Tom's Blog

Friday, June 17, 2016

Modifications of the "leaf spritz" technique for invasive plants

I first published in 2010 on the leaf spritz technique for "selective" control of invasive plants without affect on nearby "good" plants. The spray solution is a 15-20% solution of Garlon 4 in bark oil.

Invasive sunflower that was leaf-spritzed two weeks earlier.
I returned next year and found only three or four stems that had survived (or had been missed).

Since then I (and others) have used this technique for a wide variety of herbaceous plants. Many modifications can be done, depending on the species and the extent of the infestation. A later post provided more detail.

The original technique was to use a spray bottle to "treat" a few leaves in the upper part of the plant. However, some folks prefer to use a sponge to treat the leaves, and this technique also works. The advantage is that there is less chance of herbicide dripping onto "good" plants. This post shows how this modification works.

Buckthorn leaves that
had been spritzed
six days before.
The roots were also killed.
A major advantage of the "spritz" technique is that this is a "low-volume" treatment. Because the herbicide concentration is high, one doesn't need to "soak" the whole plant, as agriculturalists do. The fact that the herbicide is oil-based may have some significance here. (The original reason I was using this mixture was because I was doing basal bark treatment of woody plants, so I had the spray bottle in my hand. Why not try a few nearby herbaceous plants? Also, the leaf spritz technique does work for woody plants, as the buckthorn photo shows here.

Among other species that the leaf spritz works on are burdock, mullein, bird's foot trefoil, alfalfa, sunflower, and sweet clover (basal stem treatment).

I especially like this for dealing with large multi-stem patches of sweet clover that are too thick to dig quickly. I pull the stems back toward me, then lean down and spray the stem bases on the far side of the patch. Within three days they show distress and within six days they are dead!

Friday, June 10, 2016

Ancient (hidden) bur oaks (Quercus macrocarpa): Can they still be saved?

According to numerous reports (reviewed in this publication), bur oak (Quercus macrocarpa) populations have decreased dramatically since European settlement, and conservation and restoration of this species has become a management priority in many areas. According to the U.S. Forest Service, in the early 1900s, bur oak savannas occupied 32,000,000 acres (13 million hectares) in the Midwest U.S., of which only about 6,400 acres (2,600 ha) remain. Loss is due primarily due to agricultural development, but fire exclusion is another important factor.

The seriousness of the loss of this important species has motivated some parks and natural areas to carry out programs with school children and others to collect acorns and raise oaks for planting. This is a meritorious endeavor although not likely to produce ancient oaks in the foreseeable future.

However, it seems to me that there is another approach that holds promise.

There are extensive areas in the Midwest where venerable bur oaks already exist. Observations of wooded hillsides in some areas often reveal the presence of large bur oaks that are hidden among extensive invasive brush and trees. These trees, often called “wolf trees”, can often be seen through the dense shrubbery, especially in the winter when leaves are absent and snow provides a contrasting background. Although these open-grown bur oaks are probably in weakened condition due to shading, it is possible that many might still be saved.

Pleasant Valley Conservancy (PVC) can provide an object lesson of what can be done.

When restoration began at PVC about 20 years ago, we knew that hidden among all the invasive brush and trees were many large bur oaks, especially on the upper slopes and ridge tops. Many of these were large open-grown trees and subsequent age determination showed that many were over 200 years old.

In the 1937 air photo shown here most of the large scattered trees are bur oaks (see later photo below).

Early air photo of the area that after restoration became Pleasant Valley Conservancy

As the years went by in the absence of fire, this landscape filled in with invasive trees and brush, as the air photo from 1990 shows. However, the large bur oaks are still present, but hidden from view.

Air photo from 1990 showing the same area, before restoration work had begun.

After some years of restoration work, the habitat was opened up, permitting the existing bur oaks to flourish. The 2013 air photo shows the result.

Air photo from 2013, after restoration was complete. 
When restoration work began, the goal was to remove all woody plants, both shrubs and trees, that were crowding open-grown oaks. Many of the open-grown oaks, especially on the ridge top and south-facing slope, were either bur or white oaks. Over a six-year period, about 60 acres of woody areas were restored. All invasive woody plants and trees were removed. Trees removed included all fire-sensitive species such as black walnut, slippery elm, black cherry, aspen, box elder, red maple, and basswood. Even red, black, and Hill’s oaks were removed if they were crowding open-grown bur or white oaks.

Once the restoration work was completed, a census of all trees over 10” in diameter was made. Those trees greater than 20 inches in diameter would be trees that were present at the time of the 1937 air photo. There were 251 bur oaks and 111 white oaks that were greater than 20 inches in diameter.

The table below provides the bur oak data.

Size classes; inches diameter
Number of bur oaks

Using GIS, a map was prepared that overlays the >20 inch oaks onto a georeferenced version of the 1937 air photo. 

GIS map showing the 2013 distribution of large bur and white oaks overlaying the 1937 air photo

Note that the large bur oaks overlay quite well the 1937 trees (within the accuracy of the GPS device used). It is evident that most of the large oaks are superimposed on top of the black tree patches in the 1937 air photo. 

It can thus be concluded that most of the large oaks that were present in 1937 are still present today. The ages of some of these venerable oaks were determined by the U.W. Platteville TREES laboratory by dendrochronology. The oldest living tree has a start date of 1736 (280 years old in 2016).

The map shows that bur oaks are mainly in the prairie border and savanna areas of the Conservancy (see yellow dots on the map). The largest area, which includes the major ridge-top savanna and upper part of the south-facing slope, was 18 acres. The smaller area, which includes the basin savanna, was 4 acres. (There are also bur oaks scattered within the North Woods and the smaller woodlands on the far east side of the Conservancy.)

It is likely that PVC is not an isolated example, and that there are numerous other sites in in the Midwest where ancient bur oaks still survive. They may be heavily overgrown and struggling, but the bur oak is a remarkably resilient tree, and with care may still be saved.

Using automobile surveys, venerable bur oaks may well be located today by casual observation in heavily wooded areas. Once such areas are found, the historic air photo of that area can be used to confirm the site, and then a detailed “on-the-ground” visit made.

It is recommended that using historic air photos (in the public domain and available on-line in Wisconsin or from the U.S. National Archives), potential areas for bur oak restoration should be located and visited today. Look for the presence of open-grown oaks on south-facing slopes, most of which will probably be bur oaks. Visit the same locations now. Because an identified area now is most likely unlogged and hence thickly wooded, the open-grown oaks may still be visible within the thicket. The best time to do an on-the-ground survey is in the winter with snow on the ground.

Note that recent air photos will not reveal the presence of these ancient bur oaks (unless the area has been restored) because of the heavy tree growth. One must use the oldest available air photos. Fortunately, the air photos taken in 1937-1941 by the Soil Conservation Service are now available free of charge (in Wisconsin from the State Cartographer’s Office. Access the Wisconsin Historic Aerial ImageryFinder.

Monday, June 6, 2016

Bur oaks at Black Earth Rettenmund Prairie

I once saw an exhibit at a Nature Center that said: “Where does the prairie end and the savanna begin?” The answer given was: “At the first oak tree.”

There are quite a few small bur oaks at Rettenmund Prairie that have survived various fires over the past 15 or so years. I don’t know where they came from but they are thriving, and some day will cast enough shade to convert their immediate domain into an open savanna.

Saturday after the work party I took some photos of these small trees. They are found in two places: 1) At the top of the North Unit and on the hill facing north to Fesenfeld Road; and 2) on the middle of the Saddle. The photo from Google Earth shows the North Unit. Most of the green in this 2013 photo (cropped) shown here is not bur oaks, but prairie willow and hazel, but several small green “dots” are definitely bur oaks (see the photos of the larger bur oaks farther below).
Georeferenced image cropped from Oct 2013 Google Earth. This is the top of the knoll on the N unit (the footpath shows clearly). The largest bur is at the top of the hill mixed in with the prairie willow (see photo with Kathie below), and the three green “dots” in the upper right hand corner are burs on the hillside (see photo below).

There is a clone of may apple surrounding one of the bur oaks on the side of the hill (see photo below), which represents a “legacy” from when this area was heavily wooded. (See the Converse map from April 1984 below). Although may apples can hang around a long time in sunny habitats, they need fairly substantial shade to get started.

Map drawn for the Nature Conservancy by C.K. Converse in April 1984, before any restoration work had been done at Rettenmund Prairie. Note the woody patch (aspen etc.) on the top of the hill in the North Unit and the large woody patch in the Saddle (labeled by the long leader). Both of these areas have bur oaks today.
Photo taken of the North Unit in 1987 (before any restoration work had begun), 
showing the large woody vegetation in the area where small bur oaks live today. 
Although most of the trees here were aspens, bur oaks might also have been present 
and have been removed as part of the prairie restoration process.

Head-high bur oak on the lower slope of the N unit, surrounded by a clone of may apple. 
Note also the two other bur oaks farther up the slope.

Small bur oak “grub” on the North Unit. 
Presumably arisen from an acorn sometime in the past few years. 
There are no acorn-bearing trees anywhere near Rettenmund Prairie or anywhere within a mile.

Two bur oaks on the Saddle, in an area that once had a large woody patch. The large specimen is about 15 feet tall. The small one consists only of resprouts. The flame height of this year’s fire was probably less than 4 feet high, so that the tall tree, with its corky fire-resistant bark, was unaffected.

The largest bur oak on the top of the knoll in the North Unit. 
Although this area has lots of fine prairie plants, it has also been 
invaded by woody vegetation, including prairie willow, hazel, and gray dogwood.

 Bur oaks and fire: Both units where the bur oaks are present were burned this spring and are burned two out of every three years. Because the grass fuel at Rettenmund is fairly low, flame heights are not very high. The three larger trees shown in photos here would not have been affected, as shown by the fact that their bottom branches have all leafed out. If flames had been higher, the buds on these branches would have been killed. Once a tree gets as high as these three, because of their thick corky bark they can usually survive most fires. Small trees and grubs, however, are almost always killed, even by small fires, but then resprout from the base. Grubs can do that over and over, always extending their root systems, until a year may pass when the fire misses them and they get large enough to turn into “legitimate” trees.

What will happen to Rettenmund as the years go by. Will parts of it turn into a savanna?

Probably only after the three larger bur oaks get old enough to make acorns. How old must a bur oak be before it can flower and make acorns?

According to Silvics of North America, bur oaks must be 35 years old before they can make acorns. However, that age is not based on any real research. In fact, at the UW-Madison Lakeshore Preserve bur oaks that were planted in early 2000s have already made acorns.

Monday, May 30, 2016

Serious tree damage (windthrow) from storm 5-28-2016

We finally got the rain we wanted on Saturday afternoon (May 28 2016). Unfortunately, it was accompanied by extremely strong winds that did serious damage to trees at Pleasant Valley Conservancy. Kathie and I spent part of Sunday discovering just what sort of damage took place.

We have a lot of venerable oaks, both bur and white. The wind seemed to affect primarily bur oaks at the west end of the Conservancy, mainly at the top of the hill, although there were also some cherries and several shagbark hickories. The largest hickory at the conservancy came down (see photo here).

Largest hickory along the Mid Savanna Trail lost its whole top, converting this tree into a "snag".
This location is close to a large milkweed clone that provides prime Monarch habitat.
Fortunately, the milkweeds will be unaffected.
Most of the trees were not uprooted, but rather lost their tops. Some of them still retain enough living material to remain alive, but quite a few lost all living branches, remaining standing as snags.

The photos here give little idea of the extent of the damage, although they do show the type of destruction we observed. Kathie's notes, given below, give lots of details.

The gravel road should be clear in a few days, but the rest of the damage will have to wait, as we are in the middle of invasive plant season.

These big branches are from a large black oak that was standing exposed to the full brunt of the wind.
It lost its whole top and was converted into a snag.

The rest of the black oak shown above.
In the background is our prized bur oak, 280 years old.
Fortunately, it stands slightly downhill on the north side and was protected from most of the wind damage.
A small branch was knocked off.
Kathie's detailed notes

Here are my observations from the big storm that hit at PVC on Saturday, May 28, from about 4 to 5 pm.  Not a happy visit, all in all. But NOTHING we could have done to prevent it.

I will list what I saw in order as I travelled along the roads and lanes:

1. Nothing much in the lower areas, only several smallish branches from the black walnut at the entrance to the Pocket prairie, and a dead walnut down on the other side of the road.

2. Cherry tree down across gravel road between triangle and Unit 20.

3. Tree branch a little farther on, near first bluebird house.

4. Tree broken in 12A, down the hill from about the middle of Toby’s.

5. Giant dead oak in 12A blown down.

6. Can see tree down along mid savanna trail.  More later

7. Can see big branch/tree down in 11 D  ?  More later.

8. East overlook:  Big birch down across trail down to mid-savanna trail. Tore up root ball from E. overlook. Cedar tree blown over, leaning into other cedars.

9. Rocky Overlook:  South firebreak trail—cherry tree down near Rocky overlook.

10. BIG oak down in Unit 10 (along South Fire Break). [This one was uprooted!]

11. Also Unit 10:  Whole top of black oak across from oldest oak down across road.  Knocked relatively small branch off oldest oak. [See photo in this post]

12. Oak in middle of Unit 10 down: was one of two trunks.

13. Unit 8:  one/third of huge oak down. 

14. Unit 19A: small dead oak fell—#2338.

15. Ridge trail. Huge walnut in 19A fell to north—into other trees.  Also big dead birch fell across ridge trail. Also another birch, but not across trail.

16. South Firebreak: Unit 8, going east from Overlook:  2 big branches across firebreak.  Also 2 others nearby. One branch/tree down below that in Unit 5 (9?)

17. Unit 8: Dead walnut trunk leaning heavily into big oak.

18.  South firebreak, from Tom’s Prairie, going East along south firebreak:  2 oaks with branches down.  HUGE bur oak down right ON firebreak—big root ball.  Large basswood down below firebreak. Huge branch or half of oak down in Unit 10 and on firebreak.

19. North firebreak:  west of chairs.  Big oak down.

20.  Mid-savanna Trail  (see note 6 and 7):  small branches on trail.  HUGE hickory (#405) broke off at base. Fell mostly off trail, and just east of the big milkweed patch.

21. Broken tree farther along mid savanna trail. 

See also Kathie's Facebook page for her photos.


In the post given at this link there is a brief discussion of a straight-line wind called a derecho that happened some years ago. That storm mainly affected already dead black oaks that had been killed by oak wilt.

Friday, May 27, 2016

Eradication of invasive plants (2): perennials

This is the second of two posts on invasive plant control. Last week’s dealt with biennials.

The table at the end provides an overview of key perennial weeds and a summary of control methods.

Perennial weeds may start as seeds or from underground roots or rhizomes. The life span of perennials varies widely. Some last only a few years whereas others may last indefinitely. Because of their root systems, it is unlikely that a perennial will be eradicated by digging the plant up. Thus, permanent control of perennials almost always requires the use of an herbicide.

Eradication of most perennial weeds requires great effort and extended time periods, generally over a multi-year period. Neither fire nor mowing will eradicate any perennial weed, although these procedures may find good use along with herbicide.

Most of the weeds in the table are dicots and hence susceptible to broad-leaf-specific herbicides such as 2,4-D, clopyralid (Transline), metsulfuron methyl (Escort), and triclopyr (Garlon). The one monocot in the table, reed canary grass, is controlled by a grass-specific herbicide such as clethodim (Intensity). Under certain conditions it may also be possible to use a nonspecific herbicide for these weeds such as glyphosate (Roundup). Details on the manner of use are given in the herbicide label specifications.

In the rest of this post, I give our own experience for successful eradication.

Spotted knapweed This is more of a problem in dry, sandy areas. However, when our gravel road was redone about 6 years ago, the contractor brought in gravel that was contaminated with seeds of this species. Each year for the next few years we waited until it was in flower and then spot-sprayed each flowering plant along the whole roadside with aqueous Garlon 3A as a foliar spray. This was effective and by year 4 this species had been eradicated.

Spotted knapweed growing in contaminated gravel brought in for road repair

Canada thistle This is one of the few weeds that is listed by the State of Wisconsin as a noxious weed. As far as I know, it is the only thistle species that is a perennial. It forms an extensive underground rhizome system. However, it does not compete well with prairie plants so that it is often only a problem in the early years of a prairie restoration. In the early years of our restoration work, small or larger patches of this weed popped up in planted prairies or in open savannas. Some of the smaller (i.e. less than 6 feet) patches could be controlled just by mowing consecutively for several years at the time of flowering. Larger patches were controlled by mowing at flowering time and returning later to spray the resprouts with glyphosate or triclopyr. We haven’t seen Canada thistle at PVC for at least six years.

Crown vetch This is a very aggressive plant which is very difficult to control. It has an extensive rhizome system and the seeds, like many other legumes, are very long-lived in the soil. The key is to not let it get started. US Highway 18/151 is heavily infested (probably planted when the road was rebuilt) and it is now moving off onto some of the nearby county highways. I watched one nice prairie remnant over which I had no control get taken over by crown vetch over a period of ten years, despite frequent burns. At PVC we had a single patch of crown vetch pop up on the lower part of our south-facing slope. I have no idea where it came from. It is easy to spot when flowering, and I sprayed it immediately with Garlon 3A. It quickly died and has so far not returned.

Leafy spurge This is another plant that is troublesome along roadsides and is a potentially serious invader of natural areas. It has a deep tenacious root system and spreads rhizomatously. Fortunately, we have never had to deal with this nasty plant, although we see it spreading along US 14 between Middleton and Cross Plains. Currently, the recommended herbicide for leafy spurge is imazapic (Plateau), spraying twice in the growing season, late spring (before seeding) and in the fall just before a killing frost.

Birds-foot trefoil This legume was once planted extensively agriculturally and because of its long seed life (as bad as sweet clover!) it can be a problem in prairies that are being established on former cropped fields. It is not rhizomatous but forms a deep tap root from which stems arise that spread out along the top of the soil. Because of its low-growing character, it is hard to see until it flowers. We have been dealing with this in Toby’s, the Pocket, and Ridge Prairies since they were first established. Our procedure is to find the center of the plant and give it one or two brief spritzes with 20% Garlon 4 in oil. The plant should be dead within a week. Details of its ecology and control can be found in my earlier post.

Reed canary grass (in upland sites) Reed canary grass is a major problem in wetland systems but does occur occasionally in upland sites. We have been dealing with this in some of our savannas for at least 15 years. It generally occurs as relatively small patches which can best be found at the time of flowering. Spray each patch with Intensity. If that herbicide is not available an alternative is to cut with a hand clippers each plant about six inches to a foot above the base, tie the stems together in a bundle, and use a spray bottle to treat the cut stems with 50% Roundup. This is a fairly time consuming procedure but is effective.

Motherwort This perennial is primarily a problem in heavily disturbed areas. It appears fairly early in the spring, before most native species are still dormant, and should be sprayed with foliar glyphosate or a broad-leaf specific herbicide.

Latin name
Common name
Severity (1)
Control methods
Centaurea maculosa
Spotted knapweed
Biennial or short-lived Perennial
Especially dry prairies and sandy habitats; more serious in western states; don't let it get started!
Spring and fall spray with broad-leaf-active herbicide
Cirsium arvense
Canada thistle
Moderate; generally outcompeted in well established prairies; don't let it get started!
Spring spray with broad-leaf-active herbicide; summer mow; fall spray with broad-leaf-active herbicide
Coronilla varia
Crown vetch
Now a potentially serious invader of prairies and savannas; don't let it get started!
Spring and fall spray with broad-leaf-active herbicide
Euphorbia esula
Leafy spurge
Now a potentially serious invader of prairies and savannas; don't let it get started!
Spring and fall spray with broad-leaf-active herbicide
Leonurus cardiaca
Broad-leaf herbicide
Lotus corniculatus
Birds-foot trefoil
Broad-leaf herbicide; longlife seed bank; difficult to eradicate
Lythrum salicaria
Purple loosestrife
spray with broad-leaf-active herbicide when found
Phalaris arundinacea
Reed canary grass
Spring and fall spray;summer cut followed by spray of cut stems
Trifolium repens
White clover
Low; outcompeted in established prairies (except along edges)
Spring spray with broad-leaf-active herbicide
(1)    Severity refers to prairies and savannas only. Wetland habitats will be different.

Saturday, May 21, 2016

First "official" Monarch sighting in Wisconsin at Pleasant Valley Conservancy

According to Prof. David Hogg, Monarch specialist at UW-Madison, the first "official" 2016 sighting of Monarch butterflies in Wisconsin was made Thursday May 19 at Pleasant Valley Conservancy.

Here is the report: The first “official” 2016 sighting of Monarch butterflies in Wisconsin was made yesterday at Pleasant Valley Conservancy, specifically in the oak savanna habitat on the south facing hillside.  I’ve attached photos of the adult (female) and one of the eggs she deposited.  We (Cameron Fullerton and me) watched her flit from milkweed to milkweed, and it appeared that she laid eggs on a dozen or more stems.  We examined a number of milkweeds after she left, attempting to target those she had visited (not easy to do with the large number of milkweed stems in the patch) and were able to find four of her eggs on stems ranging from 4 to 9 inches tall.

The sighting was recorded with the Southern Wisconsin Butterfly Association  <>.

Monarch season has begun!
Monarch butterfly on shoot of common milkweed (Asclepias syriaca). David Hogg photo

Monarch egg on milkweed leaf. David Hogg photo

Those interested in helping further the Monarchs at Pleasant Valley Conservancy are invited to be volunteers Sunday May 22, 2016 from 10 AM until 4 PM (or any fraction thereof). We will be planting swamp milkweed and meadow blazing star "plugs", favorite Monarch plants.

Friday, May 20, 2016

Monarch butterfly project at Pleasant Valley Conservancy: volunteers needed Sunday May 22, 2016!

Monarch butterflies need all the help they can get! Pleasant Valley Conservancy (PVC) has lots of Monarch habitat, but more is  needed to replenish the diminishing populations of these important and attractive migrating insects.

At PVC, thanks to Kathie's efforts, we have been awarded a grant from the U.S. Fish & Wildlife Service to encourage Monarchs. Among other things, this grant has supported the purchase of seedlings of two important Monarch plants: swamp milkweed (Asclepias incarnata) and meadow blazing star (Liatris ligulostylis).

Volunteer help is needed to plant these seedlings.

Meet at the PVC Barn at 4609 Pleasant Valley Road. Hours are from 10 AM until 4 PM. Bring your lunch. Drinks and desert will be provided.

For information, call Kathie at 608-238-5050.