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Showing posts from August, 2011

Verticillium Wilt in Shrubs and Shade Trees

Michelle Grabowski, UMN Extension Educator



M.Grabowski, UMN Extension
Photo 1: foliar symptoms of verticillium wilt on smoke bush


Several shrubs and shade trees exhibiting symptoms of verticillium wilt have been recently observed in Minnesota. Verticillium wilt is caused by the fungus Verticillium dahliae. This pathogen infects through roots and moves into the vascular system of the plant. Infected trees and shrubs may have small pale leaves or leaves with scorched edges in chronic infections. In severe infections, leaves may be completely discolored yellow to red, curl, wilt and die. Often symptoms of verticillium wilt appear on one to a few branches in the canopy. If you suspect Verticillium wilt may be a problem in a shade tree or shrub, peel back the bark on an infected branch and look for grayish streaking in the sapwood. To learn more about Verticillium Wilt visit the UMN Extension web publication Verticillium Wilt of Trees and Shrubs.

Be Aware of Wasps

Jeffrey Hahn, Asst. Extension Entomologist




Jeff Hahn
Photo 1: Aerial yellowjacket nest

This is a common time of the year for wasp (primarily yellowjacket) nests to become conspicuous and more noticeable by homeowners. These nests have been present all summer but were small enough that they were not noticed then. Although this year would be considered to be no more than an average year for wasps primarily due to the late spring we experienced, if you have a wasp nest present on your property they are still a potential problem. What you decide to do with a nest can depend on a number of factors, such as how close to human traffic the nest is, is the nest is exposed or not, and how close to a hard frost we are.


For more information, see the following article on wasps (yellowjackets),


Late Leaf Rust on Raspberry

Michelle Grabowski, UMN Extension Educator



M.Grabowski, UMN Extension
Photo 1: Late Leaf Rust on Red Raspberry
Bright orange powdery spots on red or purple raspberry leaves are symptoms of late leaf rust, a fungal disease caused by Pucciniastrum americanum. This pathogen can also infect individual druplets in the fruit, turning them into small bright orange powdery masses on an otherwise delicious looking fruit. Late leaf rust needs to alternate between raspberry and white spruce trees. It does not survive on raspberry plants from year to year. Removing nearby white spruce trees is not an effective way to control this disease, however, as spore can travel long distances on the wind. High humidity in Minnesota this summer has favored infection with late leaf rust.

Calendar: September 1, 2011

Dave Hansen, UMN Extension


It's that time of year again! The Apple House at the Arboretum is officially open for business. Purchase apples from a changing inventory of 50 varieties throughout the season - from long-time favorites to recent University of Minnesota introductions, including Minnesota's new State Fruit, the Honeycrisp! Select from a variety of specialty food items and merchandise in the AppleHouse Gift Shop. All proceeds benefit the University of Minnesota's apple research program. See the Arboretum website for more information.

Bonus: the Apple House was featured this morning on WCCO!

Now is the time to start prepping your amaryllis plant to bloom in time for the holidays. Cease watering around Labor Day, and store the plant in a cool, dark room for 8-12 weeks. Bring the plant back out mid-November, and remove dead foliage. Set the bulb in bright light and water the soil thoroughly. Usually one or more flower stalks appear first, but occasionally they are prece…

Bacterial Spot Shows up on Tomatoes

Michelle Grabowski, UMN Extension Educator


M.Grabowski, UMN Extension
Photo 1: Bacterial spot on an heirloom tomato


Bacterial Spot, caused by the bacteria Xanthomonas campestris pv. vesicatoria, has been found in several areas of Minnesota. This bacterial pathogen causes dark brown to black leaf spots with a pale yellow halo around them. Often the leaf spots dry up and crack, resulting in tiny holes at the center of the spot. Probably the most noticeable symptom of bacterial leaf spot of tomato, are the raised brown or black corky spots on fruit. These spots range in size from the diameter of a pencil tip to the diameter of a pencil eraser. Fruit spots can be seen on both green and ripe tomatoes. The spots are superficial and do not rot the fruit. Therefore the tomatoes can still be eaten, although they may be difficult to peel if you plan to use them in your next batch of spaghetti sauce. To learn more about managing bacterial spot of tomato read 'What are those spots on my tomat…

Peppers - Sweet and Heat!

Karl Foord
Photo 1: Sweet peppers



Karl Foord, UMN Extension Educator


I traveled to Bagley, Minnesota to Ter-Lee Gardens, the home and farm of Terry and Loralee Nennich. Ter-Lee Gardens offers Pick-Your-Own strawberries at the farm and almost every vegetable that you can think of, most of which is marketed at the Bemidji Area Farmers' Market. I had heard that Loralee was growing more than 50 varieties of peppers and was intrigued. Terry is a colleague of mine and he persuaded Loralee to give me a tour of the two high tunnels where she was growing her peppers. You can see the peppers she showed me on photos 1 and 2.



Karl Foord
Photo 2: Hot peppers



Most pepper cultivars come from the species Capsicum annuum, whose center of origin is Mexico. The Habanero and Tabasco peppers come from C. chinense and C. frutescens, respectively. The center of origin for these species is the Amazon River basin in northern South America. The amount of variation in size shape and color is impressiv…

The Garden Blues

Samantha Lahman, University of Minnesota Extension Horticulture Intern, Douglas County

Centaurea cyanus, more commonly known as the annual Bachelor Button or Cornflower, is in full bloom in the garden this summer. Cornflowers are easy to grow and come in a great variety of colors, which has made them a long time favorite for novice and experienced gardeners. The Cornflower received its common name from the flowers that bloom wildly in the grain fields of southern Europe. It is even rumored that the Cornflower was selected as Germany's National Symbol of Unity because Queen Louise of Prussia; upon fleeing Germany to escape Napoleon, reportedly hid her children in a cornfield and kept them quiet by weaving Cornflowers into wreaths.



Samantha Lahman


Cornflowers are tall annuals that grow on beautiful grey-green stems. The most common color is a bright blue (Blue Boy), but other varieties range from pinkish white to deep maroon. Growing to a height of 24-36 inches, they can be easily plac…

Lydecker/BlackIce™ Plum: A New Plum for the Midwest

Brian Smith, UWRF
Photo 1: Lydecker® BlackIce ™= Plum. 'Oka' ( Prunus besseyi x P. salicina) x Z's Blue Giant (P. sal.).



Emily Dusek, University of Wisconsin River Falls

Plums have long been regarded as a fruit that can be grown in the Midwest, but the size and quality has never measured up to that of California's plums. Well we Midwesterners need not lament anymore because the new Lydecker/BlackIce™ Plum (bred by Dr. Brian Smith from University of Wisconsin-River Falls) exhibits many of the characteristics of Californian Plums all while being a winter-hardy plum!

This was achieved because the BlackIce™ was bred from a flavorful Californian plum (Z's Blue Giant) and a winter hardy plum (Oka). With this combination of genes, the BlackIce™ has a dark purpley-black tender skin, with rich juicy red flesh on the inside, and free-stone pit that does not stick to the flesh. All while being winter-hardy to as low as -35 ºF (Zone 3b) and ripening 2 to 3 weeks earlier then …

Apple Sunburn

Photo 1: Sunburn necrosis of apple.



Karl Foord, UMN Extension Educator

Sunburn to apples should be distinguished from sunscald. Sunscald is damage to the bark of the tree when strong winter sun warms up tissues on the south facing side of the tree. When the sun sets, the temperature plummets and this softened tissue is damaged by freezing.

Sunburn is damage to the peel of the fruit. The temperature of the apple peel can be significantly greater than the ambient temperature ranging from 18°F to 29°F above ambient temperature on a clear day when other conditions are favorable (Schrader et al., 20011). Factors influencing peel temperature include solar irradiation, air temperature, relative humidity, wind speed and direction, and tree vigor.


Photo 2: Sunburn necrosis of apple.



David Bedford, a research scientist at the University of Minnesota Horticultural Research Center, noted seeing a lot of this type of damage due to the high temperatures and high dew points experienced this summer.

What's Happening in the Orchard and Calendar: August 15, 2011

What's happening in the orchard? Blueberries!



Tomato tip:
Consider pinching the growing tip of your indeterminate tomatoes in the next few weeks. By eliminating the growing tip the energy produced by the plant is focused on ripening the tomatoes presently on the vine. If not the vine will continue to produce flowers and fruit that will not ripen before the first frost. The rule of thumb is about 1 month prior to historic first frost. If you have ways to protect your tomatoes from the historic first frost you can likely extend the season for another month, and can prune accordingly.

Japanese Beetle (JB) Q & A

Jeffrey Hahn, Asst. Extension Entomologist


Q. Where did JB come from?


A. The first JB was found in Minnesota in 1968 after which the Minnesota Dept. of Agriculture (MDA) started a trapping program. Despite traps being set up in the Twin Cites area, between 1969 - 1979, only three beetles were captured. Between 1980 - 1983, only 16 JB were found. There were no trapping between 1984 - 1991.



Jeff Hahn
Photo 1: Japanese beetle adult close-up. Note feeding damage.


The trapping program resumed in 1991 and in 1992 298 JB were trapped. In 1994, over 6,800 were trapped in 12 counties. In1999, nearly 36,000 were trapped; over a half million in 2000; and over 1 million JB trapped in 15 counties in 2001 (99% of these were found in Hennepin and Washington counties). Then in 2002, the numbers crashed and only 1,682 in 19 counties were found.

MDA discontinued their trapping program after that, feeling that JB was established. Very few reports were received by Extension over the next severa…

Gray Mold on Geraniums

Michelle Grabowski, UMN Extension Educator



M.Grabowski, UMN Extension
Photo 1: Gray Mold on Geranium


Gray Mold is a common disease of flowers and even some vegetables. The fungus Botrytis cinerea is the pathogen that causes gray mold. This fungus thrives in wet weather. Recent rains have resulted in increased sightings of gray mold. Gardeners should look for brown spots on leaves with concentric brown rings like a bull's eye. Flowers can be blighted by gray mold at any stage. Brown blossoms or petals can all be caused by gray mold. A fine fuzzy gray mold can be seen on infected plant parts when moisture sits on the plants. Early morning is a good time to check for this pathogen as dew often encourages the fungus to produce spores.

Read more about gray mold.