University of Minnesota Extension
www.extension.umn.edu
612-624-1222
Menu Menu

Extension > Yard and Garden News > June 2010

Wednesday, June 30, 2010

Sapwood Rotting Fungi Kick Trees When They Are Down

Michelle Grabowski, UMN Extension Educator

schizo dieback Y&G.jpg

Photo 1: Canopy dieback caused by sapwood rotting fungi Photo by M.Grabowski UMN Extension.

When shade trees are stressed by environmental conditions or wounded by storms, ice, insects, sunscald or mechanical damage, sapwood rotting fungi often show up to take advantage of the trees weakened state. There two sapwood rotting fungi commonly found in Minnesota, Schizophyllum commune or Cerrena unicolor. These fungi infect the tree through wounds. They then rot the sapwood and kill the bark. When severe, the infection can grow to completely encircle a branch or the main trunk, killing all leaves and branches above the infected area.

Sapwood fungi infect a wide variety of common shade trees. Maple (Acer), linden (Tilia), willow (Salix), elm (Ulmus), oak (Quercus), ash (Fraxinus), poplar (populus), and many more may all suffer from this disease.

How to Recognize Sapwood Rotting Fungi
Gardeners often first notice dead branches throughout the canopy of infected trees. Cracked and peeling bark may be seen on the main trunk or branches. Upon close examination, clusters of small white shelf fungi can be found growing on the infected wood. These are reproductive structures of the sapwood rotting fungi and can be easily seen this time of year in Minnesota. A gardener can determine which of the two fungi is causing the problem by closely examining these fungal spore producing structures.

cerrena Y&G.jpg

Photo 2: Spore producing structures of Cerrena unicolor Photo by M.Grabowski UMN Extension .

The spore producing structures of Cerrena unicolor are ½ to 3 inch semi circular shelf fungi. They are white to green gray in color and often rings of growth are apparent on the top surface of the fungi.
schizo Y&G.jpg

Photo 3: Spore producing structures of Schizophyllum commune Photo by M.Grabowski UMN Extension.

Teeth like ridges can be seen on the lower surface of the fungi.

Schizophyllum commune also produces small shelf fungi on infected wood. These shelf fungi are smaller (1/4th to 2 inches across), cupped downward, and pure white. When examined up close, the upper surface appears fuzzy. Gills can be seen on the lower surface of these shelf fungi.

Keep Trees Healthy and Strong to Avoid Sapwood Rotting Fungi
Prevention is the best management strategy to control sapwood rotting fungi. Avoid wounding trees with weed whips, lawn mowers or other lawn equipment. If trees are damaged in a storm or by ice, remove broken and cracked branches with a clean pruning cut. This cut will be easier for the tree to heal than a long jagged rip caused by a storm. Water trees during times of drought. Mulching the base of the tree out to the canopy drip line with an organic mulch like wood chips can help maintain soil moisture and reduce competition with turf grass.

If infection appears on a branch, prune the infected branch on a cool dry day and remove it from the area. If the infection appears in the main trunk, the only thing that can be done is to reduce stress on the tree and hope for the best.


Summer Lawn Care on the Heels of a Wet and Stormy June

Bob Mugaas, UMN Extension Educator

With the recent rains and storms across the state, most lawns have had sufficient moisture to remain actively growing and green through the month of June. In fact, in some instances there has been too much rain causing lawns to remain in excessively wet conditions for several days or more at a time.

bob1.JPG
Temporarily ponded water from excessive rainfall
Bob Mugaas
Under moderate temperatures and partly sunny or cloudy conditions, water that temporarily (a day or two) remains at or near the lawn surface is usually not a problem. (See Picture 1). Once the water drains away and soil oxygen levels rise such that normal root functions can continue, the grass will resume normal activity and growth with little to no evidence of having been temporarily submerged. However, under sunny conditions and high temperatures, lawn areas remaining in saturated soil conditions or submerged for even a few hours can suffer serious damage and even death. Once the moisture does recede, grass plants will appear dark brown to black indicating they are no longer alive. These areas often have a foul smell associated with the dead and dying plant tissue. Following those conditions and once the area has dried out, it will be necessary to reseed or resod the area due to the grass that has been killed.

Moist conditions in the lawn have also given rise to the random appearance of many different kinds of mushrooms. These are the result of fungi feeding on the dead and decaying organic matter in the soil and thatch layers of the lawn. As these fungi continue to grow and carry out their decomposer role in the soil and thatch, they will periodically, especially under moist conditions, send up fruiting structures that we know and see as mushrooms. See Pictures 2 & 3.

bob2.JPG
Lawn mushrooms emerging during moist conditions
Bob Mugaas
bob3.JPG
Another species of mushroom growing in the lawn
Bob Mugaas
These are not indicative of problems in the lawn or of an impending lawn disease outbreak. Most of these fungi carry out the beneficial process of decomposing soil organic matter which ultimately helps recycle nutrients back to the grass plants for growth and development. There are fungi that cause the appearance of darker green circles or arcs in the lawn. This pattern or symptom is commonly known as fairy ring. See Picture 4. If these are what you are seeing, you can check out turfgrass disease section of Extension's Gardening Information page. One should not eat mushrooms appearing in the lawn! Where there is concern about children or pets possibly consuming them, simply break them off with a rake, pick them up and dispose of them in a manner that keeps them completely out of the reach of children or pets.

bob4.JPG
"Fairy ring" in lawn
Bob Mugaas
With the excessive amount of rainfall and the continued vigorous growth of our grasses all during June, it is very possible that our lawns will benefit from a light application of nitrogen fertilizer. Nitrogen can be lost in a number of ways from the lawn including leaching (i.e., carried with water draining through the soil), gaseous loss back to the atmosphere and taken up and used by grass plants for growth. Hence, under the moist conditions and rapid grass growth that we have been experiencing lately, many of our lawns will benefit from ¼ to ½ pound of actual nitrogen, per thousand square feet. It's important to not fertilize excessively going into and during the potentially hot summer months of July and August. That can unnecessarily stress the grass plants and perhaps result in injury during those hot, dry summer periods we expect to encounter in Minnesota during July and August.

bob5.JPG
Excessive clippings from waiting too long to mow.
Clippings should be removed from lawn surface before
causing damage to underlying grass
Bob Mugaas
While it's tempting to mow the grass much shorter once it has gotten too long, that will be extremely stressful for the grass plant and actually results in a slowing or even stoppage of growth and recovery, and perhaps even the death of some plants. That slowing or stopping of growth may seem like just the result you are looking for, but, it's really not. Our lawn grasses are much healthier, competitive, and stress tolerant when they grow at relatively uniform rates. Under those conditions, the amount of food produced by the leaves is sufficient to meet the plants growth needs as well as create some additional stored reserve. When large amounts of leaf and stem tissue are removed at a single mowing, shoot and root growth slows or even stops. That additional stress can open the door to certain disease and insect problems as well as increased potential for weed invasion while the grasses are recovering. If the excessive clippings are left on the lawn, there can be enough sunlight reduction to the plants underneath the clippings that they can be injured or even killed causing a thinning out of the lawn. (See picture 5.)

The loss of large amounts of leaf tissue all at one time forces the use of stored plant reserves just to survive. As a general rule, when our grass growth gets a little too far ahead of us, initially mow as high as your mower will safely allow. Then, begin lowering the height of cut by mowing more frequently and gradually reduce the mowing height back to the desired level. This is much healthier and less stressful for our lawn grasses.

Birch Erineum Gall

Jeffrey Hahn, UMN Extension Entomologist

bircherineum.JPG
Birch erineum gall
Jeff Hahn
Some birch trees are exhibiting red, fuzzy patches on some of their leaves. It is common to assume that this is a type of disease but it is actually a type of gall. Galls are abnormal plant growths due to a variety of different organisms. In this case is caused by a species of eriophyid mite. Eriophyid mites are very tiny and nearly microscopic. This gall is similar to ones found on maple, viburnum, and linden. Like other insect and mite leaf galls, birch erineum galls have very little, if any, impact on tree health. You do not have to do anything if you find this gall in your tree, just ignore it.



Strawberry Root Weevils

Jeffrey Hahn, UMN Extension Entomologist

srw2.JPG
Strawberry root weevils
Jeff Hahn
Strawberry root weevils have been common around homes lately. This insect is about 1/4th inch long, reddish brown to dark brown to black in color. They are bulb-like in shape with rows of shallow pits running down their back. They have a conspicuous pair of antennae which can look like a pair of legs. This could be why some people confuse these insects for ticks. However, when someone says they have ticks in their house, double check for the presence of strawberry root weevils.

Despite their name, the larvae actually feed on the roots of a variety of plants including strawberry, arborvitae and other evergreens, raspberries, and grapes. The adults notch feed along the edges of leaves. However, despite this feeding, strawberry root weevils are not considered a plant pest in Minnesota.

It is common for strawberry root weevils to enter homes looking for moisture. They are commonly found around sinks, basins, and tubs. Fortunately, strawberry root weevils are harmless to people and property. Once, they are indoors, the only necessary control is physical removal.

Earwigs Are Active Now

Jeffrey Hahn, Extension Entomologist

People have been commonly reporting European earwigs recently. An earwig is about 5/8 - 3/4 inch long, with a flat, reddish brown body and very short wings. They are beetle-like and are sometimes confused with cockroaches. However, it's easy to identify an earwig as they have forcep-like pincers on the tip of its abdomen: males have stout, curved pinchers while females possess more slender, straight pincers. Despite these pinchers, earwigs are harmless to people and our property.

DSC_0493.JPG
Female European earwigs
Jeff Hahn
Earwigs love to be in dark, confined, damp areas and are found under potted plants, leaves, welcome mats, in cracks between pavers and similar places. They may also be found on plants in tight, protected areas. They are mostly active at night when they feed on decaying plant tissue, live and dead insects, as well as live plants. Occasionally, earwigs can be a pest when they feed on flower blossoms. They are also reported to attack corn silk and seedlings.

People are most concerned about earwigs when they come into their homes. To keep them out, caulk and repair any obvious spaces, cracks, or gaps around the outside of your home, especially at ground level. Also clean up debris around the house that earwigs can hide under, such as leaves and plant debris. It may also be useful to thin out or remove mulch to reduce earwig numbers. You can supplement this with a residual insecticide treatment, e.g. permethrin or cyfluthrin, around the perimeter of the building. However, if earwigs are determined, some will still get inside your home. For those interlopers, just remove them with a vacuum or a broom and dust pan.

July 2010 Garden Calendar

- Time to set out apple maggot traps in apple trees.

- Strawberry picking is just beginning in the north, and starting to wind down in the south.

- Raspberry picking is underway.




Spotted at the Arboretum: Canada Geese and Wild Turkey


goose2-2.jpg

goose1-1.jpg
turkey.jpg

Photo credits: Karl Foord


Yard and Garden News Editor: Karl Foord, UMN Extension Educator
Technical Editor: Bridget Barton


Tuesday, June 15, 2010

Peony Flower Types

Karl Foord, UMN Extension Educator

I just finished photographing the peony collection at the Minnesota Landscape Arboretum and was amazed at the variety of flower types and colors. Peony flower types fall on a continuum starting with single and progressing through semi-double, Japanese, and double. The single flower has a central cluster of carpels surrounded by a ring of stamens surrounded by a ring of petals, a basic flower structure. The following flower types all have modifications of this basic structure. The semi-double flower may have a fertile center surrounded by several layers of petals. "Japanese" peonies have modified stamens (staminoides) which may have some functional anther material and pollen, but the stamen filaments are now more like petals. In double peonies all flower parts are petals.

kf12-1.jpg

kf34-3.jpg

kf5-1.jpg

kf89-1.jpg

kf10-1.jpg

According to some estimates, there are over 3,000 cultivated varieties of peony.


To identify peonies, a fairly comprehensive list is available at http://www.paeo.de/ - (Carsten Burkhardt's Web Project Paeonia). If you are interested in buying peony bulbs suppliers can be found through the plant info tab on the Minnesota Landscape Arboretum's website. (http://plantinfo.umn.edu/ and http://www.arboretum.umn.edu/ hit the plant info button top center of page). I did a search for peony and got 1297 search result(s) for Paeonia on this site.

Photo credits: Karl Foord



What's Happening in the Orchard?

Karl Foord, UMN Extension Educator

kf1.JPG

Photo 1: Strawberry field showing some almost ripe berries and developing fruit.



Strawberries


Pick-your-own strawberries should be in full swing as of this writing. The picture below was taken at Apple Jack Orchards in Delano on June 10, 2010. Don't miss the opportunity to taste fresh strawberries. You can find a strawberry field near you by going to http://www3.mda.state.mn.us/mngrown entering your location and clicking on the strawberry button. The Minnesota Grown Strawberry fields will be listed in order based on proximity to your location.




Apples

Continue to protect your small young apples. I found damage from a few green fruitworm as well as plum curculio. Plum curculio causes feeding and egg laying damage to young apple fruit. Practice sanitation and remove all infected fruit. Do not let the fruit fall to the ground permitting the curculio larvae to burrow into the soil pupate and come back next year in greater numbers.
kf234-3.jpg

Some minor damage by green fruitworm - a climbing cutworm. (Photo 5.)kf5.JPG

Photo 5: Damage to young apple fruit by green fruitworm.



kf6.JPG

Photo 6: Pine Tortoise Scale on Uncle Fogy Pine.


My roving garden camera also found Pine Tortoise scale in my Uncle Fogy Pine. The scales were so thick on this tree that it looked like the scales were the bark of the tree. Because plants contain low densities of the nitrogen compounds needed for building proteins, the scale needs to consume an excess of sap to satisfy their nutritional requirements. The excess is expelled as "honeydew" which acts as a substrate for the growth of a sooty mold fungus that blackens affected plants. My tree was stunted by the scale and blackened by the fungus.



Thanks to Jeff Hahn and Emily Hoover for identification of insect pests. Photos by Karl Foord.

Gray Mold

Michelle Grabowski, UMN Extension Educator

YG botrytis 1.jpgRecent wet weather has provided perfect conditions for a common fungal disease of flowering annuals known as gray mold. Gray mold is caused by the fungus Botrytis cinerea

Photo 1: Gray mold from an infected flower moves to leaves M.Grabowski UMN Extension.

and can occur in a wide variety of annual flowers including impatiens, zinnias, geraniums and many more.

YG botrytis 3.jpg

Photo 2: Brown leaf spot from gray mold infection M.Grabowski UMN Extension.

Often called Botrytis blight, gray mold causes a dark brown to black blight of flowers, buds, leaves and stems. Flower petals are especially susceptible to infection by the gray mold fungus. Brown spots may be seen on petals or the entire flower may turn brown. As flowers age, they fall off onto healthy leaves below. The gray mold fungus then infects the leaves. Removal of these rotted petals often reveals a brown target shaped spot on the leaf which quickly grows to rot the entire leaf. With high humidity a cloud of fluffy gray spores forms on old infected leaves and petals. These spores are easily blown or splashed to new flowers to start the infection cycle all over again.

yg zinnia botrytis.jpg

Photo 3: Zinnia seedling from the center of a nine pack is killed by Gray mold M. Grabowski UMN Extension.

Gray mold thrives in wet crowded conditions. This time of year it can easily be found in over crowed annuals. Gardeners may have flats of annuals waiting to be planted. As these plants outgrow their small containers, humidity builds, and gray mold takes off. It is not unusual for a gardener to find the center plant of a six or nine pack completely blighted by gray mold.

YG botrytis 2.jpg

Photo 4: Gray spores of gray mold on rotted leaves and petals M.Grabowski UMN Extension.

The best management strategy to minimize gray mold in annuals is to space out plants so that leaves and petals dry out quickly after rain or irrigation. If the annuals cannot be planted in the garden due to weather conditions or other factors, take pots out of the flat and space them out to allow good air movement between plants. If plants in multipacks cannot be planted quickly, transplant them into larger pots where they will have room to grow and will not crowd one another. When planting in the garden, place plants to allow room for the mature plant. Gray mold can show up anytime wet weather occurs during the growing season.

Spent flowers and infected leaves should be pinched off and removed. Fungal spores are formed on these old rotted plant parts, so do not leave them lying in the garden. Rather collect all infected plant parts in a paper bag and dispose of them. It is ok to compost leaves and flowers infected with gray mold because Botrytis cinerea is commonly found in soil and old plant debris. With a little care most plants can recover from gray mold once warm dry conditions return.


Monday, June 14, 2010

Prepare For Mosquito Season

Jeffrey Hahn, UMN Extension Entomologist

Aedes sp.jpg
Aedes mosquito
Jeff Hahn
With the rains that have fallen on most of Minnesota recently, you can expect the number of mosquitoes to significantly increase. However, keeping away from these blood-lusting insects is easier said than done. The bites are bad enough but we also have to worry about mosquito transmitted diseases, especially West Nile virus. There are certain precautions you can take to protect yourself when you are in mosquito-infested areas. You can minimize your exposure by avoiding times when mosquito activity is the highest, i.e. dawn and dusk and also wear long-sleeved shirts and long pants.

However, the best method for protecting yourself from mosquito bites is using a repellent. The Centers for Disease Control and Prevention (CDC) recommends several repellents that you apply to your skin and clothes for mosquito control. The best overall repellent has traditionally been DEET (N,N-diethyl-m-toluamide). DEET has been available to the public since 1956 and has been consistently very effective. The CDC also recommends picaridin, considered a conventional repellent, and oil of lemon eucalyptus and IR3535, considered to be biopesticide repellents, derived from natural products.

You can also consider using 0.5% permethrin on clothing, shoes, netting, tents, and other camping gear. This insecticide will kill mosquitoes on contact. However, unlike repellents, don't apply permethrin to your skin.

The U.S. Environmental Protection Agency (EPA) has a web page that allows you to find a repellent that is appropriate for your use. You can enter information on whether you want to use this repellent for mosquitoes or ticks, how long you want the repellent to be effective, and if you are looking for a particular active ingredient.

Watch For Meal Moths

Jeffrey Hahn, UMN Extension Entomologist

MVC-004S.JPG
Meal moth
Unknown
There have been a number of reports of meal moths in homes recently. When at rest, the forewings of this moth have a dark reddish brown band across the top and bottom of the wings while there is an olive or yellowish green band, outlined by wavy white lines in the center. They have a wingspan of about 3/4 - 1 inch. Their abdomen is typically curved up at a 90o angle when at rest.

Meal moths are not as common as Indianmeal moths, although they both feed on dried food products. Meal moths are known to feed on flour and grain products, seeds, and hay especially when they are damp. These moths are generally not common in homes but are more typically found in mills, barns, and warehouses.

If you do find meal moths in your home, the best control is to find the source of the infestation and remove it. Look where you store dried food products. Don't forget about places where grain and flour products, bird seed and other types of seeds, and dried pet food may have been spilled and forgotten about. Start looking where you most commonly find the moths; this is probably close to where the infestation is. Because meal moths do not generally occur in large numbers, it will be more challenging to find the infestation and will probably require some detective to discover the source of the problem.

Cutworms Common This Spring

Jeffrey Hahn, UMN Extension Entomologist

cutwormspoatosesharonsmith.JPG
Cutworm damage on potatoes
Sharon Smith
Cutworms have been a very common insect problem in many home gardens this year. They have also been commonly reported in Wisconsin and Iowa as well. Most of the cutworms that occur in Minnesota overwinter as large larvae. It has been speculated that the heavy snow cover we experienced this spring increased the survival of the overwintering cutworms. That coupled with the early spring allowed them to occur early in the season. There are some non-native cutworms, e.g. black cutworms, that move up to Minnesota from the south, but they did not appear to have been as damaging this year.

Cutworms hide during the day in the soil near the plants, then feed on plant stems at night. Their damage is most severe right away in spring when plant stems are more tender but not a problem later in the summer. Unfortunately, it's too late to manage cutworms any longer this year. That cutworms were very common this year does not necessarily mean that they will be numerous next spring. There are too many factors that influence cutworm numbers to make a prediction now for 2011. Regardless of how numerous they will be next spring, if you have had an issue with them this year, be on the watch for them in 2011. For more information, see Cutworms in Home Gardens.

Tuesday, June 1, 2010

Ash Anthracnose or Emerald Ash Borer?

Michelle Grabowski, UMN Extension Educator and Jeff Hahn, UMN Extension Entomologist

ash anthracnose.jpg
Ash tree defoliated by anthracnose
J. O'Brien USDA Forest Service, Bugwood.org
With the discovery of emerald ash borer (EAB) in Minnesota in 2009, many homeowners are keeping a close eye on the ash trees on their property. This has resulted in a great deal of concern as many ash trees began to drop their newly formed leaves early this spring. In most cases, however, the cause of this early leaf drop was a common fungal disease known as ash anthracnose.


Emerald Ash Borer

eab killed tree - Jeff Hahn.JPG
Thin canopy of an EAB infested tree
Jeff Hahn, UMN Extension
If a tree is suffering from infestation with EAB, the tree's canopy will appear thin, with few to no leaves. Eventually dead branches will be noticed within the tree. Cracks and D shaped exit holes can be found in the bark of infested trunks, and woodpeckers may be noticed frequently visiting infested trees to feed on EAB larvae. The emerald ash borer itself is a slender, ½ inch long, iridescent green beetle. It is active anytime from late May into August.

Ash Anthracnose

In contrast, trees infected with ash anthracnose will have dark brown to black water soaked blotches on leaves and young shoots. These leaves are often distorted and curled around the infected area of the leaf. Infection on petioles and young shoots can result in leaf drop. In some years, leaf drop can be quite severe, resulting in almost complete loss of the first flush of leaves. Infection is often most severe in the lower and inner branches of the tree, where high humidity favors fungal growth. Ash anthracnose is very common in cool wet spring weather, but does not persist in warm dry summer weather.

Help Diagnosing the Problem

Concerned homeowners have many resources available to help them determine which problem is occurring in their ash tree. What's wrong with my ash? Is an online diagnostic tool that helps gardeners diagnose ash problems through a series of simple questions about what symptoms they are seeing. Gardeners should also visit the UMN Extension EAB resource webpage. This page includes many useful tools including a step by step guide to determine if EAB is a possibility in your tree, a publication on insects that may be confused with emerald ash borer, and maps showing where EAB has been found in MN. Those without internet access can call Forest Resources Extension at 612-624-3020 for further assistance.

What is Ash Anthracnose?

Anthracnose Y&G.jpg
Leaf symptoms of ash anthracnose
M. Grabowski, UMN Extension
Ash anthracnose is caused by the fungus Discula fraxinea, and is a common problem on Minnesota ash trees early in the growing season. Whereas Emerald Ash Borer is a serious threat to ash trees, ash anthracnose is closer in severity to a common cold. It's not pretty, it can be stressful to the tree, but it is rarely life threatening.

The ash anthracnose fungus can infect most species of ash trees (Fraxinus spp.). In the Great Lakes states, green ash (F. pennsylvanica) is often most severely infected. The ash anthracnose fungus overwinters in last year's infected leaves and twigs. New fungal spores are produced in early spring in these old infections. This coincides with the opening of tree buds and the emergence of new leaves and shoots. These young undeveloped plant parts are highly susceptible to the ash anthracnose fungus. If cool wet weather persists, ash anthracnose can be quite severe.

The good news is that mature ash leaves are relatively resistant to the ash anthracnose fungus (although infection can occasionally be seen associated with insect feeding or other wounds). As the weather turns warm and dry and tree leaves mature, ash anthracnose is no longer able to spread rapidly throughout the tree canopy. Trees that lost their first flush of leaves, replace them. By midsummer, symptoms of the disease are often difficult to find.

What to Do About Ash Anthracnose?

Ash anthracnose is considered a minor stress to the health of a tree. A mature vigorously growing tree can tolerate complete leaf loss for 2-5 years. Reducing other stresses on the ash tree throughout the growing season can help the tree recover. Simple activities like watering trees during periods of drought, mulching the soil at the base of the tree to reduce competition with turf grass, and avoiding wounding trees with lawn equipment will help the tree recover its strength. Raking up and removing infected leaves at the end of the growing season will help to reduce the amount of fungi that survive from one season to the next, although some fungi often survive in infections within the tree canopy.

Although there are fungicides that will prevent ash anthracnose, it is too late this year for fungicide applications to be effective. Fungicides must be applied early in the growing season to protect young emerging leaves and shoots. Homeowners should not apply fungicides to mature shade trees. The spray equipment available to homeowners will not provide effective coverage in a mature tree, and serious safety risks can occur to homeowners that attempt fungicide application with inappropriate equipment. Fungicide applications are only recommended in trees that have suffered severe leaf loss due to ash anthracnose several years in a row. In this situation a tree care company with a certified pesticide applicator (licensed by the MN Department of Agriculture) should be contracted to safely apply the fungicide at the appropriate time of year.

What's Happening in the Orchard?

Karl Foord, UMN Extension Educator

As you know, this has been another unique spring for Minnesota. We started out several weeks ahead of normal and lost some ground with a cold spell. Unfortunately, in some areas the cold spell was more than a delay. In certain parts of the state the nighttime lows on May 9th reached 25.5 degrees F.


Strawberries

Strawberry flowers are most vulnerable to frost damage when fully open. At this growth stage 30 0F will damage the flowers. The fruit can tolerate a few more degrees and sees damage at and below 28 0F. A "popcorn" stage closed flower bud shows damage at 26.5 0F and a tight bud at 22 0F. A damaged strawberry flower will turn black in the middle whereas a healthy flower will be yellow in the middle (Photo 1). This frost damaged open flowers and some "popcorn" flowers. All is not usually lost with strawberries as they flower over a two to three week period (note the variation in stage from open flower to young fruit (Photo 2) and the healthy clusters of young fruit that survived the frost (Photo 3). Look for pick-your-own strawberries to be available the second or third week in June depending on your location. Experience strawberry flavors beyond those available in grocery stores where the plants have been bred for shipping at some cost to flavor.

kf123-2.jpg

Apples

It took a week to discern what damage these low temperatures had done to apple flowers. Unfortunately, fields with early flowering cultivars that experienced these temperatures were damaged (Photos 4 and 5).
kf45.jpg

There may be some apples available as only 10% of the flowers are needed to produce a full crop. Note the size advantage in fruit that can accrue from being the first flower in the cluster to open - the king flower (Photo 6).
kf6.jpg

If your apple flowers were not damaged by frost and you experienced good seed set, it will soon be time to thin. The tree will naturally drop a number of these apples in the so called June drop, but it is likely that you will still benefit from your own thinning. Thinning to one fruit per cluster or spur is recommended. Proper thinning promotes big apples and helps to avoid alternate bearing where you have a surplus of apples in one year and a surfeit the following year. Photos 7 and 8 show and apple flower/fruit cluster before and after thinning. Keep an eye out for leaf rollers (Photo 9) and plum curculio.

kf789.jpg

Raspberries

Fruits are forming on the first raspberry flowers (Photo 10). We may see the end of strawberry picking overlap with the beginning of raspberry picking.
kf10.jpg

Acknowledgements:
Sincere thanks to Apple Jack Orchards for permission to photograph their plants. Also thanks to Mike Dekarski and Tom Marxen for their insights into strawberry, apple, and raspberry culture. Photo credits: Karl Foord.

Flowering Lawn Grasses Create Curiosity and Concern Among Homeowners


Bob Mugaas, UMN Extension Educator - Horticulture

Minnesota lawn grasses are known as cool season grasses as their peak periods of growth and activity occur during the (usually) cooler seasons of spring and fall. These grasses include Kentucky bluegrass, fine fescue, perennial ryegrass and tall fescue. The middle of May through most of June is the prime flowering period for these cool season grasses in Minnesota. Kentucky bluegrasses tend to be the first of the grasses to begin flowering with the fine fescues, perennial ryegrasses and tall fescue coming on slightly later. See Picture 1 of Kentucky bluegrass flowering.

Picture 1. Kentucky bluegrass flowering
Kentucky bluegrass flowering
Bob Mugaas
Grass flowering is an entirely normal process whether observed in a mowed lawn or an unmowed area. However, the height of the flowering stem will usually be slightly to significantly taller in an unmowed situation than a mowed lawn. The initiation of the flowering process actually begins late the previous fall when the growing point (crown) of a mature grass shoot goes through a biological change from producing stems, roots and foliage during the late summer and early fall period to one that will produce a flowering stem the next spring. The crown remains in that condition until the following spring. As temperatures warm and day length gets longer during late April and May, these shoots begin to send up a flowering stem known as a 'culm' in grass terminology.

Picture 2.  Kentucky bluegrass inflorescence
Kentucky bluegrass inflorescence
Bob Mugaas
In most instances, even if we are regularly mowing the lawn, these shoots continue to elongate in an attempt to produce their flower cluster known as an 'inflorescence'. See picture 2. The result of mowing regularly is that we often do not see the fully elongated flowering stem and hence, the lawn appears normal and we observe little to no grass flowering. Whether mowed or unmowed, or whether a flower cluster was visible or not, these flowering shoots eventually die off during late June and into early July. This is often a time when folks express concern about their lawn looking a little thin and lots of brown stemmy material in the lawn. As it is entirely normal for these flowering shoots to die once flowering is completed, lawns can temporarily look a little thinner. The apparent increase in brown stemmy material is actually the remnants of those original flowering stems. Eventually, they will fall back into the turfgrass canopy and begin decomposing leaving little to no evidence of their prior function.

Of course, not all of the shoots present in a lawn will have gone through the biological changeover to a flowering 'bud' the previous fall. Hence, our lawns have enough growing shoots present, even though the lawn may be a little thinner, it still looks and functions like a lawn. Also, by the time we get to early August, a new round of grass shoots will be starting to form along with the production of new leaves, rhizomes, tillers and roots. This growth will continue through the fall period when once again grass shoots with sufficient biological maturity will make the changeover to flower buds that will again produce next spring's flowering shoots.

Because these flowering stems temporarily disrupt the otherwise uniform appearance of a healthy lawn surface, their presence is often viewed unfavorably. The important point here is that grass flowering is a normal, temporary condition common to most lawns. There really is little that we can control within this naturally occurring process. If desired, mowing slightly shorter for a couple of times to remove more of the inflorescence can make the flowering stems less apparent. Also, increasing mowing frequency for 2 to 4 weeks during peak flowering will help keep flowering stems from becoming too visible and disruptive. However, since flowering occurs just before the warmer and drier parts of the growing season, it will be important to raise mowing heights back up as soon as possible to encourage as much root growth and rooting depth as possible before those more stressful conditions settle in.

On the flip side of the grass flowering question is whether or not any of seed produced will actually provide some 'reseeding' back into the lawn. In other words, if one lets their lawn go to seed will they receive some benefit from the seed produced in terms thickening up the lawn. The short answer to that question is usually not. Since the process of mowing continually cuts off the developing flower cluster, any seed that starts to develop doesn't reach sufficient maturity to actually be viable. In an unmowed situation such as would be the case in a seed production field, the flower stems are allowed to fully ripen, turn brown and dry. The seed is then harvested just before it has a chance to naturally disperse from that dried flower cluster. That harvesting usually occurs from mid to late in June to perhaps early July.

Picture 3.  Kentucky bluegrass
Healthy Kentucky bluegrass
Bob Mugaas
While flowering grass stems may be an unsightly disruption to an 'attractive', uniform lawn surface, remember this is an entirely natural process of our grass plants. It is also important to keep in mind that this is a temporary process that runs its course over a few weeks in mid to late spring. Once that cycle is completed, those remaining shoots that did not flower as well as newly produced shoots continue to grow and fill-in those thinner, empty spots left behind by the dead flowering shoots. See Picture 3.
  • © Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy