In this issue of the Yard and Garden News...
September 2011 Archives
In this issue of the Yard and Garden News...
Jeffrey Hahn, Asst. Extension Entomologist
Fortunately, fall webworm normally has little impact on the health of large, vigorously growing, well-established trees (it is possible that small trees or shrubs can be completely defoliated in one season and could be injured). Fall webworms are usually no worse than an eyesore because of the webs they construct, making management unnecessary. This is especially during late summer as this feeding has little impact on plant health. There are also natural enemies that help keep fall webworms in check and prevent serious outbreaks.
If you want to try to improve the tree's appearance, you can try to pull the webbing and caterpillars off the branches (assuming you can reach them). Although it may be difficult to remove the entire web, you may be able to damage it enough to eliminate the fall webworms. You can prune out branches containing webs as along as removal is not excessive or the tree or shrub is left unsightly. Do not attempt to burn webs; this is more harmful to the tree than any control that is achieved.
If there are circumstances where it is necessary to treat fall webworms, they are vulnerable to insecticides if they are applied soon after the caterpillars start to construct their webs. There are a variety of residual products that can be effective, including permethrin and bifenthrin. If you wish to use a low impact product, try Bacillus thuringiensis, a bacterial insecticide. It is specific to butterfly and moth caterpillars and has no impact on other insects as well as people and animals. Once webs are larger, direct sprays do not penetrate through the webbing very well. Another option is to use the dinotefuran, a type of systemic insecticide. Another, systemic insecticide, imidacloprid, however, is not very effective against caterpillars.
Karl Foord, UMN Extension Educator
Whenever I weed my gardens I always manage to find a number of Canada thistle plants, Cirsium arvense (L.) Scop. These are not the rosette seedlings that I see in my lawn which are fairly easily dealt with (photo 1). These are aerial shoots coming from established roots (photo 2). A mixed planting garden bed presents its own set of problems in dealing with this weed. Why is Canada thistle so persistent?
Canada thistle is persistent for three reasons. Seed production, deep roots giving rise to stems, and root pieces that can regenerate plants.
Seed production per plant averages 1,500 seeds per plant but vigorous plants have been known to produce more than 5,000 seeds with viabilities greater than 20 years. So it will take persistence to reduce the seed load in the soil. Lesson 1: never let thistle go to seed. This will not remedy seeds coming in from an adjoining property, and seeds are reported to be able to travel a half mile in the wind.
Photo 3: Two years underground growth of Canada thistle from original one foot of root.
Canada thistle can reliably regenerate from half-inch long cut root pieces. Lesson 2: attempts to dig out the plant or chopping it up will likely not be successful and may only serve to propagate it.
Canada thistle is a perennial with a complex system of deep-seated roots that spread horizontally and give rise to aerial shoots (photo 2). The seedlings grow slowly at first producing a fibrous taproot which thickens and develops lateral roots in 7-9 weeks. Aerial shoots usually develop from buds on the branches of the horizontal system. The root system goes deep (6 - 10 ft.) and wide (> 10 ft. per year) with some 60% of roots existing at depths greater than 2 ft (photos 3 and 4).
To eliminate Canada thistle one needs to prevent regrowth from the potentially extensive underground root system. The non-chemical approach involves strategies that persist until the starch reserves in the roots are exhausted. The chemical approach involves application of herbicides at the correct dosage avoiding damage to nearby plants.
Simply removing the aerial shoots can eventually exhaust the root reserves. One study showed that mowing the plants would eliminate the top growth similar to pulling the aerial shoots, but will not deplete the starch reserves unless it is repeated at 7-28 day intervals for up to 4 years. It is more likely that the thistle would win given this strategy.
If the plant can be isolated, it can be smothered with an impenetrable barrier like plastic or a landscape weed cloth. This would require clearing out the bed and dedicated time to starving the root system. The key problem here is isolating a plant with a creeping underground root system that could send up shoots in adjoining areas which would replenish the root system.
Photo 5: Canada thistle in sedum bed. A situation where a bedding plant could be isolated from spray on a Canada thistle.
If the chemical route is chosen, a non-selective herbicide like glyphosate (Roundup®), which has little or no soil residual, would be the chemical of choice. In some situations sensitive plants can be separated from the thistle and protected from spray with a physical barrier like plastic (photo 5). The plastic may be removed as soon as the spray dries.
In other cases protecting sensitive plants is not possible such as a thistle nestled in a cotoneaster bed (photo 6). In this case one can apply material with a paint brush or spot spray taking care not to get spray material on the sensitive plant, and if you do wash it off immediately.
The goal is to kill the root system by getting as much chemical throughout the plant as possible. Use the lower of label recommendations as higher rates will kill the leaves and not get to the roots making the treatment ineffective. Make sure that the plants are not drought-stressed and that there is plenty of moisture. If the plants are stressed the chemical will not be effectively translocated throughout the root system. Be sure to read and follow all label directions carefully. It is highly likely that multiple applications may be needed to eradicate this weed.
Given the look of the below ground root systems it looks like the most we can hope for with Canada thistle is not elimination but rather a certain level of control.
"Canada Thistle." Midwest Weeds, Missouri State.
"Control Practices for Canada Thistle." Purdue University, Department of Botany and Plant Pathology.
Robin Trott, UMN Extension Educator, Douglas County
My house has been full of beautiful floral arrangements all summer, and the fall arrangements are outstanding, however, we will soon enter the cold months, and I can't envision a house without the color from my garden. To avoid this, I have made sure to include some everlasting plants in my cutting garden: Limonium sinuata (Statice), Helichrysum (Strawflower), Gomphrena, Achillea (Yarrow), Celosia (Cockscomb), and ornamental Grasses are all good candidates for air-drying. Once dried, I use these everlastings in bouquets, sachets, wreaths and holiday crafts.
Harvest your everlastings when the flowers are not fully open and in good condition. Don't wait too long, because flowers too far along will not dry satisfactorily. Select flowers or seed pods that are as close to perfect looking as possible because flaws, such as insect damage, become more obvious once they are dried. Pick your flowers in the late afternoon, after the heat of the day has passed and before the evening dew has set in. Using a sharp, clean tool, cut flowers close to the base of the plant (to keep stems as long as possible) and remove foliage from the stem to preserve the best color and shape. Group stems together in small bunches so the flower heads do not touch, secure with a rubber band or string and hang upside down in a warm, dry, dark area. Your garage, attic, spare room, garden shed or even a closet will do. With good air circulation, flowers take 1 to 3 weeks to dry completely. Store dried flowers in an airtight container until ready to use. Dried plant material can be stored in cardboard boxes; however, plants are better protected from insects and rodents if they are stored in airtight containers.
If you have never tried to dry your flowers, and are not sure what to include in your cutting garden, try some of these flowers and seed heads that lend themselves to air drying:
Achillea Spp. (Yarrow) - perennial
Ascelpias (Butterfly Weed) - perennial, primarily for seed pods
Astilbe - perennial
Artemisia annua (Sweet Annie) - self seeding annual
Calendula (Pot Marigold) - annual
Celosia - annual
Centaurea cyanus (Bachelor's Buttons) - annual
Echinacea (Purple Cone Flower) - perennial primarily for cones
Eryngium (Sea Holly) - perennial
Helichrysum (Straw Flower) - annual
Hydrangea- woody perennial
Gaillardia (Blanket Flower) - annual
Echinops (Globe Thistle) - perennial
Physalis alkekengi (Chinese lantern)
Grains (Oats, Wheat, Millet)
Gypsophila (baby's breath) - perennial
Limonium (statice) - annual
Lunaria annua (Money Plant, Honesty) - annual
Nigella damascena (Love in a mist) - annual, primarily for seed pods
Rudbeckia (Black Eyed Susan) - perennial, primarily for cones
Solidago (Goldenrod) - perennial
Good luck with all your everlasting adventures!
Jeffrey Hahn, Asst. Extension Entomologist
There have been numerous sightings of winged ants during August and September throughout Minnesota. These winged ants are reproductives, i.e. new females (soon to be queens) and males. The fly out of their nests at the same time, usually in large numbers for the purpose of mating. After mating, the queens fly off in search of favorable sites to build their own nests and the males die shortly afterwards.
Although nearly all ants swarm, different species do so at different times of the year. Right now cornfield ants and field ants are the primary swarmers that are active. Both of these ants nest in the soil in exposed sites and can be commonly found in lawns and other turf areas. Cornfield ant queens are about 1/4 inch long while field ants are a little larger.
Because of their size, field ants are sometimes mistaken for carpenter ants. However, carpenter ants do not nest in the soil and swarm just during spring. These swarms sometimes are mistaken for termites. However, termite swarms are rare in Minnesota and when they do fly, they occur in the spring. They are also have four wings of equal length which are much longer than their bodies.
Despite the impressive numbers that nests can generate, these swarming ants are harmless. They presence is also temporary, usually lasting just a few days. No control is necessary.
Michelle Grabowksi, UMN Extension EducatorDiseases of Rudbeckia.
Emily Hoover, professor and department head, UMN Department of Horticultural Science
Question: What is the implication of the freeze warning on the apple crop?
Answer: It depends on how cold it gets. The temperature within an orchard is not consistent. The "rule of thumb" is about 10% of the fruit on the tree will freeze if the temperature drops to 28 degrees Fahrenheit and remains so a few hours. Ninety percent of the apples will freeze if the temperature drops to 25 degrees Fahrenheit and remains so for a few hours.
However, the level of sugar in an apple also changes the severity of the event. The higher the amount of sugar, the lower the temperature has to be before freezing will occur because sugar lowers the freezing point of a solution. (Think Chemistry 101). Note that if the fruit freezes on the tree, but is not touched until it thaws, the fruit is fine to harvest.
Emily Hoover is a professor and department head in the UMN Department of Horticultural Science. Her research focuses on apple rootstocks.
Original source: "Over the Backyard Fence," blog of Master Gardener state program director, Julie Weisenhorn.
According to the Minneapolis Star Tribune, the Minnesota DNR is predicting the best fall color in ten years, thanks to abundant rain during the growing season, as well as a hot, humid summer. The DNR fall color reports are now available, to help find the most vibrant color in the state. The University of Minnesota Climatology Working Group, a division of the DNR, has more interesting information about the cause of the spectacular color show we enjoy each fall. The Star Tribune also has a great interactive fall color map.
The Minnesota Landscape Arboretum and the Minnesota Grape Growers Association are teaming up for the upcoming collaborative, 4X4 Culinary Series at the Arboretum. For the series, U of M Enologist Katie Cook will lead participants through four food and wine pairings over a series of four dinners prepared by leading Twin Cities chefs. Participants can sign up for any or all of the dinners to experience a full array of local wines and meals this fall and winter. More information can be found on the MN Landscape Arboretum website; Kare 11 also did a feature highlighting the series and local wines.
Order spring flowering bulbs to plant later this month or next. Water them thoroughly after planting. Unless there's ample rainfall, continue watering every couple weeks so they develop good roots before winter. Mulch them once the soil freezes. The longer you wait to plant your bulbs, the less likely they'll come through winter successfully. Tulips are more forgiving than other bulbs, but it's still best not to plant them too late.
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Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton
In this issue of the Yard and Garden News:
Jeffrey Hahn, Asst. Extension Entomologist
Emerald ash borer (EAB) has been confirmed in two new locations by the Minnesota Dept. of Agriculture (MDA) on Friday August 26. One find was detected in the city of La Crescent in Houston county while the second was found in the Great River Bluffs State Park in Winona county, just eight miles apart. This is the first time EAB has been found in Winona county. Both discoveries were made when an EAB adult was found on sticky purple panel traps that were deployed by the MDA. No infested trees have been found to date, although surveys in those areas are ongoing.
For more information see the MDA news release.Late Breaking News: On Wednesday August 31, MDA reported that EAB was found on another purple trap about 7 miles northwest of the positive trap location at Great River Bluffs State Park and about 7 miles east of Winona.
Bob Mugaas, UMN Extension Educator
The arrival of the Minnesota State Fair and its wrap-up on Labor Day weekend, mark the beginning of one of the best times of the year for initiating and renewing home lawn care activities. When it comes to repairing and rejuvenating your lawn after it has endured the stresses of another summer, avoid the temptation to also be winding down your lawn care efforts once Labor Day has passed. The main reason is that our grass plants are entering a very active period of growth triggered by a shortening of the days, cooler temperatures and usually a return to more frequent rainfall. Following are a number of brief lawn care tips that can help restore any lawn's health and vigor.
1. The middle of August through the middle of September is one of the best times of the year for lawn renovation and reseeding. Practices such as dethatching and aerifying are all best done at this time of year. Again, the primary reason for this is related to the grass plant's active period of growth and recovery during early to mid fall.
2. In addition, our soils are nice and warm from the summer heat. Warmer soil temperatures and ample moisture make this one of the best times of year to be doing some (re)seeding. Grass seed germinates and establishes more quickly increasing the chances of good winter survival. Also, because we have passed the time for many of our annual weed seeds to germinate and grow, there will be virtually no competition from annual weeds such as crabgrass, yellow foxtail, lambsquarters or common ragweed.
3. Putting down some nitrogen(N) fertilizer at the rate of one pound of N per 1000 square feet from late August through about the middle of September will be beneficial. This is the time of year when our grass plants readily absorb the nitrogen applied and use it to support various plant processes during the active fall growth period.
4. By later in the month, we are getting to the time of year when we can be most effective with herbicides at controlling those perennial broadleaf weedy plants such as dandelions, white clover, creeping Charlie and broadleaf plantain. Like our grass plants, these weedy plants are also actively growing and will actively take up and transport the weed killer throughout the plant giving better control. For example, dandelions are best treated from about mid-September to early October in the Twin Cities area. Plants will be killed this fall but the real difference will be observed next spring when there are few to no dandelions in what may have been a previously heavily infested area. However, this is not the time of year to be putting a preemergence crabgrass killer down hoping to have success next spring. Preemergence crabgrass killers are much more effective when used and applied properly in the spring.
5. One of the most common questions this time of year is, "How long into the fall should I continue to water my lawn?" The easiest answer is to continue watering so long as the plant continues to need water. In other words, if we have extended dry periods in the fall, grass plants will still need water to support active growth at this time of year. Remember that just because temperatures are cooler and days are getting shorter, soils will still dry out during extended periods of no rainfall or supplemental irrigation. It is desirable to gradually lengthen the time interval between watering to allow the soil to slightly dry before adding some water. This will help prepare the grass plants to better survive harsh winter conditions.
Likewise, these same conditions can make it easier to overwater and keep the plants too wet. Overly wet soils are very stressful for grass plants and can significantly increase certain diseases and just generally weaken the plant. As a gauge for your own lawn, check the soil moisture level periodically. If it feels damp to maybe just slightly dry and not wet and sticky that's probably about right for soil moisture during the late summer fall period.
6. At least during the month of September, mowing should continue on a regular basis maintaining a lawn height of about 2.5 to 3.0 inches. Heights can be gradually reduced back to about 2.0 to 2.5 inches by the time we get into late October. Remember that right now and for the next several weeks grass plants can take advantage of higher heights of cut by producing more food via photosynthesis due to more leaf tissue present. That also translates into very active root growth such that roots will extend deeper into the soil and in general develop a more robust root system. Both conditions aid in the uptake of water and nutrients from the soil thereby contributing to a healthier plant.
For many people, September marks the beginning of many family things like vacations ending, children going back to school, volunteer activities resuming and the like. With as busy as things can get in our family lives, try to remember this is also a time of new beginnings and renewal for our grass plants and lawns. Providing some additional nitrogen nutrition, watering during dry periods, mowing regularly and doing some reseeding to those injured and damaged areas of the lawn are all perfect activities for this time of year. In addition, restoring and maintaining a healthy lawn in the fall significantly contributes to better winter survival and a healthier lawn next spring.
For more information on any of the above topics see the lawn section on the University of Minnesota's website under Garden. You can also find lots of information about Minnesota home lawn care on the Sustainable Urban Landscape Information Series website. Got an unfamiliar weed in your lawn? Check out our on-line weed identification guide at "Is this Plant a Weed?" from the Garden link mentioned above. You can also find out how to control many of the common lawn weeds on that site as well.
Jeffrey Hahn, Asst. Extension Entomologist
There have been several reports of people seeing giant swallowtails, Papilio cresphontes, in the Twin Cities areas recently (they undoubtedly have been seen in other areas of Minnesota as well). This is noteworthy as these spectacular butterflies are not native to Minnesota but can occasionally be found during the summer as migrants from the south.
You can recognize a giant swallowtail because of its size, its wingspan ranges from 4" - 5 ½", and its black wings with yellow spots; the yellow spots on the forewings form an 'x'. Don't confuse it with a black swallowtail which also has black wings but is smaller, its wingspan is as large as 3 ½" and the yellow spots on its forewings are parallel and do not cross. Giant swallowtails can not reproduce in Minnesota as they need citrus trees and related plants for food for the larvae.
Karl Foord, UMN Extension Educator
The fresh peach season is upon us, and there are few things as bad as the anticipation of a delicious peach only to discover that the flesh is mealy and mostly inedible. I have been burned enough by mealy peaches to be wary of buying them in grocery stores. It is extremely difficult to look at a peach and determine whether the flesh is mealy. This makes peaches a risky purchase because you never know whether you will be delighted or disappointed. This article addresses two topics; 1) how you can improve the chances of not getting a mealy peach, and 2) how does peach flesh become mealy?
Carlos H. Crisosto, Department of Plant Sciences, UC Davis
Top: Flesh browning. Bottom: Healthy peach.
The best way I know to reduce the chance of buying a mealy peach is to reduce the time from farm to your house as well as the number of transfer points that the peach travels through in getting to you (Figure 1). One way to do this is to purchase fruit in bulk from a local Pick-Your-Own (PYO) farm that will deliver fruit direct from a peach grower in Michigan. The farmer contacts these entities when the peaches are ready. A truck is procured and the peaches travel to a central PYO and from there to your PYO where you are called to pick up the peaches. The peaches can get to you in a matter of days.
Explaining how a peach becomes mealy requires understanding the fruit distribution process and the physiology of the peach. Peach flesh becomes mealy if a physiologically immature peach is placed in cold storage or a physiologically mature peach is stored at suboptimal temperatures. To avoid the first problem, peaches are harvested and then "conditioned" at 68°F for 24 hours to ensure that all are physiologically mature. To avoid the second problem, following conditioning the peaches should be chilled to between 32° and 37°F and kept in this range throughout the processes taking the peach from farm to retail store. At the retail store the peaches can be brought back to 68°F where they can ripen in a 4 to 6 day range at which point they will be ready-to-eat.
Peaches stored in the 38° to 51°F temperature range develop mealy brown flesh and ripen inconsistently. Peaches stored in the 31° to 34°F temperature range with 90% relative humidity can maintain quality for two weeks or more. If peaches are exposed to temperatures at or below 30°F, their tissues will be damaged by freezing.
If the most likely cause of mealy peaches is storage in the 38° to 51°F temperature range and we are still buying mealy peaches, then somewhere in the shipping and distribution process the peaches are experiencing this temperature range. This could be because it is difficult to maintain this cold chain or because of the great variety of fruits and vegetable being shipped, compromises must be made during transport. Not all fruits and vegetables have the same optimum storage temperature. Apples and peaches do well at 32°F, whereas grapefruit like 50° to 60°F, lemons like 45° to 48°F and the temperature optimum for oranges depends on where they come from. California oranges have a different temperature optimum (45-48°F) than Florida (32-34°F) which has a different temperature optimum than Arizona and Texas (32-48°F).
As a scientist it would be interesting to know where the system breaks down, however as a consumer I just want to find the easiest way to get a great tasting peach.
Ask your Pick-Your-Own farmer if they purchase Michigan Fruit for sale through their business.
L. Kitinoja and A. A. Kader, Postharvest Horticulture Series No. 8E, Postharvest Technology Research and Information Center, University of California, Davis 2002.
Michelle Grabowski, UMN Extension EducatorVerticilium Wilt of Trees and Shrubs.
Jeffrey Hahn, Asst. Extension Entomologist
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),
Michelle Grabowski, UMN Extension Educator
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 preceded by leaves. Flowers usually develop in about 4-6 weeks from dormant bulbs, so they can be timed to flower at Christmas, or for Valentine's Day. For more information, see the Extension publication "Growing and Caring for Amaryllis."