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August 2010 Archives

Contents: August 15, 2010

In this issue of the Yard and Garden News:

  • Fungus Among Us

  • Be on the watch for Yellowjackets

  • Plant Hardiness Zones Revisited

Fungus Among Us

stinkhorn YG.jpg

Photo 1: Stinkhorn fungi Photo by M.Grabowski UMN Extension.

Frequent summer rains, wet soils and humid conditions have created a favorable environment for a wide variety of fungi this summer. Gardeners are noticing mushrooms, shelf fungi, and other odd and interesting fungal spore producing structures of all shapes, sizes and colors sprouting in the landscape. The question then arises, which of these fungi should a gardener be concerned about?

Although it is true that more plant diseases are caused by fungi than any other type of pathogen, only 11% of all fungi are capable of causing disease in plants at all. The grand majority of fungi are saprophytes. That is they survive by breaking down organic matter and absorbing nutrients from it. In many cases, the mushrooms sprouting in the woodchip mulch or pushing up through the lawn are not harming the nearby plants, but are working on breaking down woodchips, plant debris or other organic matter.

Two saprophytic fungi commonly found in Minnesota landscapes are stinkhorns and birds nest fungi.

Several kinds of stinkhorns can be found in Minnesota. These fungi start as round to oval egg like structures. When mature a spongy looking stalk with a slime covered cap emerges. Often the remains of the 'egg' can be seen at the base of the mature stinkhorn. Stinkhorns get their name from the smelly sticky slime that caps the mushroom. This slime is full of fungal spores. The smell attracts flies, which will carry the spores to new locations. Stinkhorns can be found in mulched beds, under trees and shrubs and occasionally in lawns.

Bird's nest fungi
There are two common genera of bird's nest fungi found in Minnesota; Cyathus sp. and Crucibulum sp. These two fungi form tiny cup shaped structures with small round disks inside known as peridioles. The cups are designed to catch rain drops and send the peridioles (full of fungal spores) flying to a new location. These hard dark disks can often be found nearby clinging to plants, siding, or whatever else is in the way. Bird's nest fungi commonly grow on woodchip mulch in landscapes.

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Photo 2: Cyanthus striatus - Bird's nest fungi Photo by M.Grabowski UMN Extension.

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Photo 3: Crucibulum laeve - Bird's nest fungi Photo by M.Grabowski UMN Extension.

Mushrooms and Shelf Fungi of Plant Pathogens

Mushrooms or shelf fungi that are growing directly on the trunk of the tree, out of the root flare or right at the base of the tree indicate that the tree is suffering from heart rot, root rot or butt rot. Trees suffering from internal wood rot may or may not have symptoms in the canopy. For example a honey locust with Ganoderma root rot may have a shiny brown shelf fungi growing at the base of the tree and several dead or wilting branches within the canopy. These branches have died because the trees rotted roots were no longer able to provide the nutrients and water they needed. In contrast a cottonwood tree with heart rot may have a full healthy green canopy despite internal rot in the trunk of the tree. Regardless of how healthy the canopy appears, all three types of rot can greatly weaken the tree due to internal decay.

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Photo 4: Car trapped below a fallen branch from a cottonwood suffering from heart rot Photo by M.Grabowski, UMN Extension.

This year's strong winds and thunderstorms have resulted in many broken branches from trees weakened by decay. In severe cases, the entire trunk may break or the tree may fall over. If you suspect a tree on your property has been weakened by a decay causing fungi, consult a certified arborist ( as soon as possible. These professionals can help determine the structural stability of the tree and recommend appropriate action.

Be On the Watch For Yellowjackets

Jeffrey Hahn, Extension Entomologist

The early spring has contributed to an above average number of yellowjackets this summer. Yellowjackets can be found nesting in a variety of different places, depending on the particular species. They range from aerial nests, e.g. hanging from tree limbs or the eaves of homes to subterranean nests, e.g. nesting in old mouse burrows to nesting in various voids in buildings. These nests, especially the cryptic ones, are present all season, but may not be noticed until late summer when the workers are more numerous.


Photo 1: Aerial yellowjacket nest. Jeff Hahn.

If a yellowjacket nest is located in a site away from human traffic and is not a risk for stings, then just ignore it. Yellowjackets are beneficial because of the insects on which they prey. All of the inhabitants of the nest will eventually die in the fall when freezing temperatures arrive. If however, the nest is located somewhere where people could get stung, then the nest should be eliminated. There are some situations where you can eliminate the nest yourself. A professional pest control technician is always an option any time you do not want to deal with a wasp problem.

Nests that are out in the open are fairly easy to deal with. Wait until dark when the wasps are much less active. Use an aerosol can of insecticide, something that is labeled for wasps and hornets (or something similar) and spray into the opening. Check the next day to see how effective the treatment was. If you still see wasps flying, repeat the spray the following evening.


Photo 2: Ground-nesting yellowjacts. Jeff Hahn.

Yellowjackets nesting in the ground are more challenging. You do not see the nest itself but you see an opening in the ground where they yellowjackets fly in and out. It is not unusual to walk by a nest in the ground all summer without knowing it is there. Then one day, the yellowjackets will react to a disturbance, e.g. mowing the lawn, and will come out to vigorously defend their nest. The most effective way to control a subterranean nest is with a dust labeled for ground dwelling insects (e.g. Bonide Eight Garden Dust), although these dust formulations are generally difficult to find. Apply it at the entrance of the nest at night when yellowjackets are less active. Check after a day to see how effective the treatment was and repeat if necessary. Another option is to use a liquid insecticide, pouring into the nest entrance, but this is less effective.


Photo 3: Hidden yellowjacket nest in home. Jeff Hahn.

The most challenging yellowjacket nests are those found inside homes in wall voids, attics, concrete blocks, or similar spaces. You can not see the nest, similar to a subterranean nest, but you can see the workers flying in and out of an opening or crack. These nests are very difficult for a homeowner to control on their own. A dust labeled for use in homes is the most effective or a foam formulation, but unfortunately these products are generally not available to the general public. A liquid aerosol, while readily available, is generally not effective. Sometimes an aerosol spray can cause the yellowjackets to look for another way out, which often leads them to the inside of the home. Also, don't seal the nest opening until you know all of the yellowjackets are dead as you can cause the same reaction. The best method to control hidden nests in buildings is to have a professional pest control company treat the nest.


Photo 4: Close up of photo 3. Jeff Hahn.

Remember that yellowjackets are annual nests, i.e. the old queen and the workers only live until the weather gets below freezing, then they die. If you are dealing with a yellowjacket nest late in the season, it might be easiest to wait until the cold temperatures kill them. Nest are also not reused the following spring.

Plant Hardiness Zones Revisited

Karl Foord, UMN Extension Educator

If a particular temperature recording station has an average minimum low temperature of between - 30F to - 25F then the station would be in 4a. If the range was - 25 F to - 20 F then this station would be part of the 4b hardiness zone. The same logic determining the temperature ranges for Zone 2b [-45 to -40 F], Zone 3a [-40 to -35 F], and Zone 3b [-35 to - 30 F].


The average part of this calculation gave me concern because if it is an average then there must be numbers less than and greater than the average. The question then becomes how wide is the distribution around the average?

Minneapolis is in the 4a plant hardiness zone with a low minimum temperature range of -30 F to - 25 F. Over the last one hundred and eleven years low minimum temperatures have exceeded this range 10% of the time, but only by four degrees at the most1. Temperature data for the last 10 years (2000-2009) places Minneapolis in hardiness zone 4b. If we are willing to accept a 10% chance of a low minimum beyond the -20 F to -15 F range, then Minneapolis would be placed in zone 5a. The question is how many of your 5a plants would have died given the low temperature of -24 on January 30, 2004. The relatively milder recent winters gave rise to a revised plant hardiness map that can be viewed here. This map was subsequently rejected by the USDA.

I think it is critical to point out that the low minimum temperature is only one of a number of factors that come to play on a plant's winter hardiness.

Other factors include snow cover, temperature patterns favoring the development of dormancy, moisture conditions, and microclimate effects to name just a few.

Snow cover
Snow functions as an insulator protecting the root system of overwintering plants. Nine inches of snow can lead to a 42 F differential between a - 14 F air temperature and a 28 F soil surface temperature.


Reliable snow cover increases the temperature that the plant experiences and puts the region in a higher plant hardiness zone. This is why locations like the Upper Peninsula of Michigan are functionally zone 5 due to consistent deep snow falls, whereas without this snow the UP would likely be zone 3a.

Temperature Patterns Favoring the Development of Dormancy

The plant's ability to withstand cold temperatures is a function of the metabolic status of the plant. If the plant experiences gradually decreasing temperatures and is allowed to achieve full dormancy then it has achieved its optimum genetically programmed degree of winter hardiness. However in winters that are warm in the beginning of December followed by a significant temperature drop to average temperatures at that time of year, the plants are not metabolically prepared and will be damaged.

Moisture Conditions

Cold dry winds tend to desiccate plants especially evergreen plants with exposed leaves. Plants entering winter under draughty conditions are further stressed leading to weak plants and mortality.


Local conditions can modify the climate experienced by the plant. Protected locations reduce the stress caused by cold dry desiccating winds. Highly exposed locations can increase plant stress. Slope affects airflow as cold air sinks into lowland areas called frost pockets. South facing hillsides capture more heat which can be advantageous for plants like grapes, but disadvantageous if the heat stimulates early flowering subjecting the plant to the risk of late spring frosts. There is an art to finding the right plant for the right location. I am a big fan of Japanese maples. Their microclimate over the winter is my garage. I for one am not willing to accept the risks of the one in ten chance of a true 4a or even 3b winter that we might experience in the Minneapolis area zone 4a. Especially consider microclimates if you live in 4a or 4b and have a lake home or cabin in 3b or 3a.


Data from the Minnesota Climatology Working Group for Minneapolis

Garden Calendar: August 15, 2010

  • The apple harvest is starting, with Paula Reds and State Fairs already ripe. The Zestar in Southern Minnesota should be ready for harvesting within the next week or two.
  • Sooty blotch and fly speck fungi have shown up. (See pictures)
  • Disease and insect pressure has been high this summer.





Photo credits: Karl Foord

Yard and Garden News Editor: Karl Foord

Technical Editor: Bridget Barton

Contents: August 1, 2010

In this issue of the Yard and Garden News:

  • Imidacloprid, Found in Most Homeowner Insecticides, is Translocated to Nectar and Pollen and Kills Good Bugs

  • Rose Classes and their Performance in Minnesota: Part 2

  • Home Lawn and Landscape Turfgrass Fertilizer Recommendations Being Revised to be More Environmentally Sensitive

  • Canna Yellow Streak Virus

  • Field Ants in Home Lawns

  • Garden Calendar: August 1

Dr. Vera Krischik, Department of Entomology, University of Minnesota

Native plants used in restoration for wildlife and food plants from apples to zucchini require pollinators. Bees and other beneficial insects offer valuable ecosystem services in both natural and managed agriculture ecosystems, so it is essential to protect them. Pollinators and beneficial insects are experiencing serious decline due to insecticide use, lack of nutritionally rich native plants for pollen and nectar, and lack of habitat. Continued loss of pollinators will have an impact on the natural resources and the economy. This issue has been addressed by the Xerces Society, National Research Council Report, the Congressional Research Report, testimony by the National Academy of Sciences to the US Congress, and the media in newspapers and television programs.

Systemic neonicotinyl insecticides used on landscape plants and crops are considered as a major factor in pollinator decline. After the 1998 ban in France of the systemic seed treatment Gaucho (active ingredient, imidacloprid), French researchers found that imidacloprid is translocated from coated seeds at planting thru the growing plant to nectar and pollen in flowers. In May 2008 a large number of bees died in Germany and the government banned the use of 5 neonicotinyl insecticides, including imidacloprid and clothianidin. A similar event was document in April 2010 by bee researchers at Purdue University. However, in the US use of these 5 neonicotinyl insecticides is very common in greenhouse, landscape, and crops. Almost all of the seed and furrow insecticide applications to corn, canola, soybean, and potato use neonicotinyl insecticides. Native plants grown in greenhouses and transplanted outside may contain high levels of imidacloprid which may kill pollinators.

Research in Vera Krischik's lab in the Department of Entomology at the University of Minnesota demonstrated that nectar and pollen from greenhouse plants treated with soil applications of imidacloprid contained significantly higher amounts of imidacloprid and its metabolites, than from a Gaucho-seed treatment. The label of Gaucho states that 0.375 mg AI for corn and 0.11 mg AI of for canola of imidacloprid should be applied. The greenhouse rate used on perennial landscape plants states that 300 mg AI/ 3gallon pot with 1 plant can be used. This is an 800 times higher rate for corn and 2700 times higher rate for canola. Consequently, greenhouse and urban landscapes use higher concentrations of imidacloprid, which are often reapplied and used at peak flowering, which results in higher concentration being translocated directly to flowers. Consequently, these levels have great potential to alter behavior or kill pollinators and beneficial insects more than the seed treatment Gaucho where most of the research has been done.

Our research on greenhouse rates of imidacloprid showed that the amount of imidacloprid found in nectar of 2 flowering plants was 20 ppb to 41 ppb from a single soil application compared to 1.9 ppb imidacloprid in sunflower nectar and 0.6 to 0.8 ppb in canola nectar from a seed treatment. For buckwheat and milkweed landscape plants, a label rate of soil applied imidacloprid (Marathon 1%G) was translocated to buckwheat nectar at 16 ppb (Krischik et al. 2007) and milkweed at 41 ppb/flower (Krischik et al. 2010). These concentration of caused high mortality of beneficial insects, such as lady beetles, lacewings, and a small parasitic wasp (Smith and Krischik 1990, Rogers et al. 2007, Krischik et al. 2007, Krischik et. al 2010).

There are multiple ways that plants in urban landscapes can contain imidacloprid -contaminated nectar, since it is commonly applied in the landscape for many pests (Krischik and Davidson 2004) and many greenhouse plants are treated with prior to sale and transplanting. Imidacloprid may persist in nectar for a long time, since soil applications were effective against foliar pests for 1 to 2 years in containers (Szczepaniec and Raupp 2007, Gupta and Krischik 2007, Tenczar and Krischik 2007) and landscape trees (Cowles et al. 2006, Frank et al. 2007, Tenczar and Krischik, 2007). Injections of concentrated volumes of imidacloprid (Imicide, Pointer) applied to trees trunks and roots were effective for 12 months for ash (McCullough et al. 2003) and linden (Johnson and Williamson 2007). A soil application of imidacloprid to Eucalyptus tree resulted in 500 ppb in nectar and pollen, which will kill any insect feeding on nectar and pollen. Tree injections of imidacloprid at flowering are cause for concern, since linden flowers are a good source of nectar and pollen for bees, butterflies, and other beneficial insects.

Practice IPM and only use insecticides if you actually witness an insect and associated problem. Think kindly and widely of the need to conserve pollinators and beneficial insects. Apple, cranberrie, blueberries, almond, citrus and 45% of our food plants need pollinators.

Rose Classes and their Performance in Minnesota: Part 2

Kathy Zuzek, UMN Extension Educator

Old Garden Roses

The earliest rose classes fall within a group of roses called the Old Garden Roses. These are the classes that were in existence before 1867 when the first Hybrid Tea was developed. The earliest classes in chronological order are the Gallicas, Damasks, Albas, Centifolias, and Mosses. These five classes were all in existence before 1800 and share some common traits. With few exceptions, they bloom only in spring on previous year's canes. In contrast to the Hybrid Teas, these roses are valued for their mature flowers rather than their buds. Buds are often round or globular and open to produce blooms that are cupped, domed, or are shallow saucers. Oftentimes small inner petals are enclosed within larger outer petals; sometimes petals are produced in a quartered arrangement. Colors among these 5 classes are restricted to pink, white, mauve, maroon, or purple.

Gallicas are the oldest class of Old Garden Roses and are known for their beautiful fragrance and blooms of rich colors like deep pink, violet, mauve, purple, or crimson. You can also find varieties with striped or mottled petals (Photo 1, below). Leaves are typically dark green, stiff, and a bit rugose or wrinkled. Plant habit is compact and upright and many Gallicas will sucker (Photo 2, below). At the Minnesota Landscape Arboretum (MLA), Gallica canes typically suffer some winter injury. They commonly die back to the snowline. If snow cover is absent, they often die back to the ground. When dieback to the ground occurs in Gallica cultivars or any other cultivar that blooms on previous years' wood, flowering does not occur the following spring bloom. 'Alika' is a very hardy Gallica and rarely suffers from winter injury at the MLA. Many Gallicas at the MLA show high levels of blackspot tolerance.

The first Damask rose was probably a hybrid created in nature from a Gallica rose and Rosa phoenicea, a species rose with small white flowers. Damask blooms are usually a clear pink or white and are known for their strong fragrance. Typical leaves are gray-green, downy on the underside, and composed of long leaflets. Damasks produce long arching canes but at the MLA, some winter injury is common among Damask cultivars so plant height is often reduced. Most cultivars have slight levels of blackspot infections. 'Cesonie' is a very blackspot-tolerant Damask cultivar (Photos 3&4, below).

Albas were created when a natural hybrid occurred between a Damask rose and Rosa canina, a European rose species often called the dog rose. Alba flowers are usually white, ivory, or light pink and leaves are gray-green or blue-green. Albas are typically taller and hardier than Gallicas, Damasks, Centifolias, and Mosses but some winter injury to canes still occurs at the MLA. 'Alba semi-plena' (Photos 5&6, below) has historically shown the best combination of winter hardiness and blackspot tolerance among Albas at the MLA.

Centifolias were developed by the Dutch in the 1600s from R. canina, R. gallica, R. moschata, and R.phoenicea. Flower buds are globular and open to display pink or white, fragrant, cupped blooms (Photos 7, below). Flowers have a high number of tightly packed petals that envelop each other like leaves of a cabbage, hence the common name "cabbage rose". Leaves are smoother and less wrinkled than Gallica foliage. Cabbage roses are taller like the Albas and the Damasks and their plant habit is often described as floppy or lanky (Photo 8, below). At the MLA, some winter injury is common can reduce plant height the following summer. Blackspot infections are more severe on Centifolias than on the Albas, Damasks, and Gallicas.

In the late 1600's a spontaneous mutation occurred on a Centifolia roses that resulted in the development of balsamic-scented glandular growths that look like moss on the stems and flowers of the rose. These mutated plants or sports were called the Moss Roses. The development of new moss rose varieties was a fad in the last half of the 19th century and cultivars were developed that ranged from small to large in plant habit with white, pink, and maroon blooms that had either soft or hard, prickly moss covering stems, flowers and occasionally leaves. Winter injury on Moss Roses is common at the MLA. 'Henri Martin' is a particularly blackspot-tolerant cultivar (Photo 9, below).

In the late 1700's R. chinensis, the China rose, and R. odorata, the tea rose, arrived in Europe from Asia. China roses have an open and airy plant habit, sparse foliage, and blooms that are shapeless compared to the Old Garden Roses. The tea rose is very similar to the China rose except that it is less hardy, has larger blooms that open from tall elegant buds, and flower scent is similar to fresh tea leaves. What excited gardeners and breeders was the ability of both the China rose and the tea rose to bloom repeatedly through the growing season. Soon repeat-flowering plants were created by combining the Gallicas, Damasks, Centifolias, and Mosses with the China rose and the Tea rose and four new rose classes developed. Portlands and Bourbons are both descended from the Damask and China roses. Portland Roses are known for their short stems and compact plant habit, dense foliage, and attractive purple, pink, or white flower forms. Bourbons are known for fragrant, rich-colored, many-petalled blooms that are produced on tall arching canes. In warmer climates bourbons are used as climbers and pillar roses. Hybrid Perpetuals resulted from crosses among many rose classes when rose exhibitions became popular. In this class, plants were selected for lovely flower buds and flowers. Plant habit was of little concern. As a result, hybrid perpetual plants are often described as clumsy and too large. Tea Roses, known for their tall, elegant buds, were created when R. odorata was crossed with the Bourbon roses and another rose class called the Noisettes. All four of these classes are more suited to growth in warmer climates and are not adequately hardy for Zone 4 winters.

Modern Roses

When Tea Roses were hybridized with the Hybrid Perpetuals, the Hybrid Tea class was created and the era of modern roses was started. Hybrid Teas with their tall elegant buds and beautiful flower form (Photos 10, below) dominated the rose world as a garden plant in the last half of the 20th century. They are not hardy in Minnesota and are typically very susceptible to blackspot.

The first Polyantha Rose was probably the result of an accidental cross of a China Rose and R. multiflora. Polyanthas are a class of small-statured roses who inherited their large clusters of small one-inch flowers and superior hardiness from their R. multiflora ancestor. 'The Fairy' (Photo 11, below) and its darker pink sport 'Lovely Fairy', are reliably crown-hardy and very blackspot-tolerant in the southern half of Minnesota and bloom freely all through the growing season. The Northern Accent Roses 'Ole', 'Sven', and 'Lena' are crown-hardy with rapid spring regrowth in Zones 3&4, have high blackspot-tolerance, and flower throughout the growing season.

When Polyantha Roses were combined with Hybrid Teas, Floribunda Roses were created. Floribundas produce blooms in clusters like their Polyantha parent but also have the more elegant bud and flower form and the decreased cold hardiness of their Hybrid Tea ancestors. Floribundas are typically not hardy in Minnesota. Two cultivars that are Zone 4-hardy and blackspot-tolerant are 'Nearly Wild' and 'Chuckles' (Photo 12, below). Both show high levels of blackspot tolerance.

Hybrid Rugosa cultivars are descended from R. rugosa with its rugose or wrinkled foliage and large colorful round hips. There are two types of Hybrid Rugosa cultivars. The first are plants that are 100% rugosa and typically show no winter injury, little blackspot incidence, produce mauve, white, or pink blooms through the growing season (Photo 13, below), and produce a beautiful crop of large round colorful hips in fall (Photo 14, below). These plants thrive even in the coldest parts of Minnesota as long as 1) soil pH is neutral or slightly acidic and 2) rose stem borer and mossy rose galls are removed and destroyed promptly. Examples in this group include 'Blanc Double de Coubert', 'David Thompson', 'Frau Dagmar Hartopp', and 'Jen's Munk'. The second group of Hybrid Rugosas have one R. rugosa parent , but the 2nd parent is a non-rugosa rose such as a Shrub Rose, a Hybrid Tea, a Floribunda, or a Miniature Rose. This group usually has less rugose foliage, few or no hips, more susceptibility to blackspot, a wider variety of flower color, and a dramatic loss of cane hardiness that prevents them from being grown in Zone 3 and oftentimes Zone 4.

Shrub Roses are a "catch all" category for roses with diverse genetic backgrounds that don't fit anywhere else. Common traits among this group include a "shrubby" plant habit compared to cultivars in other modern rose classes, increased winter hardiness, and improved disease resistance. Some are repeat-blooming. Others bloom only in spring. Minnesota gardeners can enjoy the shrub roses that resulted from Canadian breeding efforts in the 20th century and resulted in older cultivars like 'Therese Bugnet' or 'Lillian Gibson' and newer cultivars in the Explorer (Photo 15, below) and Parkland/Morden Series. Gardeners in the southern half of Minnesota can also take advantage of some of the repeat-blooming cultivars developed by Dr. Buck at Iowa State University during the last half of the 20th century such as 'Applejack', 'Country Dancer', 'Folksinger', 'Prairie Flower', 'Prairie Harvest', and 'Prairie Princess'. Newer Zone 4 additions to the shrub group that rebloom and show high blackspot tolerance include 'Candy Oh! Vivid Red', 'Carefree Delight', 'Carefree Spirit', 'Golden Eye', 'Pink Gnome', 'Polar Joy', and 'Snowdrift.'









Bob Mugaas, UMN Extension Educator; Dr. Brian Horgan, Associate Professor and Extension Turfgrass Specialist; and Dr. Carl Rosen, Professor and Extension Soil Scientist.


Bob Mugaas.

New research results from the University of Minnesota and the University of Wisconsin-Madison necessitate updating our current lawn/turfgrass fertilizer recommendations. For the past 20 to 30 years, one of the more important fertilizer application times was considered to be the end of October and into early November in the Twin Cities and southern Minnesota. Indeed, lawns respond positively with good green color and active growth significantly earlier the following spring when given about 1# of N per 1000 square feet late in the previous growing season. This application came to be known as a late fall or more accurately a late season fertilization. In most years, this typically coincided with about the last mowing of year and with hoses put away or irrigation systems winterized for the year.

Even though this research was conducted on creeping bentgrass these findings demonstrate that nitrogen uptake late in the season is significantly less than when applied around Labor Day to the middle of September. So, what happens (or potentially can happen) to the remaining nitrogen not used or taken up by the grass plants? Other recent research on Kentucky bluegrass at Michigan State University points to increased leaching of N fertilizers when plants are not actively growing which is often the case with the late season fertilization. Nitrogen can also be converted to a gaseous form and lost back to the atmosphere. In some situations it can even be lost through runoff, particularly when soils are frozen. Some may also be taken up by other landscape plants that happen to share the same rootzone as the turfgrass (e.g., trees and shrubs).


Bob Mugaas.

So, back to our original question, "If only a small portion of available N is utilized by the grass plant, what happens to the rest of it?" A more complete answer to that question rests with additional research which is ongoing. Nonetheless, available and unused nitrogen can pose additional environmental risks as noted above and be uneconomical for the user. After all, no one wants to be spending money on fertilizer and the labor to apply it if only a small fraction of that material is being utilized by the grass plant with the rest potentially being wasted.

It should be noted that results from the University of Minnesota soil testing lab may indicate significantly less nitrogen be applied on an annual basis depending on information provided about the care and use of the turfgrass area tested as well as the level of soil organic matter present. Leaving clippings on the lawn typically results in about one application of a complete fertilizer (i.e., a fertilizer containing nitrogen, phosphorus and potassium) annually back to the lawn. Hence, when clippings are returned, the amount of nitrogen needed is also reduced. The four options below assume clippings are returned to the lawn.


Bob Mugaas.

Likewise, areas with soil test levels of organic matter above 3.1% will also indicate a reduced need for nitrogen. As soil organic matter continues to breakdown over time, there is some nitrogen released back to the soil that in turn becomes available for the grass plants to use. The soil testing lab considers that when suggesting annual amounts of nitrogen to apply.

Based on this current research, the following revised lawn/turfgrass fertilizer programs are suggested. These are applicable to lawns and other turfgrass areas predominantly composed of Kentucky bluegrass with varying amounts of fine fescue and perennial ryegrass. Whenever possible be sure to take a soil test to determine how much fertilizer is needed. It should be noted that ongoing analysis and interpretation of these and other research results may further refine suggested turfgrass fertilizer programs. Hence, it is important to check back periodically on the U of MN Extension website for the latest in lawn fertilizer recommendations.

Irrigated average quality lawns/turfgrass - full sun conditions; soil organic matter >3.1%; clippings not removed
2# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • At first mowing in spring: 0.5# N per 1000 ft2, (20 - 25 % slow release)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release)

Irrigated average quality lawns/turfgrass - full sun conditions; soil organic matter <3.1%; clippings not removed

2.5# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • At first mowing in spring: 0.5# N per 1000 ft2, (50% slow release N)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release N)

  • First week of August: 0.5# N per 1000 ft2, (50% slow release N)

Non-irrigated, average quality lawns/turfgrass - full sun to lightly shaded conditions; soil organic matter <3.1%; clippings not removed

1.5# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release N)

On occasion, an additional application of N to enhance growth and color may be needed:
Apply at the rate of 0.5# N per 1000 ft2, (50% slow release N; often this will be in late June to early July especially if weather conditions prior to that period have produced abundant and frequent rainfall.)

Non-irrigated, average quality lawns/turfgrass - full sun to lightly shaded conditions; soil organic matter >3.1%; clippings not removed
1# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

On occasion, an additional application of N to enhance growth and color may be needed:
Apply at the rate of 0.5# N per 1000 ft2, (50% slow release N; often this will be in late May to early July especially if weather conditions prior to that period have produced abundant and frequent rainfall.)

Canna Yellow Streak Virus

Michelle Grabowski, UMN Extension Educator


Photo 1: Leaf streaking due to CaYSV Photo by M.Grabowski, UMN Extension.

Cannas are popular tropical plants that can be easily grown in Minnesota if rhizomes are brought indoors and protected from frost each year. In addition to a variety of flower colors, cannas also differ in leaf color. Leaves that are green to greenish blue, reddish purple, bronze, or variegated with white to yellow stripes can all be found in different varieties of canna. It is important to know what color leaves a particular variety should have however, because a very common virus can cause leaf streaking that many gardeners mistake for variegation.

Canna Yellow Streak Virus (CaYSV) causes yellow to brown streaks along leaf veins of infected plants. Severely infected plants may have poor growth and reduced or no flowers.

Although many viruses are transmitted from plant to plant by an insect vector, there is no known vector for CaYSV other than humans. Cannas are propagated by splitting the rhizome of one plant, and growing the pieces into many new plants. If the original plant is infected with the CaYSV, all new plants arising from that plant will also carry the virus. Once infected with CaYSV, a canna is infected for life. The only effective control is to throw out infect rhizomes and start over with healthy virus free plant material.

Field Ants in Home Lawns

Jeffrey Hahn, Asst. UMN Extension Entomologist

Some people are finding field ants nesting in their lawns. Field ants are about 1/4 inch long and black (some species are red and black). Their nests are slightly raised and mound-like and can cover a fairly large area in the ground, up to two feet in diameter. It is not uncommon for people to confuse field ants with carpenter ants. Although these two ants are somewhat similar in size and color, carpenter ants do not nest in the soil. The prefer to nest in cavities in rotting wood or in voids found in buildings. Field ants are most active during the day while carpenter ants are most active at dusk, dawn, and during the night. Because of the mounds created by field ants, some people assume these ants are fire ants. Fire ants are about 1/8th inch long or a little larger. They only occur in the southeastern area of the U.S.; the closest fire ants to Minnesota are in southern Tennessee. Minnesota winters are too cold for fire ants to survive.

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Photo 1: Field ant nest. Unknown.

Unlike cornfield ants which are found in bare or thinning areas of lawns, field ant nests are found in healthy, vigorously growing turf. Despite the appearance of the excavated soil on top of the grass, field ant nests typically do not cause any lasting damage to the grass (just rake the soil periodically to prevent it from mounding up). Field ant activity may also make the turf look like it is being undermined from all of the tunneling but this is not likely - a very large nest would need to be present to cause that kind of damage. However, these nests can cause problems when mowing. The blades can become dulled when they strike the mound. Field ants can also be an issue because they can bite, especially when their nest is disturbed.

It may not always be necessary to treat field ants in your lawn. If the nest is not intrusive in its appearance or cause problems in the maintenance or enjoyment of your grass, then just ignore it. If the nest is troublesome, then your best bet is treat it with a granular insecticide labeled for ants found in turf (follow all label direction carefully). Some people want to try a non-chemical method and will pour hot water on the nest to kill it. However, this is not effective; at best you might get the ants to move to another area of the lawn. Others will try much more dangerous tactics like trying to burn and destroy the nest with gasoline or lighter fluid. Not only does this not destroy the nest but you risk causing injury to yourself and damage to your property in the process.

Garden Calendar: August 1, 2010

Warm wet weather is favoring the growth of many fungal and bacterial leaf spot diseases in the flower garden. To identify which disease or pest problem you are seeing, visit 'What's wrong with my plant?'

For more information about managing leaf spot diseases, read 'Seeing Spots'in the June 1, 2009 Yard and Garden News.

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

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