Table of Contents Ryan A. Blaedow and Jennifer Juzwik Spatial and Temporal Distribution of Ceratocystis fagacearum in Roots and Root Grafts of Oak Wilt Affected Red Oaks ....................................................................................................... 28 Abstract. The spatial and temporal distributions of the oak wilt fungus, Ceratocystis fagacearum, in the roots of symptomatic and adja- cent asymptomatic northern red oaks (Quercus rubra) were investigated. Root systems of 12 pairs of such trees were exposed to 1 m (3.3 ſt) depth using an air excavation tool. In only one case was the fungus found in more than two cardinal directions of symptomatic trees based on isolation attempts from 192 root segments excised from 1.2 m (3.5 ſt) lengths of primary roots extending in four cardinal direc- tions from the root collar. Many (162) self graſts occurred in all oaks. Few (13) inter-tree graſts were found in less than one-third of the tree pairs. The fungus was isolated from the roots involved in two of thirteen inter-tree graſts and 14 of 62 self graſts assayed. The spo- radic and unpredictable distribution of the fungus in roots of wilting red oaks supports current control approaches that assume the fungus is present in roots extending out in all directions once crown symptoms are evident. Additionally, self graſts may serve as a con- duit for circumferential movement of the fungus around the main stem, but outside the root collar, through the interconnected roots. Key Words. Ceratocystis fagacearum; Oak Wilt; Quercus rubra; Root Graſts; Vascular Wilt Disease. Palle Kristoffersen, Oliver Bühler, Søren Ugilt Larsen, and Thomas Barfoed Randrup Growth of Newly Established Tilia platyphyllos ‘Rubra’ Roadside Trees in Response to Weed Control and Pruning ......................................................................................................... 35 Abstract. This tree establishment study investigates the effect of weed control and pruning treatments on stem and branch diameter incre- ment of newly planted broad-leaved lime (Tilia platyphyllos ‘Rubra’) roadside trees. Weed control significantly increased stem circumfer- ence four years aſter establishment by 3.6 cm (1.4 in) from 24.5 cm (9.7 in, untreated control) to 28.1 cm (11.1 in). In terms of Danish nursery sales prices, this corresponds to an increase of tree cash value of 1201 DKK (160.90 €, 235.40 US$) per tree. Calculating with 400 DKK (53.60 €, 78.40 US$) as cost for contract weeding per hour, this corresponds to 0.75 hours per tree per year for a period of four years. In addition to weed control treatments, trees were pruned at establishment, two years aſter establishment, or at both times. None of the pruning treatments affected stem diameter growth, but branch diameter and branch:stem diameter ratio were sig- nificantly reduced by all pruning treatments. Branch diameter ranged from 40.1 mm (1.6 in) on unpruned trees to 34.6 mm (1.4 in on trees pruned both times. Branch:stem diameter ratio ranged from 0.54 on unpruned trees to 0.49 on trees pruned both times. In consequence, weed control is recommended as a strong management practice. Mild pruning is also considered advis- able, if structural crown problems can be avoided at an early stage, and if the tree has to be prepared for later pruning operations. Key Words. Branch Diameter Growth; Branch:Stem Ratio; Establishment Care; Linden; Stem Diameter Growth; Transplanting; Tree Valuation. Glynn C. Percival Effect of Systemic Inducing Resistance and Biostimulant Materials on Apple Scab Using a Detached Leaf Bioassay .................................................................................................... 41 Abstract. A detached leaf bioassay was used to evaluate several systemic inducing resistance agents, a range of biostimulant prod- ucts and a conventional triazole fungicide (myclobutanil) on apple scab (Venturia inaequalis) development under laboratory condi- tions. None of the biostimulant products (seaweed extract, betaine, molasses, humic acid, yucca extract, and plant hormone/vitamin complex) evaluated in this study inhibited germination of apple scab conidia, subsequent formation of appressoria or reduced leaf scab severity compared to water treated controls. All SIR agents used in this investigation (potassium phosphonate, potassium phosphite, harpin protein, salicylic acid, salicylic acid derivative) inhibited germination of apple scab conidia, subsequent formation of appres- soria and reduced leaf scab severity. The synthetic fungicide myclobutanil resulted in the greatest levels of germination inhibition, reduced appressorium development and leaf scab severity. Results suggest application of an appropriate SIR product may provide a use- ful addition to existing methods of apple scab management; however, use of biostimulants as scab protectant compounds appears limited. Key Words. Fungicides; Integrated Disease Management; Pathogen Control; Plant Health Care; Urban Landscapes. ©2010 | International Society of Arboriculture | ISSN:1935-5297
January 2010
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