Category Archives: Botany

The impact of a deep freeze on the emerald ash borer


It’s bitter cold in the Ann Arbor area and throughout the country; temperatures have been below zero most of the last two days.

One of the things we’re looking for a silver lining in super cold weather is its impact on bugs, especially invasive species like the emerald ash borer that are not used to unusual weather. A story in the The Gazette (Cedar Rapids Iowa) has a description of the effects of extreme cold on these destructive beetles.

In Minnesota, where arctic outbreaks are colder, more frequent and last longer, they do inhibit the spread of the emerald ash borer, according to Lee Frelich, director of the University of Minnesota Center for Forest Ecology.

In parts of northern Minnesota and North Dakota, frequent, protracted cold spells may actually establish a zone in which ash trees can survive, Frelich said….

Citing recent research conducted in Minnesota, Frelich said 5 percent of emerald ash borer larvae die when exposed to a temperature of 0 degrees Fahrenheit. The mortality rate increased to 34 percent at 10 below, to 79 percent at 20 below and 98 percent at 30 below, according to that research.

However, the exposure must last at least several hours to overcome the insulating effect of the bark beneath which the larvae live.

More details on Minnesota Public Radio News, again from Frelich:

I think the forecast temperatures that we will experience in the next several days will cause a lot of mortality for emerald ash borer in MN. Details below–probably more than you need. I looked up the most recent research this morning, because I figured I will get a lot of questions about this over the next week.

Winter mortality for emerald ash borer is definitely temperature dependent. The larvae can supercool to a certain point, but they die if they freeze, and there is variability in tolerance among individual insects. A recent study from the Forest Service (Venette and Abrahamson–see attached) in Minnesota showed that 5% of the insects die at 0F, 34% at -10F, 79% at -20F and 98% at -30F.

The recent study is Venette and Abrahamson, Cold Hardiness Of Emerald Ash Borer, AGRILUS PLANIPENNIS: A new perspective. The abstract:

This study was designed to assess the cold hardiness of emerald ash borer larvae, the
overwintering stage of the insect. We began by measuring larval supercooling points, the
temperatures at which larvae freeze. We found that larvae collected from naturally infested trees in St. Paul, MN between late October and early December had an average supercooling point of -25°C (-13°F). Research elsewhere indicates that when these insects freeze, they die. Our laboratory assessments of cold hardiness were confirmed during field tests. Naturally infested logs were held outdoors in St. Paul, MN (low winter air temp=-28°C) and near Grand Rapids, MN (-34°C) for ca. 5.5 weeks. Approximately 40% of larvae from logs in St. Paul were inactive or brown, both evidence of death; approximately 90% of larvae from logs near Grand Rapids were inactive or brown, compared with the approximately 10% that showed evidence of death prior to exposure or after being held under cool, non-lethal conditions. Overwintering mortality
may help to minimize the damage caused by emerald ash borer in areas with extremely cold
winter climates.

So there you go; the colder the weather, the more of the bugs die.

Image credit:


Holdridge vegetation classification system

Another triangle, this one found in a University of Michigan Global Change lecture on the Tropical Rain Forest, by George Kling. 

The triangle is the "Holdridge triangle", dating to 1947. 

  • Holdridge, L.R. (1947) Determination of world plant formations from simple climatic data. Science, 105, 367–368.

image from

All materials © the Regents of the University of Michigan unless noted otherwise.

Sand County Almanac, June: “The Alder Fork – A Fishing Idyl”

We found the main stream to law that the teeter-snipe pattered about in what last year were trout riffles, and so warm that we could duck in its deepest pool without a shout. Even after our cooling swim, waders felt like hot tar paper in the sun.

Aldo Leopold, A Sand County Almanac. This 1989 Oxford Paperbacks edition, ISBN 0-19-505928-X, as an introductory essay from Robert Finch commemorating the 100th anniversary of Leopold’s birth.

We see Leopold, the rural sage, tracking a sunk in January, cutting a venerable dead oak, stalking a legendary fish on Alder Fork or an elusive grouse on an abandoned farm, surveying his private unofficial domain before dawn, wrestling with god-like decisions about tree-thinning, or experiencing a “curious transfusion of courage” from his pines in deep winter.

Sand County Almanac is a good book to come back to every month year round.

purple beans for dinner; or, anthocyanin pigmentation in Phaseolus vulgaris

We had purple beans for dinner, from farmer's market.  I heated some olive oil in a pan and cooked them through until they had turned all green, and then salted them a little at the end.

The recipe called for adding chopped almonds but it didn't happen; instead I served the boys tofu that I had cut into cubes and boiled (boiling it improves the texture quite a bit, firming it up more to my liking).

I don't know which variety of purple beans we had.  A search of the net unearthed the "romano purpiat bean" (from Territorial Seed)

60 days. Everything about this purple Romano bean is noteworthy:
healthy robust plants, deep violet stems, lilac blossoms, and lustrous
purple pods. The 5 inch, flat pods are so tender, crisp, and delicious
that we found them irresistible picked fresh from the plant. Cooking
the pods turns them a brilliant jade-green with a nearly stringless
texture. Remarkably productive plants reach 24 inches tall and tolerate
cool, early plantings. Brown seeds.

and Peaceful Valley has the Royalty Purple variety

Phaseolus vulgaris Tender Annual Bush. Purple bushes with
short runners and purple flowers. Bright-purple stringless 5"-6" pods
cook to dark green. Buff colored seeds germinate in cold, wet soil.
Bred by E.M. Meader at the University of New Hampshire and introduced
in 1957.

Why are beans purple?  Good question.  I got as far as finding this:

Genetics of flower and pod color in Phaseolus vulgaris

Christian A. Okonkwo, and
Carl D. Clayberg

The Journal of Heredity 1984:75(6):440-444

© 1984 The American Genetic Association 75:440-444

A new locus, Prp (purple pod), having five alleles affecting anthocyanin pigmentation of corolla and pod, is described in Phaseolus vulgaris L. The allele Prp produces dark-purple corolla and is fully dominant in this respect over the other four alleles that determine light-purple corolla. In the absence of Ro, Prp is responsible for medium-purple pod when homozygous and light-purple pods in combination with the other alleles. The alleles prpsh2 and prpsh give green pods shaded with purple and are codominant with the prpst allele, which causes green pods to be striped with purple. These four alleles are dominant for pod color over prp, an allele causing green pods when homozygous. The interaction of these alleles with the genes Gri, V, and Ro, which also affect anthocyanin pigmentation of corolla and pod, is described. No linkages among these four loci were observed.

That's from 1984; I don't know enough about bean genetics to go any further.

(Oh, and they are delicious.)

saturday Ann Arbor farmer’s market report, u-pick fruit coming up, and what’s in bloom

I was at market on Saturday (yesterday) and kept an eye out for fruit and for new things at market.  Here's some details.

Sour cherries were gone; sweet cherries were $5-$6 per quart.
Both Erie Orchards and Sodt's Berry Farm had blueberries for $40 for a 10# lug.
Basil, $1.00 to $1.25 a small bag, or $10/# (organic).
Grandma from Grandma's Kitchen brought 70 dozen eggs and was sold out at noon.

The U-Pick local report from Mark Charles:

Dexter Blueberry Farm's web site says they'll open on July 20. 

Makielski's raspberry farm says "2 weeks"  (about July 25.)

and the field report from the Buhr Park wet meadow from Andy Brush

Today at wet meadow II, I saw the following in bloom:
  • Bee Balm
  • Black Eyed Susan
  • Yellow Coneflower
  • Prairie Dack (just getting going)
  • Butterfly Milkweed
  • Hoary Vervain
  • Daisy Fleabane
  • Common Milkweed

the violets growing in my yard make me happy

They are nothing special, really, just ordinary lawn violets.  I love them, and I love it when they come out in the spring time.  When they appear I have warm memories of my great aunt Gail Clark who kept violets at home and who was named after the plant.

Candied violets are said to be very easy – dip the violet flower in egg white and then in sugar.

More reading, of course:

but best to just be outside