©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(1): January 2023 39 borer adults, which means a higher number of borer larvae actively feeding on the internal wood structure of infested trees (McCullough et al. 2005; Anulewicz et al. 2007; McCullough and Siegert 2007; Pontius et al. 2008). Quantification of exit holes can be in terms of numerical categorization (Pontius et al. 2008) or direct density measurement expressed as the number of exit holes per unit area (McCullough et al. 2005; Anulewicz et al. 2007; McCullough and Siegert 2007). Actual counts of larvae and estimation of lar- val mortality rate can be done by cutting and splitting branches and trunks of infested trees (Mercader et al. 2013). Whole branches or entire trees can be cut to allow accurate measurement of exit holes and larval density. Although these methods can provide rela- tively accurate estimations of borer infestation level, branch removal can affect tree form and canopy balance. Meanwhile, measuring tree health is based on the principle that prolonged infestation causes tree decline over time, which manifests into symptoms such as defoliation, canopy thinning, dieback, leaf yellowing, and, in extreme cases, death of the infested trees. To quantitatively capture this information, categorical scoring or percentage infestation are commonly used techniques. For instance, Smitley et al. (2008) estab- lished pictorial examples for different percentages of canopy thinning. Health classes based on canopy conditions can be operationally defined as seen in Murfitt et al. (2016). At larger scale, tree mortality rate can be used to indicate the infestation level of an area (Morin et al. 2017). However, a decline in tree health indicated by canopy thinning, dieback, or leaf yellowing is only observed when the infestation has become severe. Delayed manifestations of the men- tioned symptoms imply that these variables are gen- erally not sensitive to the progression of infestation in early stages. Furthermore, besides X. globosa, rain trees can be infested with multiple pests (e.g., defoli- ator moths such as Pandesma quenavadi and root rot fungi Ganoderma sp.) which can also induce decline symptoms. Currently in Singapore, park and streetscape man- agers rely on signs of exit holes and adult X. globosa, as well as symptoms such as bark peeling, dieback, leaf yellowing, and canopy thinning, to assess rain tree infestation. The major gap in the current protocol is the lack of a systematic approach to integrate all of this information into a unified calculation to quantitatively assess the infestation level of rain trees. Consequently, managers face challenges in determin- ing appropriate control measures and ascertaining the effectiveness of such measures. To bridge this gap, the present study aimed to develop a mathematical expression that integrates visual signs and symptoms associated with X. globosa infestation (e.g., bark peeling, exit holes, dieback, leaf yellowing, and canopy thinning) to give a unified scoring that (1) distinguishes between infested and noninfested trees, (2) reflects the general level of infestation of a tree or trees in the area, and (3) allows monitoring of the temporal progression of X. globosa infestation. To achieve these objectives, tree surveys were conducted on 388 rain trees located in 5 different locations in Singapore: Siglap Link (SL), Bedok South Avenue 1 (BSA), East Coast Park Service Road (ECP), Penjuru Road (PR), and Geylang East Central (GEC) from May 2020 to July 2020. For each tree, we recorded a quantitative estimate of defolia- tion, dieback, exit holes, bark peeling, and proximity of observed exit holes and/or bark peeling to the trunk base. Correlation between these variables and infesta- tion was analyzed using principal component analy- sis (PCA), and a formula to estimate infestation level from the linear combinations of the most informative principal components was derived. MATERIALS AND METHODS Tree Survey A total of 388 rain trees along roadsides were assessed at 5 different locations from May 2020 to July 2020 (Table 1). Locations were selected based on alerts of an incursion of borer infestation. Of all assessed trees, 48 infested trees along East Coast Park Service Road (ECP) with a Borer Infestation Score (BIS)(the defi- nition and calculation of which will be explained in a later part of the paper) within the interquartile range of BIS distribution were selected. These infested trees were reassessed in October 2020 to investigate the progression of infestation. These 48 trees were not treated with any chemicals or pruned from July 2020 to October 2020. Recorded Variables A total of 7 variables were recorded (Table 2). As dis- cussed earlier, larval stages of X. globosa bore deep inside branches and/or trunks of rain trees and cannot be visually detected. Therefore, trees showing no signs
January 2023
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
