’s no longer a question of if EAB will spread to the Denver metro area but, rather, a question of when.