Just Around the Bend

Supply of FTC low statewide,
but still available locally.

In a stroke of brilliance, one of our loyal emissaries has deduced there will indeed be parts of the state in which forest tent caterpillars are still locally abundant. And this a year when the common consensus was that the outbreak was finished and the price of caterpillars would rise faster than a gallon of gasoline. This once again demonstrates the value of keeping one's antennae up at all times lest an opportunity be missed.

The outbreak is on the decline and likely all but over in much of the state. Acres of defoliation declined from a high of 7,374,000 in 2002 to 2,225,000 last year. Less defoliation is expected this year but as in past outbreaks higher populations can be expected to linger in some locations. An egg mass survey conducted recently between Remer in Cass County and Winton in Lake County found egg masses at all surveyed locations. Expected defoliation predicted by the number of egg masses are:

  • Remer - Moderate
  • South of Cohasset - Light
  • Northwest of Nashwauk - Moderate
  • Northeast of Nashwauk - Heavy
  • West of Hibbing - Heavy
  • Between Hibbing and Chisholm - Heavy
  • North of Chisholm - Light
  • East of Buhl - Light
  • Mountain Iron - Light
  • Southwest of Vermillion Lake - Light
  • West of Ely - Moderate
  • East of Winton - Light

In this survey, egg masses are counted on only three small aspen trees at each location so defoliation a short distance away can vary greatly from the prediction. Also, as the outbreak ends, populations become much more variable and spotty and more difficult to predict. Connoisseurs and collectors of forest tent caterpillars are advised to do their own scouting to find the hot spots. This may be your last chance to stock up for those lean years as the population is expected to continue to decline.

Forest tent caterpillars began hatching from the egg masses on May 6 and 7th in most northern locations.

Populations of the parasitic fly, which we all know is native and was not imported, will again be high, especially in areas where the forest tent caterpillar was abundant last year.

Two-lined chestnut borer

Unfortunately the drought appears to be continuing and that means oaks will continue to be attacked and killed by the two-lined chestnut borers. From late May through mid-July, adult beetles will emerge from trees attacked last year. They will be attracted to nearby stressed oaks and lay eggs starting this year's population.

The area of greatest mortality last year was, again, centered within about a 15 mile radius of Grand Rapids although scattered mortality occurred throughout northern Minnesota. If drought and other stress factors continue the mortality is likely to expand in other locations as well.

Two-lined chestnut borer is a native insect that is attracted to stressed oaks and in combination with other secondary insects and fungi, such as Armillaria, kills trees. All species of oaks are attacked. Northern red oaks seem to be the most susceptible in northern Minnesota, however, all oaks including bur oak can be killed.

The best way to reduce damage from the borer is to try to reduce current stresses and prevent additional stress on your trees. Protect trees from defoliation. Avoid disturbing and damaging trees and their roots during construction or other activities near trees. Mulch around your yard trees. Avoid using lawn herbicides under or near trees. And last but best, water your valuable lawn trees. You should have started watering your trees as soon as the frost left the ground because that is when the roots started growing. Many people have more trees than they can possibly water. It is better to pick out the trees you most want to survive and give them adequate water rather than giving all your trees an inadequate amount of water.

Also be cautious about bringing oak firewood into your yard. Adult two-lined chestnut borers will be emerging this spring from trees that they attacked last year. Even if a tree attacked last year was cut down and split for firewood late last summer, adult beetles will emerge from the firewood pile this spring. Bringing this wood into your yard and piling it near your valuable oak yard trees is not a good idea. The beetles are good fliers and can probably fly a couple of miles but they are most likely to attack trees near the woodpile.

Ask your firewood supplier to delay delivery of the wood until late July after the beetles have emerged from the wood. If you have to bring it into your yard now or if you have cut wood yourself, cover the wood pile with a tarp or heavy plastic. Dig a shallow trench around the pile, put the edge of the plastic into the trench and put the dirt back in the trench on top of the plastic to anchor it. Keep the firewood pile covered from now until mid- to late July, then uncover it and let it dry.


Oak tatters is an elusive condition that affects emerging oak leaves, causing them to appear lacy or tattered. The condition affects primarily oaks, and hackberry. Tatters has been observed throughout several mid-western states for more than ten years. Look for tatters during the first week in June and report any sign of tatters to your Regional Forest Health Specialist.

Yellow-headed spruce sawflies

Look for sawfly larvae (small caterpillars) feeding on spruce needles during the first and second week in June. Unlike deciduous trees, conifers can suffer serious injury from a single defoliation! Defoliation of spruce can lead to dieback. Adults (that look like small wasps) emerge in the spring at the time lilacs are in full bloom. The female deposits eggs at the base of the new needles. The larvae hatch in seven to fourteen days and are present in late May through mid-June.

The young larvae feed on the edge of new needles. The leaders and tops of seedlings and saplings will appear thin and will become brown. Older larvae will consume the entire needle often leaving only a short brown stub. Full-grown larvae are 3/4 inch long, have a yellow to reddish-brown head and an olive green body with gray longitudinal stripes. When larvae complete their development and feeding they drop to the ground, form a dark brown papery cocoon in the soil and over winter. Hand-picking may be adequate on a few small trees but chemical control will be necessary on larger or more numerous trees.

Jack pine budworm

The history of past outbreaks shows that jack pine budworm is a cyclic defoliator of jack pine. Outbreaks have been documented since the 1930's. Outside of the west/central counties, outbreaks rarely occur. It has been twenty years since outbreaks occurred in northeastern jack pine forests; along the Gunflint Trail in Cook Co., near Esquagama Lake in St. Louis Co. and in St. Croix State Park in Pine County. Here outbreaks rarely last more than three years and only occasionally have a serious impact.

In Beltrami, Crow Wing, Cass, Wadena and Hubbard Counties, outbreaks generally last five to six years with an interval of only six years between outbreaks. Outbreaks do not develop simultaneously in these counties, rather, there will be two or three population foci the first year in one or two counties and the outbreak will intensify and spread locally during the second year. During the third year, the outbreaks collapses in the original counties, but new foci take shape in two or three more counties. These foci last about two years, also. The regional population finally collapses in year five or six. Then, it's about six years before the population starts building again.

In west/central counties, the longer duration and increased frequency of outbreaks leads to significant losses in growth, wood production and mortality. On a region-wide basis, these are the typical losses during an outbreak:

  1. Mortality of 10% of dominant/ co-dominant jack pines (ranges from 2 to 40%, sometimes higher).
  2. Mortality of most suppressed trees and some intermediates.
  3. Growth reductions follow heavy defoliation, year 1 = 50%, year 2 and 3 = 100%.
  4. Pollen cone production ceases for 3 years following the outbreak.

If you find yourself managing jack pine stands that are in the midst of an outbreak, there are three management options.

  1. Do nothing and let nature take its course.
  2. Use insecticides to keep the foliage green.
    (This option is usually not justified in most forest settings.)
  3. Use salvage sales in severely defoliated and over-mature stands to utilize the wood.

Ash anthracnose

In late spring and early summer, anthracnose is the most common leaf disease on green ashes. During the first half of June, watch for falling leaves after rain events. Anthracnose is a common name for several leaf diseases that are found on a large number of hardwood species but are most severe on ash, oak, and maple. Anthracnose leaf diseases are caused by a few species of fungi, which over winter on the buds, bud scales, and branches. Growth of these fungi begins early in the spring. Sufficient spores are produced for leaf infection and disease development during any period of warm, wet weather in the spring and summer. The severity varies greatly from year to year. Symptoms of anthracnose on infected leaves range from tiny, dead spots to large, dead blotches. Many leaves become curled and distorted due to the infection. Infected and dead leaves are shed. The symptoms are more severe in the lower crown. Defoliated trees will continue to add foliage and the rate of infection will decrease as the season progresses.