Q&A: Some insects have a lot of gall

Maple Eyespot Gall, caused by a native midge (tiny fly) that occurs throughout the state. Photo: M. Talabac

Q: What on Earth is going on with this maple leaf? I saw it on a wild tree while taking a walk down a neighborhood path, but wonder if it’s something that can spread to nearby gardens.

A:  This is a great example of a gall, which is a tissue deformity on a plant caused by either insects, mites, fungi, bacteria, or nematodes. Usually galls cause swelling or weird projections on leaves or plant stems, but sometimes the more obvious feature is a color change like this.

The activities of the organism responsible creates chemical changes in the leaf tissue, redirecting tissue formation to suit its needs. For instance, insect-made galls give the larvae their own little house to feed in while being protected from most predators or harsh weather. (Impressively, tiny parasitoid wasps, little bigger than a dash on this page, still find their prey inside these structures and interrupt their life cycle. Isn’t that amazing?)

Despite how drastic galls may look to us, they don’t cause much harm to their host plants, which can be trees, shrubs, or perennials. Oak trees are renowned for harboring many kinds of eye-catching galls, some of which become most noticeable when they fall out of the canopy onto our lawns or gardens. See if you can find anything living inside those swollen red or brown lumps or balloon-like pockets on leaves. A wise bird or other insect may have beaten you to it, though, or the culprit is long gone and already flew away as an adult before the plant jettisoned the injured leaf.

If an eyesore, you can clip off heaviest infestations of leaf galls on witchhazel (caused by insects), azaleas (fungus), oak saplings (usually insects), and any other easy-to-reach plant. Keep in mind that the unaffected portions of those leaves are still functioning to feed the plant, so don’t remove too much growth. Otherwise, I suggest you leave them alone and just marvel at the intricacies of the natural world. Gall-forming insects can feed songbirds and don’t risk the health of the plant. As with any organism, populations wax and wane over time and galls might be prevalent one year and nearly absent the next.

At the Home and Garden Information Center, we have several web pages with more information about galls, including Shade Tree Galls and Eyespot Galls on Trees.

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

Have a plant or insect question? University of Maryland Extension has answers! Send your questions and photos to Ask Extension.

Q&A: Fruit tree considerations for the home garden

a grove of peach trees
Peach trees. Photo M. Talabac

Q: I’d like to eventually grow some of my own fruit. What’s a good starting point and what do I need to consider?

A: It’s fun to try growing your own food, though fruit trees require the greatest amount of commitment and patience to be rewarding. Ill-prepared first attempts can easily end in failure. We suggest inexperienced gardeners or anyone short on time try small-fruit (berry) cultivation first before diving into fruit trees – they’re much simpler to grow, need little to no spraying, and take up less space – but if you do enough research to know what to expect, you can certainly start small so it’s not overwhelming.

Easier crops for a novice grower to start with include fig, persimmon, and some of the more esoteric fruits like jujube, serviceberry, and pawpaw. Ironically, the most popular fruits – apple, pear, peach, plum, cherry – are the hardest to grow well in our mid-Atlantic conditions. This is not due to temperature hardiness but rather disease and pest pressures.

Plan as much as possible first: where do you have enough space and the best conditions, how will they be cared for year-round, what problems should you anticipate, and how will you process the perishable harvest? Even when grown organically, there’s a lot of intervention and preventative treatments that will typically be needed to produce a useful harvest and to keep the tree healthy. After a problem arises, curative options are few, so knowing ahead of time what to look for and when is important in avoiding plant damage or a ruined crop for that year.

“Location, location, location” applies in gardening too. Fruit-bearing plants usually require full sun (6+ hours daily in summer) and well-drained soil to perform well. A site with good air circulation reduces disease, and proper pruning and training will make harvesting easier. Choose an area where you have enough space to avoid crowding and competition between plants. Different varieties mature at different sizes, and training style will also impact how much room trees use.

Most fruit trees are propagated by grafting. That means the variety you want is joined to a rootstock of a related variety for the purposes of improving hardiness, disease resistance, and/or dwarfing the plant’s stature for ease of maintenance and harvest. Terms like semi-dwarf, dwarf, and miniature refer to the overall growth habit compared to a full-size tree, not the fruit size itself.

Check which varieties need cross-pollination to fruit well, as some will not produce fruit if planted alone. Self-fruitful groups include figs, peaches, nectarines, and apricots, plus some varieties of apple, cherry, pear, persimmon, and plum. Keep like with like when you can, because cross-compatibility may not occur; for instance, don’t rely on pollination between an Asian and a European pear, or an early-blooming apple with a late-blooming apple. Web-based suppliers sometimes provide cross-pollination charts to illustrate compatible pairings. Avoid multi-graft plants (trees with several varieties grafted onto a shared trunk) unless you’re quite experienced because they run the risk of increased maintenance headaches or the loss of an entire variety’s crop.

ripening figs on a fig tree
Fig fruits.

Good inherent disease resistance goes a long way to reducing pesticide use and lowering the risk of bad outbreaks. No varieties are immune to problems, but those with noted resistance aid your efforts tremendously. It may surprise you to learn that some of the most popular varieties found at supermarkets are not the more disease-resistant options or even easy to grow overall. Ideally, narrow your options down by resistance traits first, desired flavor and other traits second.

Our website has a lot of information about growing fruit. You can search for a specific fruit type and find information on plant selection and good care practices.

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

Q&A: Why do my hollies and other evergreens have brown and pale leaves?

holly with leaves showing sections of brown and pale color
Winterburn symptoms on holly. Photo: David L. Clement, University of Maryland Extension

Q: Several of our evergreens (different kinds) have brown or pale, bleached-looking leaves. Do they have a disease already, and can anything be done? Is it preventable in the future?

A: Most likely it’s winterburn, especially since most infectious diseases won’t cause symptoms this early and seldom impact several unrelated plants to the same degree. Winterburn is an abiotic disorder or injury – abiotic translates to without (a-) life (biotic) – meaning the condition has a non-living cause. Abiotic plant disorders are environmental, and causes include wind, water, temperature, and soil pH. In comparison, biotic factors would include insects, mites, fungi, or bacteria.

No treatment is recommended because the damage has been done, but winterburn is rarely a serious threat to a plant’s long-term health. As new growth resumes, the plant will eventually shed the damaged leaves. If it’s too much of an eyesore, you can selectively trim away the worst of it this month. Causes for winterburn typically involve a combination of cold temperatures, wind, and exposure to sun. Any autumn pruning that results in tender regrowth is priming a plant for winterburn, which is one reason it’s not recommended.

Why are cold-hardy evergreens damaged? Leaves “breathe” through tiny pores on their surface, and this gas exchange also allows water vapor to leave the leaf. Moisture leaves our bodies the same way – picture foggy breath on a cold day. Breezy days, especially in winter’s drier air, speeds-up this evaporation, as can the sun’s weak warmth. Meanwhile, during cold snaps, moisture in the surface layers of soil freezes, which prevents roots from absorbing it. Since the plant cannot replenish all of the moisture it’s losing, the leaf tissue starts to essentially freeze-dry. A thaw won’t reverse the damage because the cells have been injured, just like skin with frostbite. (Unlike our skin though, which can heal to an extent, leaf tissue can’t repair itself.)

Broadleaf evergreens are more vulnerable to winterburn than needled evergreens because the leaf surface area and evaporation potential is so much greater. Younger plants also have greater vulnerability because they are still establishing roots. This is the main reason it’s risky to plant evergreens late in the fall. Cherry laurel, boxwood, holly, rhododendron, camellia, and southern and sweetbay magnolias are common winterburn victims in our area. Plants kept in containers are also susceptible because their roots dry faster and experience more drastic temperature swings than they would in the ground.

The only actions you can take to minimize winterburn risk is to site evergreens out of the brunt of winter winds and to periodically monitor their root zones for moisture, irrigating when dry during a warm spell. Plants overwintering in pots can be sheltered a bit near a wall or windbreak, but don’t bring them inside as the interruption of dormancy may detriment their health.

Learn more and see additional photos on the Home & Garden Information Center website: Winter Damage on Landscape Plants.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. 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.

Fine-tuning your indoor plant lighting choices

This is the final article in our four-part series about indoor plant lighting. You can also read the first, second, and third articles.

You may see two other details provided in lamp specifications aside from the terms introduced in my last installment. They are not critical factors but can influence your satisfaction with how the lights look by themselves, and how plants, decorative pots, and other objects look underneath them.

The appearance of plants under the lights is not only important for aesthetics, like seeing the true colors of blooms, but also for detecting leaf discoloration, which can be a key symptom of malnutrition, light stress, or pest or disease damage.

Color Rendering Index (CRI)

While this doesn’t affect actual light intensity, it does impact our perception of how colors will look under a light and is a matter of personal preference.

On a scale of 0 to 100, the higher the CRI value a lamp has, the more accurate the colors will look compared to viewing in natural light. At the low end of the scale, colors are lackluster (desaturated) and less distinguishable from each other. Since incandescent, fluorescent, and LED lights all produce light by different means, they have different CRI ranges, though improvements in technology are closing this gap. Ideal ratings are in the 80s and above, with the 90s considered “high CRI.”

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Indoor lighting options: terms, types, and measurements

terrarium plants under LED lights
Terrarium under LED lights. Photo: M. Talabac

This is the third in our four-part series of articles about indoor lighting for plants. You can also read the first, second, and fourth articles.

Artificial light sources come in several forms, all relatively easy to acquire. Costs can vary wildly, and some are more electrically efficient than others. The variety of available options allows you to customize setups to your needs and the preferences of your plants. Before you dive into an overwhelming list of web search results, here are traits of the basic categories:

Light-Emitting Diode (LED)

  • best energy-efficiency in terms of light produced per watt consumed (especially if the light has the ideal spectrum)
  • coolest to the touch except for high-powered units, which usually have small built-in cooling fans
  • can be expensive for high-quality fixtures, though costs are decreasing
  • light output does not dim significantly over time, though diodes do have a finite lifespan
  • reach full brightness immediately or very quickly when turned on
  • diodes can either be exposed or under a frosted or textured cover to help diffuse the light
  • diodes are directional, meaning they don’t emit light in every direction the way a fluorescent tube does, so reflectors aren’t usually needed
  • more even light output from one edge of the fixture to the other
  • can be round like a spotlight (with a cluster of diodes) or straight strips (or strips inside a tube) with one or more rows of diodes
  • some replacement “tubes” can be used in place of fluorescent tubes in a fluorescent fixture, but you must check with the fixture’s manufacturer for compatibility as mixing components is a matter of electrical safety
terrarium LED spotlights
Terrarium LED spotlights. Photo: M. Talabac
LED panel lights
LED panel. Photo: M. Talabac

Why light levels are important for indoor plant growth

plants growing under artificial light indoors
Photo: Miri Talabac

This is the second article in our four-part series about indoor plant lighting. You can also read the firstthird, and fourth articles.

Typically, insufficient lighting is the limiting factor for indoor plant growth and flowering, plus the reason for spindly seedlings. Most light fixtures in our homes and offices – especially those still using incandescent bulbs or those with energy-saving bulbs that mimic incandescents – don’t give off enough energy for plants to survive or thrive on long-term. In addition, windows block a surprising amount of sunlight intensity compared with the same spot just outside the glass. Insect screening outside a window reduces intensity even more.

Artificial lighting can either supplement natural light or be the sole light source for plants. Plants tolerate levels of light outside of their preferred range, but sensitivities vary from species to species. Over time, the consequences of inappropriate light levels may impact a plant’s health and alter its appearance, even if it isn’t immediately noticeable.

The importance of light to plants

For plants, light is food. We think of fertilizer as plant “food,” but in reality, it is more akin to a multivitamin than it is a meal – it supports how they use their food (carbohydrates from photosynthesis) and helps build tissues, pigments, hormones, defensive chemicals, and so forth – but it’s not providing the calories they need to survive and grow. They certainly can “fast,” so to speak, such as spending a few days in a box in transit or remaining semi-dormant in winter, but prolonged light deprivation from insufficient lighting will have negative impacts on plant health akin to slow starvation.

Plants may lack eyes, but they can still “see” light by detecting its colors, intensity, and duration. Coupled with temperature or precipitation, it can tell them what season it is for the purposes of growth and reproduction (flowering). Weather can fluctuate from year to year, but the patterns of daylength and general light intensity remain the same and are the most reliable environmental cues for the plant.

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Q&A: Winter gardening tasks

Q: Is there any outdoor garden task this time of year that I may be forgetting to do? I’ve foregone a fall clean-up for the benefit of overwintering wildlife, and the lawn and veggie garden are “asleep” for the season.

A: There are a few things that are good to accomplish during the dormant season. Yard tools like pruners, loppers, shovels, spades, and mower blades are best stored clean, sharpened, and oiled. There may be local businesses that offer sharpening services, but you can also do it yourself with a metal file or sharpening stone or rod.

Ideally, sharpen mower blades annually so the turf doesn’t have the added stress of ragged, torn leaf blades which can be more vulnerable to infection. A steel wool scrubber or a wad of sandpaper can take off early stages of rust and caked-on sap before you focus on the blades of pruning tools and shovels. Good-quality hand pruners can usually be disassembled for easier maintenance, and lightly wiping with oil afterwards helps lubricate the metal and resist rust. Linseed oil (or vegetable oil in a pinch) can be rubbed into wooden tool handles to protect them from aging.

Check on the location of pesticide containers and protect them from extreme temperatures (including freezing). Always store them away from human and animal food and well-secured from children and pets. Products you rarely use should be dated (if you recall when you bought or opened them) since they may only have a useful shelf life of a couple of years. Old pesticides can be disposed of by looking for household hazardous waste collection sites near you.

If you have staked any new plantings, check their ties to make sure the plants still have wiggle-room and bark isn’t being abraded. Stakes that have been in place for six to twelve months can be removed; they’ve either done their job by now or weren’t working in the first place. (Staking is actually not often needed, but at the very least it’s key to let a staked plant’s trunk sway in the breeze so stabilizing root growth and trunk thickening are stimulated.)

Similarly, if you left ID tags tied to any plants, remove them and any other plastic or elastic nursery tags before they damage the stems. Otherwise, any material that gets embedded in expanding growth will be impossible to remove and could cause branch decline in the future if it interferes with sap flow. Alternatively, tags may disintegrate over time and fall off, which means you’ll have lost your plant name. Tags will be easier to spot now on deciduous plants. Keep a record of the plant ID another way – a garden diagram or journal, or written on a stake at the plant’s base – as variety-specific features might impact care advice or future troubleshooting.

Lastly, if you’re overwintering hardy plants in containers, consider using “pot feet” or “pot risers” to raise the pot’s base off decking or pavement by an inch or two. This lets excess moisture clear the drainage holes so it doesn’t freeze into an ice dam, which would risk flooding roots. Any sturdy material where you can find several pieces the same height would suffice, but you could also purchase them in an array of materials, often in packs of three or four “feet” per pot.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read additional articles by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension.