PRAIRIE GARDENER: Cold winter might prevent spread of Dutch elm disease

February's frigid temperatures boded well for the Grand Forks Park and Recreation crew who will combat Dutch elm disease this year.

Typically, warm winters mean more bark beetles will survive, spreading the dreaded disease to elm trees the following summer. But with more than two weeks of nighttime readings in the minus 20- to 30-below range, beetle numbers should have been thinned.

Dutch elm disease losses in Grand Forks have held steady for several years. There was concern there might be a spike in numbers two years ago, such as experienced in the Twin Cities and elsewhere. But that didn't happen, reports Mike Fugazzi, forestry operations manager for the Grand Forks Park District. He cites excellent detection, sanitation and removal for keeping cases down.

The situation isn't as bright in East Grand Forks where Dutch elm disease continues to claim what elms remain. While East Grand Forks doesn't have a preventative program, Grand Forks does. That city sets a special mill levy for battling Dutch elm disease.

Stricken trees are removed from both public and private property in Grand Forks. There also is a winter pruning program and a mandatory elm firewood removal in spring. In summer, there is a scouting program to spot and then quickly remove stricken trees.

Steady numbers

Fugazzi reports 70 cases of Dutch elm disease were discovered in Grand Forks in 2006. That compares to 71 in 2005. The number of stricken elms has held steady for the past four years, and he's hopeful it will continue in this range for 2007.

There is no pattern where the diseased trees are found. They have been discovered in new areas of the city as well as in the river corridors where there are more aged elms.

Combating the disease is a year-around job. Beginning Oct. 1 and continuing through March 30, city crews trim and prune elm trees around the city. Inspectors also check firewood piles for elm wood. Elm wood must either be burned or hauled out prior to April 1.

Beginning in late May and continuing through the summer, scouts check elm trees around the city for "flagging" or yellowing of branches. Stricken trees are removed upon discovery to prevent spread.

Most disease cases are found between June 15 to July 12 with a second lighter round occurring in late August through September.

ReplacementsThe city plants about 1,200 trees each year to replace any Dutch elm victims or other trees that have to be removed. Hackberry, basswood and ash are the main shade trees planted.

Due to the threat of the emerald ash borer - a destructive insect native to China - they are scaling back ash plantings. The disease kills all ash varieties - white, black and green. He says that's a bigger threat to urban forests than Dutch elm disease. The city plants some ornamental trees, including maples and flowering crabapples, too.

Disease-resistant elms also have been tested. A system by which chemicals are injected into vulnerable elms has not worked well and has been dropped.

Sugar mapleMarch can mean only one thing - it's maple sugar time. Ideal conditions are sunny days with temperatures in the 40s, following nights when the mercury dips into the 20s. A single tree can yield more than a quart of finished maple syrup.

The process begins when sun warming a tree converts its starches into a sugary sap. Sugar or hard maples are found in forested areas of Minnesota, where they are commercially tapped.

Taps (known as spiles) are inserted into the tree with a drill. Trees under a foot across shouldn't be tapped, one per tree that is a foot across and additional one for each additional 6-inch diameter of trunk.

Besides sugar maples, you also can tap box elder (a maple species), ornamental red and Norway maples and silver or soft maple. Each tastes a little different.

Maple sap is only 3 percent sugar, so it must be concentrated to make syrup of about 63 percent sugar. Large batches call for an outdoor kettle and fire; small batches can be made in the kitchen.

But beware, the cooking sap will give off lots of moisture. You can tell when the syrup is ready by taste and color. Or, you can use a candy thermometer in boiling your sap. Finished syrup will boil at 219 degrees Fahrenheit. Once buds break on the trees, the syrup will have a somewhat bitter taste, meaning the season is over.

Garden tourThe winter program schedule of the Grand Forks Horticulture Society winds down with a March 17 trip to the greenhouse at the University of Minnesota-Crookston. Susan Jacobsen will host.

The group will meet at 9:30 a.m. at the Campbell Library, 422 Fourth St. N.W, East Grand Forks, to car pool. The meeting is free and open to the public. Bring a favorite dish for the potluck that will follow in the U's coffee shop. No regular meeting is scheduled next month with Gardening Saturday set for April 14.

Koehler is the Herald's garden columnist. Send garden questions to him in care of the Grand Forks Herald, Box 6008, Grand Forks, ND 58206-6008.