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Extension > Yard and Garden News > Archives > July 2010 Archives

July 2010 Archives

Contents: July 16, 2010

In this issue of the Yard and Garden News:

  • Springtails
  • Leaf Spots are Sprouting in the Vegetable Garden
  • Rose Classes and Their Performance in Minnesota
  • Tasty Tomato Container Gardens

Springtails

Jeffrey Hahn, UMN Extension Entomologist

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Photo 1: Typical springtail. Brenda Postels.

The rainy weather that much of Minnesota has experienced this year has lead to increased numbers of springtails in and around homes and other buildings. Springtails are very small, between 1/16th - 1/8th inch long. They are usually slender, elongate insects (there is a group of springtails that is round and stout) with moderate length antennae. Most springtails are dark-colored, brown, grey or black although some species are also white, and some are even iridescent and brightly colored

Springtails are wingless and do not fly but they can jump. Unlike grasshoppers, crickets, and other insects that use large back legs for jumping, a springtail uses a forked appendage called a furcula (located underneath the abdomen) to propel itself. When not in use, a furcula is tucked up under the body, set like a mouse trap. When it is released, it extends down rapidly sending the springtail forward. A springtail can jump many times its body length.

Despite their small size, springtails can occur in tremendously large numbers and are one of the most abundant insects. One source estimates you would find millions of springtails in one hectare (about 2.5 acres) of land. They are associated with damp conditions and are found in soil, leaf litter, lichen, under bark, decaying plant matter, and other areas of high moisture. They feed on fungi, pollen, algae, or decaying organic matter.

They are occur indoors for several reasons. They can be found in the soil of overwatered houseplants and sometimes adjacent areas. They also occur in damp areas with high moisture, e.g. around plumbing leaks and damp basements. They can also move in large numbers indoors from the outside when moist conditions exit around the home. Springtails can vary in abundance indoors from just a handful to very large numbers. Fortunately, however many you find, they are harmless to people and property and are just nuisances.

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Photo 1: Typical springtail. Jeff Hahn.

If you are finding just a small number of springtails occasionally, just ignore them or physically remove them by hand or with vacuum. However, if you are seeing persistent number of springtails they are associated with a moisture problem. The best management is to dry out these areas with a fan or dehumidifier as springtails do not tolerate dry conditions. Also make any structural changes to correct the moisture problem.

If springtails are migrating in from the outside, check around the house for moisture problems. This could include rainspouts that do not carry the water far enough away from the foundation, landscapes that slope towards buildings, or excessive irrigation. It could even be a moisture problem with the roof. Correcting existing moisture conditions will help decrease springtails. As we receive less rainfall, the number of springtails will also naturally lessen.

Although it may be tempting to spray a springtail problem with an insecticide, the products available are not very effective against them. Moisture control is the most effective strategy.

Leaf Spots are Sprouting in the Vegetable Garden

Michelle Grabowski, UMN Extension Educator

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Photo 1: Bacterial Brown Spot on Beans Photo by M.Grabowski UMN Extension.

This summer early warm weather and frequent rain alternating with sunny days have created conditions allowing vegetable gardens to flourish. Many gardeners are amazed at the size of their tomato and corn plants. Recently, however, gardeners have been noticing yellowing and spotting of their prized plants, especially on the lower leaves. This discoloration is caused by several different fungal and bacterial leaf spot pathogens. Unfortunately warm wet weather also favors growth of these pathogens.

Leaf spot fungi and bacteria come into the garden on infected seed or transplants or are blown in on the wind. Many of these pathogens can survive from one season to the next on infected plant debris. Splashing rain carries fungal spores and bacteria from the soil and plant debris onto this year's leaves. Moisture in the plant canopy then allows these pathogens to start new infections. Established leaf spots create a whole new generation of bacteria and fungal spores, starting the cycle all over again.

Luckily several basic cultural control practices can help to keep leaf spot pathogens in check.

1. Reduce moisture on leaves and fruit by watering the base of the plant with drip irrigation, a soaker hose, or simply by directly the hose at the soil and not the leaves.

2. Stake plants like tomatoes, runner beans, and cucumbers.

3. Mulch the soil with straw, wood chips or a plastic mulch to prevent the pathogen from being splashed up onto the lower leaves.

4. Inspect plants regularly. If a few leaf spots show up, pinch off the infected leaves and remove them from the garden. Never remove more than a third of the plants foliage!

5. At the end of the growing season, remove infected plants or till under the plant debris to speed up breakdown of infected plant parts.

6. Rotate crops. Wait 3-4 years to plant the same plant in the same location. It is best to rotate between plant families. Follow tomatoes with broccoli, corn or beans since they are not closely related. Peppers and eggplant should not follow tomatoes since they share many of the same diseases.

The leaf spot diseases below have been recently found in Minnesota.

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Photo 2: Peppery Spot on Turnip Photo by M.Grabowski UMN Extension.

Peppery Leaf Spot - Seen here on turnip leaves, this bacterial leaf spot disease is caused by Pseudomonas syringae pv. maculicola. This disease can occur on turnip, cauliflower, broccoli, and Brussels sprouts. The peppery leaf spot bacteria enter the field on infected seed and then return each year by surviving on plant debris. Bacteria spread from plant to plant by splashing water, on tools, gardener's hands and insects. The outer older leaves are typically infected first. Pinch off severely infected leaves and remove them from the garden. Do not plant any of the susceptible brassicas in the same location for three years.

Black Spot and Gray Spot - These two fungal diseases of brassicas are caused by Alternaria brassicae and Alternaria brassicicola. Disease can occur on cabbage, cauliflower, Chinese cabbage, broccoli, Brussels sprouts, kohlrabi, kale, turnip, and rutabaga. Leaf spots start out as small dark pinpoint spots, but quickly grow into a large gray to brown circle. Dark rings within the spot make them look like a target. Leaf tissue around the spots turns yellow, and dark brown spots may be seen on the heads of cauliflower and Alternaria .jpg

Photo 3: Gray Spot on Chinese Cabbage Photo by M.Grabowski UMN Extension.

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The black spot and gray spot fungi can be blown into the garden on wind or brought in on infected seed. The disease thrives when high humidity occurs. To reduce problems with these fungal leaf spot diseases, remove diseased leaves from the garden and till in infected plants at the end of the season. Be sure to remove weeds from the brassica family because they can harbor these fungi even when vegetable plants are not around.

Early Blight - This common fungal disease of tomatoes is caused by Alternaria solani. The fungus can also infect potatoes and occasionally eggplant and peppers, but the most severe damage in gardens often occurs on the tomato plants. Fruit, stems and leaves can all be infected by the early blight fungus. Infection on all three plant parts results in large brown spots, with concentric dark rings, that look like a bulls eye.

Like many leaf spot fungi, the early blight fungus survives in plant debris in the soil from yearearly blight leaf.jpg

Photo 4: Early Blight on Tomato Photo by M.Grabowski UMN Extension.

to year and is splashed on to leaves and fruit by rain or irrigation. It thrives in moist conditions.Reducing moisture around plants through staking, spacing for good air movement, pinching off lower leaves, pruning to one or a few stems, and mulching the soil can all help reduce disease problems. Often cultural controls reduce the disease enough to produce a good crop of tomatoes even though a few leaf spots can still be found on the plant.

Bacterial Brown Spot - This bacterial disease of beans is caused by Pseudomonas syringae pv syringae and can affect both the leaves and pods of the bean plant. Leaves have round brown papery spots. Leaf spots occasionally fall out, resulting in a shot hole appearance of the leaves. Infected bean pods also have brown spots and may be bent or twisted around the infected area. To reduce problems with bacterial spots on beans, space plants to allow good air movement between plants. Stake runner beans. Avoid working in plants when leaves are wet. Instead, wait until a cool dry day to pinch off infected leaves Septoria ls2.jpg

Photo 5: Septoria Leaf Spot on Lettuce Photo by M.Grabowski UMN Extension .

and pods. Remove this diseased material from the garden.

Septoria Leaf Spot - This fungal leaf spot disease of lettuce is caused by Septoria lactucae. Spores from this fungus often come into the garden on seed, but can also survive in plant residue and on some weeds. Gardeners that have problems with Septoria leaf spot of lettuce might consider looking for lettuce seed that is produced in a desert area, like the south western states, as these seeds are less likely to be contaminated by this moisture loving fungus. When growing successive crops of lettuce, be sure to seed the next crop in a location away from any currently diseased plants. Do not plant lettuce in the same area of the garden for one year to allow infected plant debris to break down.

Rose Classes and Their Performance in Minnesota: Part 1

Kathy Zuzek, UMN Extension Educator

The number of rose cultivars in the world defies logic. If you open a copy of Modern Roses 12, the most recent edition of the American Rose Society's rose cultivar list, you will find thousands of rose cultivars or varieties listed along with each rose's class, year of release, the breeder who developed the cultivar, parentage, and descriptions of each cultivar's floral and foliage traits, plant habit and thorns.

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Photo 1: Flower of R. acicularis, one of Minnesota's native roses. Kathy Zuzek.

Before cultivar selection and development, there were only the species or "wild" roses. There are 120 or more rose species in the world and they are found in the temperate and sub-tropical regions of the Northern Hemisphere: the Middle East, Oriental Asia, Europe, and America. The oldest species have single flowers with only 5 or occasionally 4 petals and bloom only once each year in spring. As mutations occurred in some rose species over the course of time, stamens or the pollen producing part of the plant were replaced by more petals. This gave rise to newer species with semi-double or double flowers that have more than 5 petals. Eventually mutations also arose that led to repeat-flowering rose species that bloom throughout the growing season.

There are 18-20 roses native to the United States. Four of these (R. acicularis, R. arkansana, R. blanda, and R.woodsii) are native to Minnesota. All 4 of these species are single-flowered, pink, and bloom in spring (Photos 1 & 2). Photo 2-1.jpg

Photo 2: R. acicularis.David Zlesak.

Given the thousands of rose cultivars in the world, you might think that many of the rose species were used in developing all of these cultivars. With few exceptions, only 8 species are ancestors to our rose cultivars and all 8 are from Asia.

As rose cultivars are developed, they are placed into classes. There are 36 classes of roses. Classes that Minnesota gardeners might be familiar with are the Hybrid Teas, the Shrub Roses, or the Hybrid Rugosas. Every rose cultivar is placed in a class with other roses who share common ancestors and/or similar floral, foliage, or plant habit traits.

Which classes and which cultivars can be grown in Minnesota? That depends on a gardener's taste in rose appearance, the choice of how much time he or she wants to devote to maintaining their roses to insure good performance and long term survivability, and a willingness or reluctance to spray pesticides. Some of the biggest factors that impact these decisions are choosing between repeat-blooming and spring-blooming cultivars, cold hardiness and pest tolerance of individual rose cultivars, and the pH of your soil.

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Photo 3: Spring flower display of 'Prairie Wren', a spring-blooming shrub rose. Kathy Zuzek.

Most gardeners today are looking for repeat-blooming roses. These are the roses that bloom repeatedly throughout the growing season. There is nothing wrong with this except that it does eliminate the potential for enjoying some of our hardiest and largest cultivars that can produce hundreds of blooms during their one season of bloom to provide a spectacular spring display (Photo 3). Entire classes of roses that bloom only in spring can be eliminated from your list if you want a repeat-flowering rose.

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Photo 4: Green canes below the snowline are alive while canes above the snowline are brown
and dead.Kathy Zuzek.

Gardeners in Minnesota also need to consider cold hardiness. Our hardiest roses that show no cane injury after a Zones 3 (northern Minnesota) or Zone 4 (southern Minnesota) winter where minimum temperatures fall to somewhere between -20 degrees and -40 degrees F belong to only a few classes of roses. Some of these hardy cultivars are repeat bloomers and some are not. Other "hardy" repeat-blooming cultivars within those same few classes will have part of their canes killed by winter injury each year after a typical Minnesota Zone 3 or 4 winter. Oftentimes these cultivars have canes alive in the lower portions of the plants that were protected by snow cover while cane portions above the snowline are winter-killed (Photo 4).

What is important in Minnesota is a plant's ability to re-grow vigorously during the following growing season after experiencing some winter injury. Because repeat-blooming roses produce flowers on the current year's wood, a repeat-blooming plant that grows vigorously in spring and summer after some winter injury can perform beautifully in spite of our harsh winters. There are also entire classes of roses that are not hardy in Minnesota. Unless a gardener is 1) willing to consider a rose as an annual plant or 2) tip and bury roses or provide some other measure of winter protection, these roses should not be grown in Minnesota.
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Photo 5:Blackspot on a rose leaflet. Dave Hansen.


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Photo 6: Swellings on a rugosa cane indicate where rose borer larvae have girdled the rose cane. Dave Hansen.


Roses are hosts to many pests. The pests that most impact rose survival in Minnesota are blackspot, the rose stem borer and a wasp that causes mossy rose gall.

Blackspot is a fungus that results in defoliation of rose plants across all classes (Photo 5). Roses without leaves cannot photosynthesize to produce and store the energy reserves that a plant lives on. Many roses that defoliate from blackspot in early or mid-summer also try to produce a new second set of leaves in late summer. This depletes the energy resources of the plant even more. Plants that are susceptible to blackspot are severely weakened by repeated rounds of defoliation and have little ability to survive our harsh winters. Plant size and vigor is diminished with each year of blackspot incidence until finally the rose is too weak to survive over winter. Along with blackspot's impact on winter survivability, few gardeners are willing to tolerate a defoliated rose in their garden. This leaves two options: planting blackspot-tolerant roses or repeated fungicidal sprays during the growing season. Some classes of roses have a higher percentage of blackspot-tolerant cultivars than other classes.

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Photo 7: Mossy rose gall on a rugosa rose. Dave Hansen.

The rose stem borer (Agrilus aurichalceus) (Photo 6) and the cynipid gall wasp (Diplolepis spinosa) that causes mossy rose gall (Photo 7) can be bothersome pests on cultivars within the Hybrid Rugosa class, especially when rugosas are mass planted. Both pests girdle a cane, resulting in cane mortality from the swelling or gall to the tip of the cane. Large infestatations of these pests that are allowed to re-infest year after year can eventually cause so much stress to rugosa roses that they die.

Roses prefer a soil pH of 6.0 to 7.0. As pH increases above these levels, iron chlorosis becomes a problem and can lead to plant stress, low vigor or mortality. Cultivars within the Hybrid Rugosa class are particularly susceptible to iron chlorosis on high pH soils (Photo 8).
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Photo 8: Iron chlorosis on a rugosa rose growing in a high pH soil.
David Zlesak.


Coming August 1 in Rose Classes and their Performance in Minnesota: Part 2: Descriptions of some common rose classes planted in Minnesota gardens and a look at some attractive, low maintenance cultivars within classes.

Tasty Tomatoes in Containers

Karl Foord, UMN Extension Educator

There is little doubt that one of the best taste treats in a Minnesota Summer is a vine ripe tomato. In this case I am referring to a vine that you grew and a tomato that you picked when you decided it was ripe. In addition the distance it had to travel to your kitchen is measured in feet not thousands of miles. As an aside where did tomatoes come from in the first place?

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Photo 1: Tumbler. Karl Foord.

Tomatoes were first domesticated by early Indian civilizations of Mexico. Cultivars were taken to Europe in the mid 1500's and then back to North America by colonists in the early 1700's. Tomatoes were slow to catch on because of their similarity to the poisonous belladonna of the nightshade family. The appeal for tomatoes took hold in the middle of the 19th century. In 1863 there were 23 known cultivars whereas in 1883 there were several hundred cultivars. Presently there are around 7,500 cultivars with a great variety of fruit sizes shapes and colors. Tomatoes also demonstrate different plant types commonly classified as determinate or indeterminate. Determinate, or bush, types bear a full crop all at once and top off at a specific height. Note the mass of flowers positioned above the foliage in the variety 'Tumbler'. Indeterminate varieties develop into vines that never top off and continue producing until killed by frost. Note the smaller inflorescence of flowers located nestled within the vine in the variety 4th of July. kf2.jpg

Photo 2: Fourth of July.Karl Foord.


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Photo 3: Tumbler flowers. Karl Foord.


One goal would be to have tomatoes for as long a period during the summer as possible, and one strategy to achieve this is based on variety selection. Many but not all of the early maturing tomato varieties are determinate; however an early maturing determinate tomato is a good way to start the season. An early maturing indeterminate variety will keep fruit coming connecting early and later maturing determinates as well as the late season indeterminates.


There are advantages and disadvantages to growing tomatoes in containers. The advantages may include avoidance of; damage by critters, problems associated with soil born diseases, and most leaf diseases because the leaf surfaces dry quickly when containers can be placed in an airy location such as an elevated deck. The ambiance created by container tomatoes on a deck or patio is very appealing.

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Photo 4: Container varieties. Karl Foord.

The disadvantage of containers is water related. Because determinant and indeterminate varieties develop into different size plants they have different combined leaf surface areas and thus different water needs especially at maturity. The indeterminate vines can get big and require a lot of water. If they are grown in small pots that dry quickly the plant will experience problems associated with constant water stress, one of which is blossom end rot. One way to avoid this is to select a pot size related to the tomato cultivar's growth type. In this way one can avoid the water stress problem by having a large enough pot that will hold enough water permitting the plant to be watered only once a day.


A demonstration of variety type matched to pot size is on display at the Minnesota Landscape Arboretum as part of the Powerhouse Plants exhibit.


This demonstration shows 5 different cultivars of various growth types and maturity dates in several different pot sizes (Table 1 and photo of varieties).

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Table 1.

Garden Calendar: July 16, 2010

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Photo 1: Apple Maggot Traps Karl Foord.


Apple maggot flies are out there! See what I caught in my traps. Note the small plastic bag containing a pheromone to attract the flies.

Correction from July 1 edition of Y&G News. Past editor and Rose expert David Zlesak noted an error in last editions rose pictures. The Frau D.H. rose that is labeled at the Arboretum in the main garden is incorrect. There was one there, but a sucker from a neighboring rose snuck in and people pruned the true Frau out accidentally. See attached picture for correct flower.

Time to renovate strawberries!

We are still in the picking season for summer raspberries.

Wondering what those spots are on your rose? Black spot is common this time of year but so are several other leaf spot diseases. Check out "What's Wrong with my Plant?"

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Photo 2: Frau Dagmar Karl Foord.


Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

The Japanese Beetles Are Coming

Jeffrey Hahn, UMN Extension Entomologist

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Photo 1: Japanese beetle. Jeff Hahn.

Actually they are already here as their presence was reported on June 21 (in the Twin Cities area). Japanese beetles are typically first active in the Twin Cities the first week of July but the early spring allowed them to emerge sooner than normal. These beetles are broadly oval and about 3/8th inch long with a bright emerald green head and prothorax (the area directly behind the head) and shiny bronze colored wing covers. An important distinguishing feature are the five small white tufts of hair along each side of the abdomen and two larger white tufts on the tip of the abdomen.

Japanese beetle adults feed on over 300 different plants, commonly eating the foliage of rose,DSC_0412.JPG

Photo 1: Skeletonizing feeding on grape leaf. Jeff Hahn.

grape, linden, birch, crab apple, cherry, birch, Norway maple, mountain ash, and willow. They skeletonize the foliage, eating the leaf tissue between the veins. They particularly like to feed on plants in sunny areas and typically will start eating leaves at the top of plants and work their way down. The adults also commonly eat flower blossoms, like rose. Japanese beetle grubs are also pests feeding on the roots of turf grass.

Don't be tempted to use pheromone traps to control the Japanese beetles in your yard and garden. Although they can capture what appears to be an impressive amount of beetles, research has proven that these traps attract more Japanese beetles into the area than they actually capture. You are likely to see more Japanese beetles on your plants as a result. Pheromone traps are a useful monitoring tool to determine if Japanese beetles are in the area but they are not meant to control them.

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Japanese beetle damage on rose. Jeff Hahn.

If you are only seeing a small or moderate number of Japanese beetles, just handpick them. Pick them off or knock them into a pail of soapy water. This is more effectively done in the evening as Japanese beetles are active feeders during the night but anytime you can do it will help. Remember to check your plants regularly as Japanese beetles are active through September (even into October if we are enjoying a mild fall).

If you are interested in using a low impact insecticide, try a product containing neem. This insecticide deters Japanese beetle from feeding but it's much less effective on large numbers of Japanese beetles. Spinosad, usually effective against other foliage feeding insects, does not have much effect against Japanese beetles. There are a variety of residual garden insecticides that you can spray on the leaves of plants, including carabaryl and pyrethroids such as bifenthrin, cyfluthrin, lambda-cyhalothrin, or permethrin. Repeat applications may be necessary, especially if large numbers are present.

There are a couple of systemic insecticides available to home gardeners, imidacloprid and Safari (dinotefuran). If you are treating trees and shrubs, there will be some lag time (days or weeks) while the product moves up the plant. However, these insecticides are generally long lasting and should only require one treatment during the summer. There has been concern recently about imidacloprid adversely affecting pollinating bees so it would be best to avoid treating plants that are attractive to bees.
Some people want to manage adult Japanese beetles by treating their lawn for Japanese beetle grubs. This would work if the Japanese beetles in your yard and garden only came from your property. However, Japanese beetles are quite mobile, and there will still be a lot of them that will come from outside your yard to find your garden. Only treat your lawn if you are finding damage due to Japanese grubs but don't rely on treating your grass to reduce Japanese beetle adults.


The Top 14 Best Roses for Minnesota

Karl Foord and Kathy Zuzek, UMN Extension Educators

I photographed the rose collection at the Arboretum last week and tried to make sense of the many rose classifications and the varieties within each classification. Twenty three classes are evaluated in the publication Roses for the North(1). The British Association of Rose Breeders (BARB) has identified 30 rose classes, and the American Rose Society has identified 56. Regardless of which system you choose, the situation is complicated. Being faced with this situation, I consulted our rose expert Kathy Zuzek, who is the lead author of the Roses for the North publication. We decided to address the issue with two articles. The first would suggest the best rose cultivars for Minnesota based on Kathy's twenty plus years of experience. The second would be an historical article describing why there are so many categories, what each looks like, and how that category performs in Minnesota. The second article will appear in the July 15 edition of the Yard & Garden News.

The choice of best rose cultivars for Minnesota is based on three criteria, cold hardiness, tolerance to black spot disease, and repeat blooming. Simply put, the rose has to tolerate Minnesota winters through a minimum of cane die back and good regrowth vigor in the spring. The plant must tolerate black spot and not defoliate in July from pressure due to this fungal disease. The plant should produce a good flower show throughout the season.

Fourteen varieties met the criteria mentioned above. Twelve of the varieties are pictured below; varieties Cuthbert Grant and Topaz Jewel were selected but are not pictured below. Consult Roses of the North for more complete descriptions of the selected varieties.

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Photo credits: Karl Foord

1. K. Zuzek, M. Richards, S. McNamara, and H. Pellett. Roses for the North - Performance of Shrub and Old Garden Roses at the Minnesota Landscape Arboretum. Minnesota Agricultural Experiment Station University of Minnesota, Minnesota Report 237-1995. 1995.

What's Happening in the Orchard?











Bacterial Blight Blacken Lilac Shoots

Michelle Grabowski, UMN Extension Educator

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Photo 1: Bacterial leaf spot of lilac Photo by M.Grabowski UMN Extension.

Recent wet weather has favored the growth of a bacterial pathogen of lilac called, Pseudomonas syringae pv. syringae. This bacterial pathogen can infect shoots, young twigs, leaves and occasionally flowers. Dark brown to black spots can be seen on infected leaves. The spots are often surrounded by a pale yellow halo. With age, the center of the leaf spot often falls out, resulting in a shot hole appearance to the leaves. Often several spots grow together into large irregular black blotches on the leaves. Even more dramatic is infection of shoots and young stems. Sunken black lesions can be seen on green stems. If the infection encircles the stem, all of the leaves beyond the infection, turn black and wither. This often results in 6-8 inches of blackened withered leaves.

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Photo 2: Bacterial shoot blight of lilac Photo by M.Grabowski UMN Extension.


Although most gardeners are willing to tolerate a few small leaf spots, many blackened withered shoots inspire gardeners to look for solutions. Sanitation is the first step in clearing up this bacterial disease. Choose a cool dry day and prune out infected shoots. Be sure to closely examine the branch before making a cut. Often oblong sunken black lesions can be seen on the stem just below the severely infected shoot. It is important to make the cut low enough on the branch to remove these infections as well. Severely infected leaves can be pinched off if desired but remember to never remove more than 1/3 of a plants leaves. Sterilize pruners between cuts and when the job is done with a 10% bleach solution, Listerine or Lysol. Bacteria are sticky and can be transferred to healthy plants on pruners used to clean up an infection unless the tools are properly cleaned.

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Photo 3: Stem lesion on lilac Photo by M.Grabowski UMN Extension.

Bacterial pathogens thrive in moist conditions. The next step in reducing damage from bacterial blight of lilac is to reduce moisture in the plant canopy. Reposition nearby lawn sprinklers or irrigation systems so that water does not spray onto the lilac leaves. If the plant is dense, prune out several branches to allow better air movement through the bush. This will help the leaves dry quickly after rain and dew. If the bush is crowded by nearby plants, remove weeds and relocate overgrown perennials or other plants to improve air circulation around the lilac.

Often these two simple steps combined with warm dry summer weather, reduce bacterial blight of lilac to the point where only a few small leaf spots remain.

Sapwood Rotting Fungi Kick Trees When They Are Down

Michelle Grabowski, UMN Extension Educator

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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.

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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.
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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.

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Photo 1: 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.

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Photo 2: Lawn mushrooms emerging during moist conditions.Bob Mugaas.

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Photo 3: 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: http://www.extension.umn.edu/gardeninfo/diagnostics/turf/circular.html for more information. 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.

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Photo 4:"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.

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Photo 5: 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

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Photo 1: 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

Strawberry root weevils have been common around homes lately. This insect is about 1/4th srw2.JPG

Photo 1: Strawberry root weevils. Jeff Hahn.

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.

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Photo 1: 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

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Photo credits: Karl Foord

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

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