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Extension > Yard and Garden News > June 2016

Monday, June 27, 2016

Water Wisely: Five steps to conserving water in your garden



By Robin Trott, Extension Educator - Douglas County, MN and Julie Weisenhorn, statewide Extension Educator
2016 is the year to water wisely! From container plantings to lawns and gardens, in 2016, the Consumer Horticulture Team at University of Minnesota Extension are working statewide to help landowners use their water resources wisely. Excellent new Extension resources for gardens, trees and shrubs, and lawns can be found here: http://www.extension.umn.edu/garden/yard-garden/watering/
Five easy steps to conserving water in your yard and garden
1. Water thoroughly after planting, then water once or twice a week, applying enough water to wet the soil to a depth of 12-18 inches for trees and shrubs or 6-8 inches for annuals. If you're not sure how much water this is, do this easy test. Water your garden, wait an hour or so to allow the water to sink in, then dig a hole about 1 foot deep. Is the soil moist at the bottom of the hole? If not, water more. If it is sopping wet, water less.
2. Water your garden in the morning and containers in the afternoon. Research shows that containers watered after noon outperformed plants that were watered in the early morning. The optimal watering time for the rest of the garden is early morning before the temperatures start to rise. Avoid evening watering, as this can lead to fungal growth.
3. Mulch, mulch, mulch. Up to 70 percent of water can evaporate from the soil on a hot day. Mulch is one of the best moisture holding tools you can use. Use coarse mulch at a depth of 3-4 inches. Rock mulch might look pretty, but in full sun, rocks can heat up the soil.
4. Xeriscape. Select plants that are drought tolerant. Many of these plants require less water throughout the season. One way to tell if a plant is a good choice for your xeriscape is the color of its foliage. Plants with silvery foliage, such as many of the herbs, are almost always drought tolerant. Some examples of these are the Artemisia, catmint and Perovskia (Russian sage). Other drought tolerant flowering perennials include black-eyed Susan, Rudbeckia; butterfly weed, Asclepias; and obedient plant, Physostegia. For more information, visit www.arboretum.umn.edu/droughttolerantplants.aspx.
5. Increase organic matter in your soil. Organic matter absorbs many times its own weight in water, which is then available for plant growth. One of the easiest ways to build organic matter is to add compost that breaks down to humus. This has an amazing potential to hold moisture, nutrients and build soil health. It has a buffering effect against drought and plant stresses too.

Friday, June 24, 2016

Watch for lecanium scale

Jeffrey Hahn, Extension Entomologist

Lecanium scales, Parthenolecanium spp., have been commonly reported this year on a variety of hardwood trees, including oak, crabapple, ironwood, hickory, and maple. Look closely for them as appear as 1/8 inch reddish brown helmet shaped insects. They are typically clustered together along branches. Adults are covered by a waxing shell and move very little while newly hatched scales, called crawlers, are mobile but lack the waxy covering.
Lecanium scales. Photo: Dan Potter, Univ. of Kentucky

Scale insects use piercing-sucking mouthparts to feed on sap in the phloem layer of plants. The damage caused by this feeding varies. In most cases, especially on large healthy trees, little to no damage occurs. As scale infestations grow larger and more persistent, branch dieback can occur, and under extreme situations, plant death. Soft scales, like lecanium scale, are also prolific honeydew producers. Honeydew is a clear, sticky waste material. Its presence in a landscape can be very annoying.

There are several options for management. In most cases, trees can tolerate lecanium scale feeding and should be ignored. There are a variety of predators and parasitic insects that help minimize scales numbers. But they need time to build their numbers so patience is necessary.

However, if scale numbers are building too quickly and it is necessary to use insecticides to reduce their numbers, there are some options. It is important to know that direct insecticide treatments are not effective against adult scales because of their waxy covering. Instead, they are most vulnerable in the crawler stage. Different scale species hatch at different times of the year. Lecanium scales hatch in June and July and are vulnerable to insecticide sprays at that time.
Branch dieback on an ironwood due to
lecanium scale feeding.  Photo: Jeff Hahn,
UMN Extension

If you want to ensure crawlers are present before treating, there are a couple of methods for detecting scale crawlers. First you can shake an infested branch over a sheet of white paper or a paper plate and watch for tiny yellowish colored actively moving insects. If you see insects with wings, they are not crawlers. You can also place double-sided sticky tape around infestation and they check the tape for signs of crawlers.

Once you know crawlers are present, you can consider different insecticide options. If you want to use a low impact insecticide to protect natural enemies, consider insecticidal soap or horticulture oil. Both have to cover the crawlers directly as there is no residual. Repeat applications may be necessary. Horticultural oil can also be sprayed during late winter as a dormant application. There are also a variety of residual insecticides, such as permethrin, that can also be used if management is desired.

For more information about scales, including lecanium scale, see Scale insects on Minnesota trees and shrubs.




Thursday, June 23, 2016

Spotted wing drosophila now active

Jeffrey Hahn, Extension Entomologist

If you grow raspberries, blueberries, blackberries, cherries, strawberries, or other soft-skinned fruit, beware that spotted wing Drosophila (SWD) has been detected. They were first discovered in apple cider vinegar traps in several locations in the Twin Cities on June 13. This is about two weeks earlier than they have been detected the last several years in Minnesota.
Male spotted wing Drosophila.  Note the dark spot near the
tip of the wing.  Photo: Bob Koch, UMN Extension

This small fly has become a very damaging pest in both commercial fields and home gardens. The larvae tunnel into ripening fruit causing brown, sunken, soft areas in the fruit, rendering them inedible. If you have susceptible fruit in your garden, monitor for SWD to determine if this insect is present in your garden. The adults look just like a typical fruit fly that you might find in your home except males have a dark spot on the tip of the wings.

If you find SWD in your garden, it is necessary to protect your crops with an insecticide application. There are several products to choose from; be sure that the specific product you wish to use is labeled for the fruit you want to treat.  Repeat applications will be necessary as SWD is active throughout the summer.

For more information on spotted wing Drosophila, including management, see Spotted wing Drosophila in home gardens.




Inspect for wasp nests

Jeffrey Hahn, Extension Entomologist

Now is a good time to inspect your home for wasp nests that are being constructed. It is easy to overlook nests when they are small and there are only a few wasps present. However, that is the best time to treat them when you can find them. Some wasp nests are built out in the open, e.g. under an eaves, and are the easiest to find and control.
A wasp (yellowjacket) queen constructing her nest during
June. The nest and queen were removed in a container and
the queen was later released to nest else where.
Photo: Jeff Hahn, UMN Extension

If a small, exposed nest is discovered, there are a couple of options for controlling it. Regardless of which method you use, deal with nests at night when the wasps are not very active. The easiest method is to spray a wasp and hornet insecticide into the nest to kill all of its inhabitants. If you want to control it nonchemically, remove the nest by placing a clear glass or plastic container over it and moving the jar so the nest is knocked down into the container. Slide a piece of cardboard (or something similar) so you can bring the jar down without the wasps getting out. Then slide the lid on the jar. Either release them so they can build a nest somewhere else or place them in a freezer to kill them.

Nests that are hidden, such that you can see wasps flying in and out of a space, but the nest in not seen, are more challenging to find because there are not as many wasps flying back and forth to give away the location of their home. These nests are typically not discovered until late summer when larger numbers of wasps are present. Control of these nests is more challenging because spraying into the opening rarely gets into the nest to kill the wasps. An insecticidal dust is the best option. However dusts labelled for buildings are not commonly available to residents and are often difficult to find. The best option then is to contact a pest management service to treat the nest.

A European paper wasp nesting in a bird feeder. This nest
and the wasps was removed in a jar and removed from the
property.  Photo: Jeff Hahn, UMN Extension
The nests of European paper wasps are particularly interesting because they will nest in such a wide variety of sites. They can be found exposed on horizontal and vertical surfaces as well as in all kinds of cavities. They can be found in the most unexpected places, like in bird feeders. Deal with them as you would other wasps.

For more information about wasps, see Social Wasps and Bees in the Upper Midwest.




Friday, June 17, 2016

Squash vine borers are out now

Jeffrey Hahn, Extension Entomologist

Are you growing squash, pumpkins, cucumbers, or melons in your garden this year? If so, now is a great time to start monitoring for squash vine borers. In fact a gardener in Minneapolis has already spotted several adults flying around his plants. Squash vine borers are a potentially devastating pest as the larvae bore into the stems, causing plants to wilt and eventually die. The best management is well timed insecticide treatments when adults are active and laying eggs.
Are squash vine borer moths in your garden now?  Check now
so you can take action when they first show up.
Photo: Jeff Hahn, UMN Extension

Adult squash vine borers are day time flying moths that resemble wasps. They are about 1/2 inch long with an orange abdomen with black dots. The first pair of wings is an iridescent green while the back pair of wings (which may not always be seen plainly) is clear. There are a couple of methods for detecting them in your garden - watch for them flying around while you are in your garden and/or place yellow containers (like pans or pails) half filled with soapy water. These moths are attracted to yellow; when they fly to the container, they will fall in. It is then an easy matter to check the container for their presence.

As soon as you spot one squash vine borer, start treatment. There are a variety of insecticides that can be applied. If you don’t see any but have a history of these pests in your garden, begin treatment by late June or early July (the further north you are located, the later the moths will emerge).

For more information, including management, see Squash vine borer management in home gardens.





Thursday, June 16, 2016

Bountiful blister beetles

Jeffrey Hahn, Extension Entomologist

There have been a lot of sightings throughout the state of Say blister beetles. Blister beetles are ant-like with soft wing covers. The Say blister beetle, Lytta sayi, is green with orange and black legs and is about ¾ inch long. These blister beetles have been conspicuously feeding, sometimes in large groups, on a variety of flowers, including lupine, iris, false indigo and prairie indigo (Baptisia), lilac and mountain ash. They have also been known to feed on rose, daylily, and peony.
Close up of Say blister beetle. 
Photo: Jeff Hahn, UMN Extension

All blister beetles secrete a defensive oil called cantharidin which can be very irritating and even raise blisters when skin is exposed to it. Fortunately, Say blister beetles generally do not possess a sufficient concentration of this substance to cause very severe problems to people.

If Say blister beetles are in your garden, there are several options for their management. First consider whether the damage can be tolerated; if it can then just ignore them. Also consider that Say blister beetles do not feed much past June so the closer to the end of the month it is, the closer the beetles are to being finished with their feeding.
Large number of Say blister
beetles on lupine. Photo:
Beth Berlin, UMN Extension

If you want to take some action against these beetles, consider physical removal. You can shake the plants and knock the beetles into a container of soapy of water. If there is concern about exposure to cantharidin and blisters, wear gloves to be on the safe side. Of course, physical removal may not be practical in all gardens.

If you are interested in a low impact insecticide, try neem oil. Spinosad is also a low impact product. While it has little effect on most beneficial insects, it is toxic to bees. However this toxicity is greatly reduced once the material is dry. If using spinosad, treat foliage when bees are not active, giving it time to dry before bees are active again. You can also apply pyrethrins; to be effective this insecticide has to directly contact the insects. There is also no residual and it may need to be reapplied.

There are a variety of residual garden insecticides that can kill blister beetles, such as permethrin, bifenthrin, lambda cyhalothrin, and carbaryl. Take care when using these insecticides as they are toxic to pollinators. Do not treat plants when pollinators are active around them. Instead, treat plants during late evening or nighttime when pollinators are no longer active to minimize exposure to insecticides.

Monday, June 13, 2016

What's up with those ragged looking elms?

Kathy Zuzek, Extension Educator

Siberian elms are showing the effect
of heavy seed production this year.
Photo: K. Zuzek
Siberian elm is a non-native tree that was introduced into the United States from Asia in the 1860’s for its hardiness, rapid growth rate, and its ability to grow in a wide range of soils.  This 50-70' tree is often found growing in yards and along boulevards where it produces prolific seed that germinates easily and quickly to form thickets of new seedlings under parent trees.  Wind can carry seed to other areas and Siberian elm has also naturalized throughout Minnesota.  It invades prairies, stream banks, and disturbed open areas with sparse vegetation.  The Minnesota Department of Natural Resources lists Siberian elm on its Invasive Terrestrial Plant page because it can invade and dominate disturbed prairies in a few years’ time.

Siberian elm seed.  Photo: S. Hurst,
USDA NRCS, bugwood.org
You may have noticed Siberian elms in the landscape this spring that look sick or stressed with sparse foliage and open brown canopies.  Unfortunately, seed production on this weedy species was even heavier than normal this year.  Siberian elms are putting resources and energy into the production of the round brown wafer-like seeds at the expense of leaf production.  Siberian elm leaves are also much smaller (1-2” long and 1” wide) than those of our native American elm (2.5” or more in length and width).  The combination of small leaf size, sparse leaf production, and heavy seed production resulted in trees with open and off-color canopies this year.
Small Siberian elm leaves.  Photo: S.
Dewey, Utah State University,
bugwood.org
Larger leaves of American elm.
 Photo: P. Wray, Iowa State University,
bugwood.org

Frost Damage on Trees and Shrubs



Kathy Zuzek, Extension Educator

If you are seeing damaged leaves on shrubs and trees, it may be due to the below-freezing
Frost damage on oak leaves.  Photo:  K. Zuzek
temperatures that occurred throughout Minnesota between May 14 and 18. Nighttime temperatures around much of the state dropped into the 20’s and the succulent newly-emerged leaves of some trees and shrubs froze. Frost damage first appears as water-soaked wilted tissue that later turns brown or black as it shrivels, curls, and dies. Entire leaf kill results in eventual leaf drop. Partially injured leaves may remain on plants as misshapen leaves.

Healthy trees and shrubs will not be greatly impacted by frost damage because they use stored energy reserves to produce new replacement leaves. When frost damage occurs, trees and shrubs initiate a stress response that 1) stimulates dormant buds near damaged leaves to expand into new leaves and/or 2) stimulates production of new adventitious buds that will develop into new foliage to replace damaged leaves.

Wednesday, June 8, 2016

Slowing down leaf spot spread

M. Grabowski, UMN Extension Educator
First spots of daylily leaf streak can be
found in the garden now. M. Grabowski

In the flower garden and in the vegetable garden, the first leaf spot diseases have appeared. At this stage, garden plants still look good and it is easy to overlook a few small spots on lower leaves.

Where did these spots come from? Many are caused by fungal or bacterial plant pathogens that survive in the soil in last years infected plant debris. Splashing rain or irrigation carries fungal spores or bacteria from the soil onto new leaves. These start new infections that become leaf spots. Each leaf spot eventually produce fungal spores or bacteria that can be spread to neighboring plants or within the plant canopy. 

Severe daylily leaf streak at
the end of the summer.
M. Grabowski, UMN Extension
 Leaf spot pathogens spread in splashing rain or irrigation or by sticking to hands and tools. Some can move on wind or moist air currents. With time and the right weather conditions, a few small leaf spots in June can grow into a devastating disease that causes leaves to turn brown, wilt or fall off.

Although there is no way to cure existing leaf spots, there are several things gardeners can do to slow the spread of the pathogen and reduce the damage caused by the disease.

  • Avoid splashing the leaves with irrigation. Use drip irrigation, soaker hose or direct the garden hose at the soil, not the leaves. If sprinklers are the only option, water deeply but infrequently, at the start of a sunny day.
  • Space plants to allow air movement between plants and through the plant canopy. Stake vining
    Removing diseased leaves to reduce
    severity and spread of leaf streak.
    M. Grabowski, UMN Extension
    plants and thin overgrown perennials.  Leaf spot pathogens need moisture on the foliage to start new infections. Good air movement through the garden helps leaves dry quickly after rain or dew.
  • Mulch the soil with wood chips, straw or other organic material. This will keep moisture in the soil where the roots can use it and reduce humidity in the plant canopy.
  • Scout for leaf spot infections in early summer when disease is just getting started.
  • Pinch off infected leaves and compost them.  Each leaf spot produces hundreds of fungal spores or bacteria that can start new leaf spot infections.
    Soaker hose provides water without
    wetting leaves. M. Grabowski
    Removing early infections can reduce the number of leaf spots in the garden later. Never remove more than 1/3 rd. of a plant’s foliage or you will be doing more damage to the plant than the disease.
  • Tolerate some leaf spots. A few leaf spots will not hurt your plant’s overall health. Use the cultural control practices above to keep leaf spot diseases in check and reduce their overall impact on your garden.


Fungicide sprays are not necessary to protect the health of the plant unless the majority of the leaves are killed or dropped as a result of the disease for several years in a row. These sprays will only be effective if applied before disease becomes severe. Fungicide sprays protect healthy green leaves but will not cure existing leaf spots. Because leaf spot diseases spread throughout the season, fungicide sprays need to be reapplied at regular intervals throughout the season to be effective. As a result they are often impractical for a home garden.


When leaf spot disease has been very severe on a particular plant for several years in a row and cultural control practices have not been effective in improving the health of the plant. Consider replacing the plant with a resistant variety or a plant with similar properties (low growing, yellow flowers) from a different plant family. 

Monday, June 6, 2016

Supporting Minnesota butterflies with little bluestem, Schizachyrium scoparium


By Nicole Roth, Applied Plant Science Graduate Student and Mary H. Meyer, Professor and Extension Horticulturalist

Introduction:
150 years ago, when traveling through western and southern Minnesota, you would have seen a landscape filled with native wildflowers, grasses and dancing butterflies as far as the eye could see. If you can imagine, one-third of Minnesota was once covered in tall-grass prairies, an essential habitat for many species of butterflies, as well as other insects, birds, and wildlife. Today, only 1% of Minnesota's prairies remain mainly due to agricultural and housing developments. People have recently become more aware of the importance of planting prairie flowers to help support our butterflies and other pollinators, but most people are still unaware of the importance of growing native grasses to support native butterflies.

Background:
Native grasses are essential larval (caterpillar) host plants for many species of prairie dependent butterflies. The larva feed on the grass, use it to build their shelter, it protects them from predators, and adult female butterflies will seek out specific host plant habitats to lay their eggs on or near. Overall, native grass host plants play an integral role to the survival of many prairie butterfly populations. As a result to habitat loss, there are currently 12 species of prairie dependent lepidoptera (butterflies and moths) on the MN Department of Natural Resources endangered, threatened, and special concern list. By incorporating more native grasses into our rural, suburb, and urban landscapes, we can potentially relieve some of these habitat loss pressures to  support our native butterflies.

Supporting butterflies with little bluestem:
A wonderful grass to start with is little bluestem (Schizachyrium scoparium). Little bluestem is a very hardy MN native prairie grass that has been documented to support several species of prairie butterflies such as the once common Dakota skipper (Hesperia dacotae) and Ottoe skipper (Hesperia ottoe).
 The Dakota skipper butterfly was historically found in 40 MN counties but is now found in only 11 counties and is listed as an endangered species statewide. Dakota skipper male butterflies have brown- orange wings with darker markings  The adult females have been found to  lay their eggs on or near little bluestem. Although the larva will feed on a variety of different grasses, they tend to have better success in building their shelters in smaller bunchgrasses such as little bluestem. The Dakota skipper has so far only been spotted in native prairie habitats, which may suggest that fragmented land such as urban settings may be a barrier for this species.
The Ottoe skipper is also currently listed as an endangered species statewide although it was once a common butterfly before extreme habitat loss. The male butterflies are a golden orange color and are very strong, fast flyers. Similar to the Dakota skipper, this butterfly is a grass generalist as it will feed on a variety of grasses but prefers the structure of little bluestem for constructing a shelter.
Additional Minnesota butterflies that have been documented as using little bluestem as a larval host plant include the Cobweb skipper (Hesperia metea), Dusted skipper (Atrytonopsis hianna),  Swarthy skipper (Nastra Iherminier),  Indian skipper (Hesperia sassacus) and the Leonard's skipper (Hesperia leonardus) a special concern species. 

Growing Little Bluestem (Schizachyrium scoparium):
Little bluestem is a warm season mid-height native grass, common to Minnesota prairies. It reaches an average height of 3' with arching foliage and a clumping habit. This native perennial gets its common name from the blue stem color it develops over the summer. In the fall, the little bluestem turns a beautiful bronze-red color.
Little bluestem is a very hardy and low maintenance grass. It is capable of growing on a wide range of soil types from mesic to dry and infertile soils but overall does best in well-drained areas. Little bluestem is a very drought tolerant grass needing no irrigation once established and can be grown in areas with full to partial sun. It has no known pests and therefore requires no pesticides or insecticides.
Like many other native grasses, little bluestem provides several ecological benefits. The deep fibrous roots it develops helps to hold soil in place and reduce soil erosion and run off. Also the annual renewal of its root system increases soil organic matter and the bunch grass form provides habitat and food for prairie songbirds, as well as many native butterflies.

Conclusion:
Seen as both an ornamental gem and an environmentally sustainable plant to many horticulturalist, little bluestem can bring beauty and ecological benefits to many landscapes. This hardy low maintenance grass provides food and shelter to many species of insects, birds, and animals, helps to reduce soil erosion and increases soil fertility. By planting more native grasses, such as the little bluestem, into our landscapes, we can begin rebuilding the crucial prairie habitats we have so drastically lost.

Blue Heaven ® little bluestem fall color

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