Abstract Heterobasidion is a severe threat to coniferous forests in the northern hemisphere. Accurate forest management is needed to safeguard the economic values at stake. In this paper we investigate the efficacy of stump treatment with urea and Phlebiopsis gigantea as control treatment in Norway spruce against airborne Heterobasidion infections. The aim of this study was to examine the infection frequency, i.e. frequency of stumps infected by airborne spores, and efficacy of the stump treatments after performing precommercial thinning and final felling, representing highly variable stump diameters. Today treatment after these cuttings are not standard practice across the world. From a total of 27 Norway spruce stands in the southern and mid-regions of Sweden, five precommercial thinning stands and five final felling stands with infection frequencies higher than an economical threshold for treatment, 20%, were selected. In these stands, the efficacy of stump treatment using urea and P. gigantea against Heterobasidion spp. was assessed on stumps of variable diameter. Wooden discs from stumps were analyzed for airborne infections of Heterobasidion spp. 7–8 weeks after treatment. To evaluate the efficacy of treatments, we used the following three different measurements; infection frequency (proportion of infected stumps), relative infected stump area and number of Heterobasidion colonies per square dm, which were tested using three different statistical models each represented by an efficacy value. Overall, untreated stumps were infected to a higher extent than treated stumps, and most infections were found in untreated stumps from final fellings. Treatment with P. gigantea was more efficient for larger sized stumps than small. In precommercial thinnings, urea performed better and had higher mean efficacy values (92–94%) compared to P. gigantea (59%-72%). In final fellings there were no significant differences between the treatments, both had high efficacy values (urea 95.5–99.8% vs P. gigantea 90–98%). Our findings point at the need for accurate stump treatment after precommercial thinning and final felling, when infection rates are likely to be high. Urea seems to be more effective than the biological control agent P. gigantea in controlling Heterobasidion infections in stumps created in precommercial thinnings. We therefore recommend to use urea in precommercial thinnings if possible. In final fellings either urea or P. gigantea can be used.

中文翻译：

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大小很重要，但大总是更好吗？尿素和 Phlebiopsis gigantea 治疗大小不一的冷杉树桩上的异基孢子菌的有效性

摘要 Heterobasidion 是对北半球针叶林的严重威胁。需要准确的森林管理来保护相关的经济价值。在本文中，我们研究了用尿素和 Phlebiopsis gigantea 作为对照处理在挪威云杉中对抗空气传播的 Heterobasidion 感染的树桩处理的功效。本研究的目的是检查感染频率，即被空气传播的孢子感染的树桩的频率，以及在进行商业前间伐和最终砍伐后树桩处理的功效，代表高度可变的树桩直径。今天，这些扦插后的治疗在世界范围内并不是标准做法。在瑞典南部和中部地区共有 27 座挪威云杉林中，选择了感染频率高于治疗经济阈值 20% 的 5 个商业前间伐林和 5 个最终采伐林。在这些林分中，使用尿素和 P. gigantea 处理树桩对 Heterobasidion spp 的功效。对不同直径的树桩进行评估。对来自树桩的木圆盘进行了分析，以确定 Heterobasidion spp 的空气传播。治疗后 7-8 周。为了评估治疗效果，我们使用了以下三种不同的测量方法；感染频率（感染树桩的比例）、相对感染树桩面积和每平方 dm 的异担子菌菌落数，使用三个不同的统计模型进行测试，每个模型都由功效值表示。总体而言，未经处理的树桩比经过处理的树桩感染程度更高，大多数感染是在未经处理的最后伐木树桩中发现的。用 P. gigantea 处理大树桩比小树桩更有效。在商业化前稀释中，与 P. gigantea (59%-72%) 相比，尿素表现更好并且具有更高的平均功效值 (92-94%)。在最终采伐中，处理之间没有显着差异，两者都具有较高的功效值（尿素 95.5-99.8% 对 P. gigantea 90-98%）。我们的研究结果表明，当感染率可能很高时，在商业前间伐和最终砍伐后需要进行准确的树桩处理。尿素似乎比生物控制剂 P. gigantea 更有效地控制在商业化前间伐中产生的树桩中的 Heterobasidion 感染。因此，如果可能，我们建议在商业化前的稀释中使用尿素。