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June 2011 Archives

Contents: June 15, 2011

Michelle Grabowski, University of Minnesota Extension Educator

M.Grabowski, UMN Extension

Gardeners that grow tomatoes in Minnesota are often quite familiar with fungal leaf blights. High humidity, frequent rains and heavy dew can all favor fungal leaf blight. All three environmental conditions are common in Minnesota and it is difficult to grow tomatoes without encountering fungal leaf blights.

There are two very common fungal diseases of tomato that occur in Minnesota; Septoria leaf spot, caused by Septoria lycopersici, and early blight, caused by Alternaria solani. These two fungi thrive in very similar conditions, and it is not uncommon for tomatoes to have both diseases at the same time. Both fungi can come into the garden on contaminated transplants or seeds. They then survive in leaf debris from year to year. Rain and irrigation splash fungal spores up onto new leaves from the soil and plant debris below. New leaf spots soon produce spores. These spores are then splashed onto higher leaves with rain and irrigation. Both diseases progress in this fashion until every leaf is infected. Infected leaves first have spots, than turn yellow and finally turn brown.

Septoria Leaf Spot on Tomato

Photo by M.Grabowski, UMN Extension

Septoria Leaf Spot on Tomato

Early Blight on tomato leaves and fruit

Photo by M.Grabowski, UMN Extension

Early Blight on tomato leaves and fruit

Septoria leaf spot infects leaves but not fruit of the tomato. Leaf spots are small round spots with a dark brown to purplish border and a light gray center. Tiny black dots (the spore producing structures) can be seen in the center of the spot with a hand lens. Leaves may yellow, but most damage is done by leaf loss due to the infection. Fruit may suffer from sunscald or other rots because they are not sheltered or shaded by the tomato leaves.

Early Blight infects tomato leaves, stems and fruit. Brown concentric rings inside of leaf, stem and fruit spots are characteristic of early blight. Brown spots are surrounded by bright yellow leaf tissue. As spots grow bigger, more of the leaf tissue turns yellow, then brown, resulting in a completely blighted plant. Fruit spots are dark brown to black, sunken and leathery. Ridges of concentric rings can be seen within the fruit spot.

Preventing tomato leaf blights altogether may be impossible once the fungi are established in the garden. However, use of the cultural control practices below can delay the appearance of the disease and reduce the number of leaf spots on the plant. Often this is enough to allow the tomato plant to produce a good crop. Remember, the goal is to grow tasty tomatoes, not to have a pretty looking plant.

Photo by M.Grabowski, UMN Extension

  • Plant tomatoes where no tomatoes, potatoes, peppers, or eggplants have been for the past 3-4 years. In small yards consider moving tomatoes to pots for a year or two if tomato leaf blights occur regularly in the garden.
  • Keep tomato leaves as dry as possible.
    • Space plants so that air flows between plants even when they are full grown.
    • Stake or cage plants.
    • Use drip irrigation or soaker hose to water plants.
    • If using sprinkler irrigation, water in the morning so leaves dry quickly in the sun.
  • Mulch all exposed soil with plastic or organic mulch.
  • Examine the lower leaves once a week. Pinch off lower leaves with leaf spots. Never remove more than 1/3 rd of the plants leaves.
  • At the end of the season, remove or bury infected tomato plants to reduce the amount of fungi that survive to the following season.

All Hail to the (Ant) Queen

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Pavement ant queens (note two-segmented petiole between thorax and abdomen).

There have been questions lately about winged ants being found in and around homes and other buildings. Nearly all ant species in Minnesota (Pharaoh ants are an exception to this) produce mating swarms, i.e. winged males and females, at certain times of the year. These reproductives emerge and fly out of the nest, typically in large numbers. The males die shortly after mating with queens. The queens fly off in search for a suitable place to start a nest, although the vast majority do not survive long, being eaten or succumbing to the elements.

Upon landing, the queen breaks off their wings. As she starts construction of the nest, she lays a batch of eggs which she cares for until they mature into adults. From that point on, the workers assume all of the work responsibilities and the queen's sole job is to lay eggs. She is taken care of by worker ants and remains in the nest her entire life.

Jeff Hahn

Photo 2: Carpenter ant queen (note one-segmented petiole between thorax and abdomen).

In Minnesota, there are two common ants that people see swarming in the spring, carpenter ants and pavement ants. Carpenter ant queens are typically black and large, about ½ inch long, although some species are smaller and can vary in color. However all carpenter ants have a one segmented node between the thorax and abdomen. Pavement ant queens are about 1/4 - 3/8 inch long, brownish and has a two-segmented node.

Finding a swarm of ants indicates a nest is nearby. However, a swarm, in and of itself, is not necessarily a problem. For the most part, like when they are found in your yard, they are not anything more than a nuisance. Under these circumstances, just ignore them until they go away on their own.

If winged ants are found indoors, then there is a nest inside the home. Correctly identifying the ant species will help determine the best control. Pavement ants nest in the soil under objects, like sidewalks, driveways, stones, and concrete slab construction of homes. When found inside, they are annoying but are not a structural problem. The only necessary control when pavement ant swarmers are inside is to physically remove them, especially if you only see winged ants and not any workers

Finding winged carpenter ants indoors is another matter. They nest in water damaged wood and can potentially damage buildings. You can be somewhat patient when trying to determine where they are coming from and attempting control but you should not ignore them indefinitely. Their elimination is best done by a professional pest management company.

However, sometimes a wingless carpenter ant queen is found walking around in or around a home. Because it is a carpenter ant, people are concerned about a nest being in the home. But remember that this queen has not established a nest yet and is still looking for a place to begin one. Her presence does not mean a colony is in the home. The only necessary control is to dispatch her.

Unusual Bouquet Fillers for your Cutting Garden

Minnesota gardeners struggle to balance a short growing season with a diverse garden. Many beautiful floral varieties just don't work in our Zone 4 (with pockets of zone 3) environment. This means that we have to rely heavily on annuals for our cut flower gardens. Zinnias and sunflowers provide bright color; annual rudbeckia, helichrysum and snapdragons make wonderful focal flowers in any bouquet; but what to grow for interesting filler? Baby's breath is an option, but is overused, and readily available at your local florist. I tend to look for something unique, fragrant and maybe a little quirky to give my arrangements that unexpected touch that sets them apart from other bouquets. I grow herbs, grasses and smaller flowers to complete my floral arrangements.

Limonium sinuatum (statice) has paper-like bracts that later bloom with delicate white flowers. Once Statice starts blooming it continues to bloom until frost. When harvesting, cut the flower stalks back to the rosette leaves at the base of the plant.


Robin Trott

Photo 2: Ageratum "blue sensation".

Limonium needs no special post harvest care, and doesn't fade as it dries. Achillea millefolium (Yarrow) is perennial to zone 3, which makes it a great choice for our harsh Minnesota winters. It ranges in color from deep red, orange, purples, pinks to clear white; and blooms early summer to frost. Its silver-green lacy foliage is fragrant, and can also be used to enhance your arrangements.

Harvest when all florets are open, place in floral preservative, and store in a cool place. Ageratum houstonianum 'Blue Sensation' features fluffy lavender flowers in flattened to slightly rounded clusters on strong upright (18-30") stems. 30" Gomphrena haageana has brightly colored bunny tails that add whimsy to your bouquets (try cherry red Strawberry Fields, bright pink Fireworks or QIS mix), and contrasts nicely with Celosia's bright spikes. (Try Celosia spicata "Flamingo Feather".) Ageratum, Gomphrena and Celosia produce flowers from summer to early fall and are great for cutting and drying. Gomphrena is fairly drought tolerant


Robin Trott

Photo 3: 'Strawberry Fields' Gomphrena.

Herbs provide fragrance to otherwise unscented bouquets. Basils, such as Sweet Dani, Purple Ruffles and Red Cardinal are long lasting, fragrant and edible. Cardinal Basil plants are well branched, so you will be able to take a number of cuts per plant. Its dark green leaves are topped with maroon rosettes that make it both unusual and tasty. Super hardy mints, such as Lemon Balm, Spearmint and Peppermint, provide colorful greenery and can later be used to flavor teas, and summer beverages. Mint can be somewhat invasive, so keep this in mind before adding it to your garden space. Perovskia atriplicifolia Taiga, (Russian Sage) boasts tall blue flower spikes and silver green foliage.

Robin Trott

Photo 4: Blooming cilantro.

Deep-rooted, heat loving and drought tolerant, it's not picky about soils, and thrives in almost any location. Cilantro, a popular herb widely used in Mexican, Caribbean and Asian cuisine, features delicate foliage and tiny white flowers. One of my favorites, Artemisia annua (Sweet Annie), has abundant, lacy, fragrant foliage. A tall (36"-48") woody herb, Sweet Annie can be cut and placed in cool water, or dried and used to make fragrant autumn wreaths.

For something completely different, include tall grasses, wheat or ornamental eggplant to highlight your fall displays. Perennial grasses, such as Karl Forester, and annuals like millet can complement the fall colors of rudbeckia and wine zinnias. Dried Black tipped wheat, available as seed from a variety of garden catalogs, can be used in fresh or dried bouquets. My absolute favorite, Solanum integrifolium, also known as Pumpkin on a stick, really adds something special to your fall bouquets. The plants are quite thorny, so be careful when harvesting. Cut near the base of the plant, remove the foliage, and use in fresh bouquets, or dry in a cool, well-ventilated location, and use in your dried arrangements. (If you find you have extras, they are edible, and can be used in traditional Asian Stir Fry recipes.)

The keys to successful floral arrangements are color, texture, and imagination. Don't get stuck on the same old, same old. Try something new and different this year. Bring the pleasure of your garden into every room in your house with long lasting floral arrangements chock full of herbs, greens and colorful flowers.

Earth laughs in flowers. ~ Ralph Waldo Emerson

I never met a beard I didn't like - on an iris, that is!

Karl Foord, UMN Extension Educator

I took a closer look at bearded irises this past week and two things intrigued me.
The first thing that intrigued me was the amazing variation in iris petal and beard colors (photos 1-4). It was also interesting to observe the change in beard colors throughout their length as they moved from the exterior part of the petal to the interior part of the flower (photos 5-7).

The second was a question of how did this flower actually work given the very obvious and showy petals and the less obvious male stamens and female pistils. The iris flower has a unique structure whose purpose is to avoid having pollen from this flower's male stamens transferred to the same flower's female stigmatic surface and pistil. As the bee enters the flower tracking along the beard it passes a flap that the insect will push past and fold back exposing the moist receiving part of the stigmatic surface capturing pollen on the hairy back of the insect. As the bee continues toward the nectarines and sugar reward it then passes under the anther picking up pollen on its back. When it has finished feeding on the nectar and begins backing out of the flower, the stigmatic fold is pushed the other way exposing a dry non-receiving part of the stigma and thus transfers no pollen from this flowers anthers to the same flowers stigmatic surface (photo 8). Can you identify the same flower parts in photo 9?

The system is not foolproof, however, because the same insect could visit one of the two other parts of the same flower, or another flower on the same plant.

Note: all photos taken at the Minnesota Landscape Arboretum.

Calendar: June 15, 2011

Conserve moisture by watering early in the day, when temperatures are lowest and winds have not picked up yet. Try to water at the base of the garden and landscape plants. Use soaker hoses and sprinklers that don't shoot way up in the air; too much water will be lost to evaporation. Avoid watering at night if possible, as foliage that remains wet overnight is more prone to a number of plant diseases. Do water at night, though, if that's your only option.

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

Contents: June 1, 2011

Tent Caterpillars

Jeffrey Hahn, Asst. Extension Entomologist

Michelle Grabowski

Small eastern tent caterpillar tent.

There are two common species of tent caterpillars that are now active in Minnesota, eastern tent caterpillars and forest tent caterpillars. Both normally hatch closer to early May, but the cool spring weather we have experienced has slowed down their emergence and they only first started to appear closer to the middle of the month. Here is how you can distinguish between these insects.

Eastern Tent Caterpillars

This insect is easy to identify because it constructs silken webs in the fork of branches as soon as they young larvae hatch. The caterpillars feed outside of the tents on leaves during the day (as long as the weather is nice) and return to the webbing at the end of the day and during rainy weather for protection.

The caterpillars are bluish black with yellow and a white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. They are two inches when fully grown.

Look for eastern tent caterpillars on hardwood trees, particularly fruit trees, like apple, chokecherry, crabapple, plum, and cherry. Eastern tent caterpillars are common most springs. They maintain relatively steady populations from year to year and generally do not occur in outbreak numbers.

Forest tent caterpillars

Also known as armyworms, forest tent caterpillars are familiar insects in the north and central areas of Minnesota. These caterpillars are blue and black with distinctive footprint or keyhole shaped white spots on their backs. They are mostly smooth except for hairs that stick out along the sides of their body. They grow to be two inches long when fully grown. Despite their name, they do not make conspicuous webs on trees.

Jeff Hahn

Several day old forest tent caterpillars on oak.

Forest tent caterpillars feed on many deciduous trees, including aspen, birch, maple, crabapple, apple, ash, oak, and elm. They go through cycles of tremendously large numbers, lasting 5 to 8 years, before collapsing to such low numbers that they are not noticed. Periods of low populations lasts about 8 to 13 years. Forest tent caterpillars peaked in 2002 and their numbers have since crashed.

The Minnesota Department of Natural Resources (DNR) reports that in 2010 just over 70,000 acres were defoliated, primarily in the middle one-third of Minnesota in a crescent that extends from south of Mille Lacs Lake through St. Cloud to Wilmar and up through Detroit Lakes. There were also a few isolated areas of defoliation in Hubbard, Cass and Crow Wing Counties. Forest tent caterpillars are also found in the Twin Cities area. Their numbers are expected to increase some in 2011 compared to last year but an outbreak is not expected.


The decision to treat tent caterpillars should be made based on several criteria. First, consider what percentage of leaves have been eaten. If only a few branches are affected, the tree can tolerate that damage. Leaf feeding tends to be more a cosmetic problem and not one that threatens the health of the tree. Even if defoliation is severe, healthy, well-established trees can withstand this feeding in a given year. However, young trees are less tolerant and should be protected. Unhealthy, stressed trees should also be protected from severe defoliation.

Another important consideration is the size of the insect. Ideally these insects should be treated when they are 1/2 their full-grown size or smaller, i.e. about one inch in size. The larger they are, the closer they are to being done feeding. Because the tent caterpillars emerged later than usual, they are not as far as long as they would normally be by the beginning of June. There is still time to treat them and minimize their defoliation. However, if by the time you see them, the are close to two inches long, it is not worth treating them.

There are a variety of residual insecticides that you can use if it is desirable to protect your trees. Consider using products that have a low impact on the environment, such as Bacillus thuringiensis, spinosad, and insecticidal soap. Bacillus thuringiensis is a particularly good product if the tree is flowering since it will not harm visiting honey bees.

Early June Home Lawn Care Tips

Bob Mugaas, UMN Extension Educator

Picture 1(2).JPG

Photo 1: Newly emerging crabgrass seedlings. Bob Mugaas.

1. In many areas of the state, crabgrass, along with other warm season annual grasses are or will soon be germinating in lawns. See Picture 1. Once crabgrass has emerged from the ground, control strategies need to be changed. Herbicides directed at controlling crabgrass above ground are known as postemergence products. Be sure to select those products that are specific to visible, actively growing crabgrass plants only. Those products labeled as grass killers are usually designed to kill all kinds of grasses, including lawn grasses, not just crabgrass. Products sold as broadleaf weed and grass killers may or may not be safe for use on lawns. Be sure to read the product label carefully as to whether or not it is a product that is safe for use on lawn grasses. When treating crabgrass after it has emerged from the ground, be sure that the desirable lawn grasses are not under any kind of heat and/or drought stress as you can sometimes cause temporary yellowing. Under severe stress, permanent injury can also occur to our lawn grasses. As with most weed control options, treating the plants while they are small and tender is generally more effective than trying to control larger, more mature plants.

Picture 2(2).JPG

Photo 2: An easier to control or remove young lambsquarter weed
Bob Mugaas.

2. By early to mid-June, many of our annual broadleaf lawn weeds will also be starting to germinate. One of the best times for controlling these weeds is in this early growth stage before they have started to mature and initiate flowering. Examples of our common annual broadleaf weeds include prostrate or spotted spurge, erect and prostrate knotweed, lambsquarter, redroot pigweed and purslane. See Picture 2. The clover like plant, black medic as well as yellow woodsorrel are usually considered annuals although some plants may overwinter and behave like a biennial or short lived perennial. Taking a few minutes to walk your lawn in order to determine when some of these weeds may be germinating allows one to easily remove them by hand and/or treat them with an herbicide. Remember, removing and/or treating plants with an herbicide is much more efficient when they are small, even at the lower application rates stated on the product label. For more weed identification help and possible control options for lawn weeds see our 'Is this Plant a Weed?" section on our Extension website:

Picture 3(2).JPG

Photo 3: Raise mowing heights to encourage larger, deeper grass root systems.
Bob Mugaas.

3. Since this is the time of year when many of our weed seeds are germinating, including those of crabgrass, it is generally best to avoid lawn care operations such as dethatching or core aerating. These operations disrupt the surface of the soil and can bring additional weed seeds into a more favorable environment for germination and growth, hence creating additional competition for our lawn grasses. For that reason, it is best to wait until late summer or early fall to resume these operations. However, be sure to leave at least four to six weeks of good growing conditions for the grass to fully recover from this injury before consistently cold weather arrives.

4. Along with our cooler than normal temperatures for much of the spring, many areas of the state have also received adequate to abundant amounts of rainfall. Those cooler temperatures and ample moisture supplies have encouraged vigorous, lush growth of our lawn grasses. Vigorous growth and rainfall will have likely depleted at least some of the available nitrogen in the soil making less available for plant growth. Therefore, most lawns will benefit from an additional ½ pound of nitrogen per 1000 square feet applied in the early to middle part of June. This will help replenish the supply of N used by the plant or lost due to leaching or returning to the atmosphere in a gaseous form through a process known as volatilization. This is about ½ the normal amount of nitrogen applied per application. On the other hand, too much nitrogen encourages more rapid and excessive growth that can compromise the overall health of the grass plant going into the summer months.

5. Lawn grasses will usually have better stress tolerance when they are mowed higher from the middle of spring through early fall. See Picture 3. Higher heights of cut usually mean at or above 2.5 inches for most lawn grasses. This helps encourage deeper, more robust root systems capable of extracting water and nutrients from a greater soil volume. Access to more soil moisture and nutrients increases the plant's capacity to tolerate and survive the warmer, drier conditions often experienced late spring through the summer months.

Picture 4(3).JPG

Photo 4: Shorter than expected mowing height due to softer ground conditions. See text for more explanation. Bob Mugaas.

6. While most walk-behind rotary mowers adjust mowing heights by resetting the four wheels to the desired height, it is occasionally a good idea to see how close that setting really is to the actual height of cut. The easiest way to do this is to simply take a ruler and gently push it through the turfgrass canopy until it rests firmly on the lawn/ground surface. Then look across the grass plants just in front of the ruler and see what the height is. For example, if the ground is firm then mower wheels will ride higher and consequently the height setting will more closely approximate the actual cutting height. However, where the ground is soft or there is a significant thatch layer present, the wheels will sink more deeply into the lawn and hence the mowing height is actually less than the wheel settings would indicate. In fact, where there is significant thatch present mower wheels can ride so much lower that the lawn surface between the wheels is actually scalped. See Picture 4. Remember to take the time to adjust your mower correctly, periodically verify that the mower height settings are actually providing the desired height of cut, and always mow with a sharp blade.

7. With so many yard and garden chores needing to be completed during a typical Minnesota May and June, it is very easy to overlook the water needs of our lawn grasses. However, it's important to remember that May and June are very active growth months for our lawn grasses. While much of the growth is directed at producing flower stems, our bluegrasses and perennial ryegrasses will grow much better with ample supplies of water during this period. An 'ample supply' usually means that the lawn receives about ¾ to 1.0 inch every seven to ten days including rainfall. See the May 15, 2011 Yard and Garden News blog for more information on Lawn watering practices that encourage healthy lawns and help protect water resources.

Growing Sunflowers for your Cutting Garden

Robin Trott, UMN Extension Educator


Cherry Rose. Robin Trott.

The Sunflower, or Helianthus, is a very popular flower to include in an annual cutting garden. A native of North America, the sunflower comes in a variety of sizes, growing habits and colors, making it an ideal choice for the home gardener. From the Giant sunflowers like "Kong", to the multi branching "Italian White" to the petite "Teddy Bear", an 18" tall puff-ball; there is a sunflower to match every gardener's taste and purpose. One of my favorites from last year was a pollen-less variety called "Cherry Rose". This 6' tall, branching plant is covered with 5" lemon yellow blossoms with red overtones. Grown in full sun, the lemon color abounds, in a more shaded site; the dark plum color is dominant. Another excellent choice, "Ring of Fire", is a mid-height plant (4-5') with 5" blooms. This late bloomer boasts bi-colored petals with a dark red base and golden yellow tips surrounding a chocolate brown center. For the giant sunflower enthusiast, "Kong" is as big as it gets. Reaching 12 feet tall, "Kong" is even more impressive because it's multi-branched and covered with 4-6 inch yellow blooms offset by large, dark green leaves. The most versatile sunflower in my garden last year was the "Music Box". "Music Box" grows into a stocky, 2 ½' bush of abundant, multi-branching 4-5" golden, daisy like sunflowers. These petite, buttery IMG_0203.JPG

Ring of Fire. Robin Trott.

flowers were ideal in mixed fall bouquets, and bloomed prolifically until frost.

Keep in mind these cultural practices once you have selected your perfect sunflower variety.

  • Select a site that receives at least 6 hours of sun a day. (More is preferable)

  • Sunflowers prefer loose, well-drained, rich soil; so amend with compost if you have heavy clay or sandy soil.

  • Sow seeds directly into the garden once the soil has reached 50°. (Cooler than this will slow development.)


Music Box. Robin Trott.

  • Plants seeds at a depth 2 times their width, and space close (6") to promote tall plants; and small, bouquet sized heads. This close spacing will soon shade out weed competition and mature plants will protect and support each other.

  • Sunflowers are heavy feeders, and should be fertilized. Side dress with a balanced fertilizer (10-10-10) every 21 days during the growing season.

  • Keep your sunflowers weed free. Weed competition reduces the quality of your sunflowers.


Kong. Robin Trott.

  • Tall sunflower varieties will need support to protect them from wind damage. Stake them or grow them through horizontal support netting to ensure your plants remain standing after our typical summer "hazardous" weather.

Harvest your sunflowers during the coolest part of the day. The plants should be free of dew and moisture. Cut when petals begin to lift off the face, but are not completely open. Make sure your cutting tools and containers have been sterilized with a 5% bleach solution. Cut stems at least 24" long and at an angle for best results. Sunflowers prefer clean water to floral preservative. (Floral preservative can actually over-hydrate your flowers, making them wilt.) Place your cut sunflowers in a cool place as soon as possible after cutting. If wilting occurs, don't worry, leave them in water for 24 hours, and they should perk right up. Vase life for fresh cut sunflowers is 7 to 10 days, with pollen-less flowers having the longest vase lives.

Sunflowers are a colorful choice for your garden, make long lasting cut flowers, and provide food and habitat for wildlife. It's not too late to start them for this gardening season. Select your cheerful sunflower variety today, and get growing!

Until Next Time, Happy Gardening!
Bring me then the plant that points to those bright Lucidites swirling up from the earth, And life itself exhaling that central breath! Bring me the sunflower crazed with the love of light.
~ Eugenio Montale

Iris Show


Photo 1: Iris cristata Crested Dwarf Iris. Karl Foord.

Karl Foord, UMN Extension Educator

Don't miss the Iris show that is coming into its own at this moment. The Iris genus contains some 260 species of plants with showy flowers. The most commonly found garden iris is the bearded German Iris (Iris germanica), and its many cultivars (Photo 1). Other beardless iris types found in the garden are the Siberian Iris (I. sibirica) and the Japanese Iris (I. ensata), and their respective hybrids. The Siberian Iris can be distinguished from the Japanese Iris as the latter's flower is a more upward facing flatter flower. A number of other species are worth considering including the Dwarf Crested Iris (I. cristata) (Photo 2).

We have two excellent publications on Iris as follows:
"Iris" by Rhonda Fleming Hayes and David C. Zlesak and
"Gardens" by Deborah L. Brown.


Photo 2: The beard of a bearded iris, Iris germanica. Karl Foord.

Look for Rust Fungi on Trees

Michelle Grabowski, UMN Extension Educator

A group of pathogenic fungi known as rusts can be easily seen and identified on evergreen trees this time of year. Mild temperatures and spring rains cause the rust fungi to produce brightly colored orange or yellow spore producing structures on infected branches.

Some diseases caused by rust fungi are minor problems and only affect the aesthetics of the tree. Others can be fatal to the tree if proper action is not taken in time. It is therefore critical for gardeners to understand how to identify the rust fungi that they are seeing on their plants.

The following rusts may be catching your eye.

CAR gall Y&G.jpg

Photo 1: Cedar Apple Rust Gall with gelatinous orange spore producing structures M. Grabowski, UMN Extension.

Cedar Apple Rust

Cedar Apple Rust (CAR) is caused by the rust fungus Gymnosporangium juniperi-virginianae. This fungus infects several species of juniper including eastern red cedar (Juniperus virginiana) Chinese juniper (J. chinensis), creeping juniper (J. horizontalis) and low juniper (J. communis var. depressa). At a different stage of its life cycle, it can also infect crabapple and apple trees and occasionally hawthorns.

What to look for:

· Round brown woody galls that are about ½ to 1 inch across on juniper.
· When wet, galls develop bright orange tentacle like gelatinous spore producing structures. These dangle off the gall like an octopuses tentacles and can be an inch or more long.
· Later in summer yellow to orange leaf spots with a red border develop on nearby apple or crabapple trees.

What to do:

· Although odd looking, CAR galls do not do major damage to the juniper tree. No action needs to be taken to protect the health of the juniper. Galls will die after they have released their spores this spring.
· Many varieties of apple and crabapple grown in Minnesota have resistance to CAR and need no further protection.
· Susceptible apple varieties should not be grown near eastern red cedar or juniper trees.
JAR gall.jpg

Photo 2: Japanese apple rust gall on juniper USDA-ARS.

· For more information on CAR on apple trees - visit IPM for home apple growers

Japanese Apple Rust

Japanese Apple Rust (JAR) is caused by the fungus Gymnosporangium yamadae. To date, this Asian fungus has not been found in Minnesota but has been identified in several north eastern states. The JAR fungus infects Juniperus chinensis and J. squamata. These two species of juniper are sold as ornamental trees and shrubs in Minnesota. Like Cedar Apple Rust, Japanese Apple Rust infects apple and crabapple trees at a later stage of its life cycle.

What to look for:

· Round brown woody galls that are about ½ to 1 inch across on juniper.
· When wet galls develop bright orange gelatinous spore producing structures. The spore producing structures of JAR are short stubby projections that only stick out less that ¼ of an inch from the surface of the gall.

wpbr tree Y&G.JPG

Photo 3: Red flag on a white pineM.Grabowski, UMN Extension.

What to do:

· Report Japanese apple rust the MN Department of Agriculture Arrest the Pest Hotline
651-201-6684 Metro Area 1-888-545-6684 Greater Minnesota
· JAR infections are not likely to do serious damage to Junipers but it is unknown how Minnesota varieties of apple and crabapple will respond to the fungus. In Japan, JAR causes leaf spots and defoliation of apple trees.

White Pine Blister Rust

White pine blister rust (WPBR) is caused by the rust fungus Cronartium ribicola. In Minnesota, this fungus infects eastern white pine (Pinus strobus). Infection starts on the needles. The fungus then moves into the twig and continues on into larger branches and even the main trunk of the tree. Once the fungus has reached the main trunk of the tree, it will eventually girdle the trunk, killing everything above the infection. If the infection is identified in a twig or branch, however, these infections can be pruned out, halting the progression of the fungus and curing the tree.

What to look for:

· One or more random branches where all of the needles have been killed and turned reddish orange. These branches are often called red flags.
· Swollen, rough, cracked and discolored bark on the red flag branch.
wpbr branch Y&G.jpg

Photo 4: Blister rust canker with spores on white pine branch M.Grabowski, UMN Extension.

· Raised cushion like pustules emerging from cracks on the infected branch. These break open to release powdery yellow orange spores.

What to do:

· Prune out infected branches before the bark discoloration is within 4 inches of the main trunk.


Photo 1, Karl Foord.

Karl Foord, UMN Extension Educator

Keep an eye out for tent caterpillars and Pine sawfly larvae. Look for shriveled and missing needles on pine branches just below the newly forming candles (Photo 1). The larvae are gregarious and form in numbers on these sections of the plant. They are quite voracious and can strip a tree quickly (Photo 2). It is best to wash them off the plant with water rather than to use an insecticide. See Jeff Hahn's article for a more detailed account of pine sawfly.

Pine sawfly larvae exhibit some fascinating forms of defensive behavior. Colonies of larvae will rear their heads in unison when disturbed. This behavior may serve to startle potential predators (

Pine sawfly larvae also collect pine resin in a special gut compartment as they feed. Whenkf461-1.jpg

Photo 2, Karl Foord.

attacked by a predator, the larva will regurgitate a droplet of pine resin and try to dab it on the predator. Ants and other predatory insects will often abort the attack and try to remove the sticky resin by cleaning behavior.

Solitary Bees With a Twist

Jeffrey Hahn, Asst. Extension Entomologist

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Photo 1: Andrenid bee. Jeff Hahn.

Andrenid bees, especially Andrena spp., are common insects that are sometimes seen in yards and gardens in spring. They are small to medium sized insects, about 1/4 - ½ inch long. They are hairy, dark-colored insects, often with a thick mat of yellow hairs on their thorax.

They typically overwinter as pupae and emerge as adults as soon as the weather becomes warm, living for about a month. Andrenid bees nest in the ground, preferring sunny, dry sites with sparse grass or few plants. They create cylindrical tunnels where they spend essentially their entire life preparing these nests for their young. They provision them with pollen balls on which the larvae feed during summer.

Unlike honey bees and bumble bees, which are social insects living in colonies, andrenid bees are solitary insects that live by themselves. They are responsible for all of the work that is required to maintain the nest and provide for the larvae. However, andrenid bees typically live gregariously, i.e. many individual nests in a small area despite the appearance that they are coming from a single nest. Copy of P5180167.JPG

Photo 2: Andrenid bee nests (notice how many there are in this small area). Jeff Hahn.

Fortunately, andrenid bees are gentle and stings are extremely rare. It is possible they might sting if they are mishandled. However, there are many reports of people in close proximity to these bees without being stung.

When dealing with andrenid bees, tolerate them as much as possible. Bees are beneficial because they are pollinators and should be preserved whenever possible. Remember that they are gentle with little risk of stings. They are also only active for about a month and they shouldn't be around much longer this spring. Insecticides are a possibility but should only be used as a last resort.

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Photo 3: Cuckoo bee, Nomada sp., entering an andrenid bee nest. Jeff Hahn.

There is a plot twist in one particular andrenid bee site that was observed recently. Another insect was apparently nesting in the ground in same area as the andrenid bees. They were reddish brown with a yellow striped abdomen, few hairs on their bodies, and were a little smaller. After collecting and examining a specimen, they were identified as cuckoo bees, Nomada sp. Cuckoo bees are wasp-like in appearance and are not pollinators like most bees. Instead they are parasitic on other bees, entering and laying their eggs into the host bee's nests so the food gathered will feed the cuckoo bees' young. The world of entomology never ceases to amaze.

Calendar: June 1, 2011


Damage on Chocolate Mint Mentha x piperita f. citrata 'Chocolate'Karl Foord.

  • Fourlined plant bug nymphs love mint, as shown on the photo to the right. Their feeding causes small, necrotic spots. The damage can look a little different on different plants, but is similar enough to recognize. Thanks to Jeff Hahn for identification of the nymph.

  • Check flowering perennials closely for signs of fourlined plant bug feeding-- small brown circular depressions on the leaves. This usually doesn't injure the plants seriously, but it does make them less attractive and sometimes the bugs can truly overrun the plant. It's best to tolerate fourlined plant bugs whenever possible, but if you decide to control them, you must spray soon after you first notice feeding damage. Check out the UMN Extension Garden page for more information.
  • Assess the performance of your spring-flowering bulbs. Lift and discard any that failed to bloom well; they won't improve. Fertilize the others, and allow their foliage to mature naturally. Braiding or tying up the leaves deprives them of the light needed to store energy for next year's blooms. Planting annuals around them, though possible, may keep bulbs

Nymph on Chocolate Mint Mentha x piperita f. citrata 'Chocolate'. Karl Foord.

    too moist during their summer dormancy, resulting in poor growth the following spring.

  • If you need to prune spring-flowering shrubs such as lilac, forsythia, azalea, rhododendron or rose tree of China, in order to shape them and control their size, do it right after they're through blooming. Pruning mid-season or late summer inadvertently eliminates much of the following year's blooms because those buds actually begin to develop shortly after this year's flowers fade!

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

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