Yard & Garden Line News
Volume 8 Number 4                                                               April 1, 2006
Features this issue:

Disease-Resistant Perennials--dream or reality?
An Internet Hoax: Termites in Your Mulch
Sweet Potato Shoots
Editorial Notes

Disease-Resistant Perennials--dream or reality?
Bob Mugaas, Regional Extension Educator-Horticulture

Mildew-free
Phlox 'David' Photo credit: Bob Mugaas
The Plant Research Evaluation Program (PREP) was initiated in 2003 by Dr. Janna Beckerman, Extension Plant Pathologist, and Regional Extension Educator in Horticulture, Bob Mugaas. The project was funded through an Extension program grant and was to last for a period of three growing seasons. The project's primary goal was to conduct general disease susceptibility and overall plant performance evaluations on a number of new and existing herbaceous perennials used in Minnesota gardens. When possible, specific pathogens associated with disease symptoms were identified. In most instances, only general symptoms were noted (i.e., powdery mildew, rust, leafspot, etc.)

A secondary goal was to introduce volunteer Master Gardeners from the University of Minnesota Extension Service as well as interested individuals from the nursery and landscape industry to the art and science of conducting field research as might be done at a University or other research institution. It was hoped that this exposure would create a deeper appreciation for the value of using "research based information" in their professional or volunteer roles of providing horticultural information.

Most of the project was located in a wide open, fully exposed area at University of Minnesota Outreach, Research and Education (UMORE) Park in Rosemount, MN. This project was included as part of the Master Gardener Education and Research Display Gardens already being developed at this site. With the exception of the Geranium evaluations, all other species and cultivars were planted in an open field area. The Geranium evaluations were planted in a partially shaded area and all placed under woodchip mulch.

Classes of about 35 students each were conducted in both 2003 and 2004. Due to insufficient enrollment in 2005, classes were not conducted. However, data was collected by summer horticulture intern, Ron Claussen, to complete the three-year term of the project.

Participants in the program received training in basic experimental design as an introduction to how scientific field studies are commonly conducted. In addition, they received an introduction to the major groups of plant diseases and plant disease assessment as well as the primary diseases affecting the plant material included in the study.

As a compliment to their in-classroom activities, participants actually took data and summarized that data for presentation to the class at the end of the season. Data collected included the amount of disease present on a plant as well as ratings for overall plant quality. In some instances, insect damage was also quite high and reflected poor overall quality even though actual disease presence may have been minimal.

Monarda punctatum with leafspot and powdery mildew Photo credit: Bob Mugaas
In this study, the same number of plants was planted in a bare soil unmulched area and a wood chip mulched area. The project design included four plants of each species or cultivar in each of three replications for both the mulched and unmulched areas. Thus the total number of plants in each area was 12. Where there was not enough plant material to provide both areas with the same number of plants, all were planted in the mulched side only. The assumption was that winter survival would be better under the protection of a mulch cover, thus helping to ensure that the plants would survive for the duration of the study. In a few situations, there were sufficient plants to place three of each in both the mulched and unmulched areas for a total of nine plants of each species or cultivar.

Reading the table
The overall plant quality ratings listed in the table below are for 2005. This will generally reflect how the cultivar has performed over the last 3 growing seasons as it has had a chance to get established and acclimated to the site during that time.

In some instances, plant survival has been low due to either winterkill or loss during the transplanting process. That will be reflected in the total number of plants remaining for evaluation at the end of the 2005 growing season. The number of plants making up this overall quality rating is noted in the column next to the species or cultivar name. The mulched (M) or unmulched (UM) designation is in parentheses next to the species or cultivar name. In a few cases, there was good survival in one side while little to no survival in the other. When that situation occurred the letters 'NS' are used to indicate 'no survival'. A minimum of three plants out of an initial planting of 12 needed to survive in order to be considered in the ratings.

Plant quality includes general health and vigor of the plants, foliage color as well as accounting for any incidence of insect damage or disease infestation. The scale for the overall quality rating is from 1 to 5 with 1 being very poor quality and nearly dead to five indicating plants with outstanding health and vigor. Since the overall rating includes a number of variables, it is possible that a plant could be very vigorous but still have its foliage severely infested with a disease. A good example of that situation is our native Monarda fistulosa which grows quite vigorously and tall but has nearly all of its foliage covered in powdery mildew; a problem that does not seem to have a significant impact on the overall long-term health of this plant. Hence its' overall rating is quite high but the presence of the mildew is noted in the comments section.

Rust on 'Alma
Potschke' aster Photo credit: Bob Mugaas
The 'comments' column primarily reflects specific information about the presence or absence of any disease. Those cultivars without any comments reflect little to no disease present on any of the plants. Occasionally, there will be a special notation about the foliage being very free from any disease symptoms.

While this is not intended to be an exhaustive evaluation of the plant material included in this project, it is hoped that providing some general information about how these species and cultivars have performed at this site will be helpful for gardeners. Again, remember this is a wide open, fully exposed site and the plants received no additional winter protection of any kind other than that provided by the mulch used in the mulched side of the trial. Placing these same plants in a more sheltered, protected site may give much better winter survival and recovery than evidenced in this trial. That in turn may give rise to healthier stronger plants as well.



The University of Minnesota Extension Service is gratefully acknowledged for its financial support of this project.


Species or Cultivar Total # plants
out of 12 planted initially
that survived
through the end
of 2005		 Overall Rating Comments
Aster
September Ruby (M) 11 3.45
September Ruby (UM) 7 3.86
Alma Potschke (M) 12 4.83 good vigor and form but covered with rust
Alma Potschke (UM) 3 3.67 good vigor and form but covered with rust
Woods Pink (M) 3 3.60
Woods Pink (UM) NS
Bluebird (mulched side only) 11 4.23
Coreopsis
Moonbeam (M) 10 4.14
Moonbeam (UM) 11 4.41
Zagreb (M) 11 4.77
Zagreb (UM) NS
C. tinctorius 'Dwarf Red' (M) 1 3.00
C. tinctorius 'Dwarf Red' (UM) 4 3.25
Sunshine (M) NS
Sunshine (UM) 12 4.67
Dianthus (installed spring 2004)
Arctic Fire (M) 12 3.96
Arctic Fire (UM) 12 4.50
D. grantianopolitanus (M) 6 3.77
D. grantianopolitanus (UM) 6 3.92
Zing Rose (M) 2 3.60
Zing Rose (UM) 5 3.20
D.amurense (M) 12 3.75
D.amurense (UM) 11 3.52
Harmony (M) 6 4.17 good vigor and form but covered with leafspot
Harmony (UM) 9 4.11 good vigor and form but covered with leafspot
D.carthusianorama (M) 8 4.18
D.carthusianorama (UM) 10 3.48
Yellow Beauty (M) 7 3.93 good form but covered with leafspot
Yellow Beauty (UM) 7 4.29 good form but covered with leafspot
Monarda
Aquarius (M) 8 3.13 some powdery mildew; extensive leafspot present
Aquarius (UM) 7 3.57 some powdery mildew; extensive leafspot present
Jacob Cline (M) 2 2.40 poor plant form, but best mildew resistance
Jacob Cline (UM) 4 2.89 poor plant form, but best mildew resistance
Prairie Night (M) 8 4.00 most plants nearly covered with powdery mildew
Prairie Night (UM) 10 3.50 most plants nearly covered with powdery mildew
Blue Stocking (M) 8 3.94 one half or less of plants infested with powdery mildew
Blue Stocking (UM) 11 3.30 one half or less of plants infested with powdery mildew
M. fistulosa (M) 12 4.22 vigorous but covered with powdery mildew by mid-summer
M. fistulosa (UM) 12 4.79 vigorous but covered with powdery mildew by mid-summer
Thompson & Morgan Superb Mixed (M) 11 3.27 one half or less of plants infested with powdery mildew
Thompson & Morgan Superb Mixed (UM) 9 3.78 one half or less of plants infested with powdery mildew
Bees Favorite (M) 3 3.86 of surviving plants, all had at least 50% coverage of powdery mildew
Bees Favorite (UM) 3 3.00 of surviving plants, all had at least 50% coverage of powdery mildew
M. punctatum (M) 3 3.43 good form, smaller stature, covered with powdery mildew by late summer and extensive leafspot present
M. punctatum (UM) 6 3.69 good form, smaller stature, covered with powdery mildew by late summer and extensive leafspot present
Panorama Mixed (M) 11 3.18 most plants averaged 50% or less infestation of powdery mildew
Panorama Mixed (UM) 12 4.00 most plants averaged 50% or less infestation of powdery mildew
M. bradburiana (M) 10 3.81 most plants with 50% or less of powdery mildew; some leafspot present
M. bradburiana (UM) 10 3.15 most plants with 50% or less of powdery mildew; some leafspot present
Blue to Wine Red Mixed (M) 8 3.00 most plants with 50% or less of powdery mildew; some leafspot present
Blue to Wine Red Mixed (UM) 5 3.73 most plants with 50% or less of powdery mildew; some leafspot present
Panorama Red Shades (M) 4 3.11 all plants with 50% to 75% powdery mildew; slight leafspot
Panorama Red Shades (UM) 4 2.89 all plants with 50% to 75% powdery mildew; slight leafspot
Phlox
David (M) 12 4.58 virtually free of powdery mildew; slight leafspot present
David (UM) 11 2.86 virtually free of powdery mildew; slight leafspot present
Blueboy (M) 8 2.75 very little powdery mildew; 10% to 25% leafspot present on most plants
Blueboy (UM) 12 3.96 very little powdery mildew; 10% to 25% leafspot present on most plants
Franz Schubert (M) 9 3.26 less than 10% powdery mildew on most plants; slight amounts of leaf spot and leaf blighting
Franz Schubert (UM) 10 3.90 less than 10% powdery mildew on most plants; slight amounts of leaf spot and leaf blighting
Amethyst (mulched side only) 7 2.80 slight leafspot and some evidence of leaf blighting
P. maculata 'Natascha' (M) 7 2.64 overall plant vigor not as good but 25% or less of most plants infested with powdery mildew
P. maculata 'Natascha' (UM) NS
Veronica
Icicle (mulched side only) 10 3.90
Crater Lake Blue (M) 11 3.83
Crater Lake Blue (UM) 6 3.08
Goodness Grows (M) 12 3.71 less than 25% leafspotting present on most plants by end of season
Goodness Grows (UM) 12 2.92 less than 25% leafspotting present on most plants by end of season
Red Fox (M) 12 3.63 greater than 50% of plant foliage infested with leafspot by end of season
Red Fox (UM) 11 3.00 greater than 50% of plant foliage infested with leafspot by end of season
Giles van Hees (M) 9 3.16 extensive leafspotting present by end of season
Giles van Hees (UM) 6 2.83 extensive leafspotting present by end of season
V.s. Blue Charm (M) 11 4.23 nice plant form and growth but extensive leafspotting present by end of season
V.s. Blue Charm (UM) 10 4.25 nice plant form and growth but extensive leafspotting present by end of season
Waterperry Blue (mulched side only) 7 3.13 only slight infestation of powdery mildew
Sunny Border Blue (M) 6 3.54 only slight infestation of powdery mildew but greater than 75% of foliage effected by leafspotting
Sunny Border Blue (UM) 4 2.56 only slight infestation of powdery mildew but greater than 75% of foliage effected by leafspotting
V. schmidtiana(M) 4 2.50 only slight powdery mildew infestation; no leafspotting present
V. schmidtiana (UM) 4 2.63 only slight powdery mildew infestation; no leafspotting present
Sightseeing (M) 10 3.40 very little powdery mildew or leafspotting
Sightseeing (UM) 10 3.67 very little powdery mildew or leafspotting
Geranium
(all geranium trials were in a partially shaded area and all were wood chip mulched; 3 reps of 6 plants per rep)
G. macrorhiza cv. Album 18 4.39 relatively clean foliage with only a few plants showing up to 25% leafspotting
Alan Blooom 18 3.89
Biokovo (only 12 plants initially) 11 5.00 very clean foliage; less that 10% evidence of leafspotting and only on a few plants
G. dalmaticum 17 3.65 very clean foliage; almost no leafspot present
Splish Splash 18 2.44 a majority of plants powdery mildew infestations covering 50% to 100% of their foliage
Nimbus (only 12 plants initially) 11 3.82 a majority of plants showing leafspotting between 10% and 25% infestation
G.s. Alpenglow (planted spring 2004) 18 3.67 a majority of plants showing leafspotting up to 25% of their foliage


An Internet Hoax: Termites in Your Mulch
Jeffrey Hahn, Assist. Extension Entomologist

Termite-damaged tree from the southern U.S. Photo credit:
ARS-USDA
About a month ago, an e-mail started circulating on the Internet warning people about mulch that could be infested by termites. It spread quickly to all areas of the country causing a general panic over the potential of spreading termites in mulch. Urban entomologists throughout the country were inundated with questions from people wondering whether this was true. This e-mail warning reads as follows:

If you use mulch around your house be very careful about buying mulch this year. After the Hurricane in New Orleans many trees were blown over. These trees were then turned into mulch and the state is trying to get rid of tons and tons of this mulch to any state or company who will come and haul it away. So it will be showing up in Home Depot and Lowe's at dirt cheap prices with one huge problem. Formosan Termites will be the bonus in many of those bags. New Orleans is one of the few areas in the country were the Formosan Termite has a strong hold and most of the trees blown down were already badly infested. Now we may have the worst case of transporting a problem to all parts of the country that we have ever had. These termites can eat a house in no time at all and we have no good control against them, so avoid cheap mulch and know were it came from.

Many Minnesotans have been wondering whether this is true and could it happen in this state? The short answer is that while it's not impossible, it's very unlikely that Formosan termites could be inadvertently brought into Minnesota.

Like any good hoax or myth, there are some elements of truth to the Internet message. First Formosan termites are very aggressive and destructive termites. They cause considerable damage to structures in areas where they are established. Although they are a type of subterranean termite which nests in the ground, it is possible for these termites to produce aerial colonies and to infest damaged trees. However, after that the facts do not support the story.

This e-mail implies that it was written by someone from Louisiana State University giving it an air of credibility. However, they are not the source of the e-mail. There was a related news release written by Dr. Dennis Ring, an entomologist from Louisiana State University last October. In the release, he warned people that they could spread Formosan termites around the state and other parts of the country by using railroad ties, reusing architectural wood, or other whole pieces of wood or lumber that were infested with Formosan termites. No where did the news release mention a risk of transporting termites in mulch.

So why is it unlikely for these termites to find their way to Minnesota? First, there is the issue of trees being mulched. It is universally agreed amongst entomologists that it is highly unlikely that termites in wood would survive the destructive nature of the chipping process. Once trees are mulched, this wood debris does not remain in one place long before it is removed to be burned or deposited in an approved landfill. This gives termites in adjacent areas very little opportunity to infest it.

In fact, wood debris does not even leave Louisiana as there has been a long standing quarantine (since the previous October) in the state for the 12 Formosan termite infested parishes. This was put into place to help protect against these termites being accidently spread. No wood or cellulose materials may be moved out of these quarantine areas without Louisiana Agriculture Dept. approval, including all materials from Katrina clean-up efforts. If any type of wood debris is moved out of the quarantine area, it is being done illegally.

Even if despite all of these efforts, termite-infested mulch is moved north, the termites' chances of survival are quite low. The reduced moisture and greatly increased heat in a shrink-wrapped pallet of bagged mulch would be very detrimental to termite survival. Should they survive this trip, which is not impossible, the ability for a few termites to survive in the landscape when cut off from their colony is still very poor.

Formosan termites Photo credit:. ARS-USDA
Should Formosan termites defy the odds and end up in a Minnesota landscape, what would happen? They might survive the summer weather but as it got colder, the termites would die. Formosan termites are a tropical species and they do not tolerate cold weather. In fact, they do not survive prolonged exposure to temperatures in the mid 40'so F. Currently Formosan termites are not known to infest areas further north than Memphis and Atlanta (35ºN latitude).

What if these termites somehow infested a home where it would be warm during winter? Formosan termites are a subterranean species whose colony is established in the ground. The workers forage to sources of wood, like your home, and then return to the nest. The odds are very much against them establishing a nest in a home. Still not impossible. While Formosan termites occasionally are known to construct nests above ground it would extremely difficult for them to establish a nest in a home. If they attempted to create a nest in a structure, they would discover the environment is too dry (termites need a very moist environment) and they would die.

The bottom line is that the chances of encountering Formosan termites in Minnesota is extremely remote.

In all fairness we do have subterranean termites that are native to Minnesota but they are not common. They are restricted to southern Minnesota including the Twin Cities. There are some hot spots where you can find termites throughout most of a specific neighborhood but otherwise they are infrequently encountered even in areas where they are know to exist.

While native termites can be associated with mulch, the presence of mulch will not attract termites into yards and to your homes if they are not already present. If you are not having a problem with termites now or you do not live in areas where termites are known to be a problem, you have little chance of being infested with them.

[Note: Many sources were used to write this story including: Louisiana Dept. of Agriculture and Forestry, Dr. Mike Merchant, Dr. Ronald Shumack, Dr. William Fonteno, Dr. Faith Oi, Dr. Stephen Kells, Dr. Barbara Thorne, and www.snopes.com .

Get the low down on this month's insect pests at Insects
http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm


Sweet Potato Shoots
Beth Jarvis, Yard &: Garden Line

Sweet potato vine and coleus Photo credit:
Mary Meyer
Ornamental sweet potatoes are growing in popuarity. Now with spring approaching, the question arises, how do we get those tubers to start growing again? I found two different opinions/techniques and invite you to take your pick. The National Gardening Association says:

Get started now growing shoots to be planted outside in May. Place small to medium-sized tubers in a container that drains well, and cover them with light, sandy soil or potting mix. Keep the soil damp but not soggy and place them in a 70 to 75 degree location in bright light. Sprouts will be ready for transplanting in four to six weeks.

An easy way to start sweet potato sprouts--and give yourself an ornamental plant at the same time--is to sprout a tuber in a glass or a jar filled halfway with water. Shoots will sprout from the top half, and root from the bottom half. You may even decide you like the foliage so much you want to keep it growing as a houseplant, perhaps stringing the vines around a window.

To plant the sweet potato shoots into the garden, carefully pull or cut the 9- to 12-inch shoots from the starter root, retaining attached roots. Plant these 12 inches apart in sandy, well-drained soil. Water them in well with a half-strength solution of a balanced fertilizer, and shade them from the hot midday sun for a week.

Jackie Smith, Master Gardener Coordinator, Carver-Scott, and vegetable maven says:

I prefer to use a low, rather flat, clear container so I can watch the roots grow, but any flat container will work. Lay the potato lengthwise on about 1 inch of moist vermiculite, then fill with vermiculite to just barely cover the potato. Keep moist in a bright location (not direct sun) and expect sprouts to show up within 2-4 weeks. When the sprouts are of a size you can handle--1 to 2" long, cut them carefully from the potato with a sharp knife. Some may have already formed roots, but that's not important at this point. simply insert the sprouts as you would any cutting in either more vermiculite, or soilless seed-starting mix. Again keep moist in a bright location until rooted (about 1 week), then move to as much light as you can provide.

You need to take care to cut the sprout off the potato, WITHOUT including any flesh. My understanding is that several sweet potato diseases can spread from the tuber to the shoot, and that it is actually wisest to even cut off at least one inch of the shoot to prevent these dieseases from spreading to the new plants. I've done it both ways without problem (cut the sprout carefully from the potato, or cut off all but the bottom one inch of the sprout). Sweetpotato vines root readily from stem cuttings, which is, in effect, what we are doing. Any sweet potato vine cutting will root within a week. By cutting the shoots carefully and not injuring the potato itself, the potato can be covered back up with vermiculite or soil and will continue to send out more sprouts.

If you order sweet potatoes by mailorder, you actually get cuttings which are often unrooted - you simply insert them in soil outdoors, and 99% of them root and grow.

The most common method has long been to root in water. Certainly that will work, but water roots are "different" than soil roots and the plants actually have to re-root when transferred to a solid medium. So my best advice is: why not just start with soil and save yourself the extra step?

Editorial Notes

Swallowtail on phlox. Photo credit:
Bob Mugaas
Jackie Smith will share the results of the Master Gardeners' state-wide vegetable variety trials in an upcoming issue. Nancy Rose has provided an article on "blue" trees that I'll run in a future issue. Before you plant your next Colorado blue spruce, read what better choices you have. Colorado blue spruce are,a popular landscape tree yet a poor landscape choice due to their disease susceptibility

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Friday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations. (Scroll down for map.)

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator


icon Previous Page
iconUniversity of Minnesota Extension Service Home Page
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request.  Please contact your University of Minnesota county extension office or, outside of Minnesota, contact the Distribution Center at (612) 625-8173.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.