Devasting Threats to Iowa's Trees and Forests Emerge

By Brian Button - Editor, Iowa Outdoors Magazine

Not since Dutch elm disease are so many threats converging on Iowa's trees. Keep and eye out for these four invasive pests to avoid potential disease, widespread damage and great costs.

Proper woodland and community tree care plays a critical role in creating healthy rural and urban community forests. In 2008, more than 6 million trees died. 

THE BIG FOUR THREATS 

Emerald Ash Borer
Emerald Ash Borer is a small green invasive wood boring beetle that attacks and kills ash trees. The adults live on the outside of ash trees feeding on the leaves during the summer months. The larvae look similar to white grubs and feed on the living plant tissue underneath the bark of ash trees. The trees are killed by the tunneling activity of the larvae under the tree’s bark, which disrupts the vascular flow. EAB is a highly invasive forest pest that has the potential to kill nearly 100% of the native ash trees of any size, age, or stage of health where it is present. Over 50 million ash trees outside of Iowa have been killed where EAB is present. Much of Iowa’s forestland is populated with ash trees, and Iowa’s community street trees are heavily planted with ash cultivars. The US Forest Service 2008 inventory indicates that there are 52 million woodland ash trees and 3.1 million urban ash trees in Iowa. Trees attacked by EAB can die within two years. Once EAB killed trees are discovered in a community nearly all ash trees in that community will be dead in five to six years.

Check out this video about the EAB from Iowa State University extension  

Gypsy Moth

Gypsy Moth is a European insect species introduced in Boston, MA in 1869 as an experiment to help provide silk for the textile industry. This exotic insect continues to spread west from that introduction site and defoliate native forests. Establishment of gypsy moth in Iowa will affect the survival of mature trees. The larvae of this insect will feed on the leaves of over 300 host species during the important summer growing season, a time when a trees leaves are converting sunlight to energy. Repeated defoliation that occurs several years in a row on the same tree will deplete the stored nutrients, leading to the decline of that tree. In 2010, a record number of 2,260 male gypsy moths were captured in 31 Iowa counties.

Bur Oak Blight

Bur oak is common across Iowa. In 2008, bur oak ranked second among all tree species as measured in volume of saw timber on forest land. Bur oak provides substantial value for wood products and is an important source of wildlife habitat and mast (acorns) to many game and nongame species. Bur oak blight is a newly named disease that can cause severe defoliation, leading to mortality of branches or entire trees. Bur oak blight is caused by an un-described species of the fungus Tubakia.  Based on reports of BOB to the Iowa State Plant Insect and Disease Clinic in 2010, 27 counties in Iowa reported the presence of the disease. Within these counties there are over 8.7 million bur oaks out of Iowa’s over 32 million bur oak trees growing. However, the disease has been observed by DNR foresters across the state.

Thousand Cankers Disease of Black Walnuts

Since the 1990’s, black walnut has been dying in Western U.S. The deaths are caused by a walnut twig beetle that carries a fungus which is spread as the beetle tunnels through tree tissues. The insect disease complex had been named Thousand Cankers Disease (TCD). The introduction of TCD into Iowa would have disastrous effects economically to the wood industry in the state and the rest of the nation. Iowa has the third largest volume (979 million board feet) of saw log size black walnut in the world. Some experts believe that TCD has the potential to decimate black walnut in the same way Dutch elm disease, emerald ash borer and chestnut blight have destroyed their respective hosts.

Help Lessen an Outbreak

1) For woodlands, keep an appropriate number of trees per acre and maintain species diversity as the best insurance against native and exotic invasive tree threats.

2) Watch for signs and symptoms of the big four pests. If you see issues, contact a district forester. Have digital photos of suspect trees ready to help determine if an on-the-ground inspection is warrented.

3) Take care of your woods. Follow written management plans developed by a professional forester. Maintain proper spacing, stocking and tree diversity. Overstocked, overgrazed and under managed woods are more susceptible to all pests.

4) Cities should inventory their tree resources and work to create a diverse community forest containing no more than 10 percent of any one species.

5) Do not transport firewood, untreated wood products or wood waste. Movement aids spread of destructive pests. For campfires, use wood purchased at the park.

6) Get involved. Advocate protection and care of rural and city tree resources. learn more about tree diseases at www.idnr.gov/forestry/index or contact the IDNR's forest health coordinator, Tivon Feeley at 515-281-4915.