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Measurement of the Salinity
and Freezing Tolerance of Crataegus Genotypes Using Chlorophyll
Fluorescence
Glynn C. Percival and Gillian A. Fraser
Abstract. The effect of increasing salinity and freezing stress
singly and in combination on a range of chlorophyll fluorescence parameters
in foliar tissue of six Crataegus genotypes was examined. In general,
increased stress reduced fluorescence values and absorption, trapping and
electron transport energy fluxes per leaf reaction center and cross section,
with decreased sigmoidicity of OJIP curves reflecting decreased energy
fluxes. Based on percentage reduction in a performance index from controls
compared to stress-treated values, plants were ranked in order of tolerant
> intermediate > sensitive. Use of this PIp ranking criterion enabled the
distinguishing of marked differences in foliar salt/freezing hardiness
between the Crataegus species used. Interpretation of the photochemical
data showed that salinity and freezing affects both the acceptor and donor
side of Photosystem II, while OJIP
observations provided information regarding structural and functional
changes in the leaf photosynthetic apparatus of the test species. It is
concluded that chlorophyll fluorescence offers a rapid screening technique
for assessing foliar salinity and freezing tolerance of woody perennials.
Factors
Predisposing Urban Trees to Sunscald
Donald J. Roppolo Jr. and Robert W. Miller
Abstract. A variety of cultural practices such as deep planting
and flush-cut pruning, as well as trunk and root injuries, are suspected
of being causal factors in the development of sunscald on ornamental trees.
Emerald Queen Norway maple (Acer platanoides ‘Emerald Queen’) and
Greenspire littleleaf linden (Tilia cordata ‘PNI 6025’) were transplanted
with these conditions and injuries, and with current guidelines for transplanting
followed. These same species with sunscald injuries were dissected and
examined microscopically to determine if a source of the injury could be
determined. Trees in all treatment categories developed sunscald except
those deep planted and receiving followup watering. Most sunscald injuries
were associated with flatheaded borer (Buprestidae spp.) damage.
Dissections revealed a number of causes of sunscald injuries, including
borer damage, canker-causing fungi, and radial cracks in the xylem. Reducing
the incidence of sunscald injury may be as simple as adequate watering
the first growing season after transplanting.
Application of Systemic Insecticides
in Relation to Boxwood Leafminer's Life History
Gabriel d'Eustachio and Michael J. Raupp
Abstract. We describe the life cycle of boxwood leafminer (Monarthropalpus
flavus) in the mid-Atlantic region of the United States in relation
to growing degree-day accumulations. In addition, the efficacy of three
systemic insecticides (avermectin, imidacloprid, and acephate) for control
of the boxwood leafminer were evaluated. Avermectin and imidacloprid applied
at adult flight provided excellent control. Imidacloprid applied in the
summer when larvae were present in leaves gave good control of larvae.
Avermectin and acephate were ineffective when applied in the summer.
Effects of Tree Density, Tree
Species Diversity, and Percentage of Hardscape on Three Insect Pests of
Honeylocust
Chad E. Sperry, William R. Chaney, Guofan Shao and Clifford S. Sadof
Abstract. Honeylocust (Gleditsia triacanthos L. var. inermis) trees in urban areas are attacked principally by three insect pests: honeylocust plant bug, mimosa webworm, and honeylocust spider mite. One hundred honeylocust trees on the Purdue University campus were studied to better understand the influence of landscape characteristics on the populations of these insect pests. Specifically, the amount of hardscape, defined as imperviousness under and around trees, including roads, sidewalks, parking lots, and buildings; density of honeylocust; and diversity of tree species around each tree were calculated at numerous spatial scales and correlated with insect pest abundance on honeylocust. Each of these landscape factors influenced insect pest and their natural enemy populations on honeylocust trees at a wide range of scales. No single combination of these factors was associated with lower densities of honeylocust pests.
Hardscape Damage by Tree Roots
Lawrance M. Lesser
Abstract. Tree root damage to hardscape is a problem for most cities, costing millions of dollars annually statewide for repairs and associated legal expenses. There is a need to systematically identify which tree species are the most often associated with hardscape damage, so that urban tree managers can make appropriate species selections. This study uses TreeKeeper® data to compile a listing of those species most often associated with hardscape damage in three southern California cities, and compares results from another study.
A Summary of Forecast and Demand
for Municipal Street Tree Service on Staten Island, New York
James J. McCabe
Abstract. The objective of this study was to establish a reasonably
accurate demand forecasting model for municipal street tree services on
Staten Island, New York. Using the raw data gathered from years from 1996
through 2000, a chart and mathematical equation for anticipated monthly
demand were derived for the year 2001. The development of the model was
accomplished with simple arithmetic computations and
computer-assisted regression analysis. Although occasional storm damage
skewed some monthly figures, it is apparent that demand for public tree
maintenance on Staten Island is decidedly seasonal and predictable.