Inspector Findings in Kentucky

Shade Tree Anthracnose In The Landscape

by John Hartman, Extension Plant Pathologist

Sycamore anthracnose.  Two springs ago, sycamore anthracnose was devastating, but last spring much less was observed.  Why were the two years so different and what is likely to happen this year?  The incidence and severity of anthracnose diseases of landscape trees varies with the season.  When we have cool springs with extended periods of wet weather, anthracnose diseases are worse.  These conditions prevailed two years ago and people looking at their trees in late spring thought that there were mostly dead leaves and branches.  In reality, the sycamores showed good resilience because they readily grew out of it and looked much better last year.  Some folks worry that sycamore anthracnose may spread to their dogwood trees nearby (it won't).

Sycamore anthracnose is caused by the fungus, Apiognomonia veneta, and the fungus attacks both sycamore and London plane.  The fungus causes twig and branch cankers, shoot blight, and leaf blight.  Shoot blight, most visible and most damaging, develops after a period of cold spring weather.  Although the disease is devastating, sycamores have managed to survive many disease-favorable years.  Obviously, it costs sycamores much of their carbohydrate reserves to refoliate, but by early summer, regrowth is generally well under way, the new growth escaping infection because of heat and dryness.  The legacy of crooked branches (because lateral shoots take over when terminals are killed by anthracnose) and multiple shoots arising from the base of a killed branch may be still visible many years later. 

Ash anthracnose.  This disease, caused by a species of the fungus Discula, can also be seen in neighborhoods and landscapes following wet spring weather.  Leaflet drop may be so great that anthracnose-infected leaflets practically carpet the walks and lawns nearby.  Dead tissue appears along leaf veins or at the leaf edges because infections occur where moisture lingers longest as dew or droplets on those parts of the leaf.  Ash anthracnose causes so many individual leaflets drop in the spring that some homeowners are prompted to consider felling the tree because they think it is dying.  It isn't, and the tree simply puts out a new set of leaves, again at a cost of carbohydrate reserves that might be needed to fight other kinds of stresses.

Maple and oak anthracnose.  Symptoms on these trees range from leaf spots to shoot blight and shoot cankers.  Maple anthracnose may be caused by Discula sp. or Kabatiella apocrypta, and oak anthracnose by the fungus Apiognomonia quercina.  Although these two diseases are less common than the sycamore and ash anthracnose disease, they, too are found in cool, wet springs.  Dogwood anthracnose, caused by the fungus Discula destructiva is only found occasionally in most home landscapes, but it is very common in forest trees and heavily shaded landscapes.

Anthracnose management in landscape trees.  Keep in mind that two years ago, carbohydrate reserves were depleted because anthracnose infected trees had to refoliate, and last year, carbohydrate reserves regeneration was limited by the drought.  Thus, it is important for these landscape trees to get off to a good start this spring.  Although we can't control the weather, there are some cultural practices that may help.

+Rake up and compost fallen leaves.  Leaves can be a source of inoculum.

+Prune out and destroy dead twigs and branches, because for many of the anthracnose fungi, branches harbor fungal inoculum.  Although it is difficult to prune large trees, small trees are at greater risk, so prune out dead twigs and branches from them.  For dogwoods, pruning out dead branches and water sprouts is especially important where anthracnose might be a threat.

+Avoid unnecessary wounding and avoid construction or other activities which could injure the roots or the branches.

+Provide mulch and water as needed.  Mulch over the root system helps to retain soil moisture during dry periods.  Apply water throughout the growing season, if necessary.

+Although most anthracnose diseases can be controlled using fungicides, the attempt is usually more costly than the benefit.

Soybean Cyst Nematode: A Potential Problem for Nurseries

By Win Dunwell, Department of Horticulture, Don Hershman and John Hartman, Department of Plant Pathology and Rudy Scheibner, Department of Entomology (retired)

Soybean cyst nematode (SCN) is a microscopic roundworm that feeds on root systems of soybean plants and reduces their capacity to absorb water and nutrients.  Soybean cyst nematode (Heterodera glycines) was first discovered in Kentucky in 1957 in Fulton County. It has been confirmed in 36 west and central counties and probably exists to some extent in every county where soybeans are grown.

Soybean cyst nematode causes a problem for field production nurseries because Canada and states such as California do not allow soils (ball-and-burlapped materials) to be imported into their areas without proof that the nursery stock comes from counties free from SCN. Other states, such as Pennsylvania and New York, assume that the blanket statement “free from all pests” includes SCN.

Soybean cyst nematode can be spread by windblown soil, soil attached to hosts or nonhosts, birds, flooding of infested fields, movement of farm and construction equipment, or in stock feed. Essentially anything that causes soil to be moved from one place to another can spread SCN into previously uninfested soil. Among other factors, this rapid spread is attributed to the movement of soil. The quarantine activity is an attempt to limit the continued spread of the nematode.

Soybean growers have learned to deal with SCN by tailoring their production practices to minimize the effect of existing populations of SCN. Nurserymen will not be able to follow similar production practices because they will have to deal with a zero tolerance level when shipping into quarantined and currently uninfested areas. The following states are currently free of SCN: Pennsylvania, New York, and all New England states; all states west of and including North Dakota, South Dakota, Wyoming, Colorado, and New Mexico.

Nursery Program

We recommend that nursery operators plan a proactive program to deal with potential problems relating to the shipment of ball-and-burlapped plants out of Kentucky. The program includes:

Preplant sampling of fields.

Host control. Avoid planting host plants of SCN, and rigorously control weeds that may also serve as hosts of the pest.

Rigorous sanitation.

1.Do not bring equipment in from other farms and fields that could be contaminated with soil-carrying SCN.

2.Always clean equipment when moving from one field or farm to another.

3.When borrowing or purchasing used equipment, always be sure it is clean before bringing it to your nursery.

Quarantine your nursery. Do not bring in any plants from surrounding areas without some assurance that soil coming with the plant material is free of SCN.

One year in a nonhost crop can reduce the SCN population by as much as 90 percent. After two years only five percent of the original population will remain. However, some cysts remain viable in the soil for years; thus, it is virtually impossible to eliminate SCN from a field using nonhost crops. In fact, there is no known way to totally eradicate SCN from a field once it is established. Therefore, avoiding the problem is the only way to ensure your ability to ship into areas not currently infested with SCN.

Soil Sampling

The Department of Plant Pathology provides a SCN Soil Analysis Service at the UK Research and Extension Center in Princeton for a nominal fee. For $20 each, samples related to the nursery industry will be screened for the presence of SCN. When cysts are detected (at any level), a bioassay using soybean plants will be conducted to verify that the cysts are in fact SCN and not some other less important cyst nematode species. If SCN is determined to be absent from a field after analysis and testing, the Kentucky State Entomologist will use the test  results to certify shipments of nursery stock from that field.

Ideally samples should be taken when nematode populations are the highest in the early fall. However, it may be necessary to collect samples in the spring to avoid planting into a contaminated field. A two-month lead-time is required for the SCN laboratory to do a bioassay for SCN. Consequently, you must plan in advance to obtain results relative to planting or leasing land for field-grown plant material.

It is always best to take samples when soil moisture is adequate, but not excessive. One sample (pooled from multiple collection sites) should represent no more than five acres. Samples representing larger areas may yield misleading results. Sampling areas should have a uniform soil type and cropping history.

Collect soil from a depth of 6 to 8 inches using a soil probe or spade from at least 20 locations in each field sampled. Follow a zigzag pattern (see figure). In cropped fields collect soil from the root zones of plants within the rows.

Mix soil in a bucket and immediately place one to two pints of soil in a plastic bag. Label bags with a field number or name and location.

Protect the sample from heat and from drying conditions which could reduce detection of nematode numbers in the sample.

Take the sample to your local county Extension office for mailing to the lab at the UK Research and Extension Center in Princeton. If this cannot be done immediately, store samples in the shade or in an insulated cooler. Any prolonged storage should be done at refrigerator temperatures (approx. 40°F).

Host Plants (the following is a list of plants known to be hosts to SCN):

Many Landscape Conifers Are In Trouble

by John Hartman, Extension Plant Pathologist

Diseased pines and other conifers are beginning to appear as samples in the plant disease diagnostic laboratory.  County Extension Agents and homeowners are reporting that established conifers are declining and dying in landscapes and along roadsides.  In many cases, trees appeared normal in the fall, but are now turning brown.  Reports include various arborvitaes, spruces, particularly Norway, Alberta, and Colorado blue spruce, as well a number of pines such as Scots, Austrian, Mugo, and eastern white pine.  Many of the symptoms we are seeing now can be attributed directly or at least indirectly to last year's drought.

Symptoms being observed.  Symptoms range from needles becoming off-colored to needles turning brown and dropping off.  In most cases, the symptoms appear on the entire tree, whether it has been gradually fading since last fall, or is now suddenly affected.  And with the warmer weather, needles are quickly turning brown.  However, in some cases, especially some of the spruces, discoloration, browning and needle drop may occur only on certain branches in a random pattern, usually in the lower part of the tree.  Where individual branches are dying on spruces or on Austrian and Scots pines, it is likely that the fungi Cytospora or Sphaeropsis are active and causing branch cankers and tip blight.  Both of these diseases are more prevalent on trees growing under stressful conditions such as drought.

Throughout Kentucky drought was severe for most of the growing season, becoming extreme in some areas in July, August, and September.  In addition, most areas experienced above normal temperatures for many weeks of the summer.  Although most trees will benefit from the recent rains this past weekend, many will continue to decline because the secondary problems set in motion last summer will continue to kill the trees.

Conifers are vulnerable to prolonged drought.  Unlike deciduous trees which can greatly reduce transpiration in winter by dropping their leaves, conifers continue to transpire.  During much of the fall and winter, conifers continue to lose significant moisture from their needles.  With little soil moisture available and continued transpiration, physiological stress develops and recovery may not occur.  As trees dehydrate, needles eventually turn brown and drop, and the tree dies.  Although tree demise is being observed now, death may have occurred last fall with winter cold temperatures merely delaying the needle browning until spring warming.

A special note on Scots pines: Significant instances of Scots pine browning are also occurring due to pine wilt disease caused by the pine wilt nematode.  Pine wilt can be seen along many of Kentucky's interstate highways.  This disease is capable of killing pines by itself, but the drought has hastened the death of many infected trees.  Drought-stressed trees are attractive breeding sites for the long-horned beetles which vector the nematode.  Because the emerging beetles feed on and carry the nematode to healthy trees in spring, it would be best to remove and destroy dead and dying Scots pines now, before the beetles emerge to spread the disease.

Insect Borers of Trees and Shrubs

By Dan Potter and Mike Potter, Dept. of Entomology, Univ. of Ky.

This is an abbreviated, updated version of ENT 43 which is currently being printed.  To see the whole pamphlet, visit your local county extension agent later this year.

The dogwood borer, Synanthedon scitula, prefers flowering dogwood (Cornus florida) as its host.  Infestations in young trees usually occur in the main trunk, often around lawn mower injuries.  Infestations in older trees are likely to be higher up in limb crotches or main limbs and associated with pruning scars, cankers, or cracked bark.  Dogwood trees planted in the sun are more susceptible than trees in the shade.  Symptoms include die back of branches and coarse, sawdust-like frass expelled from cracks in the bark.  This insect species is widely distributed wherever dogwoods are cultivated.  Optimal spray timing based on calendar date is about late May to early June; spray timing based on indicator plants is about a month after flowering dogwood comes into full bloom, or about 1 week after first bloom of Washington hawthorn (Crataegus phaenopyrum), littleleaf linden (Tilia cordata), or northern catalpa (Catalpa speciosa).

The lilac borer, Podesesia syringae, is a severe pest of lilac, ash and privet throughout the United States east of the Rockies.  Most infestations offer from the root crown up to about 3 feet.  This species begins to fly in late April or May.  A single spray, applied about a week after common lilac (Syringa vulgaris), flowering dogwood (Cornus florida) or Sargent crabapple (Malus sargentii) are I full bloom will protect susceptible plants from infestation.

Rhododendron borer, Synanthedon rhododendri, attacks rhododendrons, and occasionally, mountain laurel and flowering azaleas.  Spray timing is the same as for the dogwood borer. 

The flatheaded apple-tree borer, Chrysobothris femorata, is a severe pest of landscape trees, especially flowering crabapples, hawthorns, and red maples.  This borer may attack almost any hardwood tree that has been stressed by defoliation, sunscald, drought, soil compaction or mechanical injury.  Young trees are especially vulnerable for the first two years after transplanting.

The full-grown borers are about an inch long, legless and yellow-white.  A single borer can girdle and kill a small tree.  The adult beetle is flattened, about ˝ inch long, bronze-colored above and brassy underneath.  It leaves a large 3/16- inch, D-shaped hole when it emerges from the tree.  The adults emerge and begin to lay eggs in late May or early June in Kentucky.

The first spray should be applied on susceptible crabapples, hawthorns and red maples about the time of first bloom of southern magnolia (Magnolia grandiflora) or full bloom of Washington hawthorn, northern catalpa, tree lilac, or oakleaf hydrangea (Hydrangea quercifolia).  A second spray, 3 weeks after the first one, provides extended protection.

Spray Schedule for Tree Borers