The emerald ash borer is coming - but tree professionals and landowners learned Monday afternoon about ways to prepare for the bug.
"We can't really stop this thing," said Dr. Jesse Randall, Iowa State University Extension and Outreach forester. "Many states have tried. It's a tidal wave that's coming."
Randall and Emma Hanigan, Urban Forestry Coordinator for the Iowa Department of Natural Resources, spoke at two workshops about the invasive insect that's killing off ash trees all across America.
Treatments are available that may help keep a healthy ash tree from being infected, but but they shouldn't be used too early, Randall said. Sometimes removing the tree is the best option, but not always.
"First, are you within 15 miles of a known EAB infestation?" Randall said. "These treatments aren't 'one and done.'"
There are two basic types of treatment, he said: soil drenches, and injections directly into the tree, which must be done by a professional. Both have drawbacks, so it's not necessary to start until there's an infestation in the area.
Drenches must be done early, around mid-April, because it takes four to eight weeks for the chemical to make its way into the tree. Label instructions must be carefully followed, Randall said, and there are strict limits to how much chemical can be safely used per acre.
If there are more ash trees than can be safely treated, he said, landowners must think about which ones have the most value.
The chemicals can also travel in the soil. Randall said you shouldn't use a drench within 25 to 50 feet of vegetables or fruit, flower gardens, or wells.
For trees greater than 20 inches in diameter, soil drenches aren't effective.
"If I was saving my ash trees, I would use an injection. I would have it professionally done," he said.
When insecticides are injected directly into the tree, it requires several injection sites, and must be repeated again every year or every other year. This can cause damage to the tree, he said.
Signs of emerald ash borer infestation include:
- Epicormic sprouts, growing out of the tree halfway up or at the bottom;
- Bird fleck, caused by woodpeckers digging into the bark to eat the larvae;
- Top die-back of the tree;
- D-shaped exit holes
The borers create an S-shaped pattern under the bark, he said. Both the d-shaped holes and the S-pattern can also be caused by native species. When an infestation is suspected, call the DNR or ISU extension, and a forester can take samples for genetic testing.
The trees don't usually die in the first year. Hanigan said in many cases, EAB is not discovered until it has been in an area several years.
"Because ash trees grow so fast and heal over those wounds, and the symptoms are so hard to detect, we're not finding new finds at all," she said.
People need to be alert and call in if they think they find something, Randall said.
"Really, all these finds are coming from the public. We can't really do it without you telling us, 'We think we have it,'" he said.
It's better to cut down an infested tree before it completely dies, Hanigan said, because a tree killed by the ash borer becomes very brittle and unsafe.
"You tree care people, would you rather cut down a living tree, or a dead tree?" Randall said. "An EAB tree breaks up differently than an ordinary dead tree. The cost goes up because it's more dangerous.
"If it is beyond 50 percent canopy die-back, it's done. I'd cut it down even before that."
More variety is better
If ash trees must be cut down, what should be planted as a replacement? The answer isn't maple trees, Hanigan said, even though she loves maple trees.
Instead, towns, parks and homeowners should plant a variety of trees, so whole areas are not susceptible to a one-species illness.
The Dutch elm disease wiped out elm trees in the past, and the ash borer is a problem now; in the future the big concern may be Asian long-horned beetles, which can destroy maple trees, she said.
"In our Iowa urban forests the top species are maple and ash, sometimes linden, and sometimes crabapple," Hanigan said. "It's scary how many maples we are planting."
Birch trees are a fast-growing, but short-lived, alternative, she said. They only live about 30 years.
Hackberrys are a good option for the tough sites where ashes have typically been used, and they also have interesting bark.
Kentucky coffeetrees and honey locusts are good options with small, easily manageable leaves. Sycamores and tulip trees grow quickly, and get very large, she said, and red oak is the fastest-growing oak variety.
"Another thing to think about, if you know you're moving your ash tree, and you have adequate space, is maybe under-planting a tree, and getting some years of establishment before you cut down the tree," she said. "You do need to think about, however, how that tree is going to be removed."
Under-planted trees need to be shade-tolerant, and if they're left to grow longer than about two years, they may become cramped.
MidAmerican Energy customers can get trees at a low price through the Plant Some Shade program, in partnership with the Iowa DNR. For more information, call Webster County Conservation at 576-4258.
The ash borer gets from place to place riding on firewood. It doesn't fly far enough on its own to spread to so many areas so quickly.
The whole state of Iowa was placed under quarantine in February, and no firewood can be taken out of the state into non-quarantined areas.
"We're hoping South Dakota and Nebraska have better luck," she said.
Hanigan said wood chips and firewood should be used locally. Some counties require only local wood to be used, she added.
Regardless, all firewood must now have a label in Iowa stating where it came from.
"Even if you cut it yourself, write yourself a label," she said.