Vol. 20, No. 6, May 20, 2005

Trees reverting to form
Choosing an arborist

Dave Smitley, Entomology

We have been asked, “How late can homeowners use the imidacloprid drench or ACECAP trunk injections for emerald ash borer?” The homeowner guide for controlling EAB says to use an imidacloprid soil drench in April or May, or ACECAP trunk injections in early May. In heavily infested areas, homeowners should use both of these products together the first year or two.

April to early May is the optimum time for treatment. However, you can still use both of these products through June. We have not done the research to determine when it is too late, but it is likely that they will still work well when used in June, because most of the EAB larvae are actively feeding in July, August and September.

Bert Cregg
Horticulture and Forestry

Among the “What’s wrong with my tree?” calls I get, some of the most interesting deal with a phenomenon called reversion. When a conifer or hardwood tree with an unusual ornamental characteristic begins to send out shoots with normal foliage or growth for the species, the new growth is said to have reverted.

How does a reversion take place? Remember that many ornamental cultivars begin when an alert plantsman or plantswoman notices a tree or part of a tree with a unique growth characteristic (unusual leaf color, weeping growth habit). These atypical plants or shoots arise through genetic mutation. Buds or cuttings from the plants are then grafted onto standard trees and, if they remain true to form and have horticultural merit, they ultimately make their way into the nursery trade. Just as the original genetic mutation occurred to produce the unique character, occasionally a reverse mutation occurs and portions of the plant ‘revert’ back the species’ normal growth. Some of the more common examples of reversions occur in dwarf spruces (Photo 1) and variegated plants such as Harlequin maple (Photos 2 and 3). In the case of dwarf spruces, homeowners will often report “a tree growing out of my tree.”

Bert Cregg
Horticulture and Forestry

Spring is a time when many homeowners will need the services of a professional arborist or tree service company. Between emerald ash borer, Dutch elm disease, and the usual round of spring storms, arborists will be in demand to treat, prune, and remove trees. One question we commonly receive from homeowners is how to choose an arborist.

The Arbor Day Foundation presents eight guidelines for selecting an arborist. In the interest of space I won’t list them all here, but the keys are to make sure the arborist is insured and has professional training.
http://www.arborday.org/media/stormrecovery/3_watchforscams.cfm

The International Society of Arboriculture provides professional training and certifies arborists. Arborists certified by ISA must pass knowledge tests and receive continued professional training to maintain their certification. Most arborists that are ISA certified will note this is their yellow pages ad. Also, the ISA website has a search feature that enables you to find arborists in your area simply by entering your zip code.
http://www.isa-arbor.com/findArborist/findarborist.aspx

Homeowners occasionally experience “sticker shock” when they receive a tree for service bid. Remember, as with most things in life, you get what you pay for. High quality tree work requires training, skill, experience, and proper equipment. Reputable arborists must also cover the costs of bonding and insurance. If you get multiple bids for tree repair or removal, look at the bid in terms of the overall package (site clean up, wood removal) rather than just cost.

Diane Brown-Rytlewski
Nursery & Landscape ICM Integrator

As of May 17 growing degree day accumulations (GDD) were at 273 base 50. The normal for this date is 268 GDD base 50. Last year’s GDD accumulation for this date was 422, about two weeks ahead of normal. The cool weather has prolonged bloom of some trees and shrubs on campus. Blackhaw viburnum, red stemmed dogwood, yellow stemmed dogwood, Vanhoutte spirea and ‘Tinkerbelle’ lilac are at first bloom. Maries viburnum, and red buckeye are at early bloom. Most redbuds and lilacs are still at full bloom, as are yellow buckeye, common horsechestnut and viburnum ‘Mohican’. Sargent and Japanese flowering crabapple are at late bloom or finished blooming. Herbaceous perennials in bloom in the perennial garden include: Siberian iris ‘Charming Darlene’, Allium aflatunense, and Camassia ‘Blue Danube’. Spring ephemerals in bloom include trillium, alumroot, goldenseal, merrybells, and jack-in-the pulpit.

The soft green tips of new growth are evident on most spruce and fir trees now. The appearance of new growth on fir signals the period to begin scouting for balsam twig aphids. Pine bark aphids have laid cottony masses of eggs on white pine twigs just below the base of candles. The pale whitish spots that appear where elm leafminer have laid their eggs in leaves are visible on foliage now. Adelgids on European larch are becoming more evident, as they produce their fluffy, white wax. Boxwood psyllids are still feeding on young leaves of boxwood; the psyllids have formed wing pads and will be maturing soon. Boxwood leafminers have pupated within the leaves, and the adult flies should be developing soon. Large numbers of black bean aphid, Aphis fabae, are showing up on Euonymus alatus. Foliage curls in response to feeding, and there is abundant honeydew. The aphids are coal-black in color with legs that shade from black at the tips to pale yellow in the center. Their overwintering hosts are euonymus and viburnum. Later in the year, they switch hosts to feed on vegetables such as beets, beans, cucumbers and lettuce. See accompanying photos.

‘Alleghany’)are at full bloom. Columbine leafminers are creating mines in foliage. In Washtenaw County, common lilac, European mountain ash, ‘Prairiefire’ crabapple and hawthorn are in full bloom. Korean lilac is beginning bloom. Cedar apple and cedar-quince rusts are visible on junipers. Up north in Grand Traverse County, Lilac, and apple trees are blooming; tart cherry trees haven’t started blooming yet. Some spruce trees are just breaking bud. Rhabdocline needlecast and rhizosphaera needlecast have been reported on Douglas-fir.

Other states
The Plant Health Care Report from the Morton Arboretum in Lisle, Illinois dated May 13 listed black cherry, red buckeye, red chokeberry, redosier dogwood and Vanhoutte spirea in early bloom. Blackhaw viburnum, common lilac and Ohio buckeye are at full bloom. Insects they have seen include honeylocust plant bug nymphs, leafhoppers on elm, ash and maple, and larch adelgids. Gypsy moth larvae have hatched. Their degree day total as of May 10^th was 256 GDD base 50. The full report is at http://www.mortonarboretumphc.org/

The Buckeye Yard and Garden Line (Ohio State University Extension) will have a new report on May 19. It can be accessed at: http://bygl.osu.edu/.

Phenology table
The Phenology table can be found here

Steve Gower
Diagnostic Services

In addition to soybeans, there are a number of forage legumes, beans, weeds and ornamental plants in Michigan that could potentially serve as hosts of Asian soybean rust (Phakopsora pachyrhizi). Worldwide, there are more than 30 species of legumes reported to be hosts of soybean rust in nature and more than 60 species when considering successful inoculation under greenhouse conditions. Many of these host plants are not found in Michigan. For this reason, a list was compiled of plants in Michigan that could be infected with soybean rust (Table 1).

Kudzu (Pueraria lobata) is a weedy legume that infests roadsides, fencerows, abandoned fields and non-crop areas throughout the southeastern United States. It has been described as the “vine that ate the south” because of its aggressive, climbing and trailing habit. Kudzu is a susceptible host of Phakopsora pachyrhizi. Due to the prevalence and location of kudzu, it is believed that this weed will serve as a continual source of soybean rust inoculum for southern soybean growers. The good thing – kudzu is not believed to exist in Michigan.

There are occasions when only a plant genus is listed in Table 1. In these cases, there is not sufficient information on the potential host range of soybean rust in the United States. Keep in mind that other potential soybean rust hosts could be species in the same genera as those listed in Table 1.

It is our goal to make this host list as complete as possible. If you are aware of other “legumes” or “beans” grown in Michigan fields or greenhouses, please contact Steve Gower at 517-432-9693 or sgower@msu.edu

Tom Dudek
District Extension Horticulture Educator

Drs. Bert Cregg and Tom Fernandez from MSU’s Department of Horticulture will be discussing and demonstrating pruning techniques for shade tree nursery growers on Wednesday June 1 from 1:30 to 4:00 PM at the Twin Lakes Nursery’s Tree Farm located just east of the intersection of 52^nd Street and Snow Avenue southwest of Lowell, Michigan.

If you are planning to attend please make a reservation by contacting Thomas A. Dudek, District Extension Horticulture Educator, MSU Extension, Ottawa County at 616-846-8250 before May 31. Please bring your own pruning shears.

On Wednesday June 1 from 10:00 to 11:30 AM Dr. Cregg and I will be hosting a tour of the plantings at the Clarksville site. Data on drought to tolerance, cold tolerance, pH tolerance and pest problems will be discussed.

If you are a nursery professional who is looking for some new plant possibilities, please join us that morning. Please contact Thomas Dudek before May 31 at 616-846-8250 if your planning to attend.

The Clarksville Horticulture Research Station is located at 9302 Portland Road, Clarksville, Michigan. It is 15 miles east of Grand Rapids. Exit highway I-96 at the Clarksville exit… Nash Road ( EXIT #59) go south to Portland Road ( 1/2 mile). Turn west and go 1 mile to the research station. We will meet in the parking lot by the office.

Dave Smitley
Entomology

Kevin Frank
Crop and Soil Science

They’re starting to pop-up in lawns all over the state –  not dandelions, those have been popping for weeks now – turfgrass seedheads are popping. It’s an annual right of spring for turfgrass, seedhead production. Kentucky bluegrass, perennial ryegrass, and of course Poa annua (otherwise known as annual bluegrass, po, poer, po anna etc.) are all currently sprouting seedheads. The seedheads not only detract from the appearance of the turf but the seed stalks are tough to mow. If you were derelict in sharpening your mower blade this spring, now might be the time to sharpen it up because mowing the seed stalks is a tough task. However, even with a sharp blade, you still may see a sheen or whitish look to the turf after mowing due to the seed stalks. I’ve heard of some recommendations that suggest you should lower your mowing height to get rid of the seedheads but I don’t subscribe to that theory and strongly advise you to keep your mowing height high. Poa annua seedheads are often a problem on golf course putting greens and some of those greens are mowed at heights of 1/8 inch. So, do you really think by lowering the height from 3 to 2 inches you’re going to eliminate all of the seedheads in your lawn? There are growth regulators that help reduce seedhead production in turf, but they are currently not available for the homeowner market. The best advice is to keep on top of your mowing schedule and make sure the blades are sharp.

Some things to watch for over the next couple of weeks as the seedheads hit peak. The turf may start to look stemy and lose density. This is natural, it will come back strong once this period of seedhead production ceases. Basically right now the plant is putting a lot of energy into popping those seedheads. Once it’s done the turf should be back to its old self.

Jeff Andresen
Agricultural Meteorology
Geography

Upper air flow across the Upper Midwest is expected to gradually shift from the ridging pattern currently in place to a troughing pattern by early next week. These conditons will be accompanied by a temporary moderation of temperatures to normal levels. On the surface, an area of high pressure over the northern Great Lakes region Friday morning (May 20) will maintain fair and dry conditions statewide Friday through Saturday evening. A cool front will approach from the northwest late Saturday, bringing a good chance for showers and a few thunderstorms to the state beginning overnight Saturday in northern sections of the state and continuing Sunday in the south. Rainfall totals will likely reach 0.25-0.50" in most areas of the state, with up to an inch in some areas. Temperatures will approach normal levels the next few days, with highs ranging from the upper 60's to low 70's Friday and Saturday, falling back into the 60's on Sunday. Low temperatures will range from near 40 in the north to the low 50's south through Sunday.

Slightly cooler temperatures are likely for at least the first half of next week with the chance for scattered, mainly afternoon and evening showers each day. In the medium range time frame, latest forecast guidance calls for a return of upper air troughing across the eastern U.S. with a broad ridging pattern across the western U.S. The NOAA Climate Prediction Center 6-10 Day and 8-14 Day Outlooks (for May 25-29 and May 27 through June 2) call for temperatures to fall back to below normal levels, with near normal precipitation totals. Climatological normals for the third week in May include ranges of high temperatures from the low 60's north to the low 70's south and lows from the low 40's north to the upper 40's south. Normal weekly precipitation totals range from about 0.65 inch across northern and eastern sections of the state to about 0.75 inch in far southern sections of Lower Michigan and in western sections of the Upper Peninsula.