Pst on Canada thistle
Visitors to Minnesota’s natural places will occasionally come across a stand of Canada thistle with a few plants that are whitened at the top, appearing bleached. The discoloration is caused by the bacterium Pseudomonas syringae pv. tagetis. It has been called “White‐colour Disease of Canadian Thistle,” “apical chlorosis of Canada thistle,” and “Bacterial Speck”, but it has no widely-accepted common name. It is often referred to in scientific literature as Pst.
Outside of a laboratory, a bacterium is recognized only by the symptoms it produces in its host. Pst produces the substance tagetitoxin, which blocks the production of chloroplasts, preventing photosynthesis. This results in whitened plant growth (chlorosis) on only the upper portion of the plant, stunted growth, fewer shoots, and inhibition of flowering. Pst infects plants in the Aster family, including Canada thistle, common dandelion, common sunflower, common ragweed, giant ragweed, Jerusalem artichoke, and some other plants not found in Minnesota.
Researchers at the University of Minnesota conducted a study in 2002 to assess the viability of using Pst as a biological control agent for Canada thistle.
Orange-gilled Waxy Cap (Humidicutis marginata) is a medium-sized, easily identified mushroom. It is widespread in North America but not common in the Midwest and northeast. It grows on the ground in humus, sometimes on very rotten wood, in coniferous, deciduous, and mixed forests. It may be found singly, scattered, or in small groups. It is edible but insubstantial and watery.
Three varieties are recognized; var. marginata, with an orange cap; var. concolor, with a yellow cap, more common in the northeast; and var. olivacea, with a olive-colored cap, more common in the west. The variety in most common in Minnesota is identified by the bright orange color; the cap that appears watery when wet but is never slimy; and the orange gills that retain their orange color even long after the cap has faded to yellow.
At only one tenth the width of a human hair in length, a crimson erineum mite (Aceria elongatus) is barely visible to the human eye unaided by magnification. Its claws, dorsal shield markings, and other identifying body features are not. Identification in the field is possible only by noting the properties of the abnormal growths (galls) it produces on its host.
Crimson erineum mite is a plant parasite infecting only sugar maple and possibly black maple. It is common in eastern United States and Canada. When injured by a mite, a leaf cell produces a small projection filled with colored fluid on the upper surface. Small patches of these are usually scattered over the leaf surface. They are greenish-white at first, soon becoming crimson or purplish. They reach their maximum extent, and are most noticeable, in summer. The infestation is sometimes abundant and can cause leaf distortion and premature leaf drop.
Photo by Dan W. Andree
At 1¾″ long, eyed click beetle (Alaus oculatus) may be the largest click beetle in our area. With its boldly-outlined eye spots it is certainly the most distinctive.
The body is long, thin, and black, with mottled patterns of minute, whitish scales. The thorax has a pair of large black spots boldly outlined with white. The spots look like eyes and give this beetle its common name.
On the underside, an elongated lobe on one plate fits into a groove in another plate, allowing the insect to produce an audible click. This feature gives the insect family the common name “click beetles”. If put on its back, the beetle uses this click mechanism to catapult itself up to six inches in the air, righting itself and potentially escaping a predator.
Click beetle larvae are called wireworms. Most wireworms eat plant roots, and can be serious agricultural pests. Eyed click beetle wireworms are carnivorous. The feed on the larvae of other insects, especially wood-boring beetles. This makes them a beneficial insect.
Photo by Margot Avey
There are sixteen species of Hericium fungus, four of which occur in North America, three in Minnesota. Comb Tooth (Hericium coralloides) is by far the most common of the three. It is fairly common in northeastern United States and in Minnesota. It is found in late summer and fall in deciduous woodlands and forests, on fallen logs, branches, and dead stumps of hardwoods.
The fruiting body is a loose, open cluster of delicate branches. It is white when fresh, becoming creamy-white to buff or yellowish-tan with age. The branches are themselves again intricately branched and have rows of evenly-spaced spines, like the teeth of a comb, that hang downward. The spines are the spore-producing structures of this fungus, corresponding to the gills on many mushrooms (Agaricales). The flesh is white and edible when young and soft, but the spines become brittle with age.
Comb Tooth is similar in appearance to the other two Hericium species in Minnesota. It is the only Hericium that is intricately branched and has teeth no more than ⅜″ long.
Photo by M.j. Horgan
There are more than 3,000 species of walkingsticks worldwide, 29 species in North America north of Mexico, and probably just 2 species in Minnesota. Northern walkingstick (Diapheromera femorata) is the most common walkingstick in North America and in Minnesota. The extremely long, thin, almost cylindrical body strongly resembles a leafless twig making it invisible to predators.
In Minnesota, the northern walkingstick population fluctuates on a two-year cycle. The odd numbered years are the “boom” years, the even numbered years the “bust” years. They mate in late summer. The female drops eggs to the ground one at a time. During heavy infestations, female egg-dropping can sound like falling rain. The eggs remain on the ground until the second following spring. After almost two years, they hatch between mid-June late July. During the night, the nymph crawls up the first vertical object it encounters. If that is a stem of a shrub or tree, it begins feeding. Otherwise, it returns to the ground and seeks another vertical object.
The other walkingstick known to be found in Minnesota, prairie walkingstick (Diapheromera velii), is very similar in appearance. Northern walkingstick is distinguished by its occurrence in forested habitats, the dilated and banded femur on the middle leg of the male, and the much shorter sensory appendages at the end of the abdomen of the female.
Photo by Bill Reynolds
Minnesotans are seeing the huge influx of painted lady (Vanessa cardui) butterflies in the summer of 2017. Observers from the Twin Cities to Detroit Lakes and Pennington County have reported seeing “15 plus,” “dozens”, “lots and lots,” and “plentiful” painted lady butterflies this year. Lora in Corcoran reports them “swarming the soy bean field across the road.” Ruth in Big Stone County reports seeing “clouds of them.”
Painted ladies are both migratory and cyclic. They overwinter in the southwestern United States and in northern Mexico. They migrate north in the spring in most years, temporarily repopulating the United States and Canada. Some years they do not migrate at all. In years of much rain on the wintering grounds the northward migrations are enormous. They migrate south beginning in August and continuing through November. They are cyclic because some years their populations are large, some years small.
Painted lady butterflies are very similar in appearance to American Lady (Vanessa virginiensis) butterflies. Painted lady is less orange above. The large spot near the tip of the forewing is always white, never pale orange. The black band in the middle of the forewing creates an isolated orange spot. The dark spots on the hindwing are smaller, do not touch, and do not have blue centers. There are four eyespots on the underside of the hindwing.
Photo by Bill Reynolds
Downy yellowjacket (Vespula flavopilosa) is an uncommon, medium-sized, predatory, social wasp. It is found in the northeastern United States from Minnesota to Maine, south to Virginia, and along the Appalachian mountains to northern Georgia. It closely resembles eastern yellowjacket. It is thought by some to be a hybrid between eastern and common yellowjackets. Others suggest that it probably arose as a hybrid but now queens mate with drones of the same species.
The overwintering queen emerges from hibernation in April or May. She builds a nest of 20 to 45 cells and cares for the grubs as they hatch. In about 30 days the workers emerge and take over nest building duties. Through spring and summer the queen produces a large number of worker wasps. In mid-summer, the nest grows exponentially, as more and more workers become available, ultimately with 3,500 to 15,000 cells. Only the new queens survive the winter, hibernating under loose tree bark, in a decaying stump, or in another sheltered location.
In eastern North America, four yellowjacket species, common, downy, eastern, and German yellowjackets, closely resemble each other, making identification difficult. Downy yellowjacket is distinguished from the others by a continuous, uninterrupted yellow band on the face below the compound eye; and by the shape and pattern of black markings on the first and second abdominal segments.
Trail through Henry’s Woods Park
When settlers started arriving in south-central Minnesota in the 1800’s, they encountered a large stretch of forest about 100 miles long and 40 miles wide, basically from what is now Mankato to Monticello. The predominant mix of trees was elm, sugar maple, basswood, and oak, which contrasted with the surrounding prairies, savannas, and brushier oak and aspen woodlands. In the 1700’s, French explorers called this region bois grand, which translates to the commonly used English name – Big Woods. There is a similar region in western Wisconsin, and part of this area near Lake Pepin is the setting for Laura Ingalls Wilder’s first book, Little House in the Big Woods. Over the years, the increase of farming and real estate development has reduced the Big Woods to scattered remnants and secondary stands that are mainly preserved in parks and other protected areas – about 2% of the original expanse. Nerstrand-Big Woods State Park is one of the most pristine fragments. Another well-preserved remnant is Henry’s Woods Park in Rogers, MN.
An article in the July-August 1998 edition of The Minnesota Volunteer talks more about the Big Woods and features the Henrys’ farm. Rising taxes and land values encouraged many land owners to sell their land to developers, but the Henrys instead wanted to preserve their 60-acre forest as a memorial to Lloyd’s grandparents who bought the farm shortly after the Civil War (it was Hassan Township at the time). Eventually, the current 52-acre site was gifted to Hassan Township (now Rogers), and it is permanently protected in conjunction with the Minnesota Land Trust. The main parking area is off Brockton Lane, and the first things you see are a circle garden in the middle of the parking area and a restored farm building near the trailhead by the woods. A large polished stone marker in the middle of the garden talks about the Henrys’ gift and the history of the woods. The Henrys not only farmed the area, they also had a sawmill and used the woods for lumber and firewood. In addition, they tapped the maple trees each spring and made maple syrup; the preserved building on site is the Henrys’ “sugar shack” where they made the syrup. When you enter the woods, the trail starts as minimally graveled, but then turns to bare earth as it loops through the woods. A bridge crosses over a small stream, and there are two small ponds with wood duck boxes. It’s a tranquil spot not far from a large commercial/retail area. A trip to Cabela’s could result in a purchase of hiking shoes and an opportunity to use them right away at Henry’s Woods.
Text and photo by Kirk Nelson
Photo by Christa Rittberg
Orb weaver spiders (Aranidae) is the third largest family of spiders. There are about 3,100 species in 169 genera worldwide. They spin a large circular web that hangs vertically. This web is called an “orb”, which gives this family its common name.
Marbled orbweaver (Araneus marmoreus) is a medium-sized orb weaver spider. Females are about twice the size of males. They are highly variable in appearance, but all have a light colored abdomen with black, gray, and white markings, at least at the front edge, that give them a marbled appearance.
The marbled orbweaver orb is a closed hub, 20″ to 30″ in diameter, with 15 to 35 spokes (radii) that are not sticky. The radii extend to the center of the hub and are connected to each other by sticky threads that spiral outward from the center. The spider also makes a retreat out of silk near one edge of the orb. The retreat is connected by a signal thread to the center of the web, allowing the spider to feel vibrations of prey. The web is usually consumed and a new web constructed each evening.