The Garden Professors™ – Page 100 – Advancing the science of gardening and other stuff since 2009

Porsche 911 or Toyota Camry

Earlier today I was in a meeting with some other professionals from across Minnesota (and a few from Wisconsin and other areas) to discuss the disease problems of conifers. Our discussion quickly became focused on the use, and overuse, of Colorado blue spruce, a tree that just doesn’t do well in Minnesota — Or Michigan from what Bert has written! Everyone in the meeting was yammering on about how we need to educate nurseries and consumers about how terrible the Colorado blue spruce is in our environment — you’re lucky if you can get 10-15 years out of the thing before it succumbs to one disease or another. But, though academics, arborists, and most tree care professionals (including nurserymen) talk about how lousy this tree is, customers want Colorado blue — and if a nursery doesn’t sell it, well then that nursery has lost some business.

I support the idea of warning people away from Colorado blue. Still, during our meeting I couldn’t help but have this thought running through my mind:

Colorado blue spruce is a unique and beautiful tree — it is bluish in color, tends to have a good form, and is a relatively fast grower (until it succumbs to whatever disease it dies from!). There are certainly other trees that are also beautiful — but there is no denying that Colorado blue has a distinctive look. If I were walking through a nursery this would be the tree that I’d want. If a nursery person told me that the tree was going to have a short life — 10 – 15 years of looking good — I just might be OK with that because there just aren’t that many trees which look as attractive as a Blue spruce in a nursery. Sure, I could have something that would look OK for 30 years, but, if I’m like most Americans, I won’t even be in the house that I’m living in now in 10 years, never mind 30.

To draw an analogy, You know that a Porsche 911 isn’t the best car to buy — it is a gas guzzler (for it’s size) — it doesn’t have much luggage space (or room for passengers), and it’s less reliable than your typical compact car. A Toyota Camry is better in all of the areas that I just mentioned. Still, if I were looking for a car and if they were the same price I have to admit that the Porsche would be too cool to pass up.

Fast food is unhealthy for plants, too

In early December, I posted my thoughts about fertilizing crops vs. landscapes. An anonymous reader asked if we could follow up by discussing the relationship between excessive fertilizers and plant susceptibility to pests and disease. It’s taken a month to get the scientific literature (and my act) together, but here it is.

There are decades’ worth of articles about the direct relationship between increased nutrient availability and increased susceptibility to pests, disease, and disorders. One of the earliest articles linked the incidence of celery blackheart to over-fertilization. Since that time, researchers have found similar causal relationships in vegetable crops such as rice, onions, and soybeans, ornamental crops including poppies, and perennial orchard crops such as nectarines. Unfortunately, there’s been no research on landscape species.

Happily, the way plants react to excess nutrient levels is generic – so we can apply the findings in the agricultural literature to landscape situations. Just like kids and candy, plants will greedily take up all the available macronutrients their roots can find, especially nitrogen and phosphorus. (It makes NO difference is the fertilizer is organic or inorganic.) Plants in highly nutritive soils respond with lush vegetative growth – and fewer flowers, by way. Less metabolic energy is put into protective compounds, so these succulent new leaves and shoots are prime targets for all kinds of unwanted plant-eaters and foliar pathogens.

As with so many things in life, moderation is the key. For routine landscape needs, use woody mulches rather than fertilizers and nitrogen-rich composts. This “slow food” approach not only benefits your plants, but provides ideal habitat for mycorrhizal species, which have been shown to help restrict root uptake of excessive nutrients, while assisting with uptake of less available ones.

A comment about home remedies from Catherine Daniels

In case you didn’t see yesterday’s comment that was added to Jeff Gillman’s January 6 post on home remedies, I’ve posted it here. Dr. Catherine Daniels is WSU’s pesticide coordinator:

I’ve enjoyed reading the science-based information on your site. Keep up the good work. As regards home remedies, that is slippery slope, both legally and morally. Having a written definition of what you will or will not accept is helpful, especially if done in advance. Then you can be sure of being consistent and deliberate at least. There are both state and federal laws regarding pesticides, and state laws do vary. The most important thing is to know your state’s interpretation of those laws and to be mindful that with a blog you may be talking to people in state’s where laws are interpreted differently. I mention that for your legal protection. For example, in Washington State, if you talk to a user group (such as the public), and discuss the ways to use a material as a pesticide, it becomes a de facto pesticide recommendation. A legally-liable recommendation. When a researcher publishes information in a journal it’s not directed at a user audience so is not considered a recommendation by the author. If you take it to the public, at least here, it becomes a recommendation you made, unless you insert certain disclaimers. It’s always attractive to try and “help” the public find some easier, faster, cheaper solution to a pest problem. With pesticides and the public, you offer a better service directing them to a tested material which is registered and has a consistent concentration from batch to batch. Having personal safety and storage instructions is important…things that are missing in make-it-yourself squirt bottle solutions. Home remedies encourage people to think that the solution is “safe” (for people, not pests) because it’s made out of everyday ingredients. But as we know, the dose makes the poison. Nicotine is a nerve poison which you wouldn’t want a child to come into contact with accidentally because the squirt bottle wasn’t labelled or put in a safe place. I agree that our role is to educate, not police household cupboards or public pesticide use patterns. But by the same token, because we (educators)are trained to look at the big picture, there are good reasons to consider sticking to a label. Thanks for the opportunity to comment.

Landscape conifers: The Good, the Bad, and the Underused

This week is our annual Great Lakes Trade Expo, the main trade show and education venue for Michigan nursery and landscape industry. One of my talks was for the Arboriculture track on landscapes conifers. The theme this year was “The Good, the Bad, and the Underused.” Hey, you try giving a dozen talks a year for 10 years and see if you can come up with an original title!

The selections were based the following, admittedly subjective, criteria.

The Good: These are the all-around good guys. Conifers that are well-adapted, good growers with good form and few pest problems.

The Bad: The problem children of the conifer world. Pest magnets, spoiled prima donnas, or incessantly overused.

The Underused: Trees that have the virtues of ‘The Good’ but that tend not to attract attention.

Here are three of my selections for each of the categories. I’m interested in nominees from other sections of the country and the world.

The Good:

Eastern white pine Pinus strobus This one flirts with the overused designation but I’ll give it a nod since it’s the state tree of Michigan and figured prominently in the state’s history when Michigan was the lumbering capital of the US in the late 19^th century. A fast growing tree that improves with age.

Eastern hemlock Tsuga canadensis The answer to the age-old question, ‘What conifer to you recommend for shade?’ A little finicky on site, prefers moist but well-drained – who doesn’t. But a great elegant looking tree. The main down side is the specter of hemlock wooly adelgid looming to our south.

Alaska false cypress Chamaecyparis nootkatensis (Xanthocyparis nootkatensis). Lot of confusion over the nomenclature but no question this is a great landscape tree. Graceful, weeping habit; good growth rate; and few pests in this area (knock on wood).

The Bad.

Scots pine Pinus sylvestris Is there a pest that doesn’t affect this tree? Our Forest Entomologist, Dr. McCullough, had a grad student count up all the pests that affect Scots pine and they lost count after 30. Borers, tip moths, needlecasts… the hits keep coming. The problems are exacerbated around here because of abandoned Christmas tree plantations that serve as insect breeding grounds and fungal infection courts.

Austrian pine Pinus nigra Austrian pine is a frustrating tree. In some respects it is the perfect conifer for our region. A great looking tree with dark green needles. Good growth rate, cold hardy, drought hardy, tolerates road salt. Everything you could want in a tree and then some. Then the trees get about 15 years old and the wheels fall off. Diplodia tip blight, dothistoma needle blight… Austrian pine is the ugly duckling in reverse; looks great when young and then, blechh…

Colorado blue spruce Picea pungens The tree everyone loves to hate, yet we keep planting it. I suppose it’s the allure of the blue that people can’t resist. It’s like that bad boyfriend; you know he’ll do you wrong but… He’ll lure you in with those baby blues then start hanging out with those low-life Cooley adelgids, then hook up with rhizosphaera needlecast. And by the time the cytospora cankers start hanging out you know this relationship is going nowhere.

The underused

Swiss stone pine Pinus cembra Renowned conifer aficionado ‘Chub’ Harper used to remark, “I never met a cembra I didn’t like.” Cembras are great trees, good growers with consistently good form. Underused but worth looking for.

Korean fir Abies koreana I wrote about Korean when in discussion alternative Christmas trees but it also makes a good landscape tree. In our area we can expect about 1’ of height growth per year. Symmetrical form; short needles with silvery undersides, and conspicuous cones. Lot to like about Korean fir.

Dawn redwood Metasequoia glyptostaboides A fast-growing deciduous conifer with wonderful pyramidal form. Dawn redwood is also an interesting botanical story. Only known to science from fossil records, an isolated population was discovered in China in the 1940’s. Seed were imported into the U.S. and the tree has been found to be broadly adapted.

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Pampas unpuzzled

Great discussion and answers on this one, gang! Yes indeed, this is a plant out of place – as several of you noted. But not only has it escaped from an ornamental landscape, it’s decided to grow, quite happily, in the median strip of I-5:

Another odd thing is that the species has not been officially recognized as invasive in Washington State. It’s been languishing on the “Monitor” weed list for at least two years. Our climate is a bit chilly for it, which may be part of the reason it looks so bad right now. We had a very cold week back in November which may have killed this specimen back to the crown. But never fear. New growth will emerge this spring. (Note to Washington State weed control board – maybe it’s time to list this plant as invasive???)

Finally, I do believe this specimen was sprayed last spring, as Jimbo pointed out. However, it recovered and was able to send up two seed heads…which I’m sure have lavishly sprinkled the surrounding soil.

Pampas puzzler

Here’s a photo of some pampas grass (Cortaderia selloana), much beloved by many homeowners in their landscapes:

But what’s unusual – and undesirable – about this particular specimen? Hint: the landscape has been modified a little.

Answer on Monday!

Where to Draw The Line on Home Remedies

On Tuesday Holly posted an extremely interesting article about how Bounce could help control fungus gnats. Then one of our frequent commenters (and all around great guy) Ray Eckhart pointed out that he has a problem with promulgating an off-label use of a product. And that got me to thinking. What household products is it OK for us to suggest that a consumer use for a non-labeled purpose, and what products shouldn’t we suggest? This is a question that has haunted me for a long time, so with this post I want to give you my line of thinking – I’m not trying to tell you what’s right or wrong – just trying to let you know my thoughts on the topic.

First of all, let’s admit that there are off-label uses of products which most of us hardly think about and simply accept as “generally OK.” For example, I have never been taken to task for suggesting using a plastic bag for protecting fruit from insects or for suggesting that dish washing detergent may be a good insecticide. Of course both of these pest control techniques have their drawbacks (it can get hot in the bags in the South, injuring fruit, and insecticidal soap can burn the foliage of sensitive leaves) still, using these products outside of their labeling doesn’t seem to bother people too much. Likewise, the idea of using alcohol to stunt plant growth, eggshells to stop slugs, or milk to control plant disease doesn’t seem to upset people too badly (whether they work or not being beside the point).

But there are some off-label uses of products which could be considered obviously bad. For example, controlling weeds by dumping gasoline on them and setting them on fire, or perhaps washing your ripe fruit in a cup of paint thinner.

Then there are the off-label uses of products such as mouthwash for plant disease and tobacco juice for insects. I see these as neither obviously fine nor obviously terrible. So where is the line to be drawn?

In my opinion, as an extension educator, I feel that it is my job to tell my audience (That’s you guys!) the facts about different gardening/growing techniques including those that are “off-label.” I don’t feel that it’s my job to tell you what to do and what not to do (well…maybe with the exception of telling you not to pour gasoline on your weeds and light them on fire or not to soak your food in paint thinner!) It is up to you to make your own decisions.

Let’s go through a “for-instance” here. And let’s use one that I’ve written about – using hot peppers as an insecticidal spray. Hot pepper sprays can work to control certain insects. Just mix up a few hot peppers with some water, add some dish detergent, put it into a spray bottle, and off you go. I have used sprays like this myself in small experiments to control mites, and they have worked reasonably well. I have also read a number of articles showing that these sprays have at least some effect on certain pest insects. But hot peppers certainly aren’t “labeled” for use against insects, and let me tell you, a little hot pepper in the eyes, or even the skin, and you can be in pain for hours. Long term damage is unlikely – but not impossible. So what should I, as an extension educator, do? In my opinion exactly what I just did – give you the facts and let you make your own decisions. I feel exactly the same way about Holly’s post about Bounce – she gave you the facts – if you want to try using Bounce to control something then that’s up to you. Do I recommend Bounce for controlling insects? No. But I’m the kind of person who encourages careful experimentation, so I wouldn’t tell you not to use Bounce to try to control insects either – though I would tell you to be very careful and that unintended consequences might arise.

Will cabling a tree’s crown make it stronger?

In a previous column (December 1, 2010) I discussed the problems that wet, heavy snow can cause for trees and shrubs – particularly evergreens. In response my colleague Terry Ettinger mentioned a cabling technique discussed in the 2^nd edition of Arboriculture (1991). I think it’s worth looking at the science behind this practice and some of the unintended consequences.

Harris’s Arboriculture text is considered the bible for landscape professionals, including certified arborists. In the late 1990’s, Dick Harris was joined by Jim Clark and Nelda Matheny, two other gifted academics who have crossed over into practical writing. In the 4^th edition of this book (published in 2004), the authors caution about routine use of cables and other support systems for tree crowns. They state that “evidence for the use of support systems to strengthen tree structure is anecdotal” and based on my reading of the scant scientific literature on the topic I must agree.

Older articles and texts tend to provide how-to instructions and diagrams on various cabling and bracing techniques, but little to no evidence supporting the practice. More recently, studies have provided evidence that drilling holes for cables, wires, bolts etc. increase the likelihood of introducing disease into otherwise sound wood. As the tree continues to grow and change over time, even the best of these systems may need to be modified or replaced. In fact, the systems should be inspected and maintained annually. Crown cabling is not a permanent, one-time fix – and sometimes it isn’t even a fix. Failures still occur, often just above the point of attachment of bolts and cables. In fact, many arborists believe cabling should be the choice of last resort.

Some current research is exploring noninvasive methods of securing crowns, such as belt systems, that provide support without creating additional problems. As with any new technology, long terms studies are pending. Given the potential risks and lack of reliable benefit, I would not recommend cabling or bracing unless there were no other choices for saving the crown of a tree.

Bounce – it’s not just a fabric softening sheet…

…it’s an Integrated Pest Management tool!

[Note added after-the-fact: this was a tongue-in-cheek bit of hyperbole – kind of like “it’s not just a Job, it’s an Adventure.” Did not mean to imply that it actually IS an IPM tool. Very badly worded. Hence the beating I took in the comments. Live and learn.]

Fungus gnats (Bradysia spp.) are a pain in the bottom for commercial greenhouse growers. The adults are more of a nuisance than anything else –it just looks bad when a customer picks up your 6” pot of pansies and a bunch of little black gnats take flight. It’s the larvae that are problematic. Adult females lay the eggs in especially damp growing media, and the newly-hatched larvae feed on the roots. There’s both direct damage and also speculation of easier infection of root-borne pathogens, of which there are plenty.

Fungus gnat larvae, just making a living…

Standard control measures include insecticide drenches, biological controls including a specific strain of Bt (Bacillus thuringiensis – sold as GnatrolTM), nematodes, etc. One of the easiest control measures is the one I teach my students: to not over-water, i.e. “grow dry”. But that can be difficult in a big greenhouse range with many different-sized containers, all which drain/dry out at different rates. Propagation houses also have high humidity levels and have to stay moist for rooting/germination purposes and are thus favored by fungus gnats.

Entomologist Dr. Raymond Cloyd of Kansas State University and his group were intrigued by Master Gardener anecdotes of dryer sheets repelling mosquitoes, though no research had been done. Could your common Bounce sheet also repel other pests? And, to take it a step further, what, exactly, repels them? The answers are “yes” and “lots of volatile compounds.”

Their study was published last month in the journal HortScience. Honestly, I’ve never seen descriptors like “controls static cling” and “gives clothes a fresh scent” in a Horticulture journal. Hee! Plus the researchers made it clear this experiment specifically used Bounce Original Outdoor FreshTM. Still kind of humorous, but really good science and the part that’s usually overlooked in the translation to a News Story. Do NOT extrapolate results to include Bounce Spring Fresh, Fresh Linen, and certainly not Downy or Snuggle brands.

The study had a simple design, releasing lab gnats (ha!) into a many-chambered container and observing to which chamber the gnats gravitated to (or away from). There were five different variations on this theme, including an alluringly soggy media sample; when the sample of fabric softener sheet was introduced, they stayed away in droves. All five experiments showed a fairly drastic aversion to the sheet. To determine what was fending off the gnats, they did a steam extraction on sheet samples and ran the condensate through a gas chromatograph – mass spectrometer to measure the volatiles.

Figure from Bounce® Fabric Softener Dryer Sheets Repel Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Adults. Raymond A. Cloyd, Karen A. Marley, Richard A. Larson, and Bari Arieli, HortScience Dec 1 2010: 1830–1833

Well, there you have it. Linalool is a monoterpene alcohol found in lavender, basil, and coriander, and is known to be toxic to mites and insects. Citronello is another monoterpene and lends lemony-freshness to lemon balm, pennyroyal, and rose geranium and has short-term “repellent activity against mosquitoes.” Benzyl acetate, though not specifically mentioned in the results, is another natural fragrance compound, found in jasmine – and is also an industrial-strength solvent. One man’s solvent is another man’s perfume. Or fabric softener. I bet their lab smelled GREAT, by the way.

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New Year’s Prediction: Invasive Fire Continues to Burn

Happy New Year! I hope everyone had restful and enjoyable holidays. In addition to looking back over the year that just past, a common New Year’s tradition is to make predictions for the coming year. Without going too far out on a limb, one of my predictions for the upcoming year is that the debate over invasive plants will continue to intensify, especially as it relates to Landscape Horticulture. Along these lines, a couple of recent articles by Gregorio Gavier-Pizarro and his colleagues at the University of Wisconsin and the USDA Forest Service caught my eye.

In both studies; “Housing is positively associated with invasive exotic plant species richness in New England, USA” (Ecological Applications 20:7, 1913-1925) and “Rural housing is related to plant invasions in forests of southern Wisconsin, USA” (Landscape Ecology 25:10, 1505-1518), the investigators conducted on-ground assessments of species richness and density of commonly listed invasive plants (e.g., Japanese barberry, Autumn olive, Honeysuckle, Common buckthorn, Multiflora rose) in conjunction with spatial analysis of remote sensing data to examine patterns of invasive spread in the urban/wildland interface. As one would expect, the presence and species richness of the invasives increased with development. An important ‘take home’ message, however, is that disturbance associated with rural housing development and the creation of edges appears to be the biggest driver of invasive species encroachment. That is, land clearing, road-building and other development activities create habitats that are more susceptible colonization – a condition referred to as ‘invasibility’. So whether a particular homeowner plants natives or non-invasive exotics they may still contribute to the expansion of invasive exotic plants in their region by increasing its invisibility.

The other thing that makes this work and related studies significant is that I think we will see a continued shift in the efforts to curtail the expansion of invasive exotic plants. In particular, rural housing development and associated landscape practices will become and increasingly intense front-line in the invasive battle.

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