Vol. 20, No. 5, May 13, 2005

Hosta virus X
Ash alternative resources

Dave Smitley, Entomology

Now that May is well under way and birch leafminers and hawthorn leafminers have been seen on the leaves mating and laying eggs (May 7-12, Diane Brown-Rytlewski), it is a good time to review scouting and management strategies for leafminers. In order to choose an effective pesticide you must know what kind of leafminer you have. Review the list below and note that the most important ornamental leafminers are in the orders Diptera (flies) and Hymenoptera (bees, wasps, ants and sawflies).

It is important to know which order the insects belong to because Merit works well for Hymenopteran leafminers, but not as well for the Dipteran leafminers. All of the leafminers listed above are active early in the spring. The adults lay their eggs in the developing leaves. If you have trees or perennials that was heavily infested last year, you can prevent the same damage from occurring this year by spraying the leaves as they begin to unfold. In general, spraying when the leaves are about half-size works well. Landscape professionals can use any of the synthetic pyrethroid insecticides labeled for ornamentals such as Tempo, Talstar, Scimitar, or Astro. For optimum control levels, spray when the leaves are half-size, and again 2 weeks later. For delphineum and columbine the best timing is late May and late June since they continue to grow during the summer and are subject to attack by second or even third generations of leafminers. An alternative management strategy for the Hymenopteran leafminers is to use Merit as a soil drench or soil injection. This works best as a fall treatment (October) for control of spring leafminers. For the Dipteran leafminers, Avid and Citation also work well as foliar sprays, which gives you the chance to use a more selective product that is easier on natural enemies.

Mike Bryan
Michigan Department of Agriculture

This spring, MDA inspectors found Hosta virus X (HVX) in record high numbers at sales lots in Michigan. Most experts agree that HVX has become quite common in the trade.  Plants infected with this disease can exhibit a variety of symptoms, as the disease affects cultivars differently.  The most common symptom is mottling of the leaves. Other symptoms can include stunting, twisting and puckering of the leaves.  The symptoms may be quite obvious or may be very subtle. As with most viral diseases, some varieties appear to be resistant while others are much more susceptible.  The long-term effect of HVX is to weaken the plant, which may eventually lead to death.

Like most plant producers, Hosta growers are always looking for new varieties.  Unfortunately, before much was known about HVX, some unusually looking Hosta "sports" were cultivated and later scientists found the cause of the unusual mottling and coloration was HVX. The variety "Breakdance" is reported to be of the 100 percent-infected varieties.  

  The best way to avoid getting HVX in the garden is to buy quality, disease-free plants. When buying new Hosta watch for unusually mottled plants. Collectors with high value varieties may wish to have their plants tested to make sure they are disease-free. If you do find a plant infected with HVX in your garden it should be removed and destroyed. The disease itself is mechanically transmitted through transfer of infected sap. Therefore, it is a good idea to practice good sanitation in the garden, including sterilizing cutting tools between each plant when you are trimming or dividing Hosta. A wealth of information about HVX can be found on the Internet by searching on the terms: "Hosta Virus X."

Infected plants should be brought to the attention of staff on the sales lot.  Also, incidences of infected plants can be reported to the nearest MDA office that serves your county.  A listing of MDA contacts can be found on the MDA web site at: www.michigan.gov/mda key word "Regions."

Bert Cregg
Horticulture and Forestry

This week an editorial in the Lansing State Journal suggested that Michigan State University needs to develop a guide for alternative species for ash trees lost to EAB.  As we get into tree planting time, I would like to take this opportunity to remind everyone that such a guide already exists. Recommended alternatives to ash trees for Michigan’s Lower Peninsula, MSU Extension Bulletin E-2925, is available from the MSU Extension Bulletin office or through the “Information for Homeowners” link of the http://emeraldashborer.info website.  The bulletin contains descriptions of near 40 tree species that are hardy in the Lower Peninsula.  The MSU Department of Horticulture also maintains an ash alternative website http://www.hrt.msu.edu/ash.alt/ 

In cooperation with the Michigan Nursery and Landscape Association, MSU Project GREEEN, and several cooperating nurseries, MSU has also established a demonstration arboretum of over 30 ash alternative species at the MSU Tollgate Extension Center near Novi.

Cornell Guide to trees for urban sites.  This is a great publication with information on selecting trees for stressful sites.  All plants listed are hardy zone 5 or colder. http://www.hort.cornell.edu/department/faculty/bassuk/uhi/outreach/recurbtree/index.html

Right Tree Handbook.  Nice guide to selecting trees for near power lines. http://mpelectric.com/treebook/

Diane Brown-Rytlewski
MSU IPM Program
Nursery & Landscape ICM Integrator

This time of year, a number of leaf and stem galls caused by insects or mites begin to appear. Cynipid wasps, eriophyid mites, flies, psyllids, aphids and adelgids are among the most common gall producers.  Many galls don’t cause any lasting harm to plants, although they sometimes generate a lot of notice because of their often-bizarre appearance. Whether you regard them as “insect art,” an interesting curiosity or just one more pest you have to deal with probably depends on the nature of your role in caring for their hosts. In particular, some of the galls produced on oaks are architectural marvels and can be appreciated as examples of art in nature.

Oak trees are a particularly abundant host for galls created by cynipid wasps. The galls may be marble, bullet or flask-shaped and may have elaborate spines or dense hairs.  Some particularly large ones derived from leaf tissue are called oak apples with a papery exterior and a spongy or fibrous center. The larvae of the tiny wasps that create these galls can be found in small cells within the developing galls. One interesting gallmaker, the jumping oak gall wasp, produces small disc-like galls that drop from the leaf in autumn. The developing wasps inside cause the galls to jump (think of Mexican jumping beans) until they land in a protected place for the winter.  Galls that develop on twigs, such as horned oak gall or gouty oak gall (hosts in red oak family) may be of more concern, as they are capable of causing dieback of twigs or severe injury to their hosts.

Feeding by some genera of eriophyid mites can produce dense patches of hairy or beadlike growth on leaves while feeding by others produces galls. The dense patches of hair or bead-like growth (erinea) are produced on leaves of maples, beech, walnut, birch and other trees and often turn bright red or pink.  Examples of galls include those produced by pearleaf blister mite, which creates pimple-like swellings on apple, pear and sometimes amelanchier, mountainash, cotoneaster or hawthorn leaves; ash flower gall; various spindle galls on maple, elm, cherry, plum and linden; and maple bladder gall. While injury from spindle and bladder galls is largely cosmetic, severe infestations of pearleaf blister mites can kill overwintering buds.

Galls produced by flies often appear as pouches or thickenings along leaf margins. Honeylocust podgall midges overwinter as adults and lay eggs on developing leaf tissue.  The pod-shaped galls develop as the larvae feed inside the curling leaves. Another gall you may have seen on the tips of willow twigs is the willow cone gall, which very much resembles its name.  The strange-looking gall in the photo, boxelder leaf gall, is caused by the feeding of a midge.  Tiny, white maggots can be found inside the rolled swellings of the leaves. 

Hackberry nipplegall is caused by a psyllid.  These galls are produced by the feeding of psyllid nymphs on developing leaves. They continue to feed and live inside the galls until late summer when they emerge as adults. Damage is largely cosmetic, and the psyllids inside the galls are reported to be a major food source for birds and squirrels. Boxwood psyllids cause the new leaves of boxwoods to cup. They are actively feeding on new foliage now.

Galls induced by aphids can be found on leaves, petioles and stems. Witch hazel is host to an aphid that produces pale green cone-shaped galls on the upper surface of leaves.  Birch is an alternate host for this aphid, where it feeds on foliage. This week, colonies of another genus of aphids were found on European birch, causing a corrugated appearance to the upper surface of the leaves.   The nymphs were dark gray and produced white wax.  Adults were greenish yellow. Howard Russell from Diagnostic Services identified it as Euceraphis betulae.

Many of you are familiar with Cooley and eastern spruce gall, which are both caused by adelgids. Cooley spruce gall adelgids form cone-like galls at the tips of new growth.  These adelgids may alternate between Douglas fir (where no galls are formed) and Colorado spruce, or they may develop continuously on either host. Eastern spruce gall adelgid forms pineapple-shaped galls at the base of new growth on Norway and occasionally white and Colorado spruce.  Eastern spruce gall adelgid does not have an alternate host.  Spruce bud caps are splitting now, signaling a developmental period where this insect is invulnerable to treatment.

Diane Brown-Rytlewski
MSU IPM Program
Nursery & Landscape ICM Integrator

Elsewhere in the state
In Ottawa and Kent counties, snowdrift, coralburst and Sargent crabapple, lilac and redbud are in full bloom. Bradford pear is dropping petals. Lots of deer damage has been reported in Kent County.  There also seem to be a number of Concolor firs that are losing needles from the tip down.  In Monroe County, Carol Mackie daphne, snowdrift crabapple, redbud, Koreanspice viburnum and Mohawk viburnum are full bloom. Lilac is nearly in full bloom. In Washtenaw County, freeze injury has been showing up on roses and tuliptree. Trilliums, flowering dogwood, redbud and lilac are in full bloom; Bradford pear is ending bloom. Up north in Grand Traverse County, forsythia and cherry are blooming, while lilac hasn’t started to flower yet.

The Buckeye Yard and Garden Line (Ohio State University Extension) report dated May 12 mentions pine spittlebug masses just becoming evident on Scotch pine and Eastern white pine, first generation euonymus scale nymphs and boxwood leafminer adults in southwest Ohio.  Read the full report at: http://bygl.osu.edu/

Phenology table
The Phenology table can be found here

Kevin Frank
Crop & Soil Sciences

Core cultivation of lawns
Many homeowners in Michigan do their best to manage lawns on what can best be described as pottery clay.  Managing turf on clay poses many challenges and one of the most effective management practices to help the turf along is to core cultivate.  Often I will tell callers managing turf on clay to core cultivate as often as they can to help facilitate root growth and improve aeration in the soil.  This spring due to the relatively dry conditions it may be difficult in some lawns to have a core cultivator penetrate the lawn to a depth of 3-4 inches, if this is the case irrigation should be applied prior to cultivation to help moisten the soil.  Core cultivation can certainly penetrate deeper than 3-4 inches but I’ve found that most equipment available from rental stores would be lucky to get that deep.  Core cultivate now before summer and the associated heat stress that comes along with it.  Core cultivation can also be done in the fall.  Things to keep in mind before coring any turf area – do you have an in-ground irrigation system – know where the sprinkler heads are.  Also be aware of any other underground lines, for eg. invisible dog fence wire.  Normally, these lines should be buried deep enough to avoid any trouble but it never hurts to double check.

Don’t scalp turf!
The lack of rain and the cool temperatures experienced throughout this spring have resulted in the turf growing very slowly if at all.  If fertilizer has not been applied in April the turf will probably be showing even less growth.  At this time of year there is an innate biological urge for homeowners to cut grass, and it appears that this year if the turf won’t grow up to that 3 inch cutting height that many homeowners are lowering the mowing height to meet the turf. 

Although some may think a home lawn mowed at golf course fairway height looks nifty, it’ll only set up the lawn for problems this summer.  First of all – think of what weed is likely to begin germinating in the next month or so – that’s right, crabgrass!  By scalping the lawn the perfect environment has now been created for crabgrass to germinate.  Scalping opens up the turf creating voids where many weeds can germinate and the thinner turf canopy results in soil temperature being increased which will only further enhance the likelihood of crabgrass germination.  I hope these lawn scalpers enjoy the crabgrass population later this summer!  In addition, scalping the turf forces the turf to use energy for the top-growth that was just hacked off, instead of for root growth.   The reduction in root growth will result in the turf being even more susceptible to summer heat and drought stress.  Mow high and let the clippings lay!

Jill O’Donnell
Christmas Tree ICM Agent

This spring we have had seen several cases of conifer root aphids on Fraser fir.  They appear to be Prociphilus sp. aphids. These species of root aphids feed on conifer roots for part of their lifecycle and then become woolly aphids that feed on ash trees and other hosts. They appear as large, white aphids on the roots. It is not known how much damage they cause to their conifer host; however, in North Carolina they observed when numbers exceed one hundred aphids on a single seedling, growth of fine feeder roots appeared to be reduced.

Aphids were found on small replanted trees that were showing stunting and yellowing. We also found large numbers on the older healthy trees.  It appears that the root aphids are possibly just a secondary problem. Some other causes of tree decline and mortality might be disease, transplant shock, improper planting (“J” rooting), poor nutrition, water stress or off-site planting.

Jill O’Donnell
Christmas Tree ICM Agent

Applying insecticides at the proper time is a key element in controlling pine needle scale. Pine needle scale is most vulnerable to insecticides during the crawler stage. Although crawlers are tiny, they are readily visible on the needles, especially if you use a hand lens or magnifying glass. The ideal time to apply an insecticide spray is after nearly all the pine needle scale eggs have hatched and most crawlers have reached the hyaline stage. At this point, the young crawlers are exposed on the needles and have not yet started to produce the hard, white armor.

Spring generation eggs hatch in May or early June at roughly 300 GDD50. Usually eggs hatch within about a week, and most crawlers should be in the hyaline stage by 400 to 500 GDD50. If the weather cools down, hatching may continue over two to three weeks. Good scouting will help you assess the size of the pine needle scale population in your field, determine whether control is necessary and the best timing for control.

Jill O’Donnell
Christmas Tree ICM Agent

Looking at degree day accumulation, the opening of the spray window for the Upper Peninsula will be May 15 for Dimilin and May 24 for all other insecticides. Tentatively, the closing dates will be June 25 for Dimilin and July 14 for all others insecticides. 

Since gypsy moth development will vary by location, you will need to monitor development around your farm. Weather conditions will affect caterpillar development and may effect end date of the spray windows. Growers should watch the Landscape Alert for additional announcements.

Dennis Fulbright
Plant Pathology

This is a good time to point out the fungal pathogens that cause Rhabdocline and Swiss needle cast of Douglas fir and Rhizosphaera needle cast of spruce will begin their yearlong infection of the 2005 needles unless you begin your spray programs. For these diseases to initiate infection, two events must occur – and they are occurring right now.

First, bud break and shoot elongation must be occurring. Second, the spores of the fungus must be released from last year's infected needles. These spores will ride to the new needles on rain-soaked pathways where the pathogens will begin their infection process. So bud break, spore release and rain lead to needle cast infections in Douglas fir and blue spruce, and that is happening right now in most of the Christmas tree plantations growing Douglas fir and spruce.

Since the materials that work on Rhabdocline are effective on the Swiss needle cast pathogen, you will get control of two diseases for the price of one. Always follow label instructions when spraying. The most effective material for control of Swiss and Rhabdocline is chlorothalonil. All studies show that the seed source Shuswap is resistant to Rhabdocline and these trees do not need to be sprayed for Rhabdocline saving you money and the environment fewer molecules of chlorothalonil.

Howard Russell,
Diagnostic Services
Jennie Stanger, MSU Extension Monroe County

Despite our coolish spring weather, tick season appears to be moving right along with several counties reporting lots of tick calls. Most complaints are about American dog ticks and there were several calls to the Monroe County Extension office this week from folks who have never had a tick problem in their yards before. Besides dog ticks, Diagnostic Services has received a few deer ticks and other Ixodes species as well. Ixodes ticks include the infamous deer, or black-legged tick – the tick that transmits Lyme Disease.

There was a time when I told folks that they would have a better chance of winning the lottery than they would encountering a deer tick in the Lower Peninsula of Michigan. But that has changed over the past few years, especially in southwest Michigan near the Lake Michigan coastline. More and more deer ticks are showing up in Berrien County north to Muskegon County. Deer ticks have always been relatively common in the Upper Peninsula.

We have a half a dozen or so species of Ixodes tick other than the deer tick, I. scapularis. Ixodes ticks are rather easily distinguished from other common Michigan ticks. First, Ixodes ticks do not have white markings on their backs. Our most common ticks, the American dog tick and Lone Star tick, have some kind of white marking on their backs. Another characteristic that can be used to separate Ixodes ticks from other is the shape of a “line” called the anal suture, which can be seen on the venter or belly of the tick near the posterior end. In Ixodes ticks, the anal suture appears as an upside-down horseshoe shaped-line that completely encircles the anal opening. In other ticks the anal suture does not reach the anal opening.

While Ixodes ticks are relatively easy to distinguish from other types or genera of ticks, the various species of Ixodes ticks are very difficult to distinguish from one another. One feature that can be used to “indicate” that a tick you might be looking at is a deer tick is the shape of the first leg segment or coxa (coxae if plural) of the first pair of legs. In deer ticks (and, unfortunately, in a few other Ixodes species) the coxae on the first pair of legs are projected into a long pointy affair. In American dog ticks, the first coxae are cleft or split in the middle.

While American dog ticks may not carry Lyme disease, they are known to transmit some other nasty diseases such as Rocky Mountain spotted fever and tularemia. The cases of Rock Mountain spotted fever reported in Michigan have been from primarily southern counties, particularly those located directly north of the Toledo Airport. Also, toxins injected with their bites cause itching, fever and in some cases tick paralysis. Be on alert for any rash, which is a primary symptom of both Rocky Mountain spotted fever and tularemia that develops after any tick bite.

Family members and pets should be inspected daily where ticks are known to be abundant. Insect repellents may help keep ticks from biting. Wrapping duck tape around pants cuffs helps keep ticks from crawling up your legs. If an attached tick is found, it should be removed by placing tweezers near the head and gently pulling it off. Be careful not to squeeze the body of the tick, as this can turn the tick into a hypodermic needle and inject the contents of the tick into the bite wound along with any pathogens it may be carrying. Keep in mind that they cannot feed immediately after attaching. They require several hours to imbed their mouthparts deep enough to take a bloodmeal.

• Permethrin, which is sold under a variety of brand names. Special formulations of permethrin are available as tick repellents that can be applied to clothing to help keep ticks off.
• Carbaryl, which is primarily sold as Sevin.
• Cyfluthrin, which is sold as Tempo for commercial applicators and Bayer Advanced Garden “Power Force” Multi-Insect Killer.
• S-fenvalerate, which is sold as Zema Lawn Spray (This product may be hard to find.).
• Fluvalinate, which is sold as Mavrik Aquaflow, Yardex.

There are also natural controls that help to reduce tick populations including parasitic wasps, birds and a variety of fungi and nematodes. Unfortunately, none of these organisms have any real success in controlling tick populations to acceptable levels. In fact, some of them are only found in areas where ticks are super abundant. Hence, biological control agents are not yet ready for widespread use in tick management programs.

Rebecca Finneran
Kent County Horticulture Educator

All plants need certain nutrients in order to be healthy and grow.  Although gardeners seldom proclaim to understand this earthly beast, soil is the medium by which plants take up nutrients. (You’ll notice I didn’t say dirt!)  Many of the nutrients plants need are already in adequate supply in the soil, but not all of them.  Dennis Pennington, Barry County MSU Extension Educator, says that you should test your soil at least once every three years to determine whether it has the right quantity of nutrients and is the right pH to get your garden off to a great spring start.

Although it is tempting to just buy a bag of fertilizer and apply what “looks like enough,” you could end up wasting money and affecting the environment in a negative way.  

Soil testing is easy, says Pennington.  It mainly involves collecting a representative sample of soil and submitting it to a laboratory for analysis.  Using a spade or soil probe, take 12 to 20 random samples at a depth of three inches for the lawn and four to six inches for beds. Remove any grass, thatch or debris and mix the samples thoroughly together in a pail. Mixing them together will provide an overall representation of your soil fertility.

He suggests that you try to avoid oddities like where an old stump was dug out or right next to a sidewalk where salt was used to keep the ice melted.  These irregularities will skew your test results.

Pennington says that perhaps the most valuable information you will obtain from a soil test is and an accurate pH reading.  Soil pH is what regulates the availability of nutrients for plant growth in the soil.  If the pH is out of adjustment, you will start to see nutrient deficiencies or even toxicities in your plants. 

Most plants grow best if soil pH is around 6.5-7 (neutral.)  If you have any farming blood in your veins, you’ll immediately think to add lime to the “sweeten” the soil.  Pennington says, don’t be too quick to act on that impulse because the soil tests he has worked with in the past show a trend of not needing lime.   If you have over-applied lime in the past, your number will be above 7.  Do not apply any lime to that area until a soil test tells you to do so, even if it takes a few years to draw your pH down to normal levels. 

Excessive applications of phosphorus to our soils can result in runoff during heavy rains, contaminating streams, rivers and lakes.  Excess phosphorus causes unwanted algae blooms in the water.  You can do your part in helping to protect our environment by testing your soil and managing fertilizer applications carefully.  Pennington especially warns consumers to keep the fertilizer application on target.  Pellets that fall into the road will eventually end up in a local lake or stream. 

Joy N. Landis, editor

This spring, you may have noticed this white flowering weed popping up in your woodlot or along ditch banks. Garlic mustard is an exotic invasive plant that invades woodland habitats in North America and impacts forest biodiversity. In some woodlands, dense stands of garlic mustard in the spring threaten showy spring blooming ephemerals like spring beauty, trilliums and trout lilies. Many land managers consider it to be one of the most potentially harmful and difficult to control invasive plants in the region.

This is a great time of year to manage these weeds by pulling them and discarding them in a trash bag. For more information about garlic mustard and other control measures to stop its spread, visit: http://www.ipm.msu.edu/garlicmustard.htm

Jeff Andresen
Agricultural Meteorology
Geography

Despite widespread snow and rain during the last week of April, precipitation totals across Michigan have consistently remained below normal since early March.  The extended dryness has resulted in depleted topsoil moisture levels in many areas of the state, especially given recent warm temperatures and accelerated potential evapotranspiration rates.  Some rainfall is in the forecast in the short term, although amounts and areal coverage remain somewhat uncertain due to inconsistencies in numerical forecast guidance. 

During the day Friday, a weather disturbance will approach from the southwest, bringing a good chance for showers and thunderstorms through at least early Saturday across nearly all of the state.  Drier weather is expected by Sunday continuing in to Monday.  Temperatures will vary widely across the state during the next few days.  High temperatures will remain in the 50s in northern sections of the state, with some upper 40s possible in northern lakeshore areas, to the low 70's far south. Lows will generally fall to 30s north to the 40s south.  In the medium range time frame, latest forecast guidance calls for a general westward shift of the major upper air features of the past week, which would put Michigan under the influence of northwesterly flow. 

The NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks both call for near normal temperatures and below normal precipitation totals state- and region-wide.

For the 3-month May through July period, the outlook suggests wetter than normal conditions across western sections of Michigan with the climatology scenario in the east.  Temperatures statewide are officially forecast to remain in the equal odds category, although cooler than normal temperatures are expected just west of the state across areas of the Upper Mississippi Valley.