When Plants Attack! (each other)

When you talk about killer plants, your mind may conjure images of a man-eating plant in “Little Shop of Horrors,” insect-eating Venus flytraps or poisonous plants like deadly nightshade.

While all of those scenarios are interesting in and of themselves, what about plants that attack other plants?

I’m talking, of course, about parasitic plants. These plants thrive on stealing nutrients from other plants, either weakening them or, quite possibly, killing them.

Parasitic plants connect themselves to a host plant and siphon off the sugars that plant produces and the nutrients it pulls from the soil. These plants often bend the definition we have in our heads of plants, since they don’t have to behave like other plants that make their own food.

Probably the most well-known (and beloved) parasitic plant is mistletoe. The plant that gives us the warm fuzzies and romantic feelings around the holidays makes its living by feeding off of the trees in which it lives. They don’t talk about that aspect of the plant in all those Christmas songs. It doesn’t kill the tree, but a heavy infestation can weaken a tree and slow its growth.

Indian pipe (Monotropa uniflora). Photo courtesy GP Raymond Eckhart

While they are few in number, there are some parasitic plants you may run into. Another parasitic plant in our part of the world is the Indian pipe (Monotropa uniflora), a white, chlorophyll-free plant that resembles a smoking pipe as it unfurls from the forest floor. Without chlorophyll, it can’t make its own food, so it connects itself to a nearby tree (usually beech) for nutrients.

Another plant, called a beech drop (Epifagus americana), also makes its living in the same manner. A plant called squaw root or bear corn (Conopholis americana), because it resembles an ear of corn growing out of the forest floor, is a parasitic plant that connects with the roots of oak trees.

An infestation of dodder beginning in an annual bed. Photo courtesy Ann Berry.
An infestation of dodder beginning in an annual bed. Photo courtesy Ann Berry.

These plants may cause a little damage to their host plants. This week, though, there seems to be something more sinister afoot. I received two different calls about the same parasitic plant this week, from different parts of West Virginia (one of which came from Ann Berry, associate vice president for marketing and outreach at WVU). It seems that the problem here was with a parasitic plant called dodder (Cuscuta sp.). Despite the name, I assure you that this plant does not dodder around when it comes to feeding off other plants. This plant can severely infect and potentially kill any plant it touches.

 

Seeds of the plant germinate in the soil, so it starts life just like any other plant. Once germinated, though, the seedling has about 10 days to find a host plant to attach to and begin feeding. But this is not left to chance — it seems that dodder is a pretty good hunter. Scientists have determined that dodder can, in a way, sense chemical signals from nearby plants and grow directly toward them.

Dodder is an odd-looking plant, and many people don’t even know to classify it as a plant. It grows in long strings, often without leaves (or only having inconspicuous ones). Different species can be different colors. The one that is most common here is often a yellow-orange color.

cuscuta Haustorium
Dodder, above, inserts a haustorium into its host plant.

Once the dodder touches the soft tissue of a plant (leaves or stems), it inserts a structure called a haustorium into the plant. Haustoria insert themselves into the plants vascular tissue (veins) and siphons off the water, sugars and nutrients. After the connection is made, the dodder plant detaches its roots from the ground and becomes completely reliant upon the host plant. Luckily it has trouble attacking woody plants, so it mainly goes after herbaceous ones.

One connection is bad enough, but the dodder twines its way around the plant as it grows, resembling what some would call “silly string.” Everywhere the dodder touches the host, it sends in new haustoria to strengthen its connection. If other plants are close enough, the dodder will grow outward through the air to ensnare another host. It can easily grow to encompass many plants, covering them completely and eventually strangling them or starving them out.

My advice to both of the callers this week was to remove as much of the plant as possible, as soon as possible. Unfortunately, the plant can regrow from the connections it makes with the host plant, so you often need to remove whole parts of the plant or the whole plant itself. If it has only made one or two connections, you may be able to control it just by removing the dodder from the plant.

Dodder is hard to see on the ground as it germinates, so it is only usually spotted after it has attached and grown on a plant. If you do happen to catch it before it attaches to a plant, cultivating the soil to break it up and removing as much by hand as possible will help. Unfortunately, there is no spray or control method that will kill the dodder without killing the host.

Dodder is definitely a bizarre plant that many have not seen. Keep an eye out for it this year, since it seems to be cropping up in unexpected places. It just goes to show you that sometimes it’s a plant-eat-plant world out there.

This article was originally published 08.09.15 in the Charleston Gazette-Mail.  You can find more article at wvgardenguru.com.

It’s the Next Best Thing Since Draft Beer: New Plants and Their Proper Evaluation

'Graham Thomas' rose
‘Graham Thomas’ rose

With many new nursery catalogs arriving in my mailbox at work for 2016 introductions, I thought I would focus this blog on “new” plants. With all the publicity and marketing that goes on for new plant introductions, you would think that they are the next best thing since draft beer or even bread! I am a bit cynical and question whether these new plants really live up to their performance expectations and ornamental attributes. With so many new hydrangeas, coneflowers, coralbells, spireas, etc. released each year, you may ask why am I so cynical? Why would I not jump on the bandwagon and promote all of these new plants like so many garden centers are doing across America? Let me explain.

A decade ago, I conducted research trials evaluating 20 new or recently introduced cultivars of “hardy” shrub roses, many of which are not even on the market anymore. I chose three locations in the state of Wisconsin, each having their own unique soil types, pH, soil drainage and fertility, rain/snowfall and cold hardiness zones. I replicated each of the 20 cultivars ten times at each location and arranged them into blocks with each cultivar represented in each of the ten blocks. The roses were randomly selected for each block and planted, mulched, watered with an application of a slow-release fertilizer. Plants were watered for the first year only as needed. To properly analyze plants for various traits, I allowed the roses to establish for a year with evaluation initiated the following spring. The only care the roses received the remaining years were application of a slow-release fertilizer, weeding and pruning of dead wood following winter. I was trying to replicate conditions that are common in most landscape settings. I did not spray any insecticides or fungicides to any of the roses, regardless of how bad they may have looked due to pests.

After the first winter, I evaluated the roses for winter injury, which they all experienced. The roses were all on their own root systems so if they died back significantly, the new growth would come from the same root system and produce flowers that spring. To some extent, they all grew, though voles killed some of the roses. After the roses starting growing, I evaluated them monthly at all three locations for insects and diseases as well as flowering (amount, size, duration of bloom, etc.). I also measured the plant’s height and spread. A few roses had good fall color. The first year of the trial, the roses all bloomed prolifically. So, one would think that all 20 cultivars are ideal. Not so fast, or “but wait, there’s more” as the television salesman would say to viewers in TV land about a new product. The “real” evaluation started in year two.

In year two, amount of dieback and winter survivability was recorded. To my surprise, the roses in the zone 3 location (boy, that’s cold) had better winter survival than the roses in my zone 4 and 5 location! This is due to consistent and significant snowfall in the most northern location compared to sporadic snowfall and lower amounts in the other two locations. I also evaluated the roses during the summer and fall for flowering, pests, and hip production. Contrary to the catalogs, many of the roses had hips, but some of them never colored up before the cold temperatures arrived at the three locations. Flower production was cited as being continuous all summer by their introducers, however, this was not true for some of the cultivars evaluated. Disease resistance was the most alarming quality I evaluated with many of the so-called “disease resistant” roses being the exact opposite. I explain all these variables to demonstrate what is involved in proper plant evaluation. For a complete report of my rose research trial, see: Jull, L.G. 2004. Hardy Shrub Rose Research Trials. Combined Proceedings of the International Plant Propagators Society vol. 54:429-434.

Knockout® rose is very disease resistant with non-stop blooms, but not hardy in zones 3-5 without significant winter protection Photo credit: http://www.gardeningknowhow.com/wp-content/uploads/2011/08/knockout-rose-400x600.jpg
Knockout® rose is very disease resistant with non-stop blooms, but not hardy in zones 3-5 without significant winter protection Photo credit: http://www.gardeningknowhow.com/wp-content/uploads/2011/08/knockout-rose-400×600.jpg

Now, you may ask, “Why are these new plants, including roses, promoted by these large nurseries as being the best plant around when in effect, they are not?” Many new introductions are from nurseries that trial their plants in their location only. So a plant that performs well in the state of California might not perform the same in Michigan and vice versa. There isn’t the scientific rigor applied to these new plant evaluations that would occur by non-biased, university researchers who have no stake in selling or promoting plants to the public. This is where the beauty of applied, scientific, university-based studies can play a huge role.

Also, these new plants should be evaluated over numerous years, at various locations/soil types, climates, with appropriate replications of each new plant in a random arrangement (not all planted together). This type of quality research is done by a few large nurseries but it is seldom done this extensively by others anymore as demand for new plants is never satisfied and the cost of trialing over several years and locations is too costly.

Unfortunately with increased costs and significant budget/program cuts, most university research is now geared toward larger, basic science studies that have high indirect costs built into the grants. These funds, usually 50% or more of the grant total, go directly to the university to cover overhead. The researchers do not see or can use overhead funds. Ornamental plant evaluation research is now considered either non-fundable by granting agencies, not “scientific or scholarly” enough by their own departmental colleagues or provide significant overhead funds back to the university.

Some researchers rely on their various nursery and landscape associations for small amounts of research support, while others try to piece meal together small amounts of research funds. With the increasing costs of land (yes, we do have to pay for research space at university research stations), plants (not all are freely given to the researchers), labor, supplies, etc., it is becoming critically important to seek alternative funding sources as most federal and state granting agencies do not fund ornamental plant evaluation research. Many of the new initiatives for federal grants seek to fund food crop based research, especially in organic and sustainable food production. Applied ornamental horticulture plant evaluation research at universities has plummeted with most new plant evaluations conducted by the large nurseries that introduce these plants.

There is another source for evaluation of these new plants. Various arboreta and botanical gardens around the U.S. are conducting evaluation trials. I am a fan of these studies as these gardens and evaluators are also not in the business of selling plants and can provide some analysis, though it is usually only at one location. Richard Hawke, Chicago Botanic Gardens Plant Evaluator and Horticulturist, has done an excellent job of evaluating many species of herbaceous perennials and a few woody plants. He publishes Plant Evaluation Notes: (http://www.chicagobotanic.org/research/ornamental_plant_research/plant_evaluation), a series of wonderful publications that help both the amateur and professional gardener to choose appropriate plants for the Upper Midwest. There are other botanical gardens and arboreta that do the same, with evaluations based on their local climatic conditions. I often rely on Mr. Hawke’s recommendations when choosing herbaceous perennials in my Wisconsin garden and have yet to be disappointed.

Chicago Botanic Garden Plant Evaluation Notes Source: chicagobotanic.org
Chicago Botanic Garden Plant Evaluation Notes
Source: chicagobotanic.org

So the next time a new plant comes across your way, think twice before buying it. There is the philosophy “Buyer Beware”, and I do recommend people to buy plants, but instead of buying 10 of one cultivar, try one or two of the new plant and make a judgment call the following year or two after you planted it. This is especially important for landscapers who design and plant large amounts of plants. You might be surprised to see the “best thing since draft beer” plant being anything but that. As some of us know, there is nothing better than draft beer (or whatever beverage you really like).

Laura Jull, Ph.D. aka The Lorax

When half a flower is the wrong color…

If you’ve spent enough time around flowers, you’ve probably seen this. It isn’t exactly common, but it happens, and is so distinctive that you’ll almost always notice when it happens, as I did on one of my gladiolus the other day.

sectoralchimera

Everything else is as normal, but a chunk of the flower is white instead of the usual soft peachy white.

What we have here is a sectorial chimera. Chimera means an organism with two (or more, I suppose) genetically different cell types, and a sectorial chimera is when there is one distinct section of the plant made up of a different cell type.

And why is this showing up in my usually pink gladiolus? Well, somewhere early in the development of this flower spike, there was a chance mutation in a cell. That mutation stopped those cells from producing the usual pink pigment, so the mutant cells make white flowers. The new mutation and the original cells continued to grow and divide, so some of the flower is from the newly mutated white form, and some is the original cell type.

Now, when people hear the word “mutant” they either think x-men or nuclear fallout, but the fact is mutations are a perfectly common, normal part of everyday life for organisms, and of course are critically important to continuing evolution.

This type of bicolored flower is cool looking, but certainly a one-off. Sectorial chimeras are very unstable. Next year, most likely, the flowers will just be pink again, or possible a branch will send off pure white flowers. So when you see a sectorial chimera in the garden, take a picture, put it on facebook, and enjoy it because it probably isn’t coming back.

Scientific Beekeeping

Apis mellifera
Honey bee (Apis mellifera), Courtesy of Charles Sharp at Wikimedia Commons

When I first moved to the country in the late nineties, one of the first things I wanted to do (after establishing several vegetable gardens to indulge my tomato obsession) was to become a beekeeper.

So I took a six week course sponsored by West Virginia University, read the full documentation available from the University of Maryland and Penn State as well as back issues of beekeeping magazines, and checked with some hobby beekeepers in the area.

Unfortunately, at that time, honeybees were being devastated by an invasive species … the Varroa mite (Varroa destructor), and the amount of effort needed to keep colonies free from them discouraged me, and the message I was getting from experienced hobby beekeepers was one of “be prepared”, and “I’m, regretfully, giving it up because of the effort involved.”

Basically … too much work … not something I was willing to commit to.

But I never lost my fascination with them (and other bees and wasps, for that matter.)

Then in 2006, I started hearing about Colony Collapse Disorder, or CCD, and it was while researching it, that I found the site of Randy Oliver, a biologist who also made his living beekeeping.

The site is Scientific Beekeeping.

From his About tab.

I started keeping bees as a hobbyist around 1966, and then went on to get university degrees in biological sciences, specializing in entomology. In 1980 I began to build a migratory beekeeping operation in California, and currently run about 1000 hives with my two sons, from which we make our livings.

In 1993, the varroa mite arrived in California, and after it wiped out my operation for the second time in 1999, I decided to “hit the books” and use my scientific background to learn to fight back.

The site is not a beginner’s “how to”, but a way to share what he has learned with others:

What I try to do in my articles and blogs is to scour scientific papers for practical beekeeping applications, and to sort through the advice, opinion, and conjecture found in the bee magazines and on the Web, taking no positions other than to provide accurate information to Joe Beekeeper.

(If you’ve been following my blog posts here, then you’ll probably recognize the pattern of places that rise quickly in my judgment, as ones I like)

The site has become my “go to” source for all things related to honeybees, and I recommend it to others who want to stay abreast of the subject.

Scientific Beekeeping

Robbers in the garden

Salvia azurea (maybe my favorite salvia in the world — sky blue flowers in late summer/fall, hardy to zone 5) is blooming in the garden, and the bees are all over the flowers. But while some are poking their heads into the flowers to drink nectar and transferring pollen as they do so, others are up to something more sinister.

This carpenter bee looks like it is pollinating. It isn't.
This carpenter bee looks like it is pollinating. It isn’t.

The evidence of what they are up to is clear if you look closely at the side of the flowers after they leave.

The little hole at the base of the flower is clear sign of an illegal break in.
The little hole at the base of the flower is clear sign of an illegal break in.

See the little hole in the base of the flower? That is where the carpenter bee bit a hole in the flower to get access to the nectar instead of going in the front of the flower as one would expect.

This phenomenon is called nectar robbing because it is an evolutionary betrayal of sorts. Flowers have evolved nectar to lure bees and other pollinators into the flower, so the bees will pollinate while getting their sugar fix. When the bees nectar rob, they’re getting the payment without doing the actual pollinating.

So why bite a hole in the side of the flower instead of just going in the front? Well, many flowers have evolved flower forms that make the nectar hard to reach by anything but their preferred pollinator, the species that most effectively moves pollen from plant to plant. In the case of this salvia, the nectar is down at the base of the flower, and only accessible to bees with long tongues, like whatever species normally pollinates it in its native range in the US plains. In other words, it is out of reach of the carpenter bees to save it for another bee, probably a bumble bee. Which works great to avoid wasting nectar on sub-optimal pollinators… unless, of course, those bees become robbers.

So next time you see bees on your flowers, take a look… they might just be robbers, not pollinators.

Perennial Funday: Eriogonum allenii ‘Little Rascal’

I’m going to keep posting about perennials that deserve more attention until somebody makes me stop. The fact that my subject is, once again, yellow… is merely coincidental

Definitely was a crowd favorite during the Perennial Plant Association annual Symposium’s grower tour (mentioned in my previous post).  These photos were taken at Emory Knoll Farms north of Baltimore; I believe that they were trialing and/or including it in their plant selection for green roof use.

Eriogonom allenii 'Little Rascal' at Emory Knoll Farms
Eriogonom allenii ‘Little Rascal’ at Emory Knoll Farms

Thanks to Mary Vaananen, Jelitto’s North American operations manager (and goddess of perennial plant knowledge), who just happened to be standing next to it, full of 411, when I squealed “WHAT the (blankety blank) is THAT?!” My compadre Paul Westervelt added more info, as he’s also a plant geek deluxe (and manager of the annuals and perennials section of Saunder Brothers Nursery). D’oh. Plus you rock gardening fanatics probably know this cutie as well (I may have first seen this in one of Joseph T.’s talks, now that I think about it).

Eriogonum allenii, shale barren buckwheat, is native to counties that comprise the Virginia Highlands plus those on the West Virginia side of the line in the same region. Within these counties, the scattered populations reside in the botanical wonderlands called the shale barrens.

This floriferous selection ‘Little Rascal’ is indeed from Jelitto, so you too can obtain seeds of this rarity (along with detailed germination/growing instructions). Jelitto lists hardiness to USDA zone 5. As with most species from the barrens, it requires plenty of sun and excellent drainage.

Flowers you can hear!
Flowers you can hear!

Stocky and slightly shrubby in habit, the coarse grey-green green foliage was, when I saw it at the end of July, completely smothered in deep gold flowers. Simply gorgeous.  It was abuzz with bees of all sorts, including insanely happy honey bees that could barely attain lift-off.  I have a plot of regular-old-buckwheat (same family, Polygonaceae), but our spoiled-rotten bees always seem underwhelmed.  Wait till they get a load of this!

 

A new excuse for bad pruning

I spent last week in Orlando at the ISA annual meeting (that’s the International Society for Arboriculture). It’s a great venue for networking with colleagues and hearing about the latest tree research. And once in a while I’ll have a WTF moment. (That stands for Why Trees Fail in case you’re wondering.)

My WTF experience this year revolved around some new terminology and techniques. I learned there are now “environmental arborists” who practice “retrenchment pruning.” In the last few days I’ve tried mightily to find some standard definitions from reputable sources. I don’t know what an environmental arborist is, since it’s not a certification (like an ISA certified arborist) nor is it a university degree program (like urban forestry or environmental horticulture). It seems to be a self-anointed title.

This is what a mature oak should look like.
This is what a mature urban oak should look like.

But the real WTF issue is retrenchment pruning. I looked in vain for published research through my usual data bases and found nothing – other than two articles in Arboricultural Journal (which is not the same as ISA’s journal – Arboriculture and Urban Forestry). Neither of the articles presented experimental evidence to justify this radical approach to pruning trees. Instead, they are more philosophical in nature, with a smattering of ecological theory.

Fortunately, retrenchment pruning methods are easily found on the internet, along with horrific pictures illustrating the results. As described on various websites, retrenchment pruning imitates the natural process of aging. Practitioners remove live branches or partial trunks to reduce the size of the tree and prevent future failure. These aren’t clean cuts, either: they’re “coronet cuts” or “natural fractures.” The rationale described in one of the Arboricultural Journal articles is that these jagged broken branches and trunks “promote specialist habitats and enhance colonisation rates of niche species.” In other words, this technique creates large wounds that are easily colonized by various insects and microbes.

An example of natural fracture pruning (http://www.countytreesurgeons.co.uk/veteran.html)
An example of natural fracture pruning (http://www.countytreesurgeons.co.uk/veteran.html)

So apparently we’re expected to ignore the well-established field of woody plant physiology (which happens to be my specialty) and related practical bodies of knowledge (e.g., formal and informal pruning techniques of said woody plants) and start hacking away at mature trees. In doing so, we’re removing live tissue and creating large wounds. This has the effect of both reducing photosynthetic potential of the tree as well as opening it up to possible pest or disease invasion. But nowhere are these possibilities discussed as part of the “natural aging process.” Nor was there mention about how to manage the epicormics shoots that result from improper pruning. And they do need to be managed.

These are epicormic shoots resulting from topping this tree.
These are epicormic shoots resulting from topping this tree.

I saw some very angry arborists at the ISA meeting who were incensed at the idea that we should deliberately malprune trees. But others seemed quite excited with this new philosophy. To paraphrase one of my plant physiology colleagues, “Give a bad arboricultural practice a catchy name and it magically becomes legitimate.”