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| May 1, 2005 | ||||||||||||||||||||||||||||||||||||||||||
About This Newsletter Important Regional Forest Health Issues Oak Tatters The condition was first recorded in the Midwest around 1980. When oak tatters began to be reported, it was a rare, elusive event. Since the late 1990’s, oak tatters and hackberry laceleaf are no longer rare, particularly in “corn belt” areas of Iowa , Illinois , and Indiana . The frequency, level, and repeated occurrence indicate that something has changed since the syndrome was first discovered. Anecdotal evidence suggests that the increase in occurrence of oak tatters and hackberry laceleaf corresponds to an increase in the use of chloroacetamide herbicides, which are a common component of pre-emergent broadleaf herbicide blends for use on corn. In 2004 studies conducted by J. B. Samtani, J. B. Masiunas, and J. E. Appleby have shown that white oak seedlings that were sprayed with low doses of chloroacetamide and chloroacetamide + triazine herbicides developed leaf tatters. In the experiment it was shown that the same herbicides when applied in the tight bud stage or when the leaves were fully expanded did not develop leaf tatters. It appears it is the newly unfolding leaves that are very sensitive to applications of the chloroacetamide herbicides. In 2005, tests will be repeated and will include red oak and hackberry seedlings. Seedlings will also be sprayed with only a triazine herbicide to see if that also produces leaf tatters. (A summary of the research article can be viewed on the www at: http://www.plantmanagementnetwork.org/php/elements/sum.asp?id=4589&photo=2312.) The impact of tatters on oak health is presumed to be similar to that of any other spring defoliating event. Decline and tree death is now being observed on some sites where repeated, heavy oak tatters has been observed. ‘Sudden Oak Death’The pathogen Phytophthora ramorum was identified in 2000 as the cause of high levels of mortality of tanoak and coast live oak in Marin County , California . We now know that the pathogen causes three different types of damage to hosts: On red and live oaks, it causes bleeding cankers on the main stem of trees, leading to tree death. The fungus, however, does not produce spores on oak cankers. On tanoak, it causes stem cankers, but also causes shoot blight and shoot lesions. On many, many shrub and herbaceous species, it causes foliar blight. There are already over 40 species of plants on which P. ramorum is known to produce leafspots or foliar blight, many of which are popular landscape plants, including camellias and rhododendrons. On some foliar hosts, the fungus produces a huge amount of spores that serve as a source of new infections on other plants. The potential for the pathogen to spread and cause stem cankers to oaks depends on the availability of suitable foliar hosts for the pathogen to produce spores. Scientists are beginning to understand the ecology of the pathogen and disease in California , but we do not yet know what understory plants might be important in the ability of the pathogen to survive, spread, and cause disease outside of the West Coast region. Currently, the only known established populations of the pathogen in the USA are in 14 coastal counties in California and Curry County in Oregon . It has also been found in nurseries in California , Oregon and Washington . Because the risk of movement of the pathogen in nursery stock is so great, APHIS has implemented an Emergency Federal Order that requires inspection and certification of material from CA, OR, and WA nurseries before P. ramorum host plants can be transported across state lines. Complete text of the Emergency Federal Order and other regulatory updates can be found on the APHIS website (http://www.aphis.usda.gov/ppq/ispm/pramorum/overview.html). Despite efforts to contain this pathogen, shipments of plants from infested nurseries prior to the discovery of the pathogen in the nursery have resulted in distribution of the pathogen across the USA. Because of the high potential of the fungus to have been introduced into landscapes and forests across the country, a network of surveys is being conducted in nurseries and forest stands. So far, “trace forwards” of nursery stock from infested nurseries have not yet discovered any positive incidences of P. ramorum in MO, IL, IA or IN. No established infestations in forest stands have been discovered outside of California and Oregon . Good information on the situation can be found on the California Oak Mortality Task Force website, http://suddenoakdeath.org/
Emerald Ash Borer In 2004, our Field Office conducted visual surveys at recreation areas on Federal Lands across the Midwest . Additional surveys on state and private lands were conducted by many of our cooperating state partners with Forest Service financial assistance. No evidence of EAB was observed in Illinois , Iowa , or Missouri . Survey efforts continue this summer. Additional information on the Illinois survey is included below. In 2004 ash trees were surveyed throughout Illinois particularly in the northeastern sections of the state in urban plantings, nurseries, state and private parks. No infestations were found. In the spring of 2005, selected live ash trees in some locations will be girdled by removing the bark around the trunk. Such weakened trees are often referred to as trap trees as they are readily selected by many borer species including the emerald ash borer. In the fall months the trap trees will be felled and all the bark will be removed to search for emerald ash borer larvae. The trap trees will be a good indicator whether emerald ash borers are present in the area. See the following websites for more information on EAB status: Asian Longhorned Beetle However, this is not the time for complacency. In the last 2 years, new infestations have been found in Toronto , Canada (September 2003) and Carteret , New Jersey (August 2004). Originally, the Carteret infestation was thought to be from infested wood transported from the New York infestation, but DNA analysis determined that the Carteret infestation was due to a separate introduction from Asia , since these beetle differed genetically from beetles collected in New York , Chicago , and Toronto . For the Midwest , this is a reminder that undetected ALB infestations still could be out there. ALB awareness is key to the early detection of any additional infestations, and the rapid response to eradicate the infestation. To keep current on what is new with ALB, visit the ALB website at http://www.na.fs.fed.us/fhp/alb/ Note that this is a new URL, a new look, but the same up-to-date information. Gypsy Moth Activities – Spring 2005
Weather Overview
As the maps show, winter in the Central States was generally above normal temperature and normal to above normal precipitation. Spring started off with a fairly cool, dry March across the region. The first few weeks of April were significantly warmer than usual, but temperatures have now cooled. March and April also offered a wide variety of weather events, including severe weather and hail in Central Illinois on March 30 th and a band of heavy rain and hail across much of MO, IA, IL and IN on April 20 th. The only portion of the region that is currently abnormally dry is northeast Indiana . Maps and climate information are from the Midwest Regional Climate Center ’s “Midwest Climate Watch” at http://mrcc.sws.uiuc.edu/Watch/watch.htm A Look into the Crystal Ball…
Cedar-Apple rust orange telial tentacles develop from galls formed on the Juniperus spp. and are especially prevalent right after periods of spring rains. These telial horns will give rise to spores that infect a multiple of roseaceous hosts such as apple and hawthorn. Severe infection on these hosts can cause leaf browning and defoliation beginning in May and through most of the summer. Roseaceous hosts produce spores that are blown back to junipers in mid summer to fall, where galls develop on junipers over a one and a half year period and the cycle begins again. Windborne spread of spores between the hosts of several hundred yards is not unusual and spread can be over many miles. Anthracnose leaf and twig diseases can be very prevalent on several hardwood species in early spring, especially if we have wet weather. The most common symptom is dead areas or blotches on the leaves. On white oaks, the lower leaves often get large blotches. On ash, blotches are less visible but leaf drop is very common. On sycamore, irregular blotches form, blighted leaves fall off, and cankered twigs die. Conditions that favor development of sycamore anthracnose include average weekly rainfall one inch or greater and average weekly maximum temperature in the 50’s. In Missouri , activity by the spring oak defoliator complex (loopers and cankerworms) is being reported this spring. Defoliator populations have been at low levels during the last three years, so we are probably “due” to see them rebound nearer to normal activity soon. What else is being reported across the Region Also in Missouri , especially in the Kansas City area, large numbers of tiny white; yellow; greenish larvae (1-3 mm long) have been reported dropping from oaks (esp. pin oaks).These "falling maggots" are a type of gall midge larvae (possibly Contarinia sp.). The larvae hatch early in the spring, feed first on oak flowers and then expanding leaves. By mid-April they finish feeding and drop to the soil to pupate, where they remain until emerging as adults next spring. These are not a health concern for the tree. No controls are needed. Large numbers were also seen in the St. Louis area in 2002 and KC & western MO in 2004. Editor’s comment: Although many of you work primarily with forest trees, many of you also work with the urban forestry community and/or landscape trees in parks and recreation areas. With spring tree-planting well upon us, it seemed appropriate to share this article from the experts! Feature Topic: Buried Root Systems Affect Long-Term Tree Health and Stem Girdling Root Formation During the last few decades increasing numbers of landscape trees have been declining and dying prematurely. In many of these cases the depth to the main lateral roots (syn. primary lateral and first order lateral roots) from the soil surface is correlated with premature tree loss. There are numerous explanations for why main lateral roots systems in the landscape are not near the surface. Three possible explanations are (1) nursery culture (e.g., planting and cultivation, (2) tree planting (e.g., deep holes, root balls sinking into backfill) and, (3) changes to the established tree root environment (e.g., fill over roots, excessive mulch, water table change, soil compaction). However, scientific studies to document the predominant causes are just beginning. Regardless of the plethora of potential causes, when tree root systems are placed into environments not suitable for growth they will decline and die prematurely over time if they cannot adapt. Why do roots grow where they do?
When the roots of trees and shrubs are buried too deep, their health and condition are often affected over time, and sometimes immediately. Health refers to their growth rate, leaf color, ability to recover from diseases and damage, and ability to withstand adverse environments. Condition refers to their structural integrity: sound stem wood that is free of decay, cracks or weak points; supportive root systems; and canopies that are free of large amounts of dead wood. A properly grown, planted or established tree or shrub normally will have the first main order roots at or slightly below the soil or mulch level. The root collar flare is the transition area between stem wood and the first, main order roots. In natural plantings, the root collar flare is clearly visible above the soil line, or may be slightly covered by leaf litter. When root systems are buried, less soil oxygen and water is available to the roots, and the roots must grow closer to the surface where there usually is a more reliable source of both. The energy that a newly transplanted tree or shrub must use to grow new roots and develop a normal, expanded root system must be used to grow upward before it can grow in a normal outward direction. Effects on tree health and stem girdling roots In addition to the decline in health and condition of trees, burying root collar flares may create another adverse condition. Tree root systems may respond to oxygen limitations by growing into oxygen sufficient areas, typically near the soil surface. The ascent of the roots to the surface often causes roots to lose their normal outward radiating pattern. Roots that have grown up toward the soil surface often wrap around or grow against the buried stems. As these roots enlarge over the years, along with the normal enlargement of the buried stems, the roots begin to compress and restrict the development of stem tissues. Stem girdling roots affect normal stem tissue expansion, resulting in abnormal and compressed bark and woody tissue and affect tree transport processes. This creates a weak point in the tree's stem and leaves the tree more vulnerable to stem breakage during windstorms. A study of tree failure during windstorms in Minnesota demonstrates this point. Approximately 30 percent of trees (600 surveyed trees in '97-'98) that failed completely (the entire tree went down) and were at the edges of storms were caused by deep root systems. In littleleaf linden alone, 73 percent of the complete failures were caused by deeply buried (4 inches or more of soil over the first main order root) root systems accompanied by stem girdling roots. “Edges of storms” are areas outside the direct paths of straight-line windstorms or tornadoes. In addition to the risk of complete tree failure there is a general decline in the remaining root system. The compression makes it more difficult for the roots to move water and minerals up to the foliage, and more difficult for the tree to move photosynthates ("food") to the roots. Over time, the root system declines in health and the aboveground canopy and foliage likewise declines. As root collar flares are increasingly buried, more of the stem tissue is buried and out of sight, so these below-ground problems go undetected. Research conducted in the Forest Resources Department at the University of Minnesota has revealed that buried root systems of street trees are alarmingly common. In five randomized studies, it was found that the main order roots of sampled individuals of sugar maple, green ash, linden, common hackberry and thornless honeylocust were buried with 1-11 inches of soil (total number sampled was approximately 100 trees per species). When the trees were then condition rated (a numerical evaluation of the condition of the stems, canopies and foliage), there was a direct relationship between declining tree condition and depth of soil over the roots for maples, lindens and ashes. In other words, as main order roots were covered by more and more inches of soil, the condition of all three tree species further declined. Prevention is the solution! Nursery stock is sometimes lined out with roots placed deeply to minimize wind throw before root systems grow outward. Anecdotal reports are conflicting with some nurseries suggesting this practice minimizes wind throw within a few months of lining out and others noting windthrow a year or more later on those trees that were planted deeply. A field research study implemented at the University of Minnesota in which tree roots were planted at the surface, 5 inches deep, and 10 inches deep has been monitored for wind throw among other things. Out of 360 trees planted in 2000, none have windthrown. However, when the first third of the blocks were harvested in 2003, a trend had already developed with the littleleaf lindens in the study: those planted with 5-10 inches of soil over their roots were developing stem encircling root systems, as opposed to those planted with the roots at the surface. In a similar study conducted in 2002 with containerized trees (4 species, 4 depths, 15 replicates per treatment), planting depth had no significant effect on whether the trees leaned in the containers or were windthrown from the containers. To prevent early decline or sudden failure during windstorms, make sure that those first, main order roots that originate at or near the soil line are planted at that depth in the landscape. Make certain that those roots are at the top of the soil ball of balled-in-burlap trees and containerized trees before you dig the planting hole. Either dig down through the top of the soil ball with a trowel until you find those first roots, or probe down with a stiff wire to find the depth of soil over the roots. If there are 4 inches of soil over the roots of the purchased plants, dig the hole 4 inches shallow and scrape off the excess soil before mulching the newly planted tree or shrub. These few minutes of care at planting time will help ensure that you enjoy a healthy, long-lived landscape tree or shrub. For additional information see A Practitioner’s Guide to Stem Girdling Roots of Trees at http://www.extension.umn.edu/distribution/naturalresources//DD7501.html
Upcoming Opportunities
Other Resources and Sources of Information The North Central Region Integrated Pest Management Center is one of four centers in a national network established to strengthen USDA's connection with production agriculture, research and extension programs, and agricultural stakeholders throughout the United States . Check it out at: http://www.ncpmc.org/ Forest Health Highlights webpage (with yearly forest health report for each state): |
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