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Thursday, March 31, 2016

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What to do about overwintering insects

Jeff Hahn, Extension Entomologist

It is common with the mild temperatures we have experienced recently to see various nuisance insects in homes, especially boxelder bugs, multicolored Asian lady beetles, cluster flies, and western conifer seed bugs. Despite the appearance that they have laid eggs and are hatching now, these insects have actually been in homes since last fall when they first entered structures.

These insects typically took refuge in wall voids, attics, and other nooks and crannies. As long as these areas stayed cold, they remained inactive. However, when temperatures started to warm, they 'woke up' and moved towards warmth, i.e. into the inside of your home. As we are getting into spring, we are seeing this occur more frequently.
Boxelder bugs is one of several types of insects that may have
been hiding in your home during winter and are now active
inside your home.  Photo: Jeff Hahn, UMN Extension

These insects often congregate together in clusters in these harborages so as these areas warm up, not all of the insects become active at the same time. Or these insect could be in different places in homes that warm up at different times. The end result is that they do not all emerge at the same time and you can find them in your home at different times during the winter and spring.

When you see these insects now, your options are limited. Your best bet is to physically remove them, e.g. with a vacuum. Insecticides are generally not suggested as it will not prevent the insects from emerging and you have to physically remove them whether they are dead or alive.

If this is a problem you deal with every year, be sure to target control in the fall before the insects start moving inside. The best tactics are sealing as many obvious spaces that you can find and supplementing that with an insecticide treatment around the exterior of your house. Once these insects are in your home, there is little you can do.

For more information, see Boxelder bugs, Multicolored Asian lady beetles, Cluster flies, and/or Western conifer seed bugs.

Watch out for ticks during April

Jeff Hahn, Extension Entomologist

We enjoyed a very mild March and are anticipating this weather to continue into April. As people get outside more, an old “friend” will be waiting for us: ticks! Ticks are probably the last things on our minds but in fact ticks have been active during March and people have already reported finding ticks on themselves and on their dogs. This is not too surprising as blacklegged ticks, formerly known as 
Female blacklegged tick, a potential vector of Lyme disease. 
Photo: Jeff Hahn, UMN Extension
deer ticks, can be active in temperatures as cold as the mid 30’s (F). Blacklegged ticks are the species that can transmit Lyme disease as well as several other diseases.                   

What does this mean for us? Definitely get outside and enjoy the warm weather when we have nice days. Keep in the back of your mind that ticks could be encountered, especially when you are in habitats where ticks can be common. This includes grassy, brushy, and wooded areas. Minimally check yourself to detect any ticks you may have brought home with you. If you are going into areas that are high risk for ticks and the weather is particularly nice, you may even consider using a repellent to help protect yourself.

For more information see Ticks and their control.

Wednesday, March 30, 2016

New! Upper midwest home garden care calendar

Timing can be critical to successful gardening. Wondering when you should sow seeds? Plant perennials? Fertilize your flowers? The Upper Midwest sustainable home garden care calendar provides provides best and second-best timing for tasks common to gardens in Minnesota and surrounding states. After consulting the calendar, follow up with U of M Extension publications about your particular plant or garden issue. For lawns, visit the Upper Midwest sustainable lawn care calendar.

Lack of Flowers

Lack of Flowers
Mary H. Meyer, Professor and Extension Horticulturist, University of Minnesota

Large flower buds on 'Merrill' magnolia

Why didn’t my peony, forsythia, lilac, tulips, hydrangea, apple tree bloom?
This common garden question has no one simple answer. There are many plants and many reasons for a lack of flowers. Listed below are popular flowering plants and common reasons for lack of flowers.

Peony: Recently transplanted or planted too deep is the most common reason peonies fail to flower. Peony buds need exposure to cool temperatures, which buds normally get when planted 1.5 inches below the soil surface…any deeper and flower buds may not get cold enough. When moving peonies, pay close attention to bud height and plant at the same depth. Another reason: If your newly divided peony does not flower, they may need to grow larger before buds develop. Also, see Consider the Site information below.

Forsythia: Flower buds may be killed due to cold temperatures…in MN only hardy forsythia will flower here, such as  ‘Northern Sun’; in very cold winters, even these hardy cultivar flower buds can be killed. Branches covered with snow remain protected and flower; exposed branches may have no flowers. Another reason: plants were pruned in fall, removing the flower buds. Also, see Consider the Site information below.

Lilac: Most likely reason: pruned in fall and cut off flower buds. Additional reason: Plant lacks the capacity to bloom due to limited food reserves usually from poor site…..too shady, competition from other plants, poor, compacted soil, restricted root area, very dry or too wet soils.

Tulips: Most likely reason: tulips decline after the first year, tulip bulbs decrease in size as they age, becoming smaller; the bulbs lack the capacity to flower and send up only a leaf or two. Another reason: deer ate off flower buds. Plant species tulips such as Tulipa tarda or Tulipa greigii that are perennials.

Hydrangea: Cold killed flower buds on less hardy kinds, such as Hydrangea macrophylla ‘Endless Summer,’ which is more difficult to grow in Minnesota. Pee Gee and Annabelle are specific cultivars of H. arborescens and H. paniculata, two different species that are hardy and recommended in Minnesota. There are many selections of these two species offered for sale in Minnesota. Also, see Consider the Site information below.

Apple: Age of the plant can affect flower formation in apples. Some kinds are just slow or recalcitrant (reluctant) to form flowers. This is an inherent genetic factor that we cannot regulate or control. ‘Zestar’ seems to flower at a young age, faster than ‘Honeycrisp’  both cultivars released by the U of M and recommended for Minnesota. Also, see Consider the Site information below.

Consider the Site: A shady site will limit what plants can grow and flower: flowers and fruit usually require full sun for the best performance; exceptions are plants grown for and sold as SHADE tolerant, such as hosta or perennial geraniums. Compacted or shallow soil will limit the size of a plant’s root system; poor sandy soil that holds few nutrients can limit plant growth. Have a soil test done for any area where plants are underperforming to see what nutrients are needed. If possible, remove competition from nearby plants to improve sunlight for non-flowering plants. Plant new selections better suited to a shady, dry or wet sites and incorporate organic matter or compost into the soil.

Tuesday, March 22, 2016

Is Spring 2016 a repeat of Spring 2012?

K. Foord, UMN Extension Educator

The warm temperatures encountered in the first half of March of 2016 are reminiscent of the extreme early spring encountered in 2012. However, if you compare this year’s spring temperatures with the 30 year average, we are above average but nothing like 2012.

One way to compare temperature data among years is to create a statistic called a Heating Degree Day (HDD). This number is created by taking the average temperature for the day and subtracting 65 degrees.  The average temperature for the Twin Cities yesterday March 21st was 41 degrees, and thus the HDD was (41-65 = -24).  The idea being that in that day the heat required providing for the 24 degree difference between the 65 degree reference building temperature and the 41 degree average outside temperature was 24. So the HDD for March 21, 2016 was 24. The 30 year normal for March 21st is 35 F, so the HDD for the average is -30. If we sum these numbers for all the days in a month then we can compare months between years.

The summed HDD for the month of January for the years 2012, 2014, 2016, and the 30 year average were 1,285, 1,762, 1,463, and 1,531, respectively. The lower the number the less heat required. 2012 was 246 days lower than the average and 2016 was 68 lower than the average. In 2014 the HDD for January was 231 more than the average and thus a relatively cold month.

If we compare the HDD for the month of March for the same years 2012, 2014, 2016, and the 30 year average we get the following (*with the understanding that we still have 10 days left in March of this year) 524, 1,217, 502*, 998, respectively.  So we are early but not like 2012.

Freeze damage depends on bud stage

Damage experienced from late spring frosts is a function of the temperature sensitivity of a bud which in turn depends on its type and its stage of growth. For example: A tight strawberry bud can tolerate temperatures down to 22 F. As the bud begins to open and approaches a “popcorn stage” the critical temperature rises to 26.5 F. The fruit’s critical temperature is 28 F, and the flower itself is most sensitive with its critical temperature being 30 F.

Deciduous fruit trees follow a similar pattern although the temperatures will not be exactly the same. See the following link to get more detailed information.

The extent of frost damage depends on the low temperature reached and the time it spends at that temperature.

Know your local microclimate 

To some extent frost protection becomes a local phenomenon and depends on the microclimate experienced by the plant.  This is determined by your exact location and its topographical characteristics. Is your plant protected in some way by your home?  Large bodies of water moderate air temperatures and urban areas with buildings and pavement as heat syncs that can radiate heat back at night. Topography is a factor. Southern facing slopes with early spring warmth can encourage fruit trees to flower earlier and be more vulnerable to late spring frosts. Air drainage is important. Fruit trees planted in an area where cold air collects can experience colder temperatures then plants on the upper part of slopes.

In terms of the year, yes we are early and we need to keep an eye on things. That being said the predicted upcoming cooler weather with lows in the high 20’s and low 30’s will likely not damage many buds and will slow plant growth reducing our risk of late frost damage.

Prevent Oak Wilt

M. Grabowski,  UMN Extension Educator

Large oak tree killed by oak wilt
S. Katovich, USDA Forest Service
It is no longer safe to prune oak trees in Minnesota. Any pruning cuts or wounds made at this time have some risk of becoming infected with oak wilt. This risk will only increase as the weather becomes warmer. Gardeners should avoid pruning or wounding oak trees at this time. If pruning is absolutely necessary, the pruning cut should be covered with shellac or a water-based paint immediately after making the pruning cut.

Oak wilt is a fungal disease that kills thousands of oak trees each year. Red oaks can wilt and die within a few weeks of infection, whereas bur and white oaks may survive several years before succumbing to the disease.

The fungus that causes oak wilt produces sweet smelling mats of fungal spores under the bark of recently killed red oak trees. Sap feeding beetles are attracted to the sweet smell and become covered in spores when they visit the fungal mats. These beetles are also attracted to fresh pruning cuts or wounds on oak trees and carry the oak wilt spores to healthy trees that have recently been pruned or wounded.

The risk of oak wilt infection through wounds or pruning cuts is divided into three categories, safe, low risk, and high risk, based on the presence of oak wilt spore mats and the activity of sap feeding beetles. Minnesota is currently in 'Low Risk' status for oak wilt.
Spore producing mat of the oak wilt fungus.
M. Grabowski,  UMN Extension

The only safe time to prune oak trees is during the safe period. This occurs when the sap feeding beetles and the fungal pathogen are not active. In Minnesota, the safe period for pruning oaks typically occurs from November through March. Early warming this spring, however, has resulted in an early transition to the low risk period. During the low risk period, the risk of infection is considered minor but because the disease is fatal and no treatment is possible for infected red oak trees, the recommendation during the low risk period is to not prune oaks if at all possible. If pruning cuts are necessary, the surface of the cut should be covered with water-based paint or shellac immediately after the pruning cut is made.

To learn more about how to recognize the symptoms of oak wilt, submit a sample for diagnosis, prevent and manage infection read 'Oak Wilt in Minnesota'.

UPDATE: Minnesota's Oak wilt risk status has now been upgraded to HIGH RISK.

Tuesday, March 1, 2016

Pruning Shrubs for Maximum Bloom

Kathy Zuzek, UMN Extension Educator

Late winter and very early spring are common times for shrub pruning.  Remember though that the pruning of shrubs valued for their flowers and/or fruit should be scheduled based on where flower buds are formed:
    forsythia bush in bloom
    Forsythia should be pruned immediately
    after flowering.
    Photo:  Bailey Nurseries
  • Most spring-flowering shrubs bloom on the previous year’s stem growth and should be pruned immediately after they bloom. New stem growth will occur in summer along with flower buds that will develop into next year’s bloom.
  • The flowers of shrubs that bloom in summer or fall are from flower buds that formed on the current season’s stem growth. The best time to prune these species is winter or early spring. This will lead to vigorous stem growth in spring and summer that contain flower buds which open in summer and early fall.

Blossoms on:
Scientific Name
Common Name
Previous Year’s Stems
Current Year’s Stems
azaleas & rhododendrons
Buddleia davidii
cherry, almond, plum
Daphne x burkwoodii
Hydrangea macrophyllum
hydrangea, bigleaf
Hydrangea paniculata
 hydrangea, panicle
Hydrangea arborescens
hydrangea, smooth
roses, repeat-flowering
roses, spring-flowering
Spiraea prunifolia & S.
 x vanhouttei
spiraea (spring-blooming)
Spiraea x bumalda & S. japonica
spiraea (summer-blooming)
Hypericum kalmianum
St. Johnswort
summersweet clethra
sweet shrub
Campsis radicans
trumpet vine
white forsythia
Ilex verticillata
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