plant diagnostics – Maryland Grows

Q&A: What Causes Patchy Wilting?

August 15, 2024August 13, 2024Maryland Grows1 Comment

*Sometimes individual stems wilt on otherwise healthy perennials. Photo: C. Carignan, University of Maryland Extension*

Q: Why would my perennial Lobelia be only partially wilting? I keep an eye on watering so it doesn’t get too dry.

A: This can often be the work of an infection or, less commonly, stem-boring insects. Since stem-boring insects in perennials are rarely a cause for concern, I’ll focus on the pathogens.

Sometimes it’s hard to diagnose the cause of wilting with certainty since distinctive symptoms identifying the culprit aren’t always visible; there’s a lot of symptom overlap. During summer, heat-loving fungi like Southern Blight can cause wilting because the pathogen kills the stem tissue close to the soil line, cutting the top growth off from its water supply and causing it to collapse. A wide variety of fungi and fungus-like “water molds” can cause above- or below-ground infections throughout the year, with some prospering in cool conditions while others need heat. Wilting when the soil isn’t dry can be a telltale sign of infection or physical stem or root damage.

To reduce vulnerability to diseases like Southern Blight, plant crowns need to get good airflow. (The crown is where stems emerge from the root system.) Avoid over-mulching, which covers up or crowds the crown and stem bases; nudge it a few inches away so it’s not piled against the stems. High humidity and dew are sometimes enough moisture for fungi to survive and begin infections, but over-watering plants by irrigating too often can make fungal outbreaks more likely. (This includes lawn grasses, if sprinklers are run frequently.)

Mycelium, which is the “body” of a fungus, is sometimes visible as white webbing or threads covering the infected part of the plant, but it’s not always prominent. (It is usually noticeable with Southern Blight.) Any wilting or collapsed stems need to be removed, since they will not recover. Prune them off and dispose of the debris; don’t compost it.

One or two wilted stems doesn’t necessarily doom the entire plant patch or garden bed, but keep an eye out for worsening symptoms like more rampant dieback. No fungicides can reverse this damage or eliminate spores from the soil permanently. Nor would you want to attempt chemical soil sterilization, as plenty of beneficial fungi, bacteria, and other organisms inhabit the soil. Many of them can out-compete, directly kill or consume, or otherwise stifle the development of pathogens like these. Fungicide impacts are not limited to the pathogens, and some could even have harmful consequences for pollinators.

If Southern Blight is responsible, you can dig out and dispose of the affected plant, plus remove a few inches of the surface soil with it. This is not because the plant’s roots are going to also be infected, but because plant regrowth could be infected again by the spores remaining on the soil surface, and you don’t want to give the fungus more fuel for expansion. If you dig out soil but don’t want to throw it out (soil is a precious resource, after all), just bury the layers with potential spore contamination to a depth of 6 inches or so, where the spores should not survive.

Southern Blight, as with many similar blight and rot diseases, have an extensive range of plants they are capable of infecting. Why, then, don’t we see rampant die-offs in cultivated and wild plants for such common and destructive fungi? Interactions between organisms are complex, and as with insect diversity, there are microbe species which are beneficial, especially in healthy soil that is not too compacted, oxygen-deprived, wet or poorly drained, or low in organic matter (all conditions that favor common pathogens).

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.

How to Navigate the Internet When Searching for Solutions to Home Horticulture Problems

April 24, 2024April 23, 2024Maryland Grows2 Comments

*Photo: C. Carignan, University of Maryland Extension*

All gardeners have challenges in their landscapes and at some point you may turn to the internet for answers. While the internet is a great tool for researching home gardening questions, it can come with challenges. These tips are meant to help guide you through successful internet searches. Remember you can always reach out to your local University of Maryland Extension office or use Ask Extension to get answers to all your gardening questions.

The first step when I begin research is to outline the goals for what I’m trying to figure out. Are you just curious? Is the plant or pest something that you want to try and control? Are you looking for a new plant to add to your garden or landscape? Maybe you are looking for the answers to multiple questions.

Two tips for searching the internet for garden answers

Tip 1: Be specific and always add the word “Extension” or “search term + Extension + your state” to the search phrase. This is helpful for finding the best science- and research- based information. This tip can help eliminate products or services. If you know your state’s Land Grant Universities, add those names to the search box, especially when searching for garden/natural resources related issues.

For example, if you want to research “spring blooming purple trees” you might search those words and end up frustrated without any specific answers.

screenshot of a web search for purple flowering trees — *Search results for spring blooming purple trees*

If you add the word(s) Extension, or UMD Extension as in the following example, you will get results from University of Maryland:

a screenshot of a web search for blooming trees + UMD Extension brings up content from the University of Maryland — *A search for spring blooming purple trees with “UMD Extension” added brings up content from the Univeresity of Maryland*.

Tip 2: Focus on something unique about the specimen— whether it be a plant, insect, flower, seed, etc., such as colors, patterns, or antennae on an insect. Odd characteristics pinpoint search results and make searching easier and faster.

Example: If you just search the word “beetle” with no descriptor words, you will get just that, a general page about beetles.

a screenshot of an internet search for beetles pulls up a general page from the Smithsonian about all beetles in general — *Search results are general if you use a broad term like “beetles”.*

If you add more detail like color, the results begin to get more refined:

screenshot of a web search for black beetles pulls up results like larder beetle and ground beetle — *Information about black beetles from university sources*

Extra details with an oddity highlighted will get you even more specific results:

screenshotof a web search for beetles with long antennae — *A more descriptive search about beetles with long antennae and using “+ Extension” brings up more specific results from university sources.*

How to be a good garden detective?

Often, this goes back to being thorough and paying attention. Our landscapes and gardens often “whisper” and do not scream. If we ignore small signs, symptoms, and clues, that is when it appears that the problem happened overnight.

Plant identification is something that many people struggle with— maybe it’s a weed, maybe a plant with an invasive tendency, or maybe it’s a plant that is bringing something positive to your landscape/natural area. Knowing exactly what the plant is is very important. We could spend a lot of time and energy reviewing botany but these tips are meant to help you build good searching habits.

a mass of small plants covering a drainage ditch — *Non-native watercress (Nasturtium officinale) growing in a spring-fed drainage ditch. Photo: A. Bodkins*

Next month, we will explore different plant apps for your mobile device, but ultimately with or without a plant app, correct plant identification often relies on mature plants that are intact/complete– including the reproductive structures (flowers, fruits, or seeds). Consider the photo above. There are plenty of healthy specimen plants. Questions you can use to help guide your internet searching are:

What environment is the plant growing in — sun, shade, wet, dry, etc.?
Is it an isolated specimen or are there several specimens of the same plant? Is it prolific and making a monoculture, as in the photo above?
Is there a flower on the plant? Flowers can be very helpful for figuring out the correct plant ID. Some keys and guides focus primarily on flowers to identify plants.
Is the plant mature? Are the leaves complete? Remember there are simple and compound leaves. Always look for the petiole, which is the structure/stalk that connects the leaf to the stem. Leaflets of a compound leaf will not have individual petioles.
Are there seeds/fruits/nuts? Underground plant structures, like rhizomes, bulbs, or crowns?
Plant ID apps can be helpful but might not be 100% correct all the time. More on this topic next month.

Here is another view of the drainage area full of watercress. No other plants are green yet in this photo, which is another unique fact that you could potentially use in an internet search. Often non-native plants will break dormancy and begin to grow sooner which can indicate that they do not belong in this location, as is the case here.

another view of a drainage ditch - the water surface is covered with small green plants — *A drainage ditch filled with non-native watercress (Nasturtium officinale) Photo: A. Bodkins*

For insect or arthropod identification:

What is the type of damage you’re seeing (chewed holes or tiny dots that indicate piercing/sucking?)
How many legs?
Is it an adult insect?
Are there many others present or just one specimen?
Is there more than one type of insect? Sometimes the most obvious is not the actual problem.
Are there visible wings? How many?
Interesting colors, patterns, etc.?

Tips for collecting specimens for photos or to take to your local Extension office:

Healthy and complete specimens are very important.
Photos are a great addition to a specimen, but they must be in focus.
Keep the specimen in the best condition that is possible. Digging the entire plant is a best practice, then wrap in a wet paper towel or newspaper and place in a plastic bag/container. Keeping the plants cool until you can get them to your Extension office or plant clinic is also helpful. If there is just one specimen and you are on public property, there is always a chance that it is exotic or protected. Please consider just taking photos in these instances.
Always note any flowers/fruiting structures.
Advice and suggestions from Extension professionals can only be as good as the information provided— please do your part to submit appropriate photos/specimens.

Taking photos:

Close up and complete specimens are needed.
If there are flowers or fruits, always get a photo.
Photos of the environment are helpful to gain a better understanding of the situation.

Remember, correct identification— whether plant, insect, tree, plant disease, etc.— is the key to managing landscapes sustainably! The most frustrating part of searching the internet is that you don’t know what you don’t know— so asking a specific question about a mystery is hard. The internet is full of wonderful information, but it also has misinformation especially when taken out of context and information may be incorrect for your specific location or growing zone. Once you begin applying some of the above tips you can streamline your search experience and have better success with finding answers from reputable sources.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.

Q&A: What Causes Aloe Leaves to Turn Yellow?

December 6, 2023December 4, 2023Maryland Grows2 Comments

potted aloe vera plant — Aloe vera plants.

Q: I have an aloe indoors that is developing some yellow leaves. Do I need to feed it or change something else about how I take care of it?

A: Leaf yellowing is a difficult symptom to trace back to a particular issue since in general it can be caused by overwatering, under-watering, under-fertilization, too little light, too much light, pest feeding, and a few other factors. With indoor succulents, too much light is a rare problem, and accidental over-watering is relatively common, which is why I presume low light and soil moisture are the conditions needing evaluation first.

A leaf that turns yellow is one a plant is probably about to shed, so even if the original issue is resolved, be aware that it won’t usually green up again. That’s okay, as long as the shedding isn’t excessive (and if it is, it might be too late to fix); plants can reabsorb some of the resources stored in the leaf before it dies and falls. It’s also perfectly normal for any plant to shed its oldest leaves from time to time since they have limited usefulness to the plant as they age or succumb to cumulative injuries or stresses.

Succulents like aloe thrive in bright light while indoors, so it’s possible yellowing has begun because the plant is running low on stored energy that has allowed it to tolerate insufficient light so far. (Plants make their food from light, so while occasional fertilization can supplement their nutrition, it’s not a substitute for receiving enough light.) While indoors, aloe grows best where it gets either several hours of direct sunlight close to a window or is placed under plant grow lights that can supplement or replace natural light (if window light is insufficient).

Succulent roots should get fairly dry between waterings, though each watering still needs to be thorough so all of the potting mix is well-moistened each time to eliminate dry pockets. Extra water should freely drip out of the bottom drain holes of the pot. Feel the soil about an inch deep (or more, depending on pot size) and only water when it’s become pretty dry to the touch at that depth. Be sure to empty any drained water in a saucer promptly so the pot doesn’t sit in water, as this can kill roots. Root rot can result in leaf yellowing because there are not enough healthy roots left to support all of the plant’s foliage. As with other triggers for shedding, the oldest, lower leaves are usually sacrificed first.

If you haven’t fertilized the plant in several months, it might benefit from a light dose. Normally indoor plants don’t need fertilization during the fall through winter, but if a plant has been nutrient-deprived for a while, it may benefit from replenishing those nutrients in the soil. The precise fertilizer formulation doesn’t matter much in this case, though nitrogen is likely the nutrient of greatest importance (the N in N-P-K ratios) for overall plant health and leaf color, so it can be chosen as the highest number of the three (such as 3-1-2 or 10-5-5 as arbitrary examples). Regardless of the type of fertilizer chosen, follow package instructions about how to dose it. You’d probably only need one dose (maybe at most two) to last the plant through the winter since it won’t exhaust those nutrients quickly. If you suspect scale, mealybugs, thrips, or mites are causing damage, get them under control first, since you don’t want to feed the pests extra nutrients with the fertilization.

Indoor plants grow slowly (if at all) in winter, and succulents tend to be slow growers in general, so it may take some time for the aloe to show any improvement, which is fine as long as it isn’t declining further in the meantime.