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Friday, May 20, 2016

Spring leaf drop and anthracnose

M. Grabowski, UMN Extension Educator

Fallen ash leaves infected with anthracnose.
M. Grabowski, UMN Extension 
Lawns scattered with fallen tree leaves in spring and early summer often point to infection of shade trees by anthracnose. Many common shade trees can be infected with anthacnose including ash, oak, and maple. Anthracnose is caused by several different fungi. Each fungus infects a particular type of tree. The fungal pathogens that cause anthracnose infect young developing leaves during cool wet weather. Symptoms include dark brown to black water soaked spots on leaves, curled or cupped leaves, and leaf drop in spring and early summer.

There is no management needed for trees suffering from anthracnose. Although the disease can be somewhat unsightly, it is only a minor stress on the tree. As the weather becomes warm and dry, tree leaves are able to mature without infection. Once leaves are mature they are largely resistant to the anthracnose fungi. Even trees that have dropped many leaves due to infection will produce a new flush of leaves and recover with warm summer weather.

Fourlined plant bugs are now active

Jeffrey Hahn, Extension Entomologist

If you have perennials in your garden, start monitoring for fourlined plant bugs now, especially if you have had problems with them in the past. These insects are bright red and 1/16th inch long when they first hatch. The immature nymphs and adults feed with piercing-sucking mouthparts which creates small, dark, circular, sunken spots on leaves. To determine whether these insects are present in your garden, watch for both fourlined plants bugs and their damage.
To the causal observer, these wild geraniums look pest free.
  Photo: Jeff Hahn, UMN Extension

Fortunately, while fourlined plant bug damage can affect the plant’s appearance, it normally does not seriously injure them. How much damage is deemed unacceptable is subjective and will vary with different gardeners.

Early detection is crucial for effective fourlined plant bug management. It is easy for gardeners to overlook the damage until it becomes too severe. Your goal should be to find the insects before they cause unacceptable damage. As you long as you do not find them feeding on your plants, you do not need to take any action. Even if you find that they are present, if only small numbers are present, it may not be necessary to treat them. You can also base your action on how severe their feeding has been in your garden in the past.

If you discover their presence, you have several options. Insecticidal soap, a low impact product,
However, when examined more closely, these same plants
reveal some minor feeding and a fourlined plant bug nymph.
Photo: Jeff Hahn, UMN Extension
would work reasonably well against the young nymphs but it is necessary to hit the insects directly. Insecticidal soap also does not have any residual activity so repeat applications will probably be necessary. Insecticidal soap is not very effective on older nymphs and adults. Pyrethrins, another insecticide without any residual, can be effective as long as you hit the insects directly. There are also a variety of residual insecticidal insecticides, such as permethrin, that can be sprayed to protect the appearance of the plants.

For more information, see Fourlined plant bugs in hone gardens.

Friday, May 13, 2016

The value of lawn weeds for pollinators: not all weeds are created equal

Karl Foord, Extension Educator

In my travels around the state of Minnesota regardless of rural or urban, I have encountered a significant lack of flowers. Because pollinators rely on flowers for sustenance, this lack can lead to nutritional problems for pollinators. This is why Dr. Marla Spivak is always encouraging people to plant flowers as part of the solution to the “pollinator crisis”.

The lawn is practically omnipresent in the landscapes of any building be it home residence, public, or commercial. As a culture, we have evolved into thinking that one’s lawn should be maintained in such a way that it is of playing surface quality meaning there are no broadleaf weeds present, and that the lawn is continuously verdant as a result of the choice of grass varieties, as well as fertilizer and irrigation regimens.

One potential way to address the “pollinator crisis” personally is to accept broadleaf plants (perceived as weeds) to establish in one’s lawn. Given the mindset, this creates aesthetic problems. However, if one wishes to contribute to pollinator nutrition and accept changes in appearance, the lawn offers such an opportunity.

Pollinator Nutrition

Plants contribute to pollinator nutrition by: 1) providing sugary nectar predominantly as an energy source for the high demands required for flight, and 2) providing pollen as a source of protein and other nutrients for the development of their young. However, there is significant variation among plants in regards to: 1) both the quantity of and the quality of nectar provided, usually in terms of sugar concentration, and 2) the crude protein and amino acid content of the pollen.

In this article, we will examine the nectar and pollen characteristics of two lawn “weeds”, dandelion (Taraxacum officinale) and Dutch white clover (Trifolium repens). Less information is available for creeping charlie (Glechoma hederacea) and violet species, so these will only be mentioned in passing.


Dandelions are one of the most successful plants in having adapted to the mowing regimes inherent in our lawn maintenance practices. As a plant, dandelion has characteristics that lend to and detract from its value as a pollinator plant. As one of the first flowering plants in the spring, dandelion provides a plentiful source of nectar. According to the following table, "Nectar and Pollen Characteristics of some Commonly Encountered Lawn Weeds", the dandelion flower provides between 3.7 and 7.4 ┬Ál (micro-liters) of nectar daily. In comparison with other plants, this is a respectable quantity, as we shall see. In addition, the sugar concentration of dandelion nectar varies from 42.6 to 55.1% which is also a respectable if not high percentage. Notice the variation in nectar production in one year.

Twenty percent (20%) protein content level is considered beneficial to bees; however, the pollen protein content level of dandelion is only 15%. Pollen with crude protein levels below 20% have been shown to contribute to health problems for honey bees. Dandelion pollen also lacks four of the essential amino acids required for protein synthesis. Therefore, bees feeding on dandelion pollen alone would fare poorly. In conclusion, dandelion makes a significant contribution to pollinators in the form of early spring nectar, but pollinators need to find pollen with a higher crude protein content and a complete essential amino acid complement in order to be healthy.

Note: Superscript numbers refer to references cited below.

Dutch White Clover

In contrast, Dutch white clover pollen has an excellent crude protein content level of 25% and provides all essential amino acids. However, Dutch white clover provides nectar in smaller volumes and with a lower sugar concentration per flower than dandelion (see above table) therefore pollinators feeding on white clover will have to work harder to meet their energy needs by visiting more flowers. In addition, white clover blooms later than dandelion and thus does not provide a compliment to dandelion nectar and pollen. According to Southwick et. al in "Nectar Production, Composition, Energetics, and Pollinator Attractiveness in Spring Flowers of Western New York", a given population of flowers may vary significantly in nectar quantity and quality. This does not take into account withdrawals by other insects that can be happening continually. This will likely shift the mean nectar quantity per flower in a downwards direction. From the pollinators perspective, the probabilities of greater nectar reward are reduced.

Creeping Charlie and Violets

To clarify this point, consider the nectar volumes of Dutch white clover and creeping charlie (see above table). The range of nectar volumes encountered for creeping charlie is greater than that of white clover, but the mean nectar quantity encountered for clover is more than twice what it is for creeping charlie. From a probability perspective the pollinator captures greater nectar rewards from white clover than creeping charlie in spite of the latter’s higher sugar content.

I was unable to find nectar and pollen data for our common violet (Viola sororia), but to the degree that plants in the same genus retain similar characteristics, please consider the following data. A Brazilian violet (Viola subdimidiata) contained less than average nectar volume and a significantly smaller range of nectar quantities than nectar of creeping charlie (see above table). In addition, close to 40% of the flowers sampled contained no nectar at all. If our common violet has flowers with nectar properties similar to the Brazilian species, it will rank relatively low on the pollinator attractiveness scale.


Each flower is has its own nectar production and sugar concentration profile. What any individual plant provides in any one moment in time will be affected by a series of weather conditions as well as its recent visitation history. Nonetheless the averages permit ranking of flowers relative to nectar volumes created and sugar concentrations present. This comes down to the amount of energy that a pollinator can gather from any particular plant.

Each flower will also have a pollen profile based on crude protein percentage and amino acid content. The nutritional qualities of pollen continue to be a subject of interest and it is likely that other characteristics will come to light as research proceeds. Variation among the reported nutritional qualities of pollen exists, but this variation is significantly less than that encountered for nectar quantity and quality variation. This appears to be due more to variation in research technique, and much less so to environmental influences (reference #s 6 &7).


1. T.I. Szabo, "Nectar Secretion in Dandelion". Journal of Apicultural Research, 1984 Vol. 23 (No. 4) pp. 204-208
2. Edward E. Southwick, Gerald M. Loper and Steven E. Sadwick, "Nectar Production, Composition, Energetics, and Pollinator Attractiveness in Spring Flowers of Western New York". American Journal of Botany, Vol. 68, No. 7 (Aug., 1981), pp. 994-1002
3. P.G Willmer, A.A.M. Bataw, and J. P. Hughes, "The Superiority of Bumble Bees to Honey Bees as Pollinators: Insect visits to Raspberry Flowers". Ecological Entomology (1994) 19, 271-284
4. Leadro Freitas and Marlies Sazima, "Floral Biology and Pollination Mechanisms in Two Viola Species - From Nectar to Pollen Flowers?". Annals of Botany 91:311-317, 2003
5. Gerald M. Looper and Allen C. Cohen, "Amino Acid Content of Dandelion Pollen, a Honey Bee (Hymenoptera: Apidae) Nutritional Evaluation". Journal of Economic Entomology (1987) 80(1):14-17
6. Louis Matej, "Pollen and Pollination." Master Beekeeper Certification Course. May 2004
7. "Nutritional Value of Bee Collected Pollens – Publications."

Thursday, May 12, 2016

May weed of the month: wild parsnip

From the Minnesota Department of Agriculture Minnesota Noxious Weed Program

A path cuts through a large wild parsnip infestation
A path cuts through wild parsnip. Photo: Minn Dept of Ag
May’s Weed of the Month, wild parsnip (Pastinaca sativa), is a toxic plant with an edible root. Native to Eurasia, it escaped cultivation and is commonly found throughout Minnesota and North America. Wild parsnip is a member of the carrot family. It produces a sap that can cause blistering, swelling, and discoloration of the skin when in the presence of sunlight. Protective clothing should be worn when working with this plant. Animals, including livestock, can also be burned by the sap in combination with sunlight. Read more...

Friday, April 29, 2016

Wise watering practices for newly planted trees and shrubs

Kathy Zuzek, Extension Educator

It is prime time for planting trees and shrubs in Minnesota. If planting is on your list of spring chores,
remember that proper watering is the most important practice to ensure survival and establishment of
your woody plants. No matter what planting stock you choose - bare root, containerized, balled and burlapped, or tree spaded – your new tree or shrub has a smaller root system than an in-ground, established plant. Frequent watering allows an under-sized root system to supply all the water needed by the plant while the root system expands and grows to a normal size. Under-watering and over-watering are both detrimental to plant health so it is important to know when to water, where to water, and how much water to apply. Wise watering practices for newly planted trees and shrubs can be found here.

Thursday, April 28, 2016

Boxwood leafminer: A rare insect in Minnesota

Jeff Hahn, Extension Entomologist

Boxwood is a shrub or small tree that usually grows well up to hardiness zone 5. They are marginally hardy in Minnesota (hardiness zones 4 and 3). Despite that, boxwood can be found occasionally here in the landscape. Where boxwood is commonly grown in landscapes in states further south, the most serious insect pest is boxwood leafminer. In the upper Midwest this insect is rare. A resident in a Minneapolis suburb recently reported the presence of this insect in her boxwood.

As an adult, boxwood leafminer is a small delicate orangish mosquito-like fly belonging to the gall
Boxwood leafminers: The blistering damage by the leafminers
can be seen in the top leaf while damage and larvae are seen
in the bottom leaves.  Photo: John A. Weidhass.
midge family (Cecidomyiidae). This insect spends the winter as a larva inside boxwood leaves. It becomes active when the weather warms in the spring and eventually pupates and emerges as an adult. Adults lay eggs inside the boxwood leaves which hatch later in the summer where they remain through the winter. There is just one generation a year.

The feeding of the larvae causes irregularly shaped swellings in the leaves. These damaged areas yellow at first and eventually turn brown. Despite this appearance, this feeding is generally just cosmetic, just affecting the plant’s appearance. In most cases, it is best to tolerate boxwood leafminer feeding as it is likely causing no lasting injury to plant health. Keep in mind that this is a rare insect in Minnesota and not widespread.

It is not clear where this insect occurs in Minnesota. If you live in Minnesota and have a boxwood, I would be interested to hear whether you have encountered this insect or not. Contact me at

Wednesday, April 27, 2016

Water wisely: grapes in the home garden

'King of the North' grapes
Photo: Julie Weisenhorn
By Matthew Clark, Assistant Professor
Grape Breeding and Enology
Department of Horticultural Science.

Grapes are a welcomed addition to home gardens. Successful grape breeding by universities and grape growers has resulted in a very good selection of varieties that perform well in our northern landscapes. These fruits can be grown for wine, jams and jellies, and as table grapes for fresh eating. University of Minnesota Grape Varieties

Some growers may make claims that a stressed grape plant will produce better wine. In reality, grapes need to have adequate water to enable systems like photosynthesis, evaporative cooling, and nutrient transport to work properly. Common symptoms of drought stress in grapes wilting leaves, change in leaf angle (away from the sun), and shriveling fruit. Drought stressed plants are less likely to survive Minnesota winters.  Winter injury itself can cause symptoms of drought stress and allow vines to become infected with crown gall.  Careful observation of trunks and canes of wilted plants will help to identify if the symptoms are caused by vascular damage, disease, or drought.

Soak bare root vines
3-4 hours before planting
Photo: Julie Weisenhorn
Grapes can be purchased as bare-root stock or in pots. Bare-root plants are dormant and have an   When watering the young vines, the root zone should be well saturated. Applying 5 gallons of water over a 3 x 3 foot area is a good estimate for 1 inch of water.
established root system that is in balance with the shoot. They must be soaked in water for 3-4 hours prior to planting, but will be less vulnerable to drought stress at planting than potted vines. Plants grown in pots require regular watering until the roots become established and the leaves have acclimated to growing outdoors. It will be worthwhile to monitor these plants daily to ensure they do not suffer drought stress. Young grape vines need regular watering to ensure successful establishment especially at the time of planting and the following two years. Older vines seldom need any watering unless on sandy or other very well drained soils.

According to Growing Grapes for Home Use, grapes are best planted in spring and grown in well-drained soil. The amount of organic matter in the soil may influence the growth and vigor of vines by providing access to additional nutrients.  Dig a hole large enough to spread out the root system. Cover the roots completely with soil. Create a slight depression around each vine. This will allow water to pool and soak into the soil, saturating the root area and preventing run-off.  Mulching is not recommended for grapes because mulch will moderate the soil temperature, often keeping it cooler in warmer months, and grape vines grow best in warmer soil.

Young grapes require about ½ to 1 inch of water per week, depending on rainfall, for the first two years during the growing season. By the end of the second growing season, a trunk should be established and your vine is likely to not need additional watering intervention unless specific soil conditions (sandy, well drained) or prolonged drought dictate the need. Apply water only to the root zone. Avoid getting grape foliage wet as this can encourage many grape diseases. Reduce watering young vines going in the fall to encourage the plant to harden off its canes to prepare for winter.

Managing weeds near grapevines is critical as weeds compete for water and nutrients as well as harbor potential insect and vertebrate pests. Weeds can be managed by hand-pulling, cultivation (hoeing) or through the use of well-timed herbicide applications. Cultivation and herbicide application before planting is most effective.  Combining a pre-emergent herbicide and a broad-spectrum herbicide like glyphosate before planting, and while plants are dormant in subsequent years can be a very effective strategy.  Make sure to not apply contact herbicides after the buds begin to grow as grapes are very sensitive and easily damaged by herbicides. Grow tubes can help protect the young, and sensitive vines and are a great tool when is establishing a planting.  They can even minimize damage from deer.

Additional Extension resources on grapes:

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