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Extension > Yard and Garden News > September 2016

Thursday, September 29, 2016

Temperature Control in a Bumble Bee Nest

Karl Foord - Extension Educator, Horticulture

The previous post linked to a video showing a new born bumble bee. The following video is of the same nest but involves a different observation.

To view and photograph the nest I had to pull away the straw covering the nest. This exposed the nest to the direct sun and evidently increased the temperature of the nest beyond the acceptable range of the worker bees. In this video a worker bumble bee uses her wings to fan and cool the nest. The wings are moving so fast that they practically disappear, a little like airplane propellers.

To give a sense of perspective, the engine on a propeller driven airplane rotates some 43 times in one second. I timed the wing speed of bumble bees in one of my videos to 172 beats per second. No wonder the wings are impossible to see when filmed at regular speed. In the second half of the video I have slowed the speed of the action by a factor of 4 and it is still difficult to see the wings moving. You can see the wings just when they begin to move and when they stop moving. Enjoy the blur as another one of the fascinating things one can find in the garden.

Observe a Newborn Bumble Bee

Karl Foord Extension Educator, Horticulture

Some of the folks maintaining the Display Garden located on the St. Paul Campus discovered a Two Spotted Bumble Bee nest (Bombus bimaculatus). On June 5th I found the nest with the help of Julie Weisenhorn and took some video.

This is a young nest and relatively early in the season, so the worker bumble bees are significantly smaller than the Queen. This bee is identified in the video.

In addition a new born bumble bee appears from under the top end of the nest. This individual can be recognized by the white hair covering its body. Later the hair in some places will turn golden and in other places black. Other evidence that this is a new born come from the shape of its wings. Notice that the wings on this bee are flat and curve around the base of the abdomen. The bee will proceed to pump hemolymph (the fluid of their circulatory system) into the veins of the wings. This will will expand and straighten the wings after which they will dry and become hardened. Only after this will the wings become functional and enable the bee to fly.

Tuesday, September 20, 2016

Remove white mold infected annuals

M. Grabowski, UMN Extension Educator
Zinnias killed by white mold. M. Grabowski, UMN Extension

 White mold is a plant disease caused by the fungus, Sclerotinia sclerotiorum. This pathogen is capable of infecting over 400 plant species. Flower garden favorites like zinnia, petunia, salvia, and snap dragon are highly susceptible to white mold. In the vegetable garden, tomatoes, green beans, lettuce and cabbage can all be infected. Removal of infected plants is a critical management strategy for white mold. The pathogen can survive up to 8 years in specialized resting structures produced on infected plant material. 

Tomato stem with fluffy white fungal growth on the outside and
black sclerotia on the inside.  M. Grabowski, UMN Extension

Plants infected with white mold often wilt and die. The lower stems of these plants will be tan and dry. If the humidity is high, white fluffy clumps of fungal growth may be seen on the stems. Gardeners may also see small, rough, black structures that look like seeds or peppercorns forming along stems or inside of them. These are special resting structures, called sclerotia that are created by the fungus. Sclerotia can survive in the soil for up to 8 years. Each year the sclerotia produce tiny mushroom like structures that releases spores and starts new infections. 

Gardeners that are seeing white mold in their gardens now, need to remove infected plants before sclerotia are dropped into the soil. The entire plant should be removed as soon as possible. Infected plants can be composted if the pile heats up to a minimum temperature of 148 F. Alternatively infected plants can be deeply buried (6-12 inches below ground) in an area of the yard that will not be used for flowers or vegetables in the future like a mulched are around trees or shrubs. 

Petunia bed with multiple plants killed by
white mold.  M. Grabowski, UMN Extension

Lower stems of white mold infected petunias are clearly tan and dry.
M. Grabowski, UMN Extension 

Friday, September 16, 2016

Orb weaving spiders

Jeffrey Hahn, Extension Entomologist

Spiders are particularly common around homes and gardens during late summer and fall. Undoubtedly the most common types are the orb weaving spiders (family Araneidae). These spiders can be recognized from the large, circular, flat webs that they construct. They vary in size although many are moderate to large sized.  Some species are very colorful. They typically have round, plump abdomens with relatively short stout legs.
Black and yellow argiope spider, a
common spider during late summer and
fall.  Photo: Jeff Hahn, U of M Extension

There are two common groups of orb weaving spiders that people commonly encountered, spiders in the genus Argiope and those belonging to the genus Araneus.

Argiope spiders, also referred to garden spiders are large with a body length up to one inch long, and conspicuously colored yellow and black or silver, yellow and black. Their abdomen is more oval compared to most orb weavers.

Araneus species are typically moderate sized.  They can be either brownish or colored brightly, especially orange or yellow.  Their abdomens are generally more round, sometimes even somewhat triangular.  Common species include barn (orbweaver) spider, cross orbweaver, shamrock orbweaver, and marbled orbweaver. Click here to learn about other Araneus orb weaving spiders.

Fortunately despite their appearance, orb weaving spiders are not aggressive or dangerous to people and no control is necessary. In fact, orb weaving spiders are fascinating to observe and people should consider themselves fortunate to have an orb weaving spider in their garden or yard to watch.

Wednesday, September 14, 2016

EAB found in Duluth again

Jeffrey Hahn, Extension Entomologist

(The following information is modified from a Minnesota Department of Agriculture news release).

The Minnesota Department of Agriculture (MDA) is issuing an emergency quarantine for the southeastern portion of St. Louis County (see below map) after confirming a second emerald ash borer (EAB) detection within the city of Duluth. EAB was found in Superior, Wisconsin across Lake Superior from Duluth in August, 2013. It was first found in Duluth in October, 2015 on Park Pointe; the quarantine at that time was restricted to only this island.

New quarantine area in southeast St. Louis
county due to new EAB discovery in Duluth. 
Map courtesy of MDA.
The emergency EAB quarantine limits the movement of firewood and ash material out of the quarantined area of the county. The quarantined area now runs from MN Highway 33/US Highway 53 on the west to the Lake County border on the east. The northern border of the quarantine runs from US Highway 53 along Three Lakes Road (County Highway 49) east to the intersection of Vermilion Trail. It then continues along the northern edge of Gnesen, North Star, and Alden townships. This extends south to the Carlton County/State of Wisconsin border.

To see the original MDA news release, go here.  For  more information on EAB, see Emerald ash borer in Minnesota.

Wednesday, September 7, 2016

EAB is found in Dodge County

Jeffrey Hahn, Extension

(The following information is modified from a Minnesota Department of Agriculture news release).

The Minnesota Department of Agriculture (MDA) has placed Dodge County under an emergency quarantine after emerald ash borer (EAB) was found in the city of Kasson last week. Kasson is about 13 miles west of the nearest known EAB infestation in Rochester (Olmstead County). The EAB was found in a United States Department of Agriculture (USDA) trap. MDA staff has since conducted a search of the area and discovered an EAB infested tree.
Emerald ash borer was found for the first time in Dodge
county, caught on a trap.  Photo: Jeff Hahn, U of M Extension

Because this is the first time EAB has been identified in Dodge County, the MDA is enacting an emergency quarantine to limit the movement of firewood and ash material out of the county. This will reduce the risk of further spreading the tree-killing insect. Currently 12 other Minnesota counties and Park Point in the city of Duluth are under quarantine to prevent the spread of the emerald ash borer.

The biggest risk of spreading EAB comes from people unknowingly moving firewood or other ash products harboring larvae. Take these three easy steps 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 and use the “Do I Have Emerald Ash Borer?” guide.

Emerald ash borer larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk. Since its accidental introduction into North America, EAB has killed tens of millions of ash trees in 24 states. The invasive insect was first discovered in Minnesota in 2009. Minnesota is highly susceptible to EAB as the state has nearly one billion ash trees.

For more information on EAB, see Emerald ash borer in Minnesota. Go here for the original MDA news release.

Thursday, September 1, 2016

Turf War: Overwatering our lawns is sucking up our water supply (Star Tribune)

Sam Bauer, Extension Educator

Over the weekend the Star Tribune ran an article discussing lawn watering and its impacts on our pocketbooks and our water supply.  The author, Hannah Covington, spent a day with our Extension Turfgrass Science Team as we conducted irrigation audits for several homeowners in Apple Valley.  This study is sponsored by the Metropolitan Council with the ultimate goal of reducing the amount of water being applied to our home landscapes, much of which is wasted water.  With this study, we are conducting a survey (which many of you filled out- thank you!) and we are also selecting residents in the 7-county Metro Area to have their home irrigation systems being audited.  The audits entail checking irrigation system components, conducting performance testing and making recommendations on how to save water through basic irrigation system adjustments.  You can read more about how to properly conduct an audit of your irrigation system in the previous Yard and Garden News article titled "Water Wisely: Auditing Home Lawn Irrigation Systems."  To see just how strongly people feel about lawn watering, either for or against the practice, have a look at the 170 comments following the article below on the Star Tribune website.  Click the image below to be directed to the original article.  Thank you for your support of our water saving initiatives!  

Water Wisely: Auditing Home Lawn Irrigation Systems

Sam Bauer, Extension Educator

A broken sprinkler can waste thousands
of gallons of water in a single year
Auditing irrigation systems is an important practice for maximizing water use efficiency in the home landscape.  Audits entail checking for irrigation uniformity and converting minutes of irrigation to a depth in inches of water applied.   A full irrigation audit should be conducted at least every three years, although proper irrigation requires more frequent monitoring of irrigation system components to ensure that everything is working properly.  Broken sprinkler heads and irrigation of impervious surfaces are very common issues that we observe and these must be repaired in a timely manner. 

Basic Irrigation Auditing Procedure

Step 1: System inspection
Irrigation of impervious surfaces is
bad practice and will cost you money
Run each irrigation zone.  Look for broken sprinklers, low water pressure and arcs or angles of water spray that are distributing water where it is not needed (i.e. on streets or driveways).  Replace sprinklers, correct water pressure issues, and make adjustments to the water distribution so your system is supplying water where it is needed.  

Step 2: Performance testing
Performance testing involves placing catch cans on the lawn in an evenly spaced grid pattern throughout an individual irrigation zone.  Cans should be placed 5 to 8 feet apart for small area spray-sprinklers and 10 to 20 feet apart for large area rotor-type sprinklers.  A minimum of 20 cans should be used for each irrigation zone- more cans allow for greater accuracy.  Tuna or coffee cans work great for this, or you can purchase special catch cans designed for irrigation audits from big box stores for less than $1/each (be sure to use cans that have straight sides). 
Catch cans will allow you to measure
uniformity and rate of irrigation

After the catch cans are placed throughout an irrigation zone, run the zone for a set amount of time; minimum run time should be 30 minutes, but longer run times such as 60 minutes will be more accurate.  Next, measure and record the depth in inches of water in each can.  Repeat this procedure for each individual zone of your irrigation system.

Step 3: Uniformity calculations and scheduling zones
To calculate the precipitation rate of each irrigation zone, calculate the average depth of water in the catch cans for one hour of run time.  For example, if the average depth of our 20 cans was 0.75 inches and we ran the zone for 30 minutes, our precipitation rate would be 1.5 inches per hour.  For uniformity calculations, take the average depth of the lowest 25% of cans (in this case the 5 lowest cans) divided by the overall average of all cans.  For example, if the average of our 5 lowest measuring cans is 0.5 inches, divide 0.5 by 0.75 = 0.67 or 67%.  Irrigation systems with lower than 60% uniformity should be adjusted for better uniformity.
Special cans for auditing
make measurements easy

Once you have calculated the precipitation rate for each zone, you can set the run times.  If your goal is to apply 0.5 inches in one irrigation cycle and the precipitation rate is 1.5 inches per hour, set the zone for 20 minutes.    

For more information on auditing irrigation systems, visit the Irrigation Association website.
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