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Tuesday, March 31, 2015

Wasp queens not a sign of active nests

Jeffrey Hahn, Extension Entomologist

Seal openings that allowed hidden nests in voids last year
 Wasps have been active inside homes with the recent warm weather we have experienced. A question people ask is whether this indicates that a nest with live wasps is in their house. Fortunately, what people are seeing are overwintering queens that have randomly selected a given building last fall in which to overwinter. The old queen and all of the workers in the nests died last fall when freezing temperatures arrived. When it warms up during late winter and early spring, these new queens become active but usually become trapped accidentally inside homes and other buildings.

It is important to note that while wasps do not reuse old nests (an exception to this is European paper wasps), they can reuse spaces. If a person had a problem with a hidden nest, i.e. one that is in a wall void or other space within a building, now is a good time to seal the opening where the wasps were flying in and out. This will help prevent new queens from starting any new nests in the cavities.

This is also true for ground nesting wasps that were found on your property last year. Queens construct nests in old rodent burrows and similar sites. Now is a great time to fill in these entrances so new queens are not able to start new nests in those spaces.

As long as temperatures remain cool, wasps will be generally inactive. But on days with warm, sunny weather, wasps may be seen in your home. The only necessary control is to physically remove (or crush) them. You can also capture them and release them outdoors.

Friday, March 27, 2015

Finalize pruning for tree health

Black Knot on Prunus.
M. Grabowski, UMN Extension

As a general rule of thumb gardeners are told to prune out any diseased branches from trees and shrubs before the end of March. The biology behind this rule tells us that during cold winter weather, trees and the microorganisms that cause tree diseases are dormant. When the weather warms up, trees become active and so do their pathogens. Pruning cuts made in cold weather are less likely to become infected with the pathogen being pruned out or any other pathogen.

Fire blight canker on crabapple

In addition, many plant pathogens of trees and shrubs overwinter in infected branches. Common examples are black knot galls on Prunus spp. caused by the fungus Apiosporina morbosa,  fire blight cankers on crabapples, apples and mountain ash tress caused by the bacteria Erwinia amylovora and golden canker of pagoda dogwood.

Golden Canker on Pagoda Dogwood
Cankers and galls should be pruned out by making a pruning cut 6-8 inches below visible symptoms of the disease (cracked, swollen or discolored bark are common symptoms). This will ensure that all of the pathogen is removed from the tree and only healthy tissue remains. Infected branches can be burned, buried or brought to a municipal or commercial composting facility.

NOAA map for gardeners about climate normals - MN Weather Talk, March 27, 2015

USDA Plant Hardiness Map for Minnesota
Excerpt from MN Weather Talk by U of M Climatologist Mark Seeley, March 27, 2015

NOAA - the National Oceanic and Atmospheric Administration - released a helpful guide for gardeners to use this spring which is a map depicting the new climate normals. Plant Hardiness Zones have clearly shifted geographically with the changing climate and NOAA scientists explain this in some detail at the web site in an article titled "Planting your spring garden? Consider climate's 'new normals.'" Read more

So when selecting plants for your garden, always choose plants that are listed for your hardiness zone. This indicates the plant has been trialed by the breeders and proven to survive and thrive in the zone listed. Not sure of your hardiness zone? Consult the USDA Plant Hardiness Zone Map.

Thursday, March 26, 2015

MDA confirms EAB in Anoka County

Jeffrey Hahn, Extension Entomologist

(The following information is taken from a March 25, 2015 news release from the Minnesota Department of Agriculture)

The Minnesota Department of Agriculture (MDA) announced on Wednesday March 25 that emerald ash borer (EAB) was confirmed in Anoka County for the first time when an infested tree was found on private property in Ham Lake. MDA was alerted to the infested tree through a call to their Arrest the Pest phone number.

Anoka County is the seventh county in Minnesota to confirm the presence of EAB. Additionally, EAB has also been found in Hennepin, Ramsey, Houston, Winona, Olmsted, and Dakota (which was just confirmed last December) counties.

Residents are encouraged to look at their ash trees for signs of EAB. There are several things residents should look for when checking for emerald ash borer.

1. Be sure you’ve identified an ash tree. This is an important first step since EAB only feeds on ash trees. Ashes have opposite branching – meaning branches come off the trunk directly across from each other. On older trees, the bark is in a tight, diamond-shaped pattern. Younger trees have a relatively smooth bark. See also Ash Tree Identification

2. Look for woodpecker damage. Woodpeckers like EAB larvae and woodpecker holes may indicate the presence of EAB.

3. Check for vertical bark cracks. EAB larvae tunneling under the bark can cause the bark to split open, revealing the larval (S-shaped) tunnels underneath.

4. Contact a professional. If you feel your ash tree may be infested with EAB, contact a tree care professional, your city forester, or the MDA at or

Woodpeckers often attack ash trees infested by EAB

Because of this find, Anoka County will be put under an emergency quarantine and eventually join Dakota, Hennepin, Houston, Olmsted, Ramsey, and Winona counties in a state and federal quarantine. The quarantine is in place to help prevent EAB from spreading outside a known infested area. It is designed to limit the movement of any items that may be infested with EAB, including ash trees and ash tree limbs, as well as all hardwood firewood.

The biggest risk of spreading EAB comes from people unknowingly moving firewood or other ash products harboring larvae. There are three easy steps Minnesotans can take to keep EAB from spreading: 

  • Don’t transport firewood. Buy firewood locally from approved vendors, and burn it where you buy it;
  • Be aware of the quarantine restrictions. If you live in a quarantined county, be aware of the restrictions on movement of products such as ash trees, wood chips, and firewood; and,
  • Watch your ash trees for infestation. If you think your ash tree is infested, go to Does My Tree Have Emerald Ash Borer?

For more information about EAB, see the University of Minnesota Extension publication, Emerald ash borer in Minnesota.

The original MDA news release can be found here.

Friday, March 20, 2015

MN Weather Talk: First Day of Spring & the Vernal Equinox

Excerpt from MN Weather Talk blog by U of M Climatologist Mark Seeley

A displacement of the polar jet stream north into Canada brought very warm air to Minnesota last weekend. Scores of warm temperature records were set around the state over March 13-16, including 60 new daily high maximum temperature records, and 35 new daily high minimum temperature records. ... These unusually high temperatures drove the frost out of the soil to a depth of 10-12 inches, though there is still some frost below that depth. ... Losing the frost in the soil this early in March will allow the soil to absorb more precipitation when it comes later in the month (expected late this weekend and next week).

All of the record-setting temperatures ended by St Patrick's Day (March 17th) as temperatures fell back closer to normal for this time of year. After setting a record high temperature earlier in the week, Bigfork reported snow on Thursday (March 19th). In fact Thursday brought light snowfall to a number of locations in central and northeastern Minnesota, mostly less than 1 inch. Cloquet reported 1.5 inches as did a few other locations. Read All

Tuesday, March 3, 2015

Before buying plants, understand your site

The first trip to your local garden center or nursery in spring can be exhilarating. After six months of winter, gardeners may allow their emotions and excitement rather than their site conditions to determine their plant choices. It's important to select plants that don't just grow in your landscape, but thrive. Healthy, long-lived plants can be a good investment in your landscape as well as a well-landscaped yard adds value to your home.

Take time before visiting your local garden center or nursery to gain a good understanding your soil, the quantity and quality of light in your landscape, and your space available for planting. Armed with this information, you will make better plant choices, and better choices will save time and money, and improve your chances for a healthy, beautiful landscape.
  • Understand your soil. Healthy soil is like building a good foundation for your house, and understanding your soil type is the first step to a healthy landscape. The best option is to submit a soil sample to the U of M Soil Test Laboratory. Instructions for how to collect and submit a soil sample are found on the U of M Soil Test Laboratory website. The cost for a routine test is $17. You'll receive information in a couple weeks that includes your soil type, pH, % organic matter, fertilizer and lime recommendations, etc. Explanations are included on the back of your results.

    At minimum, you should know whether your garden soil is clayey or sandy by doing the soil ribbon test. Clay soil does not drain well while sandy soil drains too quickly. Mixing in compost can help in both of these situations. Amending Soils for Perennial Beds
  • Observe the quality and quantity of light in your landscape. Plants are usually labeled with
    their optimal light requirements for best plant performance. "Full sun" means the plant requires six hours or more of complete sunlight. "Part sun" is 3-6 hours of complete sunlight. "Shade" means three hours or less of sun. "Heavy shade" means almost no sun. Remember that nearby trees cast shade as well as buildings, overhangs and fences. Quality of light is also important to understand. Six hours of morning sun is going to be less intense light and heat than six hours of afternoon sun. Some plants like Ligularia and Hydrangea macrophylla will wilt in intense heat, so locating them in a site that receives less intense morning sun may reduce wilting. The Best Plants for 30 Tough Sites

  • Know how much space you have available. The goal is to choose plants that will easily fit
    into landscape spaces when they reach their mature size and form. Measure the garden space you are planting. Locate windows, steps, driveway, walks, patios, decks, easements, and utilities on your drawing. Measure the height of windows nearby to avoid buying plants that potentially would overgrow the windows and thus require severe pruning. You may choose to draw a  base map. A base map is drawn to scale and represents your entire property on paper. It shows existing plants, topography, structures, North arrow, views, natural areas, mature trees, easements, fencelines, etc. A site survey form is helpful in identifying features of your site. A base map is especially helpful if you are planning to add / change areas of your landscape.

Monday, March 2, 2015

Upper Midwest Home Lawn Care Calendar

Many people ask for advice on the timing of lawn care - when to seed, when to apply preemergent herbicide for crabgrass, when to aerate.

The following is a very helpful calendar guide to these and other basic lawn care maintenance for the average home lawns in the upper Midwest. Note that this calendar indicates the optimal and second-best timing for general lawn care. For more details about lawn care, be sure to visit our Extension Lawn and Turfgrass Management website.

For more: Upper Midwest Home Lawn Care Calendar.

Spring in Minnesota

It seems like it would never get here, but spring in Minnesota is coming slowly but surely. March 20th is the first day of spring and the vernal equinox. There are two equinoxes each year - March and September - when the length of night and day are almost exactly the same.

One plant is starting to show itself in the the Horticulture Garden on the St. Paul campus: daylily 'Wayside King Royal' shoots are starting to emerge. The forecast calls for snow (much-needed moisture) and one more day of single digits, but then a warm up.

Lack of snow means soil is low in moisture content. As the weather warms, and if we continue to have dry conditions, water plants well. Mulching plants will help soil retain moisture longer in the root zone area as temperatures rise. Amend soils with compost (organic matter) to hold moisture as well especially in sandy soils.
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