plant diseases

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Flowers Growing Out of Flowers (Things Are Getting Weird Out There)

I’m sure that anyone living through the events of 2020 would agree, these are truly wild times. So, when I stumbled across some purple coneflowers that appeared to be growing flowers out of flowers, I thought to myself, “Of course! Why not!?!” The world is upside down. Anything is possible.

As it turns out, however, this phenomenon occurs more frequently than I was aware. But it’s not necessarily a good thing, particularly if you’re concerned about plant health. We’ll get to that in a minute. First, what’s going on with these flowers?

Flowers in the aster family are unique. They have the appearance of being a single flower but are actually a cluster of two types of much smaller flowers all packed in together. Purple coneflower (Echinacea purpurea) is a great example of this. Its flower heads are composed of dozens of disc flowers surrounded by a series of ray flowers. The minuscule disc flowers form the cone-like center of the inflorescence. The petals that surround the cone are individual ray flowers. This tight cluster of many small flowers (or florets) is known as a composite. Sunflowers are another example of this type of inflorescence.

Flowers are distinct organs. Not only are they the reproductive structures of flowering plants, but unlike the rest of the plant, they exhibit determinate growth. Flowers are, after all, plant shoots that have been “told” to stop growing like other shoots and instead modify themselves into reproductive organs and other associated structures. Unlike other shoots, which continue to grow (or at least have the potential to), a flower (and the fruit it produces) is the end result for this reproductive shoot. This is what is meant by determinate growth. However, sometimes things go awry, and the modified shoots and leaves that make up a flower don’t develop as expected, producing some bizarre looking structures as a result.

An example of this is a double flower. Plants with double flowers have mutations in their genes that cause disruptions during floral development. This means that their stamens and carpels (the reproductive organs of the flowers) don’t develop properly. Instead, they become additional petals or flowers, resulting in a flower composed of petals upon petals upon petals – a look that some people like, but that have virtually nothing to offer the pollinators that typically visit them. Because of their ornamental value, double-flowered varieties of numerous species – including purple coneflower – can be found in the horticultural trade.

double-flowered purple coneflower

Genetic mutations are one way that odd looking flowers come about. It is not the cause, however, of the freak flowers that I recently came across. What I witnessed was something called phyllody and was the result of an infection most likely introduced to the plant by a leafhopper or some other sap-sucking insect. Phyllody, which has a variety of causes, is a disruption in plant hormones that leads to leaves growing in place of flower parts. As a result, the flowers become sterile and green in color. In the case of purple coneflower, leafy structures are produced atop shoots arising from the middle of ray and/or disc florets. In other species, shoots aren’t visible and instead the inflorescence is just a cluster of leaves. In a sense, the reproductive shoot has returned to indeterminate growth, having switched back to shoot and leaf production.

Phyllody can have either biotic or abiotic causes. Biotic meaning infection by plant pathogens – including certain viruses, bacteria, and fungi – or damage by insects. Abiotic factors like hot weather and lack of water can result in a temporary case of phyllody in some plants. Phyllody plus a number of other symptoms made it clear that the purple coneflower I encountered had a fairly common disease known as aster yellows. This condition is caused by a bacterial parasite called a phytoplasma, and is introduced to the plant via a sap-sucking insect. It then spreads throughout the plant, infecting all parts. The phyllody was a dead give away, but even the flowers that weren’t alien-looking were discolored. The typical vibrant purple of the ray flowers was instead a faded pink color. The flowers that had advanced phyllody – along with the rest of the plant – were turning yellow-green.

This inflorescence isn’t exhibiting phyllody yet, but the purple color in the ray flowers is quickly fading.

Hundreds of plant species are susceptible to aster yellows, and not just those in the aster family. Once a plant is infected with aster yellows, it has it for good and will never grow or reproduce properly. For this reason, it is best to remove infected plants from the garden to avoid spreading the infection to other plants. As cool as the flowers may look, infected plants just aren’t worth saving.

Further Reading: 

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The Problem with ‘Yes’ Landscapes

This is a guest post by Jeremiah Sandler. Follow Jeremiah on Instagram @j.deepsea

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I don’t work for a landscape company, nor have I ever worked for one. The company I do work for contracts with these companies to do health care on their landscapes. For example, we scout for insects and diseases, spray pesticides when necessary, make recommendations of proper cultural practices, and fertilize.

Something has been bothering me for the past two years about the landscapes in metropolitan southeast Michigan. Both commercial and residential landscapes have at least two things in common: the same plants, and the same poor management of these plants. The clients have no idea they’re being ripped off.

The landscape companies I have experience with seem to think the homeowner is always right.

The ‘Yes’ Conversation

You want a Colorado blue spruce in humid Michigan? Sure, no problem. Let’s put six trees within 15 square feet. Don’t bother removing the cage and burlap. We also won’t tell you the massive expense you’ll pay in the future to spray fungicides on your spruce to keep it alive. If one dies, we’ll just replace it with the same plant.

You want a green hedge? Boxwoods or yews. They’ll be sheared multiple times a year by our crew of expert (and underpaid and exhausted) workers. At the first sign of new growth, we’ll be there mutilating your plants to ensure that they stay at right angles. You see all of those ripped apart, discolored leaves on your shrubs? Ignore that; plants are meant to be tamed into perfect geometry. Oh, that’ll be an extra charge to spray insecticides and fungicides.

Here’s a list of plants you can get to add to the monotony in your neighborhood: crabapple, hawthorn, cherry, honeylocust, blue spruce, oak, red maple, Japanese maple, pear, white pine, boxwood, yew, hydrangea, arborvitae, burning bush, and wax begonias.

Why is your hemlock tree neon yellow? We don’t know, let’s just replace it. Why is your Norway maple declining? Well, when we planted it, we kept the cage on its root ball, despite this tree having notorious girdling roots. Let’s get you a new one. Why are some of your shrubs rotting out? We left the soaker hoses on them for years and kept them running regularly. Yes we can spray all of your plants. We can kill everything before it’s a problem.

We’re the best landscapers in town! Our services are top of the line, and we guarantee your landscape will look exactly the same as your neighbor’s.

That’s a very sardonic, hypothetical conversation between a homeowner and a landscape company. A sensible company knows you don’t know best. As a homeowner, it is wise to heed the advice of a company’s horticulturist. Cost is always a consideration for the homeowner. However, the more expensive company is not always the highest quality. Here’s why.

So, you want a Colorado blue spruce?

A responsible company won’t let you plant a blue spruce in a place with wet springs and humid summers. They will tell you why it is not a good idea, and they will suggest alternatives. For example, a concolor fir (Abies concolor) looks similar to a blue spruce. They are resistant to needle cast diseases and cytospora canker, and they can tolerate southeast Michigan’s alkaline soils. In the long run, it is much cheaper to get the right plant in the right place.

You will pay more for your blue spruce because, not only are you paying for installation, you are paying to spray fungicides year after year to avoid having a skeleton in your yard. Companies know there is a likelihood of replacing your newly planted blue spruces, so you are charged for it.

We love boxwoods and so do you

Maybe you do like the classic, formal look of hedges. And maybe you do like the texture offered by a boxwood or yew. That’s fine. This is the problem I see literally every single day: over-shearing.

An appropriate cultivar selection is the answer. Cultivars and hybrids exist which only grow to x-amount tall and x-amount wide. Simply read the tag from the nursery. If your landscape company planted the proper plants the first time, they wouldn’t be able to charge you as much as they do to “maintain” them. The right plants in the right places need very little maintenance. I will concede, a few plants can tolerate being sheared. Once in a great while is acceptable; not three times a year.

Excessive shearing stresses out a plant. In fact, certain chemicals released by the open wounds of the leaves attract insects. Wet, exposed tissue serves as a breeding ground for fungi. Some of the problems your shrubs face are directly caused by the shearing itself.

PlantAmnesty, a website dedicated to stopping bad pruning practices states:

Any pruning book will explain that one prunes to open up the center of the plant, allowing air and light penetration to make the plant healthy. Shearing, on the other hand, creates a twiggy outer shell that gets ever denser and collects more deadwood and dead leaves every year, the opposite of a healthy condition. The results create the perfect protected place for pests and diseases, akin to locking up the house so the garbage can’t be removed. After many years, this treatment can lead to disease and general bad health without actually being a disease itself. If plants have mites and blights, bugs and mildews galore, how they were pruned may be the root of the problem.

Not to mention, the plant is spending all of its energy regrowing those leaves you continually cut off. There are correct ways to prune plants, and none of them include the excessive use of motorized shears. A plant grows to reach an equilibrium with its environment. If the environment is adequate, the plant will grow. If the environment is unfavorable, the plant will decline. In other words, if it is growing, let it grow!

What’s a monoculture?

There seems to be only 15 plants which are acceptable to the landscaper. The plant selection is predictable. Certainly there are more than 15 different species of plants you can have on your property. Sure, some redundant species are okay: white pines, oaks, maples (except that damned Norway maple). I don’t want to discourage people from exploring new options, though.

Native plants offer easy beauty. They have evolved in your region for millennia and are therefore adapted to your environmental conditions. These plants often tolerate both biological and environmental stressors better than non-native plants. Expenses are saved when you don’t have to pay for disease control. You wouldn’t buy a vehicle, for example, that you know would break down and require fixing all the time.

There are dozens of other shrub options for texture, winter interest, privacy walls, etc., that you don’t have to hire a crew to shear every month. Surprisingly, some large yucca species are hardy in colder zones, which offer a different texture. Red-twig dogwoods provide colorful winter interest; there are red, green, and yellow-stemmed cultivars. Coyote willow is native to southeast Michigan. It is a thin-leafed, rhizomatous Salix species which forms beautiful yellow walls in the fall. An entire, separate article can be written on the subject of alternatives. Just know there are plenty of species to choose from no matter where you live.

Ask, and you shall receive

This request comes from homeowners and is often fulfilled by companies: “Can’t you just spray it?” Granting this request is entirely wrong. One cannot, by law and by principle, go around as a pesticide desperado. You live in that environment. Why would you want pesticides in excess? Chemicals are used as a last resort and strictly on an as needed basis.

Appropriate timing, safety precautions, and proper insect identification are all legally required before insecticides can be applied. Some of the ‘yes’-type companies will comply with all uneducated (and sometimes unsafe) requests.

Some of the appointments I have with customers address very rudimentary horticultural problems. The homeowner’s concerns are legitimate. Most problems they are having, though, can be avoided with an ounce of foresight. Issues include planting hemlock trees in full sun, or replacing a Japanese maple killed by verticillium wilt with another Japanese maple. The list goes on…

Saying ‘No’

There’s a myriad of things that can go wrong in a landscape. It is an artificial environment containing plants which evolved continents apart. Plants often don’t have the capacity to combat pathogens that they are not exposed to in their native habitats, but certain issues are impossible to predict. There is a base knowledge one should have before making these kinds of decisions. The “customer is always right” philosophy doesn’t apply in this domain. You should have some creative influence on your landscape; it’s yours, after all. Spend the time in the nursery looking for interesting plants, make a list, and run it by your landscaper. If they say ‘yes’ to all of your choices, fire them. The people you hire cannot be too timid to tell you ‘no’ sometimes.

“Right plant, right place” is the mantra among plant health care technicians. We are the people who have to clean up the messes made by your landscapers. If your landscaper did their job with longevity in mind, I probably wouldn’t have much to do.

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Plants Use Mycorrhizal Fungi to Warn Each Other of Incoming Threats

The March 2015 issue of New Phytologist is a Special Issue focusing on the “ecology and evolution of mycorrhizas.” This is the second of two articles from that issue that I am reviewing. Read the first review here.

Interplant signalling through hyphal networks by David Johnson and Lucy Gilbert

When an individual plant is attacked by an insect or fungal pest, it can warn neighboring plants – prompting them to produce compounds that either repel the pests or attract beneficial organisms that can fight off the pests. There are two main pathways for a plant to send these communications: through the air by way of volatile organic compounds (VOC’s) or through the soil by way of a vast collection of fungal hyphae called mycelium. Plant communication by aerial release of VOC’s has been well documented; communication via mycelium, however, is a fairly recent discovery, and there is much left to learn.

“The length of hyphae in the soil and the ability of mycorrhizal fungi to form multiple points of entry into roots can lead to the formation of a common mycelial network (CMN) that interconnects two or more plants.” These CMN’s are known to play “key roles in facilitating nutrient transport and redistribution.” We now understand that they can also “facilitate defense against insect herbivores and foliar necrotophic fungi by acting as conduits for interplant signaling.” The purpose of this research is to explore the “mechanisms, evolutionary consequences, and circumstances” surrounding the evolution of this process and to “highlight key gaps in our understanding.”

interplant signaling

An illustration of plant communication (aka interplant signaling) by air and by soil form the article in New Phytologist.

If plants are communicating via CMN’s, how are they doing it? The authors propose three potential mechanisms. The first is by signal molecules being transported “in liquid films on the external surface of hyphae via capillary action or microbes.” They determine that this form of communication would be easily disrupted by soil particles and isn’t likely to occur over long distances. The second mechanism is by molecules being transported within hyphae, passing from cell to cell until they reach their destination. The third mechanism involves an electrical signal induced by wounding.

If signal molecules are involved in the process, what molecules are they? There are some molecules already known to be transported by fungal hyphae (lipids, phosphate transporters, and amino acids) and there are also compounds known to be involved in signaling between plants and mycorrhizal fungi. Exploring these further would be a good place to start. We also need to determine if specific insect and fungal pests or certain types of plant damage result in unique signaling compounds.

It has been established that electrical signals can be produced in response to plant damage. These signals are a result of a process known as membrane depolarization. “A key advantage of electrical-induced defense over mobile chemical is the speed of delivery.” Movement of a molecule through cells occurs significantly slower than an electrical charge, which is important if the distance to transport the message is relatively far and the plant needs to respond quickly to an invasion. Various aspects of fungal physiology and activity have been shown to be driven in part by membrane depolarization, so involving it in interplant signaling isn’t too far-fetched.

photo credit: wikimedia commons

photo credit: wikimedia commons

How and why does a system of interplant communication involving mycorrhizal fungi evolve? And what are the costs and benefits to the plants and fungi involved? Determining costs and benefits will depend largely on further establishing the signaling mechanisms. Exploring real world systems will also help us answer these questions. For example, in a stable environment such as a managed grassland where CMNs are well developed, a significant loss of plants to a pest or disease could be devastating for the mycorrhizal community, so “transferring warning signals” would be highly beneficial. Conversely, in an unstable environment where a CMN is less established, assisting in interplant signaling may be less of an imperative. Regarding questions concerning the degree of specialization involved in herbivore-plant-fungal interactions: if a “generic herbivore signal” is sent to a neighboring plant that is not typically affected by the attacking herbivore, the cost to the plant in putting up its defenses and to the fungus in transporting the message is high and unnecessary. So, in an environment where there are many different plant species, species-specific signals may be selected for over time; in areas where there are few plant species, a generic signal would suffice.

As research continues, the mysteries of “defense-related” interplant communication via CMN’s will be revealed. Field studies are particularly important because they can paint a more accurate picture compared to “highly simplified laboratory conditions.” One exciting thing about this type of communication is that it may mean that some plants are communicating with each other across great distances, since “some species of fungi can be vast.” CMNs can also target specific plants, and compared to communication via aerial VOC’s, the signal will not be diluted by the wind.

Since I am in the process of reading Robin Wall Kimmerer’s book, Braiding Sweetgrass, I have decided to include her description of a tree-mycorrhizal fungi relationship:

The trees in a forest are often interconnected by subterranean networks of mycorrhizae, fungal strands that inhabit tree roots. The mycorrhizal symbiosis enables the fungi to forage for mineral nutrients in the soil and deliver them to the tree in exchange for carbohydrates. The mycorrhizae may form fungal bridges between individual trees, so that all the trees in a forest are connected. These fungal networks appear to redistribute the wealth of carbohydrates from tree to tree. A kind of Robin Hood, they take from the rich and give to the poor so that all the trees arrive at the same carbon surplus at the same time. They weave a web of reciprocity, of giving and taking. In this way, the trees all act as one because the fungi have connected them. Through unity, survival. All flourishing is mutual.