Yard & Garden Line News Volume 1 Number 13                                                               November 1, 1999

Features this issue: Out Spot! Out? Debunking "dog blight" myths Watercore Growing Houseplants Without Pesticides Making Sure Your Christmas Cactus Blooms Minnesota Apples for Storing Armillaria Root Rot Nectria Canker of Shade Trees Stored Food Product Insects Winter Tree Protection Editorial Notes

Out Spot! Out? Debunking "dog blight" myths.
Bruce A. Cunliffe, DVM

Kelly loves the lawn and it shows! Photo credit: Patrick Weicherding

Dog owners share many common experiences--the smell of puppy breath, walks around the lakes, or reading a book on a rainy day with your loyal friend at your feet. However, there are some dog experiences that can be quite irritating. One is the brown spot in the yard that appears a short time after the dog has relieved him or herself. No matter what we try to do, spots still appear letting everyone know a dog lives there. Some people are so particular about their lawns that this problem prevents them from even having a dog! What causes those unsightly patches? How can they be repaired? And most importantly, can they be prevented?

Burned patches in lawns have been attributed to two properties of urine: pH and nitrogen. Turf grasses prefer a slightly acidic pH, but tolerate a fairly broad range of pH (5.5 - 7.5). Dog urine has a normal pH range of 6.0 - 8.0 depending on the dog's diet and health status. Urine pH values are not extreme enough to cause burning.

Nitrogen in the form of urea is the other suspected offender. Urine is primarily made up of water and urea. Urea is the body’s way of eliminating nitrogen waste resulting from the metabolism of protein. Dogs, being carnivores, have a relatively high protein requirement in their diet.

The actual cause of the brown patches is too much nitrogen being applied in a small area. The same patches would occur if a commercial fertilizer was spilled in a small area while filling a spreader. Dog owners know that at the edges of the burned areas the grass is green and lush. This is because the nitrogen concentration at the periphery is dilute enough to have a fertilizer effect, while the concentration in the burned area was toxic.

Urine is not the only form of nitrogen eliminated from the body; feces also contains nitrogen by-products. Feces does not burn the lawn as severely because the nitrogen is in a solid, slow-release form rather than a concentrated liquid. Feces also tend to be picked up with some frequency, decreasing the length of time the nitrogen may be released.

Timmy's a rural dog. Photo credit: Chad Behrendt

Burned areas will recover as grasses spreads back into the area by stolons or rhizomes. If a more aggressive approach is preferred, patch reseeding or sodding, if the damaged areas are extensive, may be necessary.

Perhaps the most important question is how to prevent the unsightly brown spots in the first place. There have been many suggestions related to this topic, some more reasonable than others. Some of the solutions include not having female dogs, feeding pH altering supplements, and increasing water intake.

Female dog urine does not burn lawns more than male dog urine. However, because of their urination behavior, female dogs tend to cause more brown patches. In general, female dogs squat, resulting in large volumes of urine being voided in a small area. Males, on the other hand, tend to urinate in small volumes scattered over large areas as they mark their territory. Neutering males may affect this pattern slightly but marking behavior still tends to appear in males around one year of age. Males consistently marking small trees or shrubs may kill plants due to toxic levels of nitrogen.

Since pH is not the reason for burned lawns, feeding dietary supplements or pH-altering diets is not necessary and in fact may be harmful. Additives such as Vitamin C (ascorbic acid), fruit juices, tomato juice, and Methionine result in acidic urine, which could induce the formation of certain crystals that could cause urinary tract diseases including crystaluria and bladder stones. Baking soda is an alkalizing agent. Raising urine pH may predispose the pet to bladder infections, as well as crystal and stone formation. Any dietary supplementation or urine pH alteration should be discussed and endorsed by the pet's veterinarian.

Emma prefers wood- chipped landscaping. Photo credit: Jim Calkins

Increasing the dog's water intake could result in more dilute urine and reduce the amount of nitrogen applied to the lawn but that also means more trips outside. Perhaps the most effective method is to feed canned food or add water to dry kibble. Canned food has a higher moisture content compared to dry food. However, feeding moist food usually means the dog drinks less water. Tomato juice may be more effective in this category of remedies, than as a urine acidifier, as it adds salt to the diet. Adding salt to the pet's food increases water intake, but may have detrimental effects on the kidneys or heart. Effectively increasing water intake to alter nitrogen concentration is very difficult. Owners should not alter their pet's diet without first consulting their veterinarian.

An easier way to dilute dog urine is to pour water, 3 - 4 times the urine volume, on the affected spot, after the dog urinates.

Training the animals to go in a particular area, on a material that is easy to clean, is the best way to prevent this problem. If you are going to go out with them to pour water on the spot, you may as well train them to go in an acceptable area rather than the lawn. A secluded corner of the yard or garden with sand, gravel, or wood chips would be ideal. Two or three weeks of dedicated training could provide years of enjoyment of both your dog and a well-manicured lawn.

Watercore in Apples
Doug Foulk, Extension Educator, Ramsey Co.

Watercore. Photo credit: UC Davis

Watercore is a physiological disorder that occurs in maturing fruit. Where watercore occurs, sorbitol (the sweetener in chewing gum) collects in fruit tissues, resulting in a water-soaked appearance, especially near the core. Normally sorbitol in apples is converted to fructose, but in the case of watercore, this conversion does not readily occur. Slight watercore isn't a problem--in fact, it results in sweeter fruit. In severe cases, however, watercore can result in browning and tissue breakdown during storage.

So what can a person do to help prevent watercore? About the only thing a home gardener can do is to pick the apples on the early side, say when the background color of the fruit changes from bright green to light, pale green (of course, you'll want to sample the fruit at this point to make certain it is ripe enough for your tastes). If watercore has been a problem for you, try skipping the nitrogen for a year, since excess nitrogen seems to worsen the problem. In orchards with a history of water core, commercial growers apply foliar calcium during the season, although little evidence exists that calcium sprays help.

Finally, if you have apples with slight watercore and you don't like the extra sweetness, the good news is that slight to moderate watercore usually disappears during storage.

Growing Houseplants Without Pesticides
Deborah Brown, Extension Horticulturist

Photo credit: Deb Brown

It's probably not exaggerating to say that nobody wants to use pesticides on their houseplants. Even people who are willing to use insecticides or fungicides judiciously on landscape plantings outdoors usually draw the line when it comes to spraying inside their homes.

Fortunately, with a little added care and a vigilant commitment to watching plants closely so as to catch problems in their infancy, you CAN avoid the use of pesticides indoors. I've grown houseplants my entire adult life, and never once used any sprays on them. Of course, I've thrown out a plant or two over the years, in order to protect the others.

Clearly, the best way to deal with insect pests and foliar diseases is to avoid them in the first place. And that's not really too difficult to accomplish if you're careful.

* Be picky about which plants you bring into your home. When you buy a new plant, examine it closely to make sure it's not carrying any "tiny livestock" with it. Watch out for discolored or mottled foliage, fine webbing, or signs of sticky exudate. And be sure to check the undersides of leaves, not just the tops. Resist the urge to take scraggly looking "bargain" plants home from the garden center. I know; people feel sorry for them and want to bring them back to full health and vigor, but keep in mind these aren't adorable little kittens or puppies.... only plants. Don't take a chance on introducing problem plants into your home.

If a friend offers to give you one of his or her plants, or a cutting from one, remember it's not always a bad idea to "look a gift horse in the mouth." Examine those plants at least as carefully as you would those from a commercial source.

Photo credit: Deb Brown

* Choose houseplants that are well-suited to the indoor environment you can provide. It will go a long way towards keeping problems at bay. Healthy, actively growing plants that receive plenty of light are in a better position to fend off insects and diseases. That means you must grow your houseplants in reasonably bright locations, or supplement whatever amount of natural daylight they receive with an appropriate electric light source. Fluorescent light tubes are the least expensive good source of light for indoor plants. Specialty catalogs also offer metal halide bulbs and high pressure sodium plant lights that are very bright and long-lasting, but considerably more costly.

* Prevent root rots by watering properly. Rather than watering by the calendar, water whenever your plants need moisture. Always water thoroughly, but check the soil to make sure it has dried a bit before you water again. How much it needs to dry depends on the type of plant and size of its container. Never water when the soil surface still feels moist.

* Cleanliness is next to godliness. When it comes to indoor plants,regular "housecleaning" activities mean more than keeping plants looking their best. Dust and dirt accumulating on the foliage creates a favorable environment for insect pests. By washing the leaves periodically you not only get rid of dust, you may be eliminating some mites or insects in the process.

Don't use a feather duster or fluffy dusting wand to clean your plants, though. If there are any mites, insects, or tiny eggs present, you'll end up spreading them from plant to plant.

Even though it's important to wash houseplants often enough to eliminate dust and grime, it's not a good idea to mist them frequently. Moist leaf surfaces allow fungal and bacterial organisms to invade. By keeping leaf surfaces dry most of the time, you'll reduce the likelihood of disease.

* Give them their space. Locate houseplants so there's ample air circulation to help prevent powdery mildew. When you group susceptible plants such as begonias, African violets, or grape ivies too close together, not only are they more likely to develop mildew, but reproductive spores (that powdery white stuff) are more easily spread among them.

* Keep houseplants indoors, year-round. We know that plants will put on lots of new growth when they spend the summer months outdoors on a porch or in the yard, beneath a shade tree. The obvious downside, however, is that they're exposed to large numbers of insect pests which may hitch a ride indoors with them in autumn.

If you decide the added growth is worth the gamble, you can limit your risk by hosing down your houseplants several times over the summer. Be particularly careful to direct water upwards towards leaf undersides; rainfall will help take care of upper surfaces. You'll also have to wash houseplants thoroughly before bringing them back inside. Even then, it's a good idea to isolate those plants for several weeks from others that stayed indoors -- just in case some insect or mite eggs hatch out indoors, and you need to wash them once more.

Here's a short list of some of the sturdy houseplants I've been able to grow easily, with no insect or disease problems:

Chinese evergreen	Aglaonema species
Christmas cactus	Schlumbergera bridgesii
Crown-of-thorns	Euphorbia milii 'Somona'
Dallas fern	Nephrolepis exaltata 'Dallasii'
dwarf schefflera	Heptapleurum arboricola
heart-leaf philodendron	Philodendron scandens oxycardium
moth orchid	Phalaenopsis hybrids
ovalleaf peperomia	Peperomia obtusifolia
pothos	Epipremnum aureum
rubber tree	Ficus elastica 'Decora'
snake plant and its relatives	Sansevieria species
squirrel's foot fern	Davallia mariesii
West Indian holly	Leea coccinea

Making Sure Your Christmas Cactus Blooms
Deborah Brown, Extension Horticulturist

Christmas cactus. Photo credit: Deb Brown

If you want your Christmas cactus to bloom close to the holiday season, you may need to manipulate its environment in October and November. These plants bloom in response to short days and cool nights; when night temperatures are low enough, you needn't be concerned about daylength at all.

If you left your Christmas cactus outdoors till night temperatures dropped into the mid-thirties, its flower buds may be "set" already. All that's needed is a sunny window in a room that's a little cooler at night than it is during the day.

When your plant has not been outdoors, grow it in a sunny window, but make sure it gets cold enough every night. You might have to put it in the basement or attic if your home is fairly warm at night. Night temperatures of 55 degrees or less should result in blooms within six weeks. As soon as you see flower buds developing, you may discontinue the cold night treatment.

If your room only drops to 60 or 65 degrees at night, you need to cover the cactus or put it in a dark closet for at least 12 hours each night to trigger blooming. Unfortunately, if your home is really warm at night, 70 degrees or more, it's unlikely you'll get any flowers even if you do cover the plant.... except, maybe close to a cold window.

Christmas cacti are not desert plants; they're epiphytic plants native to humid tropical forests. It's especially important not to let them dry too much when they're in bud or blooming. (Epiphytes are supported by or cling to trees. They're not parasitic, though, and do not "feed" off the trees. Many bromeliads and orchids are also epiphytic.)

Minnesota Apples for Storing
Deborah Brown, Extension Horticulturist
Early this month you can still find wonderful Minnesota grown and developed apples to store in an extra fridge or a cool spot in your basement for months of delicious eating. Look for late-maturing varieties such as Fireside or it's cosmetically more attractive relative Connell Red, Keepsake, Prairie Spy, or Regent. They can last through March. Honeygold and Haralson will last almost as long, provided they're stored cool enough.

If you've been invited to a friend or relative's home for Thanksgiving, why not bring an inexpensive wicker basket filled with Minnesota apples, as a hostess gift? It's sure to be appreciated. Another good idea? How about a copy of the Minnesota Gardening calendar for the year 2000? Find it at garden centers, gift and book stores, or call the University to have it mailed out: 612-624-4900 or 1-800-876-8636, outside the metro area.



Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/Plpa.htm
Armillaria Root Rot
Chad Behrendt, Extension Plant Pathologist

Armillaria mushrooms

Rhizomorphs appear as blackened area.

White mycelia under apple bark. "White bark" is actually sap exudate. Photos credit: U of Mn Dept. of Plant Pathology>

Armillaria is one of the most common root rot fungi known to attack woody plants. Although armillaria can infect hundreds of plants, including a variety of non-woody plants, it most frequently occurs on trees. Forest, shade, and fruit trees of all ages (seedlings to overmature) are infected. Many different species of armillaria attack trees. These species vary in their pathogenicity.

Armillaria species found in the eastern portion of the Unites States are usually considered secondary pathogens, while species of armillaria in the western United States are primarily pathogenic. In Minnesota, armillaria is generally considered a secondary pathogen, which infects stressed and overmature plants. Plants suffering from drought stress, improper planting, insect damage, or other pathogens are most susceptible. However, armillaria also attacks trees planted outside of their natural range or trees on unsuitable sites, as a primary pathogen.

Armillaria is commonly found as a decomposer (saprophyte) in the soil. The saprophytic nature of this fungus is beneficial to the environment, since it converts organic matter into required nutrients. The ability of armillaria to colonize woody debris allows it to persist in the soil for extended periods of time. Stumps, downed trees, fallen branches, and all other forms of woody debris can be colonized by armillaria.

Specialized forms of the fungus called rhizomorphs allow armillaria to move through the soil. These black, round, threadlike structures are commonly called shoestrings, thus the common name "shoe-string fungus". As rhizomorphs move through the soil, they search for new resources. If they encounter dying or stressed root systems, they infect and begin to colonize. Often, armillaria will remain inactive on the root system of slightly stressed trees until the tree is unable to defend itself.

Since armillaria attacks the roots, lower trunk, and root collar, symptoms usually develop in the upper canopy of the tree. General decline, small yellow leaves, reduced growth, and dieback are all symptoms of armillaria infection. Once armillaria has thoroughly colonized the woody material, it produces clusters of honey colored mushrooms near the base of the plant. Mushrooms produced in the fall release spores that are wind blown to other woody plants. Although these spores cause new infections, rhizomorphs are more effective at starting new infections.

To diagnose armillaria accurately, examine the lower trunk, root collar, and roots for rhizomorphs and white, fan-shaped masses of fungal material called mycelium. These structures can be found below the bark near the base of the trunk, while rhizomorphs can also be found in the soil and on the roots. Finally, examine the base of the tree for mushrooms in the fall.

Controlling armillaria is very difficult and often not possible. To reduce the risk of infection maintain tree health through proper watering, fertilizing, and mulching. If armillaria is present, remove as much of the woody material as possible before replanting to help reduce the volume of fungal material. Plant trees on suitable sites and avoid stressful conditions.

Nectria Canker of Shade Trees
Chad Behrendt, Extension Plant Pathologist

Perithecia. Photo credit: Plant Disease Clinic.

Cylindrical canker. Photo credit: Chad Behrendt

Nectria canker, a common disease of shade trees, is usually most visible in the fall after leaf drop. This disease, caused by the fungus Nectria galligena, infects a variety of trees including apple, birch, basswood, elm, locust, maple, oak, walnut, and others. Nectria typically causes a sunken canker on the branches or main stem (trunk) of the tree. Cankers occurring on the trunk weaken the tree making it vulnerable to wind throw. As a result, most urban shade trees infected by nectria are considered hazardous and need to be removed.

Spores produced on infected trees enter healthy trees through leaf scars, cracks in the bark, environmental injuries, and mechanical wounds. Infection can occur at anytime during the growing season when moisture is available and the temperature is above freezing. Spores are produced in two types of reproductive structures, sporodochia and perithecia. Sporodochia usually form in early spring and appear as small creamy white drops, while perithecia form in the fall and appear as small red-orange pincushions.

Once the fungus enters the tree, a canker begins to form. Initially small, darkened lesions develop in the young bark. Expansion of these lesions is disrupted as the tree produces a callus layer (ridge). At this point, healthy vigorous trees successfully enclose the fungus and inhibit any further growth, while stressed trees often become reinfected the following season. This cyclic process can continue year after year forming a circular target shaped canker. As a result, first year cankers often go unnoticed, while older cankers are easily identified by their concentric callus layers and sunken appearance.

Severe infections may cause branch dieback, as cankers girdle young branches. Cankers rarely kill trees outright, but do cause trees to fail at the point of infection during strong winds. Curing existing infections is not possible. To prevent initial infections avoid wounding, plant trees on the proper site, and maintain tree vigor.

Stored Food Product Insects
Jeffrey Hahn, Assistant Extension Entomologist

Indian Meal Moth. Photo credit: Clemson University Extension Service

Red flour beetle. Photo credit: U of M Entomology Dept.

There are several insects that are common pests in stored food products in our homes. They infest many types of dry food items, including cereal, macaroni and other pasta, cake mixes, pancake mixes and similar products, raisins and other dried fruits, chocolate, nuts, and spices. They also commonly infest dry pet food and bird seed. Some of these pantry pests may even infest nonfood items such as mice baits, animal carcasses, and dry plant displays.

The most common of these pests are Indianmeal moths, red flour beetles, sawtoothed grain beetles, cigarette beetles, drugstore beetles. Finding a steady number of these insects, especially in the kitchen, is evidence of a problem. Sometimes, the first sign of an infestation is finding insects and or webbing in a food package. If you find Indianmeal moth larvae, small whitish caterpillars,crawling on walls or ceilings, this also indicate a pantry pest problem.

Sanitation is the best control. First, check all potentially susceptible food for insects (and in the case of Indianmeal moths, their webbing). When you discover infested products, wrap it in plastic and throw it away. You can save bird seed or pet food (or lightly infested food products), by freezing them at 0^o F. for at least four days. You should automatically freeze unopened food packages older than 60 days, even if insects haven't been seen.

Store susceptible, insect-free food in containers with tight lids, such as glass jars or heavy plastic containers. You can also store products in the refrigerator. Do this especially for items that are used infrequently. It is less important to do this for food that is eaten on a regular basis.

Remove crumbs or spilled food to reduce the potential food sources for pantry pests. Check spice drawers, toasters, cupboards and other places where crumbs accumulate. Disinfecting counters and other places doesn't effect these insects.

Insecticides are not practical or necessary. You can't spray insects in food without contaminating the product. Spraying insects found out in the open does not eliminate the pests if a food source is present. If infested food is thrown away and uninfested food is properly stored, the cycle is broken and the problem eventually goes away on its own.

Although you may find some moths or beetles after you have cleaned up, that doesn't automatically mean there is an infestation. Particularly for Indianmeal moths, they often pupate outside of infested containers. Moths or beetles may be seen up to four to five weeks without an infestation being present. However, if the problem persists longer, keep looking for an additional food source(s).

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/Ent.htm
Winter Tree Protection
Deborah Brown, Extension Horticulturist

Protecting evergreens from winter. Illustration: MN Extension Service.

There's been some confusion lately, about the advisability of wrapping young, thin-barked trees for winter. The International Association of Arboriculture has said wrapping trunks tightly with paper tree wrap is not a good idea because A) it is not particularly effective at preventing sunscald, and B) people usually leave it on too long, which means there is moisture trapped between the wrap and the trunk, resulting in rotting and potential insect problems.

There are some ways to protect thin-barked, immature trees that won't jeopardize their health, however. You can use a plastic tree guard that looks like a big tube, sliced vertically down one side to allow it to fit around the trunk. The tube must be several inches wider than the tree trunk to allow for good air circulation around the bark. Though somewhat unsightly, most people leave these guards on year-round so they can serve double duty. Besides shielding the trunks from winter sun, they protect them from careless weed whacking and lawn mowing.

Another option is using twine to tie a length of two by four or similar piece of lumber to the south or southwest side of the tree each October or November. This surely does not add to the aesthetic appeal of any landscape, but it does serve to reflect sunlight and keep it from heating that south/southwest side of the trunk that's most at risk for sunscald from repeated expansion and contraction of cells each winter. Of course, you'll want to take the boards off in spring, but they can be stored easily and reused for years until trees develop a rougher, corky textured bark that needs no further protection.

If the trees in question are fruit trees, or you're concerned with rabbits, deer, and other critters, by all means protect young trees until they've grown a corky bark. However, the protection, again, should be a rigid tube or hard plastic band that spirals around the trunk -- or better, yet, a cylinder made of hardware cloth -- not thin paper tree wrap.

Editorial Notes

Miscanthus at Arboretum Photo credit: Beth Jarvis

Hard frosts have leveled tender landscape plants but grasses continue to provide visual interest. This shot was taken at the University of Minnesota Landscape Arboretum on Oct 1.

In the Dec. 1 issue, Patrick Weicherding, Anoka Co. Hort. educator, will discuss pruning overgrown, mature trees. They're never more obvious than when leafless!!

Looking ahead into 2000, we'll be presenting information on selecting apple trees by rootstock, new blueberry varieties, the latest in the potato field and an article on plants that provide color in the shade. I'm also looking forward to presenting the Douglas Co. Master Gardeners' research on using sandwich bags over developing apples to reduce the need for sprays.

We publish the Yard & Garden Line News twice a month during the gardening season, on the first and 15th of the month. October through March, we publish monthly, on the first.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

If you have gardening questions, please call the Yard & Garden Line at (612) 624-4771.

Deb Brownanswers gardening questions on Minnesota Public Radio's MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

Previous Page
University of Minnesota Extension Service Home Page
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request.  Please contact your University of Minnesota county extension office or, outside of Minnesota, contact the Distribution Center at (612) 625-8173.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.