This site is for people who like plants -- growers, enthusiasts, aesthetes, novices and professionals, those who appreciate wild things and those who appreciate the cultivated. I garden in Chelsea, and I've been visiting people's yards for 20+ years in the course of my work. My goal is to make this blog a community project, so if you share my interests, please consider becoming a participant and contributing content -- Guerin. Info: greenstreet@mindspring.com

Friday, June 28, 2013

Three trees in summer color

One doesn't see a lot of true chesnuts (Castanea) around. I can think of two good reasons. The burs are intensely prickly (which explains why indigenous Americans invented moccasins). And as much as I want to enjoy it, the odor of the flowers is pervasive and pretty gosh-darn awful. The specimen to the right was photographed this morning in Grosse Pointe. In Ann Arbor there is one off N Fourth near Kerrytown and another near the north end of Spring St. Just follow your nose. Dear readers, please send in addresses of other flowering specimens.

Tartarian maple (Acer tatarica) is putting on a nice show right now. The leaves of this small-stature species are mostly unlobed and resemble those of mulberry. It is a close relative of the more common Amur maple (A. ginnala), whose leaves are deeply three-lobed. I note that Tartarian maple is included in Rehder's Manual of Cultivated Trees and Shrubs, written almost 100 years ago, so this plant is not new to cultivation. I think you're most likely to run into this species as a recently-planted street tree. This one was photographed on Washington St in Chelsea.

Right now the golden-train tree (Koelreutaria paniculata) is stopping traffic on N. Fourth just north of Kerrytown. I wasn't the only one taking pictures of this specimen. If you want to grow this at home, consider collecting a seedling growing in the nearby shrubbery.


Wednesday, June 26, 2013

Big bad gypsy moth in Dexter; Arum and chestnut oak

Never saw this coming: nearly 100% defoliation of white oaks in Dexter due to a sudden explosion in the population of gypsy moths. What is strange to me is how localized this is. I have noticed no caterpillars in Chelsea. Just west of Ann Arbor, I saw a medium amount of damage, which probably would have gone unnoticed if the insect droppings hadn't been falling into a swimming pool.

An entomologist at MSU asked me and others to keep an eye on the caterpillar as it morphs into its final stages before pupation. With a high density of insects, the population is prone to collapse because the recent rains are favorable to the development and spread of an insect-killing fungus, Entomophaga maimaiga. The fungus was deliberately introduced into the environment for the purpose of controlling gypsy moth, and it has been doing an excellent job for the past 24 years.   

Enough of that! Let's look at some plants: One doesn't see Arum italicum in gardens very often, but it's an easy plant to grow, and it seeds around at a healthy but manageable rate. It's mostly grown for its foliage (absent in mid-summer!), but the flowers can make a nice effect. This picture was taken a couple weeks ago. (Also note the yellow spider-spaceship flower from an unidentified ever-flowering(!) Epimedium).

I was on the MSU campus recently and pulled my car over to check out an unfamiliar recently-planted street tree. Such luck: it still had its label, "Quercus montana." I thought I knew my oaks but I had never heard of this one. Turns out Q. montana is synonymous with Quercus prinus, the chestnut oak, which is a major species that I know from Pennsylvania and New Jersey. Previously it was listed in Michigan Flora as being native to Michigan, one specimen having been 'located' in Waterloo Recreation Area. (My guess is that the specimen was actually an exceptionally large dwarf-chestnut oak, Quercus prinoides.)
Chestnut oak along the Jersey shore
Before I test my readers' patience any longer, let me say that chestnut oak is a lovely tree, it has distinct blocky bark, and kudos for the folks at MSU for planting it.

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I've never been certain about the identity of a certain tree-forming viburnum that one sees around town, particularly around old houses in older neighborhoods. This one is at a residence on Geddes Rd, and I've seen others on Pineridge on the west side and also around Grosse Pointe. The attractive fruit starts as a pink-red but turns very dark with age. My guess is that it is Viburnum sielboldii, which my old reference books say can grow into a tree.
I don't recall ever seeing it for sale at a nursery. Perhaps one day it will become the fashion once again, just need someone to tidy it up a little and then slap a fancy cultivar name onto it.

The sad story of spruce trees in the landscape

A common, but not pretty, sight
Spruce trees are the most problematic of all conifers in our landscape right now. There are so many factors contributing to their decline that it has become nearly impossible to tease them apart. New pathogens seem to be discovered annually, and the unusual weather conditions in recent years have further complicated everything. I will try to break down our understanding of spruce decline into environmental and biotic factors.

Our environment is not good for spruces, and it is getting worse. Essentially there are no spruces native to southeast Michigan. Most of the species in the landscape come from mountainous habitats where the air is dry and the soils are cool and reliably moist.Two severe droughts in the last three summers have been hard on landscape spruces. Muggy spring weather contributes to the rapid spread of fungal diseases. Our clay soils are good for sugar maples, but difficult for the roots of spruces to penetrate and thrive in.  

Diseases old and new: insects are (in general) easy on spruces, but the fungal diseases are numerous and their numbers are growing. Some of the diseases are familiar: Rhizosphaera needle-cast causes older needles (i.e.,those not at the ends of the twigs) to turn purplish and subsequently fall off. Sometimes the purple discoloration, which usually shows up in late summer, is shocking.What remains after the infected needles drop are thin, unhealthy-looking specimens with needles only at the ends of the branches.Norway spruce is usually not badly affected by this fungus.

Cytospora canker refers to a fungal disease in which the pathogen resides under the bark of twigs and branches, and causes entire branches to die back to the trunk. Usually the lower branches are first to die, but sometimes the disease begins in the upper crown or at multiple points. Often a white resin will drip from the infected branches. Trimming off the infected branches back to the trunk will reduce inoculum and slow the spread of the disease.

Whereas spruce decline is widely recognized to be occurring throughout the Midwest, there is uncertainty and debate about the extent to which other pathogens might be involved. A species of Phomopsis fungus once know only from nurseries has now been found in the landscape. Some pathologists believe it is a key causal factor in spruce decline in Michigan. Spraying specimen trees in spring may help contain this pathogen, but no studies have yet been conducted to test this. This Phomopsis disease may be the one most aggressively attacking Norway spruce.

Additional suspects have been identified. One was given the charming name SNEED (spruce needle drop), but last I heard the consensus was that it is not a disease-causing organism. There are others, and it gets very messy.

The challenge of disease control: “Fungicide” is a misnomer. A more precise term would be “fungistat.” Those products called fungicides do not kill fungi, but rather prevent spores from germinating or retard the growth of mycelia (the fungal mass).

With insects, control is relatively easy: see a bug, spray it, and it rolls on its back, kicks up its six legs and dies. Most commonly fungicides used in the landscape only act as prophylactics. Given that the fungal spores need water for germination, disease control usually involves spraying the fungicide in between rainy periods, so that when the environment is conducive to disease spread, the fungicide is in place to act as a preventative. As long as the environmental conditions favor disease spread, fungicides need to be reapplied approximately every couple of weeks in order to guarantee control.

In the real world of landscape plant management, it is only practical to spray two or three times a season, and those applications are timed to coincide when disease spread is most likely. With crabapples, a couple sprays in early spring are sufficient since the time of disease spread is very predictable. It is much more of a challenge in the case of spruce trees: for example, needle-cast diseases are most likely to spread in the spring, but weather conditions can allow their spread to occur in summer or even fall. Also different diseases might spread at different times of the year. The plain truth is that the more often the trees are sprayed with fungicide, the more likely it is to achieve disease control.