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July 2009 Archives

Quick Update on Colorado Potato Beetles

Jeffrey Hahn, Asst. Extension Entomologist
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Do you have a problem with Colorado potato beetles in your garden? If you grow potatoes, there is a good chance you see them at one time or another on your plants. Don’t forget that in addition to potatoes, they can also attack eggplants, tomatoes and peppers. This insect can be challenging to manage but here are a few tactics you can use to deal with this pest.

Monitor susceptible plants regularly so you know if Colorado potato beetles are present in your garden. If you have a history of these insects in your garden, the odds are good you will see them again. Because you can have overlapping generations, you can find all life stages in your garden at any given time. Once they are active in spring, you will generally have Colorado potato beetles in your garden all summer.

If you have a smaller garden, and the time, handpicking is a great nonchemical control method. To be sure they are killed, just toss adults and larvae into a bucket of soapy water. For the really small, young larvae, just put on your gloves and squish them. And don’t forget the eggs. Look for them on the underside of the leaves. They are easy to recognize as they are orange and in clusters.

If physical removal is not practical, you may wish to use an insecticide. There are two low impact products available. Spinosad is produced by the fermentation of a soil-dwelling bacterium, Saccharopolysora spinosa. It is quick acting, attacking the nervous system of insects. It is most effective against caterpillars, flies (mostly leafminers), and thrips, as well as leaf beetles, grasshoppers and other insects that consume a lot of foliage.

art5-2_600.jpgNeem is derived from the neem tree, a plant found in arid tropical and subtropical areas. Neem can deter insect pests in one of several ways. They can inhibit their feeding, repel them, or disrupt their life cycle preventing them from successfully molting. Neem is generally effective against a wide array of insects, including beetles.

You might be wondering about Bacillus thuringiensis var. tenebrionis, a commonly used home garden product for leaf beetles, like Colorado potato beetles. This bacterial insecticide, which acts as a stomach poison, is quite effective against young larvae. However, this product is no longer registered in Minnesota. It was previously available from Bonide in a product called Colorado Potato Beetle Beater. If you look at Bonide’s products, you will still find a product with that name, but it now contains spinosad.

There are a wide variety of residual insecticides, such as permethrin and carbaryl that are labeled to treat Colorado potato beetles. However, there is a good chance that the Colorado potato beetles in your garden are resistant to these insecticides already. This will be particularly true if you are any where near a commercial potato field. Instead try a newer insecticide, like esfenvalerate. The beetles in your garden are more likely to be susceptible to it.

Michelle Grabowski, University of Minnesota Extension Educator

art4-1_600.jpgSeveral kinds of blight are common on tomatoes grown in Minnesota. Almost every gardener has struggled with the fungal diseases Septoria leaf spot or early blight on their tomato plants at one time or another. This year bacteria are the primary pathogens being isolated from tomato leaf spots.

There are two bacteria that result in leaf spots on tomato; bacterial speck caused by Psuedomonas syringae pv. tomato and bacterial spot caused by Xanthomonas campestris pv. vesicatoria. Bacterial speck and spot can cause spots to form on the leaves, stems and fruit of tomato plants. The leaf spots caused by bacterial speck and spot look identical but the two pathogens can be distinguished by differing types of fruit spots that form later in the season.

Leaf spots are dark brown to black, small (about the size of a pencil tip) and have a yellow halo around them. Often the center of these leaf spots dry up and drop out leaving tiny holes throughout the leaf. If a leaf is infected with many leaf spots, the leaf may turn partially or completely yellow, and may even fall off. In past years, only minor infections from bacterial spec and spot have been observed in Minnesota. This year’s weather conditions seem to favor the pathogens, resulting in much more severe infections than previously seen.

art4-2_600.jpgSome varieties of tomato seem to be more sensitive to the bacterial pathogen than others. A few varieties, like Brandywine tomatoes, have been observed with larger leaf spots (up to 3/8th of an inch across). Infections with larger leaf spots could easily be confused with one of the common fungal leaf blight diseases. If gardener’s are unsure which pathogen they are dealing with, they should use the UMN Extension Online Diagnostic Tool ‘What’s wrong with my plant?’ before making any management decisions.

On the tomato fruit, bacterial speck infections are small (the size of a pencil tip) raised black spots. These spots start on green fruit and may develop a green halo as the fruit turns red. In contrast, bacterial spot fruit infections are larger (the size of the eraser end of the pencil) dark brown to black, raised and often corky appearing. Bacterial spot infections may be surrounded by a white halo. In both cases, the infection on the tomato fruits remains fairly superficial and does not result in fruit rot.

Both bacterial speck and spot can come into the garden on infected seed or transplants. The bacteria are then easily transferred from plant to plant through splashing water, strong winds or on a gardener’s hands and tools. The bacteria survive Minnesota’s harsh winters in plant debris.

art4-3_600.jpgLuckily in most cases infection with bacterial speck and spot do not result in significant yield loss. Although the fruit with raised corky bacterial spots would not be considered marketable at the grocery store, smart gardeners know the fruit can still be enjoyed once the superficial spots have been cut away. Infected tomatoes should not be used for canning, however, because the disease may have changed the pH of the fruit.

To reduce the spread of the disease, gardeners should avoid working in tomato plants when the leaves are wet. Under moist conditions the bacteria reproduce and easily stick to a gardener’s hands and tools. Waiting until plants are dry for chores like staking, pruning and weeding will reduce the spread of the bacteria. In addition, providing good air movement around the plants by staking or caging tomatoes, pulling weeds, and spacing plants far apart will allow leaves to dry quickly. Allow 2 years to pass before planting tomatoes or peppers in the same location. Do not save seed from infected plants.

New Lily Classes Grow in Availability and Popularity

David C. Zlesak, University of Minnesota Extension Educator

Martagon, Asiatic, Oriental, trumpet, and tiger lilies (blooming approximately in this order from late spring through summer) are groups of amazing lilies that have beautifully graced our Minnesota gardens for decades. The martagon lilies have beautiful whorled foliage, flower early with wonderful clusters of typically downward facing flowers with recurved petals, and are even relatively shade tolerant. The Asiatic lilies are probably the easiest for us to grow here in Minnesota. In amenable sites they typically multiply well and provide a glorious show of blooms in probably the widest color range possible of all the different commercial lily classes. The Oriental and trumpet lilies have large, intoxicatingly fragrant flowers. The fragrance is especially powerful in the evening and throughout the night. I love coming home at night and being taken back by the rich, wafting fragrance of my Lilium regale lilies (a white trumpet lily) and ‘Casa Blanca’ Oriental lilies as I walk to the front door. Tiger lilies have magnificently speckled orange or yellow blooms typically with recurved petals similar to the martagon lilies.art3-1_600.jpg

art3-2_600.jpg We can routinely find cultivars of these traditional lily groups in our favorite catalogs and garden centers. However, in recent years there has been amazing advancements in very wide crosses between lily classes that previously were not able to produce successful offspring. Crosses between different classes have led to the development of new lily classes with many of the positive features of their parents. Special pollination techniques and techniques using tissue culture to “rescue” embryos have made it possible to recover hybrids from these wide crosses. These wide crosses are often called intersectional crosses because they are crosses made between different sections of the genus.

Botanically under the level of genus (Lilium is the genus of true lilies) there is the taxonomic level of section. Lily species that are within the same section are more similar genetically than lily species in different sections and tend to cross more easily among themselves (typically without the aid of tissue culture). For instance, crosses of multiple lily species in the section Sinomartagon led to the modern Asiatic lily cultivars we enjoy. Without tissue culture, sometimes intersectional hybrid embryos form, but the nutritive tissue (endosperm) around the embryo fails within a couple to few weeks after pollination and then it dies. If the embryo can be removed from the mother plant before it dies and placed in tissue culture where it can receive the nutrition it needs and continue growing. There are several modifications that can be made to the process in order to find ways that will work to recover different wide crosses.

These are some of the most popular intersectional lily classes on the market.

LA Hybrids

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LA refers to Longiflorum and Asiatic. These lilies are crosses between Easter lily (Lilium longiflorum) and Asiatic hybrids. They first came on the market in the early 1990’s. They look a lot like Asiatic lilies (flowers tend to be flat like Asiatics), but tend to have larger flowers with thicker petals than the Easter lily parent. Early LA hybrids tended to have colors within the pastel shades. Breeders have been able to backcross early LA hybrids to Asiatic lilies to intensify color and strengthen hardiness and other traits. Interestingly, breeders have not reported successful backcross hybrids to Easter lily parents. Modern LA hybrids tend to be as durable in Minnesota as Asiatic lilies. They are used widely in the cut flower industry and tend to be relatively easy to force in pots like Easter lilies.

Orienpet Hybrids

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Orienpets are crosses between Oriental and trumpet lilies. They tend to have huge, wonderfully fragrant flowers in a very wide array of colors and color combinations. The flowers generally tend to be more open faced like the Oriental parent. In Minnesota Orienpets tend to be more adaptable and durable than Oriental lilies. Plants typically are quite large. Many common Orienpet hybrids routinely grow to about 6’ tall and benefit from staking. The North American Lily Society has a yearly popularity poll. Those that win over multiple years are eligible to eventually be elevated into the lily Hall of Fame. Two very popular Hall of Fame lilies are of the Orienpet class and are ‘Silk Road’ and ‘Scheherazade’. ‘Silk Road’ is a lovely red / white bicolor and ‘Scheherazade’ is beautiful red / yellow bicolor.

LO Hybrids

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LO hybrids are crosses of Easter lily and Oriental lilies. They have just come into the marketplace the past few years. The most common cultivar gardeners are likely to find is ‘Triumphator’. In many ways it looks like an Easter lily with its beautiful, elongated trumpet, but the throat of the bloom is a gorgeous, rich red. It will be exciting to see more LO cultivars come on the market in the near future. Early reports are favorable for ‘Triumphator’ being able to overwinter in Minnesota. More time is needed to be confident how well cutivars of this new class will routinely perform in Minnesota.

Progress is being made on additional intersectional classes. For instance, there are beautiful hybrids in existence between martagon and Asiatic lilies. Hopefully soon they will become widely available. Recent intersectional lily hybrids offer even more great lily options for the Minnesota gardener.

The North American Lily Society (NALS) is a great resource to learn more about lilies. There are also local chapters. In addition, NALS has a nice seed exchange they host each year where members can obtain seeds of amazing lily species and also seeds of crosses and open pollination of lilies in almost every major class.

Clematis Growth Types and Pruning

Karl Foord, University of Minnesota Extension Educator

art1-1_600.jpgClematis is a genus that is best known for its vining members that produce large, colorful, showy flowers. This is at best only half of the truth. In fact many of the cultivars do produce spectacular flowers with colors from almost all 360 degrees in the gardener’s color wheel. In addition there are varieties with smaller nodding flowers that add a certain delicacy to the garden as well as some herbaceous types that are more shrub-like and die back to the ground each year. Clematis require a certain effort to make them thrive but it is well worth the effort.

The dizzying array of cultivars can be intimidating, but this can be simplified by categorizing plant types by when they set their flower buds. This will then determine when they will flower and how they should be pruned. As such, the categories are often labeled as pruning groups.

Group A*

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In this group flower buds are initiated on this year’s vine in July and then produce flowers in the late spring of the following year. If you prune off old wood you also prune off flower buds. So if you have a clematis vine and do not know the variety, observe its time of flowering. Those that flower before early summer are likely in this group. Pruning of this type should only serve to maintain the framework. Do so only after flowering and before July. Common species in this group include Clematis alpina and C. macropetala and are characterized by smaller 1” to 3” nodding flowers. Clematis alpina ‘Pamela Jackman’ and C. macropetala ‘Markhams Pink’ are cultivars of these groups that flower in May and thereafter produce attractive seed heads. Simple Rule: “If a clematis flowers before early summer, do not prune it.”(1)

Groups B1 & B2

In this group flower buds are produced on both old and new wood. The group can be divided into varieties that have two flower flushes (B1) and continuous flowering (B2). (2)art1-3_600.jpg

The B1 group flowers in early summer (May-June) from buds initiated the previous summer and in late summer (September) from buds initiated on the current year’s growth. The late summer flush is typically smaller than the early summer flush. Cultivars showing this pattern of flowering are ‘Haku Ookan’, ‘Miss Bateman’, ‘Lincoln Star’, and ‘Nelly Moser’. Interestingly, the cultivars ‘Belle of Woking’ and ‘Daniel Deronda’ produce double and semi-double flowers, respectively from old wood and single flowers from new wood.

art1-4_600.jpgRemove dead and weak stems in late spring prune after first flush of growth. Simple Rule: “Do not indulge in large-scale pruning of old wood made during the previous season(s) or there will be a loss of early flowers.”(2)

The B2 group shows a continuous flowering pattern lasting from June to September. Flower buds were initiated the previous year (old wood) and in the current year (new wood) in the same manner as the B1 group. However, this group does not demonstrate a rest period between two growth flushes. Cultivars showing this flowering pattern are ‘The President’ and ‘General Sikorski’ (photo).

Group C

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Group C plants only initiate flower buds on the current year’s growth. This pushes the flowering time to later in the season- July through September. The goal in pruning this group is to eliminate all of last year’s growth and leave the lowest pair of live buds on the plant to begin the current season’s growth. This encourages plants to produce strong new shoots from the base and flower well. Typical of this flowering pattern are the Tangutica, Texensis and Viticella groups and cultivars ‘Madame Julia Correvon’ (photos). Clematis integrifolia is a group C plant with a bush habit that only reaches two to three feet in height (photo).

art1-6_600.jpgI recommend that you consider clematis for your garden or if you have some already, consider adding more as part of you next gardening adventure. Always provide a climbing surface for the climbing clematis forms and secure stems to the surface. If this is not done winds can buffet and break the vines leading to a very unsatisfactory outcome.

*The A, B1 & B2, and C groups are often named 1, 2, and 3, respectively by some authors.




References



  1. Mary Toomey & Everett Leeds, An Illustrated Encyclopedia of Clematis, Timber Press, Portland, Oregon, 2001.

  2. Fred Wein et. al., The Concise Guide to Clematis in North America, Clearview Horticultural Products Inc., Home of ClematisTM

David C. Zlesak, University of Minnesota Extension Educator

art2-1_600.jpgEarlier this year in the May 15th Yard & Garden News, we featured Emily Tepe’s informative article on Woolch™ in the Mid-May Yard and Garden News as a new mulch for both commercial and home garden use. Emily planted a fantastic demonstration garden where Woolch™ would be featured. She invited us to come and see this garden on the St. Paul campus in front of the Plant Growth Facilities near the ‘Seed of Knowledge’ sculpture (across the street from the Display and Trial Garden). This garden is looking great and has much more to see in addition to strawberries and other plants growing with Woolch™. This garden integrates fruits, vegetables, and flowers into a very ornamental and functional landscape. Please come and visit the garden this summer. If you are not able to make it out or would like to just learn more about this great garden, Emily has created a blog about the garden at http://umediblelandscape.blogspot.com.

What's Up With That?!

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David C. Zlesak

Why do dandelions all look so similar? Other plants that reseed tend to result in individuals that have noticeable differences from each other. These differences among seedlings may be dramatic or subtle and can involve traits such as flower color, petal number, or plant habit. The answer is that dandelions primarily reproduce by apomixis. Apomixis is commonly defined as asexual reproduction through seeds. The embryos are genetically the same as the mother plant and are not the result of the union of two sex cells. Most plant and animal species rely on sexual reproduction to enhance genetic variability among individuals in populations. Variability can improve the chance that at least some individuals will have a competitive advantage when disease or other challenges come. Those individuals will hopefully survive and be able to reproduce in order to perpetuate the species. Dandelions, some turf grass species, and many citrus have a different strategy that uses apomixis. The best, well-adapted individuals clone or copy themselves through seed. A relatively small proportion of embryos are the product of sexual reproduction to support variability, while most are genetic copies of the well-adapted mother plant.

Photo 1: Bob Mugaas

Rose Acacia - A Shrub with Showy Pink Flowers

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David C. Zlesak, University of Minnesota Extension Educator

Rose acacia (Robinia hispida) is in full flower across Minnesota. It is a plant many people are unfamiliar with and are asking what it is. The abundant pendulous clusters of rosey pink, pea-shaped flowers makes it especially showy this time of year. Although it is native to the Southeastern United States and is often listed as hardy to zones 5 or 6, forms of it are perfectly adapted across Minnesota and do not suffer dieback. Although not readily for sale in the garden centers, once planted (typically shared among friends) it tends to persist. The amount of it therefore continues to increase across Minnesota landscapes.

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You are invited! Come and join us for our 2nd Annual Hennepin County Master Gardeners Learning Garden Tour. We have 10 very unique gardens designed and maintained by Master Gardeners for you to enjoy. The Master Gardener homeowner and other Master Gardeners will be on site to respond to your questions. For a preview of some of some of the gardens and event please view this video.

Each garden has a different theme and demonstration. Themes include a fairytale garden, a low maintenance garden, urban and woodland retreat gardens, a farmhouse in the city, container gardening, a sanctuary garden, and a shade garden with a labyrinth. There will be practical, informative demonstrations at each site. Master Gardeners will conduct interactive demonstrations at 10, 12, and 2 p.m. on a wide range of topics. You can learn how to create small space, container, and vertical gardens, build low maintenance water gardens in a weekend, create garden rooms and rain gardens, using color to create moods, and how to grow vegetables.

Lawn Mushrooms

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Bob Mugaas, University of Minnesota Extension Educator

With some areas of the state receiving moderate to heavy amounts of rainfall over the past couple of weeks, mushrooms are beginning to randomly appear in lawnsTheir appearance often causes people to be concerned about the health of their lawn and whether or not a serious disease might be getting started.

It’s important to remember that mushrooms are the ‘fruiting bodies’ of fungi living in the soil and thatch. They are responsible for the production of microscopic spores that in turn help propagate the fungus. The vast majority of those fungi are not associated with any lawn disease causing organisms. It’s quite common for them to appear during periods of moist conditions resulting from either natural rainfall or excessive irrigation. Again, they are not necessarily indicative of any particular lawn problem. The fungi are living on decaying organic matter in the soil and/or thatch layers. This breakdown of organic matter results in at least some of the nutrients contained in that organic matter being released back to the soil. At that point the nutrients are available for continued plant growth or used by other microorganisms. If you find the mushrooms offensive, simply knock them over with a rake and remove them from the area.

Choose Weed Control Products Carefully

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Bob Mugaas, University of Minnesota Extension Educator

When trying to select the ‘right’ weed control product, consumers are often confronted with a bewildering array of possibilities at retail gardening outlets. This prompts the honest question of ‘Which one of these products should I choose?’ Likewise, this question can have a variety of responses depending on what weeds are being targeted. This could easily be the topic of several articles.

However, there is one word of caution that is worth noting. Nonselective weed killers, that is, those that will kill all green vegetation, should not be used to treat weeds in lawns and expect the lawn not to be damaged. The result will end up like pictured where all the plants that contacted the herbicide, including the lawn grasses are killed leaving small to large patches of brown dead grass. These will now need to be reseeded or resodded since none of the grasses in these areas will come back. The two most common ingredients in these types of herbicides are glyphosate (e.g., Round-up, Kleen-up, many others) and glufosinate – ammonium (e.g., Finale). These should not be used to treat weeds in lawn areas unless the desire is to kill both the existing grass and weeds such as might be done before installing a new lawn.

Thousands Visit Morris Bedding Plant Trials

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Steve Poppe, University of Minnesota Scientist, West Central Research and Outreach Center

In the past, no other segment of the floriculture production industry has enjoyed public interest and use of its product more than bedding plants (annual flowering plants). Bedding plants are an indispensable item for landscape use, presenting an array of flowers and foliage that add color and texture to the landscapes of homes, apartment complexes, shopping malls, public buildings, city streets and parks.

The University of Minnesota supports this growing industry through annual flower trials conducted at Morris, St. Paul and Grand Rapids. In 2008, we evaluated annual flowers from eighteen major plant companies. Our gardens are open to the public and industry for selfguided tours throughout the growing season, providing a unique opportunity to compare performance of bedding plant cultivars under regional conditions. The public's response to the 2008display gardens at all locations was very positive. Several thousand people visited these sites during the summer. Numerous educational programs and garden tours were provided at all sites, highlighting the outstanding annuals in our trials.

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This special weekend features an information fair and water-wise demonstrations, art activities, music and a Heart of the Beast Puppet Theatre performance! Part of the 2009 Waterosity theme, this special weekend brings together additional resources and events surrounding the theme of water usage and water-wise practices. Here are just some of the special highlights:

The renowned In the Heart of the Beast Puppet and Mask Theatre will present Are You Thirsty?" (11 a.m. & 1 p.m. July 11 & 12).

Performances will be free with Arboretum admission.

Volunteers will be on hand to help showcase the various exhibits

The information fair will include several area industry and non-profit groups that are involved in water use and management.

While at the Arboretum, don’t miss all the great art displays dispersed throughout the grounds. The over a dozen special art displays celebrating Waterosity will be in place through early October. Artists far and wide submitted ideas this past year for consideration and a subset were selected for implementation. Here are just a couple highlights!

Water-Wise Gardening

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Julie Weisenhorn and Kathy Zuzek, Director, University of Minnesota Master Gardener Volunteer Program & University of Minnesota Extension Educator

Watering your garden and lawn… it seems so straight forward. When the soil is dry or a plant wilts, water. If it doesn’t rain for two weeks, water. If you happen to have the hose on, sprinkle on a little water.

Not so. There are many factors – the type of soil and the amount of sun and wind in your yard, the types of plants that you grow, weather patterns, and your cultural practices – that play into a landscape’s water needs. The water-wise gardener considers and plans for these factors to produce beautiful landscapes while minimizing water use.

The Cutting Edge Lawn Care Exhibit

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Bob Mugaas, University of Minnesota Extension Educator

The Cutting Edge is an educational display that is part of the 2009 Minnesota Landscape Arboretum’s Waterosity Educational Exhibit. The display focuses on how more water conservative lawn grasses combined with some small changes in lawn care practices can reduce water needs and other inputs going into the lawn.

The exhibit features small plots of several lower maintenance lawn grasses that are starting to see greater use in more water conservative lawns. For more information on low maintenance grasses, please visit Cool Season Grass Selection. Additionally, a plot of tall fescue, an up and coming turfgrass species with good drought tolerance and some adaptability to shady conditions, is featured. Prairie junegrass, a native of Minnesota prairies, is also be on display as it would appear in a lawn situation. As it already has very good drought tolerance, this shorter growing native species is currently involved in a rigorous U of M plant breeding program to increase other desirable lawn grass characteristics. In addition to viewing separate species and varieties of lawn grasses, both a no-mow mix and an ecology lawn mix are on display to provide yet another alternative to a traditionally managed lawn. For more information on turfgrass research at the University of Minnesota please visit Turfgrass Science and click on the research tab.

Drought-Tolerant Plants

Kathy Zuzek, University of Minnesota Extension Educator

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Do you live in a geographic area with little rainfall? Do your sandy soils allow water to percolate away quickly? Are you looking for a drought-resistant landscape? Are attractive landscapes and water conservation both goals of yours? Below is a partial list of trees, shrubs, and herbaceous perennials that once established, grow well with little supplemental watering. Within most of the species listed, there are cultivar choices that will provide you with a wide variety of ornamental traits.

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Michelle Grabowski, University of Minnesota Extension Educator

For most areas of Minnesota, the spring of 2009 has been an unusually dry one.  This cool dry weather has kept many of the spring leaf spot diseases of trees at bay.  Diseases like anthracnose on oak, ash and maple have been absent up until the most recent wet weather.  Anthracnose is now being reported, especially in areas that received significant recent rain like southern Minnesota. The fungi that cause anthracnose, however, may not be causing problems for long. Anthracnose fungi thrive in cool wet weather and with the recent onset of hot temperatures, the growth and spread of this disease is likely to slow down.

Poplar and Willow Borer

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Jeffrey Hahn, Asst. Extension Entomologist

All species of willow, most poplar (but rarely quaking aspen), and occasionally birch and alder are susceptible to attack by the poplar and willow borer, Cryptorhynchus lapathi.  This insect, a type of weevil, is 5/16 - 3/8 inch long with a slender snout as long as its head.  It has a roughly textured black body with mottled cream to tan colored patches on its body and its legs, including the back 1/4 of its wing covers.

Spinach Leafminer

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Jeffrey Hahn, Asst. Extension Entomologist

A spinach leafminer, Pegomya hyoscyami, is a small anthomyiid fly whose larvae attack the leaves of spinach, beets, chard, lambsquarter, and other plants.  This fly overwinters as pupae and the adults emerge the following April and May.  The adult is hairy, about 1/4 inch long, and grayish or brownish.  It lays eggs on the underside of older leaves.  A spinach leafminer larva hatches into a carrot-shaped, whitish maggot that lacks legs or an obvious head. 

The larvae tunnel into leaves, between the two leaf surfaces.  The mines are long and narrow at first, but eventually become an irregularly shaped blotch area.  These mines are opaque initially and then later turn brown.  The larvae are active for about two to three weeks before dropping to the ground and pupating.  Several generations can occur during one year.  This activity has little impact on plant growth but can be quite destructive to vegetables grown for edible greens. 

It's Too Late To Treat Ash Now For EAB

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Jeffrey Hahn, Asst. Extension Entomologist

With the discovery of emerald ash borer (EAB) in St. Paul in May, many people have been asking for information on how to protect their ash with insecticides.  While there are several options available to home residents within 15 miles of the infestation, the question people should be asking now is when should I treat my ash.  In general insecticide applications should be made from early May until early to mid-June.  With that in mind, it is really getting late to be treating your ash any longer this summer.

Photo 1: EAB galleries in infested tree in St. Paul. Jeff Hahn

It is possible that Tree-age (emamectin benzoate), which is a professional use only product, can be applied into July because its mode of action targets the larvae and not the adults.  However imidacloprid relies on being taken up by the tree into the canopy and killing adults that feed on leaves.  Because it takes three to four weeks for imidacloprid to be translocated in trees, any applications that take place now, will have little impact in protecting ash.  This is particularly true for products available to the general public.  If you are thinking of treating your ash yourself now, don’t do it.  You will be just wasting insecticides.  The next window of opportunity for insecticide applications will be this fall or next spring.

There are many factors to consider if you are thinking about treating your ash for EAB.  For more information on insecticide options for protecting ash from emerald ash borers, please see the EAB Insecticide Fact Sheet (pdf).

Garden Calendar for July

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Contributor: David C. Zlesak, University of Minnesota Extension Educator

Recent rains throughout much of Minnesota have been much needed after the dry spring.  Continue to water plants as needed.  There are a lot of great tips on watering in the Water-Wise Gardening article in this issue.  Plants to especially pay close attention to for supplemental water include those growing in containers and those that have been recently planted and are still in the process of adapting to their new site and establishing a well-developed root system.

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