Yard & Garden Line News Volume 3 Number 6                                                               May 1, 2001

Features this issue: Special Trips for Moms who Garden Spring Means Home Fruit Questions April Showers Bring May Pathogens Plotting to Infiltrate? Try Rain Gardens Soluble Salts Birch Leafminers Editorial Notes

Special Trips for Moms who Garden
Deborah Brown, Extension Horticulturist

Crabapples in full bloom at Arb. Photo credit: Beth Jarvis

Minnesota Landscape Arboretum
Next Sunday, May 13th is Mother's Day. While ads proclaim no end of suggestions for appropriate gifts, people whose moms love gardens and gardening enjoy a distinct advantage. Not only does Mother's Day coincide with the beginning of our outdoor gardening season in the Twin Cities, it's a time when flowering trees and shrubs are often in their glory.

Why not go on a special outing to celebrate the holiday? Depending on the warmth of our early May weather (my fingers are crossed as I write this), a trip to the Minnesota Landscape Arboretum on Mother's Day may find you surrounded by redbuds, crabapples or lilacs in full bloom. Even if they're not blooming, spring bulbs and wildflowers will be sure to put on a lovely display.

In fact, there's a special program about wildflowers, featuring Evelyn Moyle, author of Minnesota Wildflowers, and flower photographer John Gregor who will present a slide show in the auditorium. They will also lead a tour through the Dayton wildflower garden, and sign books. The program is free with paid admission to the Arboretum.

It's fun to eat lunch at the Arboretum's sun-filled tea room, then stroll along paths planted with spring-flowering bulbs, pansies and early perennials. You can also bring a picnic lunch, if you're so inclined. If you'd rather not walk very far, hop aboard the "Trumpet Creeper" tram for a guided tour of the grounds.

The Arboretum is located on highway 5 in Chanhassen, 9 miles west of highway 494. Admission is $5 for adults; children under the age of 18 are admitted free. Parking is plentiful, and also free. Hours are 8 am until sunset.

Japanese Garden at Como Park.

Eloise Butler woodland. Photos: Beth Jarvis

Como Park Conservatory
Another popular choice for an afternoon's outing is Como Conservatory, one of the true cultural (and horticultural) treasures of the Twin Cities. Most people who grew up in this area were introduced to Como as young school children on field trips, but the conservatory's appeal knows no age limits... and its displays change constantly.

Como Conservatory's sunken garden is a perennial favorite that attracts thousands of visitors with its dazzling combinations of flowering plants. It currently features azaleas, hydrangeas, fringed tulips, scented lilies and other spring blooms. Their heavenly fragrance, alone, will make your trip worthwhile. Recent renovation has removed some permanent shrubbery in the display area, leaving more space for plants, and allowing them to go directly into the ground, giving the room a look that's more "garden-like."

Tropical plants in the palm room have grown larger and more luxuriant than ever, now that discolored plexiglass windows have been replaced with tempered safety glass. And the Japanese Garden, located outdoors, just north of the conservatory will be open for the first time since last autumn.

You'll find Como Conservatory just east of the zoo in Como Park, about one mile east of the State Fairgrounds in St. Paul. It's open 10 am to 6 pm; admission is $1, ages 13 and up, 50 cents, senior citizens and children ages 6 to 12.

Eloise Butler Wildflower Garden
Another choice for moms whose taste runs to wildflowers: a trip to Eloise Butler Wildflower and Bird Sanctuary. You can walk along an interpretive trail that takes you through woodlands, bog and prairie habitats. Trilliums should be at their peak of bloom, but you'll see dozens of other delicate beauties, too. Be sure to wear sturdy walking shoes.

Eloise Butler Wildflower and Bird Sanctuary is open daily, 7:30 am until dusk. It's located in Minneapolis in Theodore Wirth Park, north of Highway 394 and south of Glenwood Avenue. Entrance to the garden drive is just off Theodore Wirth Parkway, less than a block south of Glenwood Avenue.

Spring Means Home Fruit Questions
Deborah Brown, Extension Horticulturist

Apple blossoms. Photo credit: Beth Jarvis

What a cool, late spring it's been in Minnesota! Despite our disappointing weather, gardeners from one end of the state to the other are raring to go. It might not be a great spring, but as we know all to well, it's the only one we're going to get this year.

Of course, some concerns arise each spring, regardless of the weather. People are interested in growing fruit in their home landscapes, but there are some commonly held misconceptions we deal with every year at the Yard & Garden Clinic.

Often a caller wishes to plant an apple tree, but has heard you need two trees -- a male and a female -- to get fruit. This idea skirts around the edges of truth, but it's not quite there.

Apple trees are neither male nor female. Their flowers all contain both male and female parts, but they must be "fertilized" with pollen from a different apple or crabapple variety in order to develop fruit. That's why planting two trees of the same variety is no better than planting one; genetically speaking, the pollen is all the same. A bee moving pollen from flowers on one tree to flowers on the other simply doesn't cross-pollinate them.

When you live in a neighborhood where several other apple or crabapple trees grow nearby, you need only plant one tree. Bees will fly from yard to yard in search of flowers, if necessary. But if your home is isolated from others, or you know of no apple or crabapple trees nearby, you'd be better off planting two different apple varieties in your yard.

(If you haven't a lot of space, opt for two or more varieties of apples that have been grafted onto dwarfing rootstock. You can plant them much closer together than standard apple trees, they'll bear earlier, and they'll be easier to maintain because of their size.)

If you're thinking about planting apricots, pears or hybrid plums, the same rules apply as for apples. You may get a few fruits with one tree, but unless there's a different variety not too far away, you won't get many -- even though your tree may have been loaded with blossoms in spring. Don't look for dwarf varieties, though. Dwarf versions aren't hardy here unless they're "natural dwarfs" that are essentially very small-statured trees.

Blueberry. Photo credit: Beth Jarvis

While it's not absolutely necessary to grow more than one variety of half-high Minnesota blueberries, experience has shown that plants will be more productive if you put in at least two varieties, to allow for cross-pollination.

Some fruit-bearing plants DO have distinctly different males and females. Both males and females develop flowers each spring, but male flowers produce anthers and pollen, while female flowers contain a receptive stigma and an ovary that will become the fruit.

It's not unusual for someone to dig a wild grape vine from a cabin up north, then discover that it never produces fruit in its new location, down in the Cities. That's because even though the female vine has female flowers that are capable of bearing fruit, it needs a male nearby to provide the pollen to fertilize the flowers. One just won't reproduce (produce fruit) without the other.

The same holds true for kiwi vines and native bittersweet. (Hybrid grapes -- named varieties -- have both male and female flowers on the same plant, so getting pollen to the female flowers poses no problem.) Even mulberry trees, which pop up like weeds from seeds in bird-droppings, are typically exclusively male or female.

What fruits can you grow at home without any concern for the plants' sex or cross-pollination? Small fruit such as strawberries, raspberries, currants, and gooseberries are all self-fertile. So are sour pie cherries, 'Meteor' and 'Northstar'. (Unfortunately, we can't grow sweet cherries; they aren't hardy, even in the southern part of the state.) Nanking bush cherries are hardy throughout Minnesota, ripening in July. And in the southern third of the state, including the Metro area, you can grow and enjoy European plums such as 'Mount Royal' or 'Stanley'.

April Showers Bring May Pathogens
Janna Beckerman, Extension Plant Pathologist
Reviewed 2010 by Carl Rosen

Phytophthora. Photo credit: Tom Volk's fungus page (see below).

As we try to dry off and warm up from our wet, cool spring, there are certain fungi that are known to revel in these environmental conditions. These fungi, or more correctly, pseudofungi, are called "water molds" (Oomycota), even though they are really plants! Cool, wet weather, like we've been having, favors their growth, development and dissemination. Two culprits in particular, Phytophthora and Pythium spp. can wreak havoc not only on newly germinated seedlings but even well-established plants suffering from flood stress.

Phytophthora (L. "Plant Destroyer") spp. cause a variety diseases on seedlings of annual vegetables to ornamental shrubs and forest trees. The most famous Phytophthora disease, Potato Late Blight(See Fig. 1), was partly responsible for the death of approximately 1 million Irish, and the emigration of many more. Most species of Phytophthora cause root and crown rots, although aerial cankers are also part of their "modus operandi"(MO). Phytophthora thrives when soil becomes too wet for good growth of the susceptible plant, and the temperature remains cool (50-75 degrees F). Seedlings and established annuals can succumb to Phytophthora in a few days to a few weeks, depending on environmental conditions. Symptoms include entire root system decay, followed by rapid plant death. In strawberries, small rootlets die, while larger roots progressively brown. Larger strawberry roots develop the key diagnostic feature called "red stele," a red inner root portion that is the name of this specific Phytophthora disease in strawberry.

Red stele on strawberries. Photo credit: Chad Behrendt

Another common Phytophthora disease we receive in the clinic includes Phytophthora root rot of azalea and rhododendron, caused by P. cinnamomi. The first symptoms of root rot are wilting and yellowing leaves that roll downward parallel to the midrib (NOTE: It is important to realize that some rhododendrons will roll their leaves due to cold weather or extreme drought like we had this fall/winter. In these cases, the affected leaves will recover.). Well-established plants exhibit symptoms of mild leaf yellowing, branch dieback, and/or loss of vigor. Careful examination of the roots reveals that fine feeder roots had become infected and died. As the infection spreads into the entire root system, it continues toward the crown of the plant. Movement of the fungus into the stem eventually results in the plant being girdled. Infected tissue turns dark brown and may develop cankers near the base of the stem.

Another genus of pseudofungi that enjoys cold, wet weather are Pythium spp. This group of fungi are well-known destroyers of seedlings and a causal agent of "damping-off." Like its cousin, Pythium growth, development and dissemination is favored by cool, wet conditions. A key difference between Phytophthora and Pythium pathogenesis is that Pythium damage is done to the seed and seedling roots during germination through emergence. After emergence, the seedling "hardens off" and is less susceptible to Pythium attack. For this reason, older plants are seldom killed by Pythium, but may suffer loss of vigor due to root rot. A key symptom of Pythium infection includes failure of seeds to germinate. On newly emergent seedlings, a water-soaked spot usually indicates the site of infection, which will spread and girdle the plant, causing it to collapse.

Azalea root rot. Photo credit: U of M Plant Disease Clinic

Management for both of these diseases is very similar. In areas that are known to harbor either fungus, drainage must be improved. This can be accomplished by creating a raised bed, and by improving heavy soils through the incorporation of sand to allow for better drainage. Where Pythium is known to be a problem, use seeds treated with fungicides to prevent Pythium infection. Be certain to avoid planting azalea and rhododendron in low lying, water accumulating areas that are conducive to Phytophthora. If Phytophthora has been previously discovered in an area, do not replant azalea or rhododendron! If red stele of strawberry has been a problem, choose red stele-resistant varieties such as 'Allstar,' 'Guardian' or 'Latestar' to name a few. Allow for spacing to discourage spread from splashing water and improving air circulation, which allows leaves to dry and prevents aerial infection. Although chemicals are labeled for home use, such an approach, without correcting the underlying drainage problem, are rarely successful.

*Tom Volk's fungus page is at: http://www.wisc.edu/botany/fungi/mar2001.html

Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/PlantPathWeb/Plpa.htm
Plotting to Infiltrate? Try Rain Gardens.
Lorrie Stromme, Hennepin County Master Gardener

Courtesy of the Friends of Bassett Creek website.

This rainy spring has been an ideal time to notice the areas in your yard where stormwater and snowmelt have ponded. Instead of making plans to fill in that low spot in your yard, consider installing a rain garden instead.

What is a Rain Garden?
The term rain garden defies precise definition. Basically, a rain garden is a strategically located low area planted with native vegetation that intercepts runoff. Other terms include mini-wetland, storm water garden, water quality garden, stormwater marsh, backyard wetland, low swale, wetland biofilter, or bioretention pond. The variables include dimensions, design, engineering components, and plant selection.

Building a Rain Garden
The design of a rain garden can be varied to accommodate soils, watershed hydrology, existing drainage patterns, aesthetics, microclimate, and purpose.

Basic design components include:

ˇ Grass filter strip
ˇ A shallow surface water ponding area
ˇ A bioretention planting area
ˇ A planting soil zone
ˇ An underdrain system
ˇ An overflow outlet structure.

The following diagram illustrates these components:

Art credit:  Zolna Russell

A shallow ponding depth - approximately six inches - is preferred, underlain by two to four feet of depth for the planting soil zones. A perforated underdrain in a gravel bed connects to a storm drain or French drain. A culvert can be installed, as well. A strip of turf or groundcover at the top edge of the rain garden slows water as it flows into the garden and filters sediments. Mulch over the surface helps to suppress weeds. Shredded hardwood mulch is recommended, because it resists flotation and has a greater surface area for binding metals in runoff. Water should infiltrate within 4 to 6 hours. If the percolation rate is lower than one inch per hour, native soils should be amended or replaced.

ˇ Size
There is no standard size for a rain garden. One formula provides that the bioretention area should be 5% to 7% of the drainage area that the rain garden is intended to accommodate. Rainwater gardens installed by the City of Maplewood in several residential areas are three standard sizes: 12' x 24', 10' x 20', and 8' x 16'. The Water Quality Garden near Lake Como is 4,000 square feet. The rain gardens in the residential development in Somerset, Maryland, are each 300 to 400 square feet.

ˇ Location
A rain garden should be placed near impervious surfaces so that rainwater and snowmelt will drain into the dip or depression. Locate the garden strategically near impervious surfaces, such as alleys, sidewalks, driveways, and under downspouts or gutters, to capture the rain as close as possible to the point where it falls. Rain gardens planted between two residential properties can channel runoff to front or back yard gardens, while simultaneously acting as a living fence between neighbors. In one instance, a rain garden located under a downspout to capture roof runoff captured approximately 14,000 gallons of water per year. Gardens should not be located over gas or water services.

Rain gardens and planted infiltration trenches have also been incorporated into parking lot designs. For example, the H.B. Fuller Company in Arden Hills, Minnesota, designed the parking lots at its corporate headquarters with planted islands and vegetated infiltration strips. The Ramsey Washington Metro Watershed District recommends using infiltration trenches on the edges of parking lots.

ˇ Soil Considerations
A blend of 20% organic matter, 50% sandy soil, and 30% topsoil is recommended. This blend will naturally filter the rain as it runs into the rain garden. Some clay is desirable, because clay particles adsorb heavy metals, hydrocarbons, and other pollutants. However, the clay content should not exceed 10% of the total. Clay soils hold water well, but high clay concentrations may cause poor drainage. Sandy soil permits water percolation, but very sandy soil is too permeable. A soil pH of 5.5 to 6.5 is ideal for pollutant removal by microbial activity. A mulch layer on the garden surface aids in the decomposition of organic matter and helps to remove metals.

ˇ Plant Selection
Plant species that can tolerate the extremes of wet soils and very dry periods are preferred for rain gardens. Most perennials demand well-drained soil. They can die if they remain in soils that are poorly drained or stay wet. But some perennials tolerate or even thrive in moist soils. Plants that can tolerate standing water should be planted in the lowest part of the garden.

Native plants have several advantages. They are best adapted to the local climate and, once established, seldom need watering or fertilizing. Many are deep rooted, which enables them to tolerate drought. Native plants are attractive to diverse native butterflies and provide habitats for wildlife, especially birds. Natives are low maintenance, but they still require care, occasional weeding, and control of debilitating diseases and insect pests.

Gardens on high-traffic streets should include plants that tolerate de-icing salts. De-icing salts affect plants in two ways. First, direct contact from spray drift can cause bud death, twig dieback, or needle browning. Second, build-up in adjacent soils can damage plant roots so that they are unable to take up water. Plant symptoms include wilting, marginal leaf browning, needle tipburn, and general stunting. Plants within 60 feet of a highly traveled roadway (i.e., over 10,000 cars per day) are at the highest risk of salt injury.

ˇ Maintenance Rain gardens require routine landscape maintenance: weeding, pruning, plant replacement, mulching, supplemental watering.

Functions of a Rain Garden
A rain garden traps rainwater and snowmelt and allows them to infiltrate the soil, instead of running over impervious surfaces, like driveways, roofs, roads, patios, and parking lots. Impervious features in the landscape do not let runoff percolate into the soil; water remains above the surface, accumulates, and runs off into rivers and streams.

According to the Environmental Protection Agency, a typical city block generates 9 times more runoff than a woodland area of the same size, because of impermeable surfaces. A rain garden is a natural, on-site means of controlling runoff. In addition to storing rainwater temporarily, a rain garden filters pollutants carried in surface runoff. Examples of pollutants generated in urban areas include: sediment from development and new construction; oil, grease, and toxic chemicals from vehicles; viruses and bacteria from failing septic systems; road de-icing salts; heavy metals; and nutrients and pesticides from turf management and gardening. The major sources of phosphorus in runoff are lawn clippings and tree leaves left in the streets and gutters. Polluted runoff becomes a water quality issue when it is released directly into lakes and streams without any treatment. Increased pollutant loads can harm fish and wildlife populations, kill native vegetation, foul drinking water supplies, and make recreational areas unsafe.

Rain gardens are designed to direct polluted runoff into a low, vegetated area, where the pollutants can be captured and filtered. The features of a rain garden aid in this biofiltration process: a shallow basin depth, gentle side slopes, soil that allows infiltration, and vegetation that traps sediment and sediment-polluting runoff. Vegetation shields the soil surface from raindrop impact while the root mass holds the soil particles in place. Improved water quality results from the nutrient removal process as the water and pollutants come into contact with roots and microbes in the soil. Plants, trees, and groundcover absorb up to 14 times more rainwater than a grass lawn.

What about mosquitoes? A rain garden is not intended to detain water for long periods. Ideally, runoff will not be detained for longer than four days, to avoid concerns about mosquito breeding in standing water. Mosquitoes will not survive in wetlands that dry out in less than a week after a summer rain. The development of a mosquito from egg to adult takes 10 to 14 days. A mosquito larva must live in water for 7 to 12 days before maturing to the adult stage.

Locations to see rain gardens in the Twin Cities metro area

In St. Paul:
ˇ Lower Phalen Rain Garden - near Swede Hollow Café (725 E. 7th St.)
ˇ 118 Virginia Street (1/2 block north of Summit Avenue near Western)
ˇ Como Water Quality Garden - near the intersection of Lexington Parkway and Nebraska, just northwest of Lake Como)

In Maplewood:
ˇ Birmingham Street, between Ripley and Frost Avenues - completed in 1996.
ˇ Harvester Area neighborhood, just south of Stillwater Road - installed in 2000
ˇ Midvale Place, Ferndale Street, Brand Avenue, Michael Lane, Sterling Street, Evar Street, Edith Street, and Glendon Street
ˇ Bartelmy Acres - to be installed in 2001
ˇ Bartelmy Lane, Mary Street, Magnolia Avenue, Sterling Street
ˇ H.B. Fuller Headquarters - 3210 Labore Road (in the parking lots)

References:
1. Barrot, S.H. 1999. Effects of De-Icers on Trees & Shrubs. University of Minnesota Extension Service Yard & Garden Brief.
2. Brown, J. 1998. Gutters to Gardens. http://www.prairiecrossingfarms.com. Accessed February 10, 2001.
3. Broughton, J. and S. Apfelbaum. 1999. Using Ecological Systems for Alternative Stormwater Management. Land and Water. Sept-Oct. 1999: 10.
4. Dirr, M.A. Manual of Woody Landscape Plants. Stipes Publishing LLC, Champaign, IL. 1998.
5. Ferguson, B.K. 1990. Urban Stormwater Infiltration: Purposes, Implementation, Results. Journal of Soil and Water Conservation. Nov-Dec. 1990: 605.
6. Feucht, J.R. 2001. Mulches for the Home Garden. Colorado State University Cooperative Extension. http://www.ext.colostate.edu/pubs/garden/07214.html Accessed April 9, 2001.
7. Friends of Bassett Creek. 2000. Rain Gardens: Gardening with Water Quality in Mind. http://www.mninter.net/~stack/bassett/gardens.html. Accessed February 10, 2001 and April 11, 2001.
8. Heger, M. and J. Whitman. Growing Perennials in Cold Climates. Contemporary Books, Lincolnwood, IL. 1998.
9. Johnson, G.R., and E. Sucoff. 1995. Minimizing De-Icing Salt Injury to Trees. University of Minnesota Extension Service Publication FO-1413-S.
10. MacKenzie, J. Perennials for Moist Soils. University of Minnesota Yard & Garden Brief.
11. Meyer, M.H. and P.Olin. 1998. Common Questions about Wildflowers and Native Plants. University of Minnesota Extension Service Publication FO-6065-GO.
12. Minnesota Department of Natural Resources. 2000. Benefits of Growing Native Plants.http://www.dnr.state.mn.us/gardens/nativeplants/index.html. Accessed April 9, 2001.

Soluble Salts
Carl Rosen, Extension Soil Scientist

Salt damage on lawn. Photo credit: Carl Rosen

The term soluble salts refers to the inorganic soil constituents (ions) that are dissolved in the soil water. Examples of common salts are potassium, ammonium, calcium, magnesium, sodium, nitrate, sulfate, and chloride. Note that except for sodium, all the soluble salts listed are essential elements for plant growth.

Pure water is a very poor conductor of electric current, whereas water containing dissolved salts conducts current approximately in proportion to the amount of salt present. Therefore, measurement of the electrical conductivity of a soil extract gives an indication of the total concentration of soluble salts in the soil. The higher the conductivity the higher the soluble salt concentration. The electrical conductivity measurement is reported in units of millimhos per centimeter (mmhos/cm). Although, some labs report decisemens per meter (dS/m). One decisemen per meter is equal to one mmhos/cm.

Soluble salt levels in the soil are important, because high soluble salts can reduce water uptake by plants, cause wilting, restrict root growth, cause burning of the foliage, inhibit flowering, and limit fruit and vegetable yields. In severe cases, death of the plant may result. Sensitivity to soluble salts differs among plant species/cultivars and their stage of growth. Seed germination and seedling growth are more sensitive to salt stress than the growth of mature plants. A soluble salt test can be useful when investigating the cause of poor plant growth, determining the suitability of a new planting site, or monitoring the quality of "black dirt" for use on landscaped areas. Routine testing of garden soils for salts is generally not necessary. Relative salinity levels for different soluble salt test values and their effect on plant growth are given in Table 1. The relative salt tolerance of various cultivated plants is given in Table 2.

Foliage burn on tomato. Photo credit: Carl Rosen

Some soils in western Minnesota are naturally high in soluble salts (particularly sodium), but most soils in Minnesota are non-saline and soluble salt problems are the result of human activities. Excessive rates of fertilizer application and placing fertilizer too close to seeds or plant roots creates soluble salt problems. Pet urine and feces can increase soluble salts in localized areas resulting in plant damage or death. The use of deicing salts (primarily in the form of sodium chloride) on streets and sidewalks frequently results in high soluble salt levels in adjacent areas that restrict the growth of turfgrass, flowers, and shrubs. Note that calcium, potassium, and magnesium deicing salts can also result in salt damage.

Correcting Soluble Salt Problems
In well-drained soils, leaching with good quality water is the most effective means for correcting soluble salt problems. Leaching refers to moving the salts through the soil with excess water. In soils where internal drainage is poor, prevention may be the only feasible approach for reducing salt problems. This is because leaching will be difficult with poor drainage.

Incorporation of gypsum (calcium sulfate) at the rate of 10 to 15 lbs/100 sq. ft. followed by leaching with good quality water can be an effective means for correcting soluble salt problems caused by high sodium. High levels of sodium in the soil will tend to disperse soil particles resulting in poor soil structure and making water infiltration difficult. The calcium in gypsum will displace sodium and the sodium will then move (leach) out of soil profile with irrigation water and/or rainfall. Soils high in calcium have better structure than those high in sodium. Use of gypsum on soils where sodium is not high has generally not been shown to be effective in improving soil structure. Thus, on low sodium soils, topdressing lawns with gypsum is not an effective way to improve soil structure and therefore not a recommended practice.

Table 1. Soluble salt test values and relative sensitivity levels of plants.
Electrical Conductivity1	Salinity level	Effect on plant growth
mmhos/cm
0 to 2	non-saline	none
2.1 to 4	very slightly saline	sensitive plants are inhibited
4.1 to 8	moderately saline	many plants are inhibited
8.1 to 16	strongly saline	most cultivated plants are inhibited
over 16	very strongly saline	few plants are tolerant
1Saturated paste extract

Table 2. Relative salt tolerance of various cultivated plants.
Nontolerant (0-2 mmhos)	Slightly Tolerant (2-4 mmhos)	Moderately Tolerant (4-8 mmhos)	Tolerant (8-16 mmhos)
azalea	apple	beet	arborvitae
begonia	cabbage	black locust	asparagus
blueberry	celery	boxwood	juniper
carrot	cucumber	broccoli	Russian olive
cotoneaster	grape	chrysanthemum	Swiss chard
green bean	forsythia		alkaline grass
onion	Kentucky bluegrass	geranium
pea	lettuce	marigold
radish	linden	muskmelon
raspberry	Norway maple
red pine	pepper	red oak
rose	potato	spinach
strawberry	red fescue	squash
sugar maple	red maple	tomato
viburnum	snapdragon	white ash
white pine	sweet corn	white oak
	creeping bentgrass	zinnia
	perennial ryegrass	'Nugget' Kentucky bluegrass
		'Seaside' creeping bentgrass

Birch Leafminers
Jeff Hahn, Assistant Extension Entomologist

Leafminer damage on leaves. Photo credit:  Jeff Hahn Damaged tree. Photo credit: Dept. of Entomology

Birch leafminers are common landscape insects in Minnesota. They overwinter as pupae in the soil. In spring, adults hatch and fly to birch trees. Eggs are inserted singly into the expanding leaves. The larvae hatch soon afterwards and feed on the plant tissue between the leaf surfaces, creating mines. The mines first appear as light green or grayish blotches and get progressively larger, sometimes covering the entire leaf. Eventually damaged leaves turn brown.

Despite the unattractiveness of the brown leaves, the tree's health is usually not at risk. When the tree is healthy and vigorously growing, birch can tolerate at least 30% - 60% leaf damage. Treatment is typically made to protect the birches' appearance. If you decide to treat for leafminers, the timing for your treatment is very important. Management is most effective when larvae are first forming mines. However, this is also when people are less likely to notice them.

On average, first mines occur in central Minnesota (including the Twin Cities) in mid-May but this can be quite variable. You can estimate when leafminers will attack your birch by watching for bud break (when birch start to leaf out but before full leaf expansion). Once bud break occurs, expect mines to begin approximately 10 days later (this number could vary by a few days). Check your birch again for evidence of leafminer activity. If you see little or no evidence of leafminers, then you don't need to treat your tree.

However, if leafminers are abundant, then treat the early mines to reduce leafminer damage. You can manage leafminers with a foliar systemic insecticide application (acephate [Orthene] or dimethoate [Cygon]). Professionals can be hired to spray large trees. They can also inject Metasystox-R (a product not available to the pulbic) into the soil to manage leafminers when they are first active. Remember, once birch leaves turn brown, it is too late treat for leafminers.

Birch leafminers have two generations; the second appears approximately in mid-June. Damage from the second generation is less severe than the first and control is rarely, if ever, needed for the tree's health.

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm
Editorial Notes

Celadine poppy. Photo credit: Beth Jarvis

Now that the weather's warmed up, plants are popping up all over. Any day now, we'll see Celadine poppy in moist woodland gardens. Celadine poppy, or wood poppy Stylophorum diphyllum, is a true poppy and is similar to Celadine, (Chelidonium majus) which has smaller flowers and slightly different leaf attachment. The plant grows 10-18" tall, blooms in May and June and produces a furry, white ball fruit. This photo was taken at Elosie Butler several years ago. I also saw it last May in John Bartram's garden (first US botanist) in Philadaphia http://www.bartramsgarden.org/ and at the National Arboretum in Washington, D.C. http://www.ars-grin.gov/ars/Beltsville/na/.

Stuff happens and the cabbage and cancer piece, slated for this issue, didn't. Happily, Carl Rosen provided the long awaited soluble salts piece to help you understand your soil test report. Lorrie Stromme, a Master of Ag student, provided an article on rain gardening. We'll reschedule the cabbage and cancer piece for a bit later.

Next issue, May 15, Roger Becker will be back with a follow up piece on post-emergence herbicides.

In June, we'll have a report on the treated lumber study conducted by U soil scientists. We'll also hear from Forestry folk on options and alternatives to treated lumber.

In future issues, in addition to the cabbage article, we'll hear what new in ornamental grasses and hopefully learn about a conservation biocontrol. Bob Mugaas has agreed to comment on fertilizers, whether organic or synthetic is truly superior plus other thoughts he may have on the subject. Look for this in August.

I rely on your comments and questions for ideas for future articles. Please, keep the story ideas coming! We really try to be responsive to your needs.

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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Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator


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