|Yard & Garden Line News
Volume 6 Number 7 May 15, 2004
Tree Cavities: To Fill Or Not To Fill?
Patrick Weicherding, Regional Extension Educator, Natural Resources and Environment
A tree cavity is similar to a cavity in your tooth. Without proper treatment, the situation will only get worse. Unfortunately, cutting down on sweets and brushing regularly will not help to prevent a tree cavity.
Large residential oak with cavity that was filled with concrete and painted brown to match the tree. Note the small tree growing out of the concrete!
In simple terms, a cavity in a tree is a neglected bark injury that can be the result of many factors. The most common are improper pruning, mechanical injury and storm damage. Storm damage and injury from gnawing animals and landscape equipment (lawnmowers and string trimmers) contribute to bark injury by tearing the bark from the tree trunk or branch. When bark injury has occurred, the exposed sapwood or heartwood is more susceptible to attack by fungi that initiate the decay process. Insects and animals such as raccoons, woodpeckers and squirrels that inhabit tree cavities utilize the tree wound as the front door to their new home. Carpenter ants, in particular, will excavate tunnels throughout the decayed portion of the tree and excrete wood preserving enzymes as they do so. While these preservatives are beneficial to the tree, the tunnels the ants create allow water to accumulate. Excess water simply facilitates the wood rotting process.
In the past, tree cavities were filled with many different materials including cement, asphalt, masonry and even rocks and gravel. These cavity-filling techniques came to the United States from Europe after the turn of the century. In fact, in Europe having cavities filled in trees was sign of affluence. Only the very wealthy could afford such service for their trees. Today we know that these materials are very abrasive. Natural tree movements, such as swaying and twisting, rub the inside surface of the tree cavity against the filling, further weakening the tree's defensive walls and allowing decay to expand. In addition, we know that these materials do not allow the tree to bend and therefore renders the tree more susceptible to storm damage. Also, because of these tree movements the cavity-filling materials do not bond with wood. Gaps are often the result and these gaps frequently trap water. This dark and moist environment allows decay fungi to proliferate.
Many early "tree surgeons" used to drill holes in the tree into the bottom of the cavity in order to facilitate water removal. We now know that any cut, drilled hole or tube installed will cause more damage to the protective walls, which leads to further decay. Biologically, there is no reason to drain water from the cavity. Draining a cavity allows fast-growing, oxygen-requiring fungi to invade. Water-saturated wood has little oxygen present and is inhabited by slow-growing organisms.
Another more recent cavity treatment involved scraping out as much of the decayed wood as possible and then filling the cavity with a urethane or polyurethane foam to fill the hole. It was believed that when the foam expanded it would eliminate all the air in the cavity and prevent the accumulation of water. Besides, the foam was supposed to be flexible and move with the natural movement of the tree. What the advocates of this practice failed to remember is that the scraping action destroyed any protective barriers that were already in place further weakening the tree's defenses and allowing decay to expand.
So how is it some trees seems to flourish in spite of their cavity? When a tree is wounded, its uses a natural defense mechanism called "compartmentalization" to create both a physical and a chemical barrier between the wound wood and the rest of the tree. The exact nature of this barrier is not yet fully understood but is apparently is related to toxic phenols that are produced by the tree at the site of injury. These chemicals help the tree to establish boundaries that reduce the spread of pathogens to uninjured parts of the tree. Compartmentalization is under moderate to strong genetic control. And, the ability of microorganisms to compete successfully with others and to spread within the compartments is also under genetic control. As a result there is a lot of variation between different species of trees in how well they compartmentalize wounds. Trees like American basswood and littleleaf linden, boxelder and silver maple, aspen and birch, red and northern pin oak, and hackberry and willows are know as "poor" compartmentalizers. Rapid and extensive decay is common in these species.
How should trees with cavities be treated? Recent research shows that it is better to leave the cavity open - remember no type of drainage, sterilization, fill material, wound paint, or scraping treatment stops decay - and simply take the necessary measures required to improve the overall health of the tree. A healthy tree has the strength to compartmentalize and wall-off decay.
Managing Vegetable Diseases of the Home Garden
Janna Beckerman, Extension Plant Pathologist
Garden vegetables are perhaps the most popular summer garden plants, despite the fact that they are subject to numerous diseases. Preventing these diseases from occurring is the best management strategy available to ensure a healthy harvest. Try to implement these management strategies before reaching for a pesticide.
Disease resistant 'Sweet Million' still has healthy foliage, unlike its neighbor!
Some cultural practices that prevent and minimize diseases include:
· Choose a sunny, well drained site for the garden.
· Improve soil by adding compost and other organic amendments.
· Choose disease-resistant or disease-tolerant varieties if disease has been a past problem. A good publication on disease resistant varieties can be found at: http://www.cce.cornell.edu/programs/hort/gardening/factsheets/ecogardening/disresveg.html
· Use healthy transplants to prevent disease introductions in your garden.
· Water your garden in the morning to allow leaves to dry quickly, thereby preventing disease. Keeping the water on the roots by drip irrigation is the best available watering method. Do not irrigate gardens in the evening by overhead watering.
· Do not work in the garden when the foliage is wet. This prevents spreading certain pathogens like bacteria, nematodes and "water molds."
· Fertilize only to meet the needs of the plant, taking care to not over fertilize. Too much fertilizer, especially nitrogen, can predispose plants to disease.
· Scout! Check the garden regularly for weeds, insect and disease.
· Remove severely diseased plants during the growing season and do not compost them. Do not allow excess fruit and vegetables to rot in the garden.
· Manage insect pests that can vector viruses and bacteria.
· Control weeds that serve as sources for viral diseases
· At the end of the year, clean up all plant residues after the final harvest.
weeds serve as
water and nutrients with nearby plants.
· Practice crop rotation. Do not plant the same vegetable in the same location more than two times in three years.
Despite your best efforts, diseases can and do occur. If the above strategies haven't successfully reduced disease pressures in previous years, then it's time to consider the use of chemicals to control disease problems before they start.
The biggest mistake gardeners make is that they begin a spray program after the disease problem has become severe. Although environmental conditions can change over time, plant diseases do not "get better," any more than plants "heal." It is important to understand that fungicides work to prevent disease-similar to a vaccine in a person. They do not work like a drug, or silver bullet, to "cure" a problem after it has become established. In order to effectively use a fungicide, you need to make sure the plant is sprayed to prevent disease from occurring.
o Begin researching a fungicide spray program
o Is your diagnosis correct? Incorrect diagnosis is the leading cause of failed chemical management.
o When spraying, focus on disease prevention rather than "curing" infected plants. Improper timing is the second most common reason fungicides fail to control disease problems.
· Always read the label before applying any pesticide. Follow the instructions and restrictions. Do not use any chemical when temperatures are above 85 degrees F, or under windy conditions. Note any restrictions and the time interval between application and harvest.
|Table I. Fungicides labeled for disease management in backyard vegetable gardens. |
|Active Ingredient >
||Ortho Multi Purpose Fungicide, Dragon Daconil 2787, Ferti-lome Liquid Fungicide, Security Fungi-Gard, Pennington Multi-Purpose Fungicide
Bonide Liquid Copper Fungicide, Acme Copper Fungicide, Acme Bordeaux Mixture, Dragon Tomato & Vegetable Dust, HiYield Copper Fungicide
||Orthocide Garden Fungicide, Bonide Captan, Green Up Captan Garden Spray
Bonide Manzate Flowable, Acme Tomato, Fruit & Vegetable Fungicide, Dragon Mancozeb Disease Control, Green Light Maneb Plus
|| Maneb Tomato & Vegetable Fungicide
||Garden Sulfur Dust, Bonide Sulfur Plant Fungicide, Bonide Liquid Sulfur , Ferti-lome Rose, Flower & Vegetable Dust, Green Light Wettable Dusting Sulfur, Safer Garden Fungicide
|* denotes accepted organic fungicide.|
Blacklegged Tick Reminder
Jeff Hahn, Assistant Extension Entomologist
We are fully into tick season now. Of the 13 or so species that occur in Minnesota, you are most likely to encounter one of two species. The first is the American dog tick, also know to many as the wood tick. Fortunately, this is not an important disease carrier in Minnesota. It is known to vector Rocky Mountain Spotted fever in the U.S. but fortunately cases of this disease are extremely rare in Minnesota (an average of less than one case per year).
left; male on right.
The second commonly encountered tick is the blacklegged tick, known to many as the deer tick. This tick is a potential vector of Lyme disease as well as human granulocytic ehrlichiosis in Minnesota. Although the blacklegged tick has been active since temperatures rose above 39o F in March, the risk of disease starts to significantly increase as people spend more time outdoors.
Blacklegged ticks are found primarily in hardwood forests and adjacent grasslands and are particularly common where white-tailed deer are found. The areas of highest risk of Lyme disease in Minnesota are in the central and east regions of the state, especially in Cass, Crow Wing, Aitkin, Morrison, Mille Lacs, southern Carlton, Pine, Kanabec, Isanti, Chisago, Sherburne, Anoka, northern Ramsey, and Washington counties. High risk areas also includes northern Wabasha, Winona, and Houston counties. Human granulocytic ehrlichiosis is also found in the east and central areas of Minnesota.
Protect yourself when you are outside in areas know to be infested with blacklegged ticks. Walk on trails and avoid moving through grassy areas. Ticks are commonly found in tall grass and other vegetation and you increase your risk of ticks finding you by moving through such areas. Wear protective clothing, such as long-sleeved shirts and pants. Although it's not much of a fashion statement, tuck your pants into your socks if you want to prevent ticks from moving under them to maximize your protection.
Perhaps the single most effective measure to protect yourself from ticks is to use a repellent. Products that contain DEET (N,N-diethyl-meta-toluamide) can be applied to your clothes and exposed skin. It is not necessary to use high concentrations of DEET — there is no evidence that increasing percentages are more effective. Do not use products containing more than 15% DEET on children. Another excellent repellent is permethrin, e.g. Permanone. Apply this repellent only to clothing. Do not overapply repellents!
Be sure to check yourself for ticks after you have been in tick-infested areas. This is especially important during summer when immature blacklegged ticks are active. Because of their very small size, nymphs can be easily overlooked. If you find a tick but it is not biting, there is no risk of disease transmission. Blacklegged ticks can only vector disease to its hosts through bites. In fact, it takes about 36 hours while the tick is feeding before the Lyme disease spirochetes are passed on to its host. The more quickly ticks are discovered and removed, the lower your risk of contracting Lyme disease becomes.
If you do find a tick that is attached to your skin, carefully remove it with tweezers. Grasp it around the head as close to the skin as possible and gently yet firmly pull it out. Home remedies such as covering the tick with vaseline or touching it with a lit match do not cause the tick to voluntarily detach itself. Save any ticks that are found biting so an expert can identify them later. Different stages of American dog ticks and other ticks can also be found. Only blacklegged ticks are known vectors of Lyme disease and human granulocytic ehrlichiosis.
Tick bite bull's eye
Symptoms at the onset of Lyme disease can include but are not limited to a red skin lesion with a clear center (bull's eye rash), malaise, fatigue, chills, fever, headache, myalgia (muscle pain), sore throat, nausea, or vomiting. Arthritis can develop several days to a month later. The bull's-eye lesion will not be experienced everyone -- only about 60% - 80% of adults and 50% of children will exhibit this rash.
Symptoms for human granulocytic ehrlichiosis are similar to Lyme disease and include fever, chills, headaches, muscles aches, nausea and vomiting.
People who think they may have contracted Lyme disease or human granulocytic ehrlichiosis should see a physician. Both diseases are very treatable, especially when diagnosed early.
Cicadas in Minnesota
Jeff Hahn, Assistant Extension Entomologist
Note: Some of the information in this article was found at the Cicada Watch: 2004 web site, http://www.msj.edu/cicada/, maintained by Gene Kritsky and Jessee Smith.
There has been a lot of discussion about the emergence of periodical cicadas in the eastern United States this spring. This insect species is fascinating because it takes 17 years to complete its life cycle and then emerges in synchrony with each other. A group of cicadas that emerge in a given year and certain geographic area is referred to as a brood. In 2004, brood X is emerging, the largest of the known 13 broods. The last time this brood emerged was in 1987. They will be seen this year in Kentucky, Tennessee, Virginia, West Virginia, Illinois, Indiana, Ohio, Michigan, Pennsylvania, New Jersey, Maryland, and Delaware (see map).
A periodical cicada is easy to recognize. It has a stout black body that is about inch in length. It has amber colored wings with orange veins that are folded over its back which extends about 1/2 inch beyond the abdomen. A periodical cicada also has red eyes.
Cicadas lay eggs in the twigs of trees and shrubs. When they hatch, the drop to the ground and burrow into the soil where they find roots to feed. Periodical cicada nymphs remain in the ground for the next 17 years. In the spring of the 17th year, the nymphs tunnel up to the surface. Sometimes they also construct small mud towers over these emerge holes. Once ground temperatures reach 64o F in mid to late May, periodical cicadas will begin to emerge. The numbers will peak in late May to early June.
In addition to the tremendous numbers that occur, periodical cicadas are very conspicuous from the sounds they produce. The males, using sound organs (tymbals) located on the sides of the base of their abdomen, produce loud, potentially deafening, sounds when they chorus and attract females. Adult cicadas survive until the end of June. Although they may be annoying to people, they are harmless to us.
Distribution of Brood X
Gene Kritsky and Jessee Smith
So when do periodical cicadas arrive in Minnesota? They actually don't occur here. We do have cicadas in Minnesota but it is a different type know as a dogday or annual cicada. No one knows exactly how long it takes them to develop but it is probably in the four to eight year range. A big difference between these two types of cicadas is that the dogday cicada life cycle is not synchronized so we have cicadas emerging in Minnesota every year. Their emergence begins later than periodical cicadas, starting in July and August. You can recognize when they are present from the powerline-like sound they produce during the day in late summer.
An Urban Legend
Jeff Hahn, Assistant Extension Entomologist
What do you know about camel spiders? According to a story being circulated around the Internet, it is a pest that our soldiers have to endure in Iraq. The following is one version that you may read:
Two camel spiders.
From someone stationed in Baghdad. He was recently bitten by a camel spider which was hiding in his sleeping bag. I thought you'd like to see what a camel spider looks like. It'll give you a better idea of what our troops are dealing with. Enclosed is a picture of his friend holding up two spiders. Warning: not for the squeamish!
This picture is a perfect example of why you don't want to go to the desert. These are 2 of the biggest I've ever seen. With a vertical leap that would make a pro basketball player weep with envy (they have to be able to jump up on to a camels stomach after all), they latch on and inject you with a local anesthesia so you can't feel it feeding on you. They eat flesh, not just suck out your juices like a normal spider. I'm gona be having night mares after seeing this photo!
Additionally, these camel scorpions are said to be the size of a dinner plate and can run up to 25 m.p.h. while making a shrieking sound. They are reputed to eat the stomachs of camels from either the outside or the inside. Their worst trait is their ability to bite its victim, including humans, inject a venom which contains an anaesthesia which allows the camel spider to gnaw on its unsuspecting victim completely unaware. U.S. soldiers have been said to be wake up and discover huge hunks of their flesh missing as the result of camel spiders.
It sounds terrible but fortunately none of it is true.
In all fairness, there is such a creature as a camel spider. It also goes by the name wind spider, wind scorpion, or sun scorpion. Despite its name it is not a true spider but a related arachnid known as a solpugid (order Solifugae). They get the name camel spider because they are found in warm, desert regions, like a camel. There are camel spiders found in the U.S. in southwestern deserts although they are more likely to be referred to as wind scorpions. They are easily recognized by their large, strong chelicerae (mouthparts)
Camel spiders are relatively large but counting their legs they are closer to about five inches in size including the legs. In the U.S. they have a body length up to over an inch long. They are pretty quick for an invertebrate animal but do no move more than 10 m.p.h. They also do not jump and are silent when traveling.
Camel spiders are predaceous, feeding mostly on insects and other arthropods. It is possible for them to eat small lizards but nothing larger. They do not attack camel stomachs and they are harmless to humans.
It appears that someone used a camera angle to make the camel spiders appear larger than they really are. Some experts do not discount that the image does not show real arachnids (perhaps just rubber ones) or the image may have even been manipulated. U.S. citizens are facing dangers in Iraq but camels spiders are not one of them.
Get the low down on this month's insect pests at
Mid-May Garden Tips
Beth Jarvis, Yard & Garden Line
Compiled from conversations with David Hanson, Urban Forestry; Bob Mugaas and Bob Olson, Regional Extension Educators; and Deb Brown, Extension Horticulturist
Drought Update for May 15
Mark Seeley, Extension Climatologist, is prediciting we'll stay on the cool and damp side for the remainder of May. The threat of frost has greatly diminshed for the southern half of the state.
Much of the state received welcome rains earlier this month. (And Roseau received some unwelcome rain because it came all at once.) Southwest and west central Minnesota remain in severe drought, while much of the rest of the state still has an accumulated deficit from last year. To put the dent in the deficit, we would need 150% of normal rainfall from May through August. Average rainfall for May is 3.5-4". Many of us have received up to 2" so we need a continued pattern of regular rainfall to maintain plant health this summer.
(These recommendation are based on Twin Cities temperatures. Adjust for northern Minnesota..)
Trees and Shrubs
Are evergreen needles disappearing right before your eyes? Have you looked? This is prime time for various sawflies on coniferous trees such as pine and spruce. They looks like tiny caterpillars but eat their way to a larger size quickly. Read about them at: http://www.extension.umn.edu/distribution/horticulture/DG6703.html
While you're out there checking, look at your birch trees. Birch leaf miner, a largely harmless insect pest of birch trees is just starting. Too soon you'll see half- brown leaves, a clear sign that the miners have been busy munching inside the birch leaves. The damage is largely cosmetic, though.
Elm leaf miners are also going to be out feeding on tender elm leaves by the end of the month. They, too are of no concern.
Speaking of elms, if you see elm branch tips all over sidewalks, it's just the squirrels going after the seeds.
Now is a wonderful time to check your landscape trees for storm damage. First, look for broken branches then for cracks in the trunks of trees. Storm Damage to Landscape Trees: Prediction, Prevention, Treatment,
Trees that were tipped may not be salvageable. If the tree is under 25 tall and is less than 45 degree out of plumb, it might be saved. The displaced roots will have to be excavated, then the tree is straightened and the roots replanted. The final step is to stake and guy the tree.
If you're planting trees this spring, look up before you plant. What will the mature tree be growing up into? Consider the ultimate spread of the tree in relationship to not only power lines but buildings. Remember too that the roots can, in sandy soil, spread as much as three times the canopy.
Lastly, when spraying lawn weeds, remember that trees are broad leafed plants and can be injured by herbicide, also. Pay particular attention to where you apply herbicides containing dicamba–such as Trimec. Dicamba is absorbed by tree roots, unlike 2,4-D.
Speaking of weed control, there's still time to get pre-emergent hebicide down. In cooler, heavy (clay) soils, Memorial Day is still timely. For warmer, sandy soils, in the Twin Cities, mid May is the about the latest.
It's a fine time to fertilize lawns, if you wish. Just remember the Twin Cities metro area has a phosphorus ban unless the lawn is new or you have a soil test proving the need. In greater Minnesota, fertilizers with 3% or less of phosphorus is legal, unless you can prove the need or the lawn is new.
It's getting too late to seed now because the disturbed soils also give any resident crab grass seeds a chance to sprout.
It's still ok to core aerify your lawn. (Spiked shoes don't do a bit of good.)
Power raking, on the other hand, is best left until fall. The problem is twofold. First, power raking is very hard on the grass plants and they need time to recover before the summer temperatures blaze. Second, to effectively power rake, you need to cut the grass short. This time of year, we encourage folks to grow the grass long, to 2.5-3". Taller grasses keep the ground cooler and sheltered from drying wind plus taller tops encourage deeper roots.
Speaking of tall grass, cool season grasses are responding to warmer temperatures and longer days and are blooming and setting seed. This occurs at any grass height, so seed heads aren't an indication that you should be mowing your grass shorter. And, no, mulching the seeds back into the ground won't make a thicker lawn. The seeds are not ripe and will never germinate.
If you want to reseed in an area you've treated with a weed and feed or regular broadleaf herbicide, check the label for replanting info. The label is the lawn.
Mulch your vegetables. You don't need to put a thick layer just yet, as the soil hasn't completely
warmed. You want to put down enough to break the impact of the rain as spores of plant pathogenic fungi get splashed from soil up onto lower leaves of your veggies.
The cool temps of a few nights ago really slowed some plants down, some were permanently slowed. Wait a few more weeks to let the temps warm before piling on more mulch. But do mulch as it preserves soil moisture and deters weeds.
Let the soil around transplants settle in before spreading pre–emergents such as Preen (trifluralin). The granules can slip through cracks in uneven soil and wind up in the root zones of transplants, where they can cause damage.
Tomatoes need to be staked or caged. By the time many get to this task, the tomato plants are getting huge. To avoid accidentally running a stake through the roots. insert the stake now, then plant your tomatoes. You'll know where the roots are.
Pull weeds as the appear. Shallow cultivation with a sharp hoe prevents lots of weeds.
Look for long handled hoes, up to 8' long, to take some of the strain out of hoeing.
Pick off the strawberry blooms the first year. This helps the strawberries become established.
Keep covers handy in case it gets down near freezing again.
When selecting apples, you need 2 vaerieties. If your neighbors have even a crabapple, you'll get apples.
Pears are a trickier matter as far a pollenation requirementsare concerned. See: .
Stone fruits are even pickier about pollen sources. Read all about it at:.http://www.extension.umn.edu/distribution/horticulture/DG1125.html
Remember, a fruit trees ability to pollenize or to accept pollen from others is as important as other fruit tree traits. Select cultivars rather than settle for what's on sale.
Remember to snap off the seed pods when tulips are done blooming.
Pick drought tolerant annuals and perennials for your bulb bed, so you don't' have to water as much. Many bulbs originated in dry climates and rot while dormant in damp summer gardens. You could also lift the tulips and keep them in the basement over summer.
Pansies must be planted now, while it's still relatively cool, if you to enjoy them. Columbine and stocks also need to be planted in cooler soils.
*If you've been bothered by bunnies:
*Trails in grass are probably voles. For guidance, see:http://www.extension.umn.edu/projects/yardandgarden/AAMG/wildlife/voles.html
Mark Seeley's piece on weather and USDA zones was delayed due to a computer glitch. He'll be in the June 1 issue.
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.
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Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.
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