August 2023 – The Garden Professors™

Preparing your landscape for extreme weather

Since my last post, the news has been full of one weather disaster after another. Wildfires in Maui. The remains of Hurricane Hilary moving north into California and other parts of the western USA with moisture even streaming as far east as Wisconsin. Record-breaking heat and humidity across most of the continental USA and severe weather outbreaks in the Midwest and Northeast. This does not even include the typhoons, floods, droughts, and heat waves occurring in other parts of the world at the same time. And today I am watching the development of a tropical system in the northwestern Caribbean that is likely to become Tropical Storm or Hurricane Idalia (pronounced ee-DAL-ya) by early next week, bringing rain and strong winds to parts of Florida and southeastern Georgia.

https://upload.wikimedia.org/wikipedia/commons/e/ed/Mullen_Fire_shadow.jpg — Photo of the Mullen Fire in Wyoming on September 26, 2020. Justin Hawkins, USFS, Commons Wikimedia.

Each of these weather events can impact our gardens and properties. Not all the impacts are bad since tropical rainfall is an important source of summer moisture in many areas. In the Southeast as much as 40% of our summer precipitation comes from tropical systems and if we don’t get that rain, we can go into a drought quickly in our hot summertime temperatures. The rain from the remains of Hurricane Hilary helped provide some needed rain to help increase reservoir levels in the desert Southwest USA, which desperately needs the water. But if we get too much very strong rain or winds the damage to our homes and yards can be severe. This week I want to discuss some ways you can prepare your gardens and landscaping for the severe weather that will inevitably occur in your area at some point in the future (and that future may be nearer than you think).

Awareness is key to proper preparation

To properly prepare your gardens and homes for severe weather, you need to know what kinds of weather to expect and how it will impact your plants and buildings. The types of weather you are likely to experience will drive how you prepare. If you live in the Pacific Northwest, you are not too likely to experience hurricanes, but you certainly can experience extreme rain storms in winter and wildfires in summer especially if you have a heat wave like you did last year. If you live in the Southeast then hurricanes and tropical storms are much more likely but damage from straight-line winds can be just as important, as I found out in late July when strong thunderstorms knocked down so many trees in my neighborhood that we lost power for 44 hours. A friend of mine lost the roof of her house to two pine trees that toppled over in the strong winds. We can even experience ice and snow storms here in the South from time to time; this means you should not just prepare for the most common disasters but for any extreme event that could occur there. Of course, getting ready for the most common natural hazards is the best way to save your homes and gardens because those are the most likely to occur where you live. But you should also think about rare events like floods even if you are not in a flood plain because the consequences of an event are so severe.

Edit this at Structured Data on Commons — Fordgate: Flooded Garden, Lewis Clarke , Commons Wikimedia.

Once you have identified the natural hazards that affect your area, then you need to think about what kinds of weather conditions are likely to occur in each of those events. In a hurricane or a strong winter storm on the West Coast, heavy rain and high winds are both likely weather conditions your garden will experience. In a heat wave, high evaporation rates and dangerous outdoor working conditions are likely to be the major dangers. Those are the impacts you will need to consider when protecting gardens and gardeners.

Look at your landscape and home to identify potential problems

Once you have determined what hazards are likely to affect your property, you need to do an assessment of where your risks are. Take a walk around your garden and look at the trees and plants you have. Are there dead trees that could fall over or broken limbs that could snap off in high winds from hurricanes or thunderstorms and become wind-borne missiles? Do you have garden decorations like garden gnomes or mirror balls that could also blow into the sides of cars or buildings? Do you live in an area that is prone to frequent flooding? How will you keep that water away from your house and out of your garden plots? Are there a lot of plants close to your home where they could spread wildfire in a drought under gusty winds?

After you have determined the risks take steps to minimize or remove those risks where you can. There are a number of ways that you can storm-proof your house and garden, many of which should be done anyway to maintain your garden’s health.

I was interested to read the story of the lone house in Lahaina, Hawaii, that survived the recent fires that destroyed much of the town because they had a large area around the foundation covered by river rock, which did not burn and helped keep fire from igniting the house (although I am sure there was some luck involved there too). One of my favorite books, The Control of Nature by John McPhee, also describes the increase in debris flows in western landscapes that occur due to fires that burn waxy plants. This creates perfect conditions for rapid land movement downhill after rain events following the fires, often right through people’s yards and houses.

Buildings still smolder days after a wildfire gutted downtown Lahaina, August 11, 2023. © Robert Gauthier – Getty Images

After the storm is over and you are safe, then it is time to assess your garden and house for damage and take care of your plants, lawns, and buildings. Be careful since there may be downed power lines and dangling tree limbs that could be hazardous. You may need professional help to prune or remove trees or clean out contaminated soil after flooding. Once the immediate hazards are taken care of, then the longer-term work of repairing drainage, eliminating the effects of erosion, rebuilding beds, and other work can begin.

Take care of your family and pets too

Of course, all this planning for your garden and property should not take the place of emergency planning for your own family. If extreme weather does occur, you need to have a plan already in place to determine where to shelter in your home if you can and how to evacuate safely if you can’t stay. Every minute saved makes a difference although in the worst cases even that may not be enough time. FEMA has a good website that provides a lot of information on how to plan for both natural hazards and other emergencies like chemical spills. Many states also have excellent resources for dealing with emergencies, such as the Resident’s Handbook To Prepare for Natural Hazards in Georgia, which covers all kinds of severe weather and how to prepare for it in Georgia and beyond.

https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Tornado_damage_is_seen_in_Moore%2C_Okla.%2C_May_23%2C_2013_130523-F-RH756-316.jpg/1280px-Tornado_damage_is_seen_in_Moore%2C_Okla.%2C_May_23%2C_2013_130523-F-RH756-316.jpg — Wind damage, Moore OK, May 23, 2013, SSgt Jonathan Snyder, Commons Wikimedia.

Diagnosing Disasters: The Case of the Mopey Mophead

This past week I was out of town at a conference, and since the week was supposed to be a scorcher I made sure my husband was going to water the container plants daily. And indeed, temperatures were in the 90s, dropping to the mid-60s at night. But the container plants looked great when I got home and I didn’t think much more about it until the next day. My husband called me into the living room, pointing at our massive mophead hydrangea which looked like it had been torched. Leaves and blossoms were wilted and browning. Every single stem was affected. Since our landscape is on an automated sprinkler system, what the heck happened?

This is when caution and objectivity are important. I wasn’t going to go cut the whole thing down, even though it looked terrible. Instead, I made observations of the site (not just the plant):

The site is on the north side of the house, where plant only receive direct sunlight in the morning and late afternoon during the summer.
No other plants were affected – not even the smaller hydrangea to the west of the damaged plant.
The irrigation system had been working normally.

***Damaged hydrangea on the left generally outperforms the smaller, undamaged hydrangea on the right.***

When diagnosing plant problems, it’s also important to consider the history of the plant and the landscape:

Hydrangea is at least 55 years old.
No soil disruption or other site disturbance
No pesticide or fertilizer use
Mulched with arborist wood chips

***\Collect all pertinent information, especially recent weather data.***

Given that no other plants were affected, the problem was with the hydrangea itself. Hydrangeas use a lot of water to support their large, thin leaves and massive flower heads. When the weather suddenly turned hotter and temperatures stayed abnormally high in the evenings, the plant could not recover its water loss overnight. Many flowers and leaves experienced terminal wilt – that means they lost too much water and tissues turned brown. Other flowers and leaves were able to recover as day and night temperatures returned to normal.

***All other landscape plants were able to tolerate the spike in temperatures – just not the hydrangea.***

What could we have done to prevent this? Had we seen the wilt occurring during the day, we could have turned on the sprinklers manually in that part of the landscape. Hydrangeas are a good indicator of low soil water. In future summers, as we continue to experience hotter and drier conditions, we will keep an eye on our hydrangea and use additional irrigation if necessary.

Plant Disease Primer: Part 1 – Shaping up the causes, signs, and symptoms of disease

Throughout the garden season, extension professionals all across the country get to play detective when trying to diagnose plant diseases and recommend specific controls or preventative measures. We often have to put on our Sherlock Holmes-esque thinking caps and our standard issue detective’s magnifying glass (or microscope) to diagnose plant maladies.

Having a basic understanding of diseases, how they function, and what they look like is key. Gardeners who bring samples or pictures into our office often get exasperated when we play twenty questions trying to figure out if it is a fungus, bacteria, or virus (or something else) causing the issue. Knowing about placement, environment, planting, etc. can all be keys in discovering what might be causing the issue. Sometimes we can’t identify an exact disease at a glance and have to send things to the diagnostic lab on campus, but by looking at signs and symptoms and identifying factors about the plant we can often figure out the type of pathogen causing the issue, or whether it might be environmental, abiotic, or insect related.

What leads to plant diseases?

Of course, the thing that causes the disease is a pathogen or a causal agent such as a fungus, bacteria, or virus (or a few other odds and ends like phytoplasmas). But there are other factors at play to get a disease infection started and sustained. You need all of the factors in place for infection. This is often represented as a triangle, where a causal agent (pathogen) must be present with the right environmental conditions and a host plant that can actually be infected by the pathogen. I’ve also seen a plant disease “pyramid” where time is added as another factor (as in, the correct conditions must be present at the same time and for a long enough period for infection to start). And still yet in researching this article I found the PLANT DISEASE TETRAHEDRON, which adds human activity as another factor. What’s next, the plant disease fractal?

But I digress. When a sample comes in to our office, we play twenty questions with the gardener asking about these different factors. Like is it irrigated (many diseases need water to be spread or to develop), does it get shade or full sun, have you seen any insect activity, when do you usually work in the garden, etc. These questions can help us identify parts of the disease triangle/pyramid/tetrahedron that could inform the diagnosis.

Keeping these factors in mind can also help gardeners reduce the likelihood of disease through IPM. For example, viruses require a vector – usually an insect, animal, or human to spread the disease. Many viruses are spread through leafhoppers, bacterial wilt in cucurbits is spread through cucumber beetles, and mosaic viruses like tobacco mosaic virus has many vectors including humans and garden tools (which is why many green industry businesses have strict sanitation rules, including rules for tobacco users and hand sanitation). Knowing that fungi and bacteria can be airborne with spores or splashed by “wind splashed rain” or irrigation water can lead to improved practices like mulching, pruning for good air flow, and plant spacing.

How can you tell which diseases are which?

Let’s face it, many plant diseases look very similar. There are usually what we call spots and rots that can be very similar. But there are some identifying characteristics that help us at least determine what type of pathogen or causal agent is causing the issue.

The first thing to keep in mind is that plant diseases have both signs and symptoms. Signs are the presence of the actual disease causing organism, visible to the eye. Fungal diseases often have mycelia, or fungal threads, and reproductive structures like pycnidia present. You may also see the causal agent itself, such as leaf rust or powdery mildew. Bacteria will often have exudates that ooze out of plant parts, water soaked lesions, and bacteria that stream out of cut stems parts. You can actually diagnose some bacterial infections by suspending a cut stem in water and watching bacteria stream/ooze out of the cut. Viruses are not visible to the human eye, therefore do not have signs.

Powdery mildew on peony Source: Douglas/Sarpy Extension – Nebraska

Symptoms, on the other hand, are the effects of the pathogen on the plant. Common symptoms of fungal infections are leaf spots, spots or rots of fruits, chlorosis, and damping off in new seedlings. Bacterial symptoms include leaf spots (often with a yellow halo around them), crown gall, stem/trunk cankers, wilting, shepherd’s crook (like fire blight), and fruit rots. And since bacteria usually depend on streaming through liquids, they often leave definitive patterns for leaf spots that align with vein structures. For example, leaf spots will often be angular because they are “trapped” in between veins on the leaf. The most common symptom of viruses is a mosaic pattern on leaves and fruit, but also crinkling and yellowing of leaves, necrosis, and stunting.

Angular leaf spot on cucumber – the symptom pattern falls within veins, giving the angular appearance. Source: UMN Extension

Special mention- phytoplasma: Phytoplasmas are single-celled organisms that aren’t really bacteria, but are descended from them. They don’t have cell walls and are transmitted to plants through an insect vector like leaf hoppers. The most common type of phytoplasma diseases is called yellows (aster yellows, ash yellows, etc.) because plants often turn yellow. The symptoms are often interesting. Witches brooming, which is irregular growth that makes branches look like brooms is common. Aster yellows is a common disease affecting many plants in the aster family. Most commonly, flowers of these plants look distorted and may grow leafy structures instead of flower structures.

Unusual floral growth as a result of aster yellows Source: Douglas/Sarpy Extension – Nebraska

To wrap it up

It can be difficult to figure out what diseases are affecting plants, if it is a disease at all. Getting help in determining what disease might be affecting plants can help you treat or prevent the problem in the future. In my next installment of this series, I’ll talk about common diseases, their signs and symptoms, and treatments and preventative measures.

Sources:

https://www.canr.msu.edu/news/signs_and_symptoms_of_plant_disease_is_it_fungal_viral_or_bacterial

https://lms.su.edu.pk/lesson/1660/elements-of-an-epidemic

Beneficial Bicarbonate?

The hot weather that stimulated the last blog is still with us! Keep up the mulch and occasional watering to help shade trees. Today I want to cover a topic that seems like a garden myth but actually has considerable science behind it. Bicarbonate! The miracle cure for all garden pests? No. My wife came across an article in her news feed about a ‘garden guru’ who touted baking soda as a miracle cure for powdery mildew and other “blight” diseases. In this blog I will review the efficacy of the bicarbonate anion in disease control.

Bicarbonate as a disease control agent is not a new concept. Many studies going back a few decades documented the efficacy of this molecule in controlling foliar diseases of plants. Most studies are on powdery mildew of many crops and ornamental plants as well. Bicarbonate is typically available with three cations: ammonium, sodium and potassium. Most of the studies and efficacy are with the potassium salt of bicarbonate (not baking soda which is the sodium salt). All the salts are more or less efficacious against powdery mildew and a few other fungi like apple scab.

The mechanism of action of bicarbonate control of fungi is not clear, however Monterey Chemical that manufactures a Bicarb. product (Bi Carb Old Fashioned Fungicide) indicates on its label that the mechanism is the disruption of the potassium ion balance in the fungus cell, causing the cell walls to collapse

One frustrating thing with internet-based articles by garden “gurus” is that everything is some kind of “garden hack” Like we are getting something done on the sly or with common household materials. Using chemistry to control diseases is using pesticides. Companies test and approve these materials based on efficacy data as shown in the references at the end of this article. The benefit of using a registered product is that there are instructions that indicate how to spray, what the target organism is and the environmental conditions under which the product will work. Much of this is never mentioned in the “hack” articles.

Bicarbonate anion is an effective control of powdery mildew often as good as commercial fungicides with very different chemistries and methods of action. There does not appear to be resistance to bicarbonate. It is a contact fungicide (not systemic), the material must contact the fungus in order for it to work. In order to get good contact usually a wetting agent such as an ultrafine oil is combined with the tank spray solution to increase control.

It is best if bicarbonate is applied early in the disease cycle. Powdery mildew organisms are obligate biotrophic fungi. This means that the mildew fungus must grow in living plant cells. So when the mildew is killed the living plant cell is also killed. Powdery mildew is a disease of the epidermal tissues of plants so cell death is superficial but if late stage mildew is control by bicarbonates there can be phytotoxicity (plant damage) as most of the epidermal cells of leaves and flowers will collapse and die.

An advancing colony of powdery mildew on Poinsettia. Attempted control with bicarbonates at this time will cause some phytotoxicity.

Powdery mildew fungi are in the Ascoymcete group of fungi and most have two spore stages. The first infections are caused by ascospores (sexual spores) that are released in the springtime. The primary infections develop and then asexual spores develop on plant surfaces that we recognize as powdery mildew. Stopping the primary infection by applying control early in the season will slow powdery mildew down on sensitive plants. Since many powdery mildews have broad host ranges they form on weeds an other plants and can move into protected plants later in the season. Frequent sprays will be required if conditions for the fungi are optimal and the spores are present. Bicarbonates do not have long-term protective effects since they work only when the solutions contact living fungus.

References

Zivand, O. and A. Hagiladi. 1993. Controlling powdery mildew in Euonymus with polymer coatings and bicarbonate solutions. HortSceince 28:134-126

Moyer, C., & Peres, N. A. (2008, December). Evaluation of biofungicides for control of powdery mildew of gerbera daisy. In Proceedings of the Florida State Horticultural Society 121: 389-394.

Holb, I.J. and S. Kunz. 2016. Integrated Control of Apple Scab and Powdery Mildew in an Organic Apple Orchard by Combining Potassium Carbonates with Wettable Sulfur, Pruning, and Cultivar Susceptibility. Plant Disease, 100(9), 1894-1905

El-Nogoumy, B. A., Salem, M. A., El-Kot, G. A., Hamden, S., Sehsah, M. D., Makhlouf, A. H., & Nehela, Y. 2022. Evaluation of the Impacts of Potassium Bicarbonate, Moringa oleifera Seed Extract, and Bacillus subtilis on Sugar Beet Powdery Mildew. Plants, 11(23), 3258.

Türkkan, M., Erper, İ., Eser, Ü., & Baltacı, A. 2018. Evaluation of inhibitory effect of some bicarbonate salts and fungicides against hazelnut powdery mildew. Gesunde Pflanzen, 70(1), 39-44.