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Yard and Garden News

Have you ever seen a maple tree with a depressed round or elliptical area on the trunk or branch? The sunken area may look healthy and is typically covered in bark. It is simply depressed an inch or so into the trunk of the tree. Close examination of these trees, however, will reveal a pathogen slowly and quietly decaying the wood beneath the bark. This pathogen is a fungus named Eutypella parasitica and the disease it causes is commonly called Eutypella canker.

It is not known exactly how Eutypella parasitica infects trees, but it is believed to enter through wounded branches or dead branch stubs. Often at the center of a canker, the remains of a broken or poorly pruned branch can be seen. However it gets into the tree, the fungus makes itself at home underneath the bark. From there fungus can grow through bark and through wood. It kills the phloem (vascular cells that transport sugars from the leaves throughout the tree) the cambium (undeveloped cells that grow into new vascular cells) and can even invade and decay the sapwood of the tree. This decay can extend close to a foot into the tree and many trees infected with Eutypella canker break during strong storms and in high winds.

Maples and other species of the genus Acer are the primary hosts of Eutypella canker. Each year the tree will try to defend itself by creating a layer of cork and wound wood around the edge of the canker. Each year, when the tree goes dormant for the season, the fungus breaks into this barrier and continues its progress. This back and forth growth can continue for decades. In very old cankers where the bark has finally sloughed off, rings of growth can be seen that reflect this annual battle between fungus and tree.

Eutypella canker can be distinguished from other fungal cankers and wounds by looking for several things. First Eutypella is largely restricted to Maple trees and close relatives like Box Elder and Sycamore. The bark often sticks to the face of the canker in this disease and is darkened by black fungal fruiting bodies called perethecia that push through the bark to release spores in wet weather. Perethecia do not form until a canker is 6 to 8 years old. If the bark is pulled off at the edge of the canker, chalky white to tan colored mycelia (mats of fungal cells) can be seen. In very old cankers, the bark may finally fall off as the wood below decays. These things will provide a clear diagnosis of Eutypella parasitica.

Unfortunately not much can be done for trees infected with Eutypella parasitica. If a branch is infected, it should be pruned out and destroyed (the fungus can produce spores even on dead wood). Many infections occur on the main trunk of the tree within 10 ft of the ground. These infections cannot be pruned out but should be monitored. Because Eutypella parasitica is capable of causing wood decay, severely infected trees may be weakened and pose a risk of breaking and falling on property or people. A tree infected with Eutypella canker should be inspected by a certified arborist to assess its stability. The good news is that this is a very slow growing disease and many trees survive decades slowly battling this fungus before becoming a risk.

 

 

 

 

 

Despite the name this insect is actually a type of sawfly growing into a non-stinging wasp as an adult. There is a resemblance to this insect’s namesake, but if you look closely, you can see three pairs of true legs near the head and about seven or eight pairs of prolegs, i.e. false legs, on its abdomen. A roseslug is light green with an orangish head. Fully grown, it is only about 1/2 inch long.

Watch for roseslugs and their damage starting in mid to late May. They feed on one layer of the leaf, chewing between the veins. This type of damage is known as windowpane feeding. This injury will appear somewhat transparent at first but the damaged areas will eventually turn brown. The health of the rose is usually not at risk although the damage can affect the appearance.

Try to tolerate roseslugs whenever possible. If you would like to protect your roses from them, you have several options. You can physically remove these insects and throw them into a bucket of soapy water. If you would like to use an insecticide, consider insecticidal soap or spinosad. Both are effective and have a low impact to the environment. You can also use products with a longer residual, such as bifenthrin, esfenvalerate, or permethrin. Don't treat roseslugs if they are near 1/2 inch long as they are almost finished with their feeding.

 

Emerald ash borer is a very destructive insect pest of ash trees.  The larvae tunnel under the bark, girdling the trunk and branches, interrupting the flow of water and nutrients.  This injury first causes branch dieback in the upper crown before eventually killing the tree.  Emerald ash borer infested trees die fairly quickly; most trees are killed in three years.  No ash is safe from this insect.  All species are attacked, including green, black, and white ash.  Emerald ash borer attacks all sizes of trees from one inch diameter to large, mature ash and they’re not particular to what condition the trees are in as both healthy and unhealthy ash are killed.

This exotic borer, native to northern China and Korea, was first found in North American in southeast Michigan in June, 2002.  It has since spread to Ontario, Ohio, Indiana, Maryland, and, as of last summer, Illinois.  Experts estimate that this destructive beetle has already killed over 20 million ash trees, most of them being found in southeast Michigan.  On its own, emerald ash borer will only move about ½ mile a year from infested sites.  But with help from people, it can travel hundreds of miles when carried in firewood and other wood products or nursery stock.  It is because of humankind’s activities that emerald ash borer could have been inadvertently brought into Minnesota. 

Inspectors discovered in late April that firewood distributed by Taylors Wood Products had been brought inappropriately from Illinois into Minnesota and sold at various Menards stores. Ash wood cannot be moved from quarantine areas unless it has been treated or the bark has been removed (the emerald ash borer lives under the bark until it turns into an adult beetle). However, this firewood was brought into Minnesota with the bark intact.  Unfortunately, some of this firewood was sold before this was discovered.  Through media news releases, people that bought any Taylor wood were asked to burn this wood by May 4 to destroy any potential emerald ash borers.  Unsold firewood has since been removed and returned to Taylors Wood Products.

Nobody knows whether any emerald ash borers were actually brought into the state in this wood.  However, Minnesota risks a lot when this insect gets here.  There are about 870 million ash trees in Minnesota, one of the largest concentration of ash in any state in the country.  Not only is this type of tree abundant in our forests, but it is also an important component of our urban landscapes.  This insect will get here eventually but the longer we can forestall its entry to Minnesota the better chance we will have of adequately dealing with it when it does arrive.

What can people do to help?  First, don’t transport firewood when you go camping, even if it is within Minnesota.  Just buy the wood you need at a local site at the campgrounds. 

Also, be alert to what an emerald ash borer looks.  It is about 1/3 to ½ inch long, somewhat bullet-shaped and iridescent green.  Keep in mind that there are some common insects that look similar, such as sixspotted tiger beetles,  and Polydrusus weevils. 

Also be aware of the symptoms of an emerald ash borer infested tree.  Noticeable damage starts with thinning foliage and dieback in the crown.  Epicormic sprouts may also form on the trunk and some major branches. You may also see vertical splits in the bark, due to callus tissue forming over old galleries. If you remove bark on the trunk, you may find larval galleries, a series of criscrossing tunnels. 

If you see an insect in Minnesota that you think may be an emerald ash borer or you find an ash tree that has suddenly started to decline and die and you suspect borers, contact the Minnesota Department of Agriculture on their Arrest the Pests Hotline at 651‑201‑MOTH (6684) or 1‑888‑545‑MOTH (6684) to report it.  You can also report suspect insects or suspiciously dying trees to your local county extension office for identification. 

For more information about emerald ash borer go to the Minnesota Department of Agriculture’s site, (http://www.mda.state.mn.us/plants/pestmanagement/eab.htm).  You can also visit a national web page on this insect, http://emeraldashborer.info/.

And don’t forget, May 20 - 26 is emerald ash borer awareness week!

 

 

1.  With the warmer than normal temperatures lately and just a little bit of rain, southern and western exposure sites in the Twin Cities area are experiencing some early crabgrass germination. In those cases, a crabgrass killer containing the active ingredient dithiopyr could be used to give some control of those seedlings already poking their shoots through the soil.  However, once these seedlings produce two or three leaves, it is often too late for even this product to work effectively.  Dithiopyr will however help prevent other crabgrass seedlings from growing due to its preemergent herbicide activity, but not those already up and beyond the two or three leaf stage. In many other locations where crabgrass germination has not begun, crabgrass preventer could still be put down within the next week to 10 days.  Remember it is important to apply about ¼ to ½ inch of water following the application such that it gets down to the soil surface where it is active on those tiny crabgrass seedlings.  This would be true for all preemergent crabgrass preventers.

2.  While not a good time of year for seeding, if it is necessary to repair damaged lawn areas, the use of a preemergent herbicide known as siduron (trade name Tupersan) can provide some short term protection from annual weedy grass invasion.  This product is the only preemergent herbicide that can be used at the time of cool season lawn grass seeding.  A commercially available product known as quinclorac (Trade name Drive) can also be used as a postemergent herbicide in newly seeded areas for annual weedy grass control.  However, there are some specific use guidelines that must be followed in order to avoid injury to desirable lawn grass seedlings and would only be available through a commercial lawn service.  A much better time for lawn grass seeding would be in the middle of August to mid September as crabgrass and other weedy warm season grass seed germination is past for the year and weed competition will naturally be less.

3.  If you are located in some of the drier areas of the state, some early spring watering will be beneficial.  It may not always be possible or a priority to water a lawn. However, because the grass is in a natural growth period at this time of year, providing some water will help minimize early season water stresses and provide for a healthier plant going into the warmer, drier periods of the growing season. 

4.  The first or second mowing is usually a good time to apply a spring fertilizer.  This will be especially true if there were no fall applications of fertilizer put down.  Grass plants require water and nutrients for healthy growth and vigor.  However, our soils often are unable to provide sufficient amounts of nutrients and moisture to sustain the active spring growth period making supplemental applications of both necessary.

5.  One of our most common lawn weeds, dandelion, is now in full bloom or even a little past in the Twin Cities area.  If there are only a few plants scattered around the yard, digging them out or “spot” treating them individually with one of the ready-to-use weed control products can be very effective and minimize the amount of herbicide introduced into the environment.  Where dandelion populations have gotten to be very large and cover much of the yard, treating the entire area with a separate broadleaf herbicide or “weed-and-feed” product for broadleaf weed control may be the most efficient strategy.  Remember, one should not depend on annual applications of an herbicide to keep lawn weeds under control.  Make necessary adjustments in your cultural practices and perhaps do a little overseeding to encourage a healthy, dense lawn.  That in it self will provide some weed control thereby minimizing or even eliminating future herbicide applications.

6.  Mowing heights should be at about 2.5 to 3.0 inches.  This will encourage deeper rooting and provide the plant greater access to soil moisture and nutrients.  This same height can be maintained throughout the summer months as well.

7.  Late May and into June is the flowering period for our cool season grasses.  In lawns, we are almost always mowing off the flower stems and hence they are rarely evident.  It is very common and natural to see grass flower stems forming and growing.  It is not a sign of poor cultural practices or a new, weedy grass that has invaded you lawn.  There is no need for any type of control practice to be done.

The information provided in this article is for educational purposes only.  Reference to commercial products or trade names does not imply endorsement by the University of Minnesota Extension nor is criticism or bias implied of those products not mentioned.

 

 

Pines have a very different growth pattern than spruce, fir, hemlock, and most other conifers.  Because of this, careful consideration must be made when we prune them in order to not have compromised, dying branches unable to generate new growth in subsequent years.  Northern-adapted pines typically have vegetative buds only at the terminal of each season’s growth.  Within the terminal buds in early spring are the beginnings of all the needles that will emerge that season as well as developing young terminal buds that will develop at the tip of that stem and give rise to growth the subsequent season.

As the terminal bud grows it develops into a soft and quickly elongating stem called a candle.  Short, quickly expanding needles along the candle length are grouped together on the main stem in bundles of 2, 3, or 5 called fascicles.  The number of needles in a fascicle depends on the tree species.  For instance, mugo, red, and Scots pines typically have two needles per fascicle, ponderosa pine has three, and Eastern white or Swiss stone pines have five.  Although the number of fascicles for the current season’s growth is already determined before the season starts, the length the candle expands to as well as exactly how long each needle becomes is strongly dependant on environmental conditions.  If water and nutrients are abundant, the candle and needles will become longer and thicker.  However, if the plant is under stress the candles and needles will likely be shorter resulting in the needles being closer together. 

Most people choose to grow pines that grow into trees and use them as specimens or windbreaks in the landscape.  Pines grown as trees in the landscape are seldom pruned except to limb up lower branches.  Some pines such as mugo pine or dwarf or weeping mutations of standard pine species can be grown in confined spaces where compact, dense growth is desirable.  In order to maintain a compact, dense plant form, careful pruning to encourage greater branching and shorter stems from each season’s growth is beneficial.  However, pruning needs to be done early in the season (typically mid May) by breaking soft elongating candles (typically one half to two thirds their length) and not later on when new growth is fully expanded.  Candles can be carefully sheared or even just pinched back by hand.

Shearing a pine after the needles have fully expanded and a strong terminal bud has developed for the following season’s growth can be disastrous.  Cutting stem tissue and removing the terminal buds will remove the potential for future growth on those stems. Eventually the old needles will fall off leaving dying stems without the ability to generate new growth. 

The key to early season pruning of expanding candles being successful is the fact that new terminal buds for the following season’s growth are capable of forming within fascicles near the cut end at this time.  By late summer the developing terminal buds for the following season’s growth can be clearly seen within fascicles at the tip of pruned candles.  The reason new terminal buds can develop on cut candles relies on the structure of fascicles. 

Fascicles are very short side branches and actually are condensed stem tissue possessing a distinct number of leaves (needles) typical for the species.  The tip of the condensed stem making up the fascicle has a terminal growing point. However, by early to mid summer the growing point within the fascicle loses its growth potential.   Hormones from the terminal bud of the elongating candles suppress the development of the growing points within the developing fascicles below until they eventually abort.  However, if the candle is broken and the hormone source is removed, the suppression is released and the growing points within the uppermost fascicles close to the cut end can develop into strong terminal buds.  New, developing terminal buds within the uppermost fascicles can then in turn suppress the development of the growing points in the fascicles beneath them.

Additional information:

• During the first year of life for seedlings of most pine species they look quite different because they do not have fascicles.  For the first season of growth there are typically individual needles attached directly to the stem tissue.  It is easy to confuse first year pine seedlings with young spruce seedlings.  In the second season and beyond, fascicles develop with the appropriate number of needles per fascicle for the species.  
• Pines are unique compared to other conifers like spruce, larch, and fir in that pines have fascicles and their cones take two seasons to mature.  These other genera do not have fascicles and have cones that mature in a single season.
• Since it is difficult to root cuttings of many species of pine, most cultivars (weeping mutations, forms with golden foliage, etc.) are grafted.  However, fascicles can be used to vegetatively propagate superior clones of pine.  Under controlled conditions and typically the use of hydroponics, fascicles can be rooted as small cuttings.  They often root at higher rates than standard, terminal stem cuttings having a few inches of stem tissue.  The key to success is to have fully expanded fascicles with a well-developed terminal bud within it, a hydroponics system with the appropriate nutrients, and patience to wait a few months or more until rooting begins.  Expanded fascicles with a developing terminal bud can be collected in mid summer off of stems having candles that were pruned in May.  In addition, careful use of the hormone cytokinin can help promote bud development on fascicles and prevent growing points from aborting.  The research team I was a part of at the USDA Forest Service used this technique to generate additional plants of elite Eastern White Pine clones because we didn’t want to complicate our experiments by introducing the variable of grafting and rootstocks.  This technique has the potential to be used more widely, especially when trying to mass propagate new, high-demand cultivars.

 

 

May is an excellent time for buying and planting container-grown trees and shrubs. Many different species and cultivars are available in a range of sizes. Here are some tips for selection and planting:

• Bigger isn’t always better. It’s tempting to buy the largest plant in the group, but an oversized plant in a small pot may indicate that the plant has been in the container too long. If in doubt, use the next tip.

• Show me the roots.  A good container-grown plant will have a dense root system that spreads throughout the potting medium in the container but is not root-bound (roots cramped, tangled, and circling around the bottom of the container). Roots should look healthy and show white, growing tips. Ask a garden center employee to slide the rootball out of the pot so you can take a look.

• Keep it healthy. Keep your newly purchased plant in good condition until you can plant it. Don’t leave container plants in a closed car for very long - the heat can wilt or even cook the plants. Keep the pots well-watered at home - they usually require daily watering to keep the porous potting mixture moist. Don’t leave the pot in standing water, either.

• Plant it right. Research shows that proper planting depth is critical to the long-term health of plants, especially for large trees.  Prepare your planting site by loosening the soil in a large area, ideally about 5 times as wide as the container. Dig the planting hole 2 to 3 times wider than the container, but only as deep as the rootball. Sometimes container-grown plants end up with extra potting mix piled over the primary roots - if this is the case, gently remove potting mix down to the first main roots. When planting, make sure the first roots are at soil level.

• Just add water. There’s usually no need for adding fertilizer when planting container-grown trees and shrubs, but do water them thoroughly. It’s very important to continue watering newly planted trees and shrubs until their roots become established in the soil. Container potting mix will dry out faster than the surrounding soil so be sure to look at the area closest to the plant when checking soil moisture. To help hold moisture, surround your new plant with a large circle of organic mulch (wood or bark chips, shredded leaves, etc.) applied 2 to 3 inches deep.

 

 

Lifting and carrying are part of most spring cleaning and gardening projects.  If you lift and carry the wrong way, you can damage your back. Back injuries may be difficult to treat and may have lengthy and expensive rehabilitation times. Make an effort to take care of your back to help keep it strong and healthy.

• Start each day with slow stretches. Warm-up stretches let you ease comfortably into your workday and help you avoid injuries.
• Size up the load – tip it on its side to see if you can carry it comfortably.  Get help if the load is too big or bulky for one person.  Check for nails, splinters, rough strapping and sharp edges. Large containers, root balls, and other garden and landscaping items can be quite heavy - use wheeled carts to help move large items.
• Lift it right – make sure your footing is solid.  Keep your back straight, with no curving or slouching.  Center your body over your feet, get a good grip on the object and pull it close to you.  Pull your stomach in firmly.  Lift with your legs, not your back; if you need to turn, move your feet and don’t twist your back.

 

 

Primary sprays for apple scab can be stopped after petals fall from the tree. At this point if the tree has no or few leaf spots, spraying should be unnecessary for the rest of the season. Trees with many leaf spots may need future sprays to protect leaves and fruit.

Start monitoring roses for black spot. Developing leaves are very susceptible when moisture is high and temperatures are between 64 and 79°F. Rake up last years leaves and prune out any stem infections to reduce the amount of fungus in the garden. Protective fungicide sprays can be used once the first spots appear or when conditions are favorable for disease.

Trees suffering from Rhizosphaera needle cast should be sprayed with Chlorothalonil when new needles are half their mature length. Severely infected trees may require a second spray.

Always read and follow all label instructions when applying pesticides.

 

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Back issues Yard & Garden Line News for the past nine years are online at http://www.extension.umn.edu/projects/yardandgarden/ygline-news.html.

Deb Brown will answer gardening questions as a recurring guest on the Midmorning show on MPR. The program 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.

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Happy gardening!

Nancy Rose
Editor
Regional Extension Educator - Horticulture

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