—by Steve Lekwa
2013 was not a good year for the future of Iowa’s ash trees. The newest plague to affect Iowa’s forest resources, the emerald ash borer (EAB for short), broke out of its original northeast Iowa infestation in Allamakee County and showed up in several more counties down the Mississippi River. More ominously, it also showed up in Union County in southern Iowa; more than 100 miles from the river. EAB beetles attack and kill all ash species as their larvae eat the tree’s cambium tissue right under the bark. Areas with well established infestations lose all of their ash trees in only a few years. Each newly infested county was placed under quarantine as they were discovered, making it illegal to ship ash wood products or nursery stock out of the area in an attempt to slow EAB’s spread. Yet another new infestation was discovered in Waterloo early this year. This prompted the Iowa DNR to place the entire state under quarantine. The quarantine restricts the movement of any kind of hardwood firewood, ash logs, wood chips, or ash tree nursery stock.
There was hope when EAB was first discovered in Iowa in 2010 that the spread of this new pest would be slow. Adult beetles can fly only a few miles in any given year and must then find another ash tree to repeat the breeding cycle. The rapid and widely dispersed jumps that showed up in 2013 indicated that people were moving ash wood products out of infested areas. The most likely culprit is transporting firewood.
It’s very likely that other infestations will be discovered as more people become aware of the problem and start looking for it. It takes several years for populations of EAB to build up to the point where trees begin showing symptoms and dying. Initial infection of ash trees where the pest has been identified probably took place at least a couple of years ago.
Ash is one of the most abundant tree species in the country and has been widely planted in cities and parks. The USDA Forest Service estimates that Iowa has 52 million rural ash trees and 3.1 million more in urban areas. The DNR is conducting inventories of urban trees in communities with less that 5000 people and has completed nearly 250 so far. Ash comprises of 16% to 17% of city trees on average, but is as high as 87% in some areas. State Forester Paul Tauke is urging all communities to complete tree inventories very soon so that plans can be made to replace ash trees as they die out.
Chestnut blight virtually eliminated the American chestnut more than a century ago. It was once one of the most common trees east of the Mississippi River. Dutch elm disease destroyed most of the country’s elms in the mid 1900s. Butternuts, too, have virtually disappeared in the last 50 years. It appears that the nation’s ash trees will be the next to go.
There is some hope that this winter’s near record-breaking stretch of cold weather may kill off some of the larvae and slow the spread of EAB. That would only be a temporary reprieve, though. EAB is on the move and experience in other states indicates that there’s little that can be done to stop its spread. ISU Extension and Outreach Entomologist Mark Shour advises that individual healthy trees can be treated to prevent infection. These treatments must be applied in April or May and will be available to people within 15 miles of a known infestation. More details are available in ISU Extension and Outreach publication PM2084 at www.extension.iastate.edu/Publications/PM2084.pdf.
No infestations have been found yet in central Iowa, but undetected infestations could already be here. The best advice is to watch your ash trees for unusual signs of decline and make plans to replace them with a diverse mixture of other trees. Diversity is still the best defense against future threats to Iowa’s forest health.