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Vol. 18, No. 5, May 9, 2003 In
this Issue |
More on winter damage to landscape trees and shrubs |
A public apology to Tracy Aichele. I feel like the Fonz in that old episode of "Happy Days." I was wr. wrrr. wrrro. wrrron. I was not right. Back in early March when Tracy assumed Jeff Andresson's duty to produce the Ag Meteorology wrap-up for the Landscape Alert, she e-mailed me and asked if I thought the warm/cold cycles we had experienced would result in significant winter injury for landscape trees and shrubs. My response (which to my chagrin, I saved) was, no, we didn't have a long enough sustained warm period to cause things to de-harden. Boy, was I was wr. wrrrr. wrrro. wrrron. Boy, was I not right. The temperature cycles we experienced in February and March have resulted in tremendous winter injury in Lower Michigan. And the damage is becoming more apparent every day as trees and shrubs continue to leaf out or - all too often - don't leaf out. I recently visited a major landscape construction in southeast Michigan where upwards of $200,000 worth of recently planted trees and shrubs may have been lost to winter injury. The culprit appears to be the cycles of warm and cold weather we experienced throughout the winter, especially the warm/cold cycle in late February and early March (Figure 1). What is surprising in looking at this data is that the warm-up in late February was not sustained and not very warm, just a couple of days in the mid-40's. Yet it apparently resulted in enough loss of cold hardiness that the five sub-zero days that followed results in extensive winter injury. So, Tracy, I'm sorry if my e-mail caused you to mislead anyone else. I was wr. wrrr. wrrro. wrrron. I was not right. |
Phenology table for May 2-May 8 |
In East Lansing, adult imported willow leaf beetles were observed feeding on willow leaves this week. First instar euonymus webworm larvae were found on burning bush. Honeylocust mites have laid eggs at the base of developing buds; honeylocust leaves are beginning to emerge. Bud caps are splitting on spruce, an indicator used for egg laying by Cooley and eastern spruce gall adelgids. Eggs are invulverable to many insecticides. Degree day accumulations in Flint were 205.1 as of May 8. In Flint, Michigan Rhododendron "PJM" is at full bloom, Koreanspice viburnum is somewhere between first-full bloom. Common lilac and Japanese flowering crabapple (Malus floribunda) are at first bloom. Degree-days and phenological indicators are being tracked at the Applewood estate as part of a GREEEN project. Thanks to Mike Belco, Mary Wilson, Master Gardener volunteers and others for their assistance. Rhododendron 'PJM' was at full bloom in West Olive as of May 6. Koreanspice viburnum was at first bloom as of May 5. Thanks to Tom Dudek for supplying data. Temperature normals for the Lansing/East Lansing area for May 8 are 192.2. We are at 197.6 GDD50 for May 8, or just about normal. The rainfall continued in the East Lansing area for most of the week. For the month of May, we have had 2.24 inches so far.
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Grubs in lawns: Hang in there for two more weeks |
Extension offices have been flooded with phone calls about grubs in lawns this past week. See articles on grubs in the last two issues of the Landscape Alert. If grubs are found around dead patches in lawns, homeowners can treat the dead patches and the area around it with Diazinon (diazinon), Sevin (carbaryl), or Dylox (trichlorfon) at this time. However, if you can make it through the next two
weeks, the grub damage will be over for this spring. The best strategy
at this time is to spot treat heavily infested areas with one of
the products above, then plan on treating the entire lawn with GrubEx
(imidacloprid) or Bayer Season-long Grub Control (imidacloprid)
in July. The July treatment will prevent grub problems next fall
and the following spring. There is no need to treat with insecticide
unless grubs and grub damage have been found. |
Perennial weedy grasses in lawns |
Perennial weedy grasses in lawns have been of interest this spring in Diagnostic Services. Numerous calls and lawn samples have been received from clients suspicious of insect or plant disease related turf problems. In many cases, no insects or plant pathogens were found - it was simply a misidentification of a weedy grass. Thin, stressed areas in lawns due to a couple droughty seasons have provided opportunities for weeds to become established. Some weedy grasses that I have seen this season in lawns include: creeping bentgrass, bermudagrass, nimblewill, quackgrass, tall fescue and orchardgrass (Table 1). A homeowner's lawn typically consists of Kentucky bluegrass, perennial ryegrass and various fine fescues. Many of these perennial weedy grasses look much different than desirable lawn grasses. Perennial weedy grasses are not generally compatible with desirable grasses because of differences in leaf shape, leaf color and growth habit. For these reasons, weedy grasses can be of great concern for homeowners. Perennial weedy grasses of lawns can be broken down into two categories - those that creep through the soil forming patches or those that form clumps (Table 1). Creeping bentgrass, bermudagrass, nimblewill and quackgrass spread in the lawn by rhizomes and/or stolons. Rhizomes are modified stems that form below the soil surface; stolons are aboveground, modified stems. The spreading nature of these grasses allows them to be very competitive in lawns, often forming dense mats when mowed. Tall fescue and orchardgrass are clump-forming perennials that do not have rhizomes or stolons. The clumps of these grasses enlarge by tillering. Table 1. Common perennial weedy grasses in lawns
Identifying characteristics of these perennial weedy grassesCreeping bentgrass. Creeping bentgrass is commonly used for golf course putting greens. It seems, however, that this plant is becoming a problem in many homeowners' lawns. Creeping bentgrass spreads in the thatch by stolons, making it easier to pull from the lawn than some of the other perennial grasses. Creeping bentgrass has a fine, smooth texture with tapered leaves. Leaves are distinctly ridged on the upper leaf surface and rolled in the bud. Creeping bentgrass has a 1 to 3 mm tall, membranous ligule. Bermudagrass and nimblewill. Bermudagrass and nimblewill are very similar in appearance and growth habit. Both are warm-season grasses and thus not well established this far north. Bermudagrass is a common lawn grass farther south because of its heat and drought tolerance. The foliage of both bermudagrass and nimblewill is grayish to bluish-green in color. Bermudagrass is a wiry plant that spreads through the soil by rhizomes and stolons; nimblewill only has stolons. Both weeds form dense mats in lawns if left unchallenged. Leaf blades of bermudagrass and nimblewill are short and linear-lanceolate in shape, which are unlike most grasses. Bermudagrass contains a very short, hairy ligule with a ring of hairs at the collar region while nimblewill has a very short, membranous ligule. Bermudagrass and nimblewill turn brown to straw-color in the fall and remain so until late spring. This is the reason why it is so noticeable in early spring when desirable grasses are greening up. Quackgrass. Quackgrass is an aggressive perennial, cool-season grass with slender, yellowish to white, sharp-tipped rhizomes. It generally grows erect but can tolerate mowing. Leaf sheaths of young quackgrass seedlings can be quite hairy to smooth. Upper leaf sheaths and the upper leaf surfaces of quackgrass are generally sparsely hairy to smooth and lower leaf surfaces are smooth. Quackgrass is characteristic of narrow, slender, clasping auricles and a short, membranous ligule. Tall fescue and orchardgrass. Tall fescue and orchardgrass are clump-forming, cool-season perennial grasses commonly used as forages. Tall fescue can be used as a turfgrass but is not usually visually compatible when mixed with most finer-leafed grasses. Tall fescue is a dark-green grass that has broad leaves with distinct, prominent leaf veins. Leaves are rolled in the bud. Orchardgrass is more of a bluish-green grass with folded, long leaves. Orchardgrass stems are very flat and cannot be rolled between your thumb and forefinger. Tall fescue has short, blunt auricles, whitish collar and a short, membranous ligule; orchardgrass has a large, membranous ligule. ControlUnfortunately, there are no selective herbicides available to homeowners to control perennial weedy grasses without harming desirable lawn grasses. Control of these weeds may be achieved with one to two applications of glyphosate (RoundupÒ, others) in the spring or fall. "Weed and feed" liquid/granular products or "3-way" broadleaf herbicides (Weed-B-GoneÒ, TrimecÒ, others) will not do the job. These products only control broadleaf weeds. It is important to kill all modified root structures of creeping bentgrass, bermudagrass, nimblewill and quackgrass before re-seeding. Creeping bentgrass and nimblewill have only stolons that may be manually pulled or dug from the lawn with extreme patience. Clump-forming grasses may be treated with an herbicide or simply dug from the soil without fear of returning. Grass seed may be planted a few days after the last herbicide application or immediately after removal from the lawn. Simply keeping up on a fertility program will not be sufficient once these grasses are established. Once initially removed, however, a healthy, vigorous, dense lawn will help keep the majority of weeds out of the lawn. |
Scare tactics used to buy ash wood |
We have heard of at least two recent incidents where timber buyers pressured landowners to sell ash trees in areas of Michigan well outside the emerald ash borer infestation. These incidents occurred in western and northwestern Lower Michigan and likely involved different timber buyers. In both cases, the timber buyers encouraged the landowners to sell off their trees at a relatively low price because of the threat posed by the emerald ash borer. Perhaps most galling is that one of the timber buyers claimed to "be from MSU" - which is certainly NOT the case! This same sort of situation occurred about ten years ago when gypsy moth populations were at high levels and sleazy timber buyers tried to buy defoliated oak trees. Please help spread the word that landowners should not sell off ash lumber in a panic, especially when their property is in western or northern Michigan. State and federal agencies have already begun an aggressive program to contain emerald ash borer in southeastern Michigan to reduce the abundance of the beetle and to eventually eradicate this exotic pest. Two primary goals of this program will be to minimize the spread of the emerald ash borer infestation and to prevent establishment of new populations. Most landowners, therefore, should not be affected by emerald ash borer unless their property is in or near the infested counties. Regardless of where the property is located, it
will be a good idea to encourage landowners to develop a sound management
plan for their forested land, if they don't already have one. The
process of developing a management plan can help landowners determine
their objectives and priorities for their land. Timber production
may or may not be part of that management plan and if it is, it
should be done in a sustainable manner. Landowners can contact their
regional Department of Natural Resources or Natural Resources Conservation
Service office or a consulting forester for help in developing a
management plan. There are several good web sites with information
on managing private forestlands and selecting a consulting forester.
Try the Michigan State University Department of Forestry site, which
includes links to the Michigan Society of American Foresters and
the Association of Consulting Foresters in Michigan: |
Identifying pitch mass borer and Zimmerman pine moth larvae |
Two species of caterpillars (Lepidoptera) we commonly see tunneling under the bark of pine trees are the pitch mass borer, Synanthedon pini (Sesiidae) and larvae of the Zimmerman pine moth, Dioryctria zimmermani (Pyralidae). Both are considered primary pests of conifers, that is, they will attack healthy trees. Like other boring pests of woody ornamentals, the timing of control measures is critical because the larvae are exposed and vulnerable for only a short period of time. The window of opportunity to control Zimmerman pine moth is early April whereas insecticides aimed at controlling pitch mass borer need to be applied in mid- to late July. Therefore, it is important to be able to distinguish between these two pests. True caterpillars (larvae that turn into moths and butterflies) can be easily distinguished from boring beetle larvae (Coleoptera) such as roundheaded and flatheaded borers. True caterpillars have rounded head capsules, three pairs of jointed thoracic legs and five or fewer pairs of fleshly prolegs on the abdomen. Wood boring beetle larvae have reduced head capsules, generally lack thoracic legs and never have fleshy prolegs on their abdominal segments. To tell the difference between pitch mass borer and Zimmerman pine moth larvae one needs to look closely at the arrangement of the short dark spines, known as crochets, located on the bottoms of the fleshly abdominal prolegs. Crochets aid the caterpillar in gripping and crawling. They are one of the most important characteristics bug geeks (like us) use to identify the many different types of caterpillars found in or on landscape plants. The crochets of the pitch mass borer are relatively the same length and are arranged in two opposing lines that run perpendicular to the midline of the body. The crochets of the Zimmerman pine moth larvae are arranged in a complete circle, and if one has the aid of a good quality dissecting microscope, one could see that there are two different lengths of crochets, which alternate around the circle. The smaller ones are just barely visible at the bases of the longer ones. More on the caterpillars...We see pitch mass borer most often on white pine but it is also known to attack Austrian, Scots and jack pine. It will occasionally infest white, Norway, and Colorado blue spruce. The eggs are laid on the bark in mid-summer and larvae burrow into the cambium area. The caterpillars feed and tunnel around just under the bark. Lots of coarse frass may be present and huge amounts of pitch often flow out of the wound area. Trees may break off above the wound area, much like trees severely infested by Zimmerman pine moth. The borer seems to be attracted to wounded trees and the pitch masses are often found at the site of pruning wounds. In situations where the insect is causing damage, avoid pruning or wounding trees in the summer months. Attacks are usually on the lower part of the tree, but larvae may feed higher on the trunk when the populations are high. This insect has a two-year life cycle, that is, the larvae feed for two years before changing into the adult moth. Pupation occurs near the opening of the wound in the tree in June or July. The only time this insect can be controlled is when the eggs are hatching and the young caterpillars are burrowing into the bark. Eggs are laid in mid- to late July. Insecticide sprays containing cyfluthrin (sold as Tempo for commercial applicators or as Bayer Advanced Garden for homeowners) applied around the middle of July then again two weeks later should be effective in controlling this pest. Another application may be necessary the following year because of the insect's two-year life cycle. The Zimmerman pine moth is a serious pest of all species of pine especially white Scotch and Austrian. We have also seen Zimmerman caterpillars tunneling in Fraser fir. The larvae or caterpillars of this insect kill terminal leaders and lateral branches of young pine trees. The larvae will also attack cones and the main-stem or trunk and repeated attacks may cause the top to break off. Adult moths emerge from mid-July to mid-August. Females lay their eggs at the edges of old feeding wounds, bark crevices, or on terminal buds. The eggs hatch in 8 to 10 days. The newly hatched larvae, without feeding, crawl into nooks and crannies in the bark and construct shelters of silk in which they hibernate until the following spring. In April or May the larvae begin feeding on the bark. They then tunnel into the cambium area to feed on new growth in terminal and lateral branches. Toward the end of June, the larvae leave the new growth and tunnel into the whorl area, girdling branches and leaders. Feeding activity results in characteristic coagulated pitch masses at branch whorls on the main-stem, lateral branches or on the terminal leader. Damaged terminals usually become "fish-hooked" and turn yellowish green. Pupation occurs in the pitch masses or tunnels. Infested trees tend to be attacked again and again, thus becoming so-called brood trees. Insecticide sprays containing cyfluthrin applied in early April will help to control this pest. Be sure to use enough nozzle pressure to drench the bark. Heavily attacked trees should be removed and destroyed. Pruning should be avoided during late summer, as the fresh resin around the pruning wound may attract female moths. |
From culture to customer: The management of plant-parasitic nematodes in nurseries |
Root-knot nematodes (Meloidogyne sp.)Host plants. Very wide host range including many herbaceous perennials, annual bedding plants and woody ornamentals Biology. Only one species of root-knot nematode is common in Michigan, the northern root-knot nematode, Meloidogyne hapla. There are three other very common species of root-knot nematodes worldwide, but apparently they do not survive winters in areas with temperate climates. However, other species are infrequently detected in our state. Plants grown in subtropical or tropical climates can potentially be infected with any of the other three most common species, M. arenaria, M. incognita, or M javanica. Another species of concern is the Columbia root-knot nematode, M. chitwoodi. This species has not yet been detected in Michigan but is known to occur in the Netherlands, a location where a great deal of propagating material originates. This nematode is of regulatory significance and should be avoided. The northern root-knot nematode (NRKN) overwinters in the soil as eggs. As temperatures increase in the spring, second-stage juveniles emerge, migrate through the soil and penetrate the roots of host plants. The nematodes establish feeding sites in provascular tissue in an area behind the root cap. As the infected root continues to grow, the vascular system differentiates in the area where the nematodes have established their feeding sites. Therefore, these nematodes cause disruption of the vascular tissue, essentially the plumbing of the plant. Shortly after successfully establishing a feeding site, the second-stage juvenile begins to swell. The nematode soon molts to a third-stage juvenile. Eventually, following two additional molts, it matures to become an adult female or male nematode. Females, similar to the other life stages except second-stage juveniles and males, are incapable of movement. For this reason, root-knot nematodes are referred to as sedentary endoparasitic nematodes because they don't move after successfully establishing feeding sites within roots. Females are quite round, whereas males are worm-like. Males typically exit roots because they do not feed. Female NRKN produce large numbers of eggs, potentially up to 1,000, in a gelatinous matrix secreted by the anus. The NRKN can complete its life cycle in a month at optimal soil temperatures. Therefore, these nematodes can complete multiple generations per growing season. Symptoms. The NRKN, like many other nematodes that parasitize plants, does not cause the production of characteristic secondary symptoms (symptoms away from the feeding sites, the foliage). Typical secondary symptoms are stunting, chlorosis (yellowing) and reduced flowering. Severely infested plants usually wilt during periods of hot, dry weather. Root-knot nematode-infested plants often appear "starved" for water. Invasion of roots by NRKN will result in the production of small swellings on the roots called galls. Galls will vary in size depending on the numbers of nematodes feeding within them and the species of root-knot nematode causing the infection. Compared to other species, feeding by NRKN results in the production of very small galls. These galls are often inconspicuous on thick-rooted hosts such as Hosta or Hemerocallis or on most woodies. ManagementAvoidance. Once established, root-knot nematodes are virtually impossible to eradicate. Therefore, attempts should be made to keep sites free from any species of root-knot nematode for as long as possible. This is primarily accomplished by using nematode-free roots and by not contaminating fields with NRKN-infested soil. Roots of plants should always be inspected for the presence of galls. If galls are observed, the roots should be treated or discarded. Roots that are suspect should be sent to a nematode diagnostic laboratory for analyses. It is advised that roots are routinely checked for the presence of plant-parasitic nematodes before propagating any plants. Population reductionBiological controls. The majority of nematodes present in the soil are considered beneficial. They typically feed on bacteria, fungi or small animals including other nematodes. Often these nematodes will just compete with plant-parasitic nematodes for space along roots. Research results indicate, as the abundance of these nematodes increases there is often a correlation in a decline in the numbers of plant-pathogenic nematodes. Steps can be taken to increase the diversity and numbers of these beneficial nematodes in fields. These types of approaches are outlined in MSU Extension Bulletins that emphasize crop ecology. It has been noted in several instances that population explosions of NRKN occur when infested plants are grown on fumigated sites. In the absence of natural-occurring organisms to keep plant-parasitic nematodes in check, NRKN numbers will frequently become extremely high and result in the expression of severe symptoms of disease. Organisms exist that are parasites or pathogens of nematodes. Most of these occur naturally in soils but often do not provide sufficient enough control of plant-parasitic nematodes to keep their population densities below damage threshold levels. Some products are available as biological nematicides, but, to date, their uses have not resulted in consistent control of nematodes in Michigan. Chemical controls. Field sites should be routinely sampled for plant-parasitic nematodes prior to establishing plants. If nematodes are detected on a site where host plants will be grown, use of a nematicide may be advised. It is important to remember that homeowners are often the ultimate customers. Other than trying to keep plants as healthy as possible and digging out and destroying unthrifty plants, there is very little these customers can do to control nematodes. It is imperative nurseries minimize infections of plants while in their care. Cultural controls. Roots should always be inspected for galls prior to planting. If galls are observed, population densities of root-knot nematodes can potentially be reduced by pruning infected roots. Some species of plants will tolerate removal of virtually all the lateral roots, whereas others will not. Experimentation is necessary to acquire this information. It should be noted, that although this tactic may result in drastic reductions in population densities of root-knot nematodes, it will not eliminate them in most situations. It is critical to start with nematode-free propagating material. If plants are infested with root-knot nematodes, it is possible to generate nematode-free material by starting from seed if possible or cuttings from stems and leaves. Root-knot nematodes feed within roots, so eliminating the roots will eradicate the nematodes. Always start seeds or cuttings in sterile growing media. Field sites with histories of NRKN problems should be kept out of host plant production for a period of two to four years. NRKN non-host crops such as corn or small grains should be grown to reduce population densities of these important plant pathogens. Some cultivars of marigold (Tagetes) can be used to reduce numbers of NRKN. Weed control is imperative. Many weeds serve as hosts for the NRKN. Genetic controls. Plants vary in their susceptibilities to root-knot nematodes. Some cultivars of certain species may be relatively poor hosts while others may be good hosts. This information, however, is usually not available due to the large numbers of plants grown in nurseries and their many cultivars. Physical controls. Hot water treatment of root-knot nematode-infested dormant roots can reduce population densities of these organisms. Typically temperatures around 45°C (113°F) are necessary to kill nematodes. Roots should be treated for at least 30 minutes and preferably longer depending on the tolerance of the meristematic tissue. Experimentation is necessary for successful use of hot water dips. Unfortunately, this tactic usually doesn't provide adequate nematode control especially in situations where roots are heavily infested. Sodium hypochlorite (NaOCl) will dissolve egg masses of root-knot nematodes. NaOCl is used by nematologists for this purpose to extract root-knot nematodes eggs for use in experiments. It is possible that using 0.5% to 1.0% of sodium hypochlorite (active ingredient) in hot water will provide better results than just hot water alone. Egg masses will dissolve so that the eggs will circulate in the water. Young nematodes within the eggs may also be killed. Although this tactic may provide better results than hot water alone, it is largely untested. Plants treated with NaOCl can be stunted. To start plants in containers either in the greenhouse or field, sterile growing media should be used. Media can be purchased already sterilized or it can be pasteurized on site. Steam or heat can be used for this purpose. |
Another ash borer, but no need to panic |
Over the past few weeks we have received several specimens of an attractive beetle known by the common name banded ash borer. The beetle is known scientifically as Neoclytus caprea (Coleoptera: Cerambycidae). This native species is known to occur throughout the northeastern U.S., west to Arizona, Utah and Wyoming. There are approximately 25 North American species of Neoclytus, of which seven species are known to occur in northeastern U.S. The most well known species is the redheaded ash borer, N. acuminatus. Hosts of the banded ash borer include ash, hickory, elm, mesquite and occasionally white oak. Adults are dark brown to almost black and from 1/2 to 1 inch long. The back of the beetle is marked with four yellowish bands with the first two joined along the midline to form two "loops." Also, there is a distinct stripe behind the head. The beetles prefer dead, dying, diseased, or stressed trees and, unlike the emerald ash borer, typically do not attack healthy trees. Adults emerge in early spring and fly to host material where they deposit eggs in crevices in the bark. Ash logs cut during the winter are especially subject to attack. The larvae feed under the bark for a period of time before boring into the sapwood where they feed for the remainder of the summer. Pupation occurs in the fall, but the adult does not emerge until the following spring. There is usually one generation per year; however, if the infested material is sawed, stored and dried out, the life cycle may require several years to complete. |