Many aspects of YHSS life history have been studied intensively, including feeding and ovipositional preferences, chemical ecology, and biological control. Although chemical control may be appropriate in some cases, we can apply life history information to anticipate and silviculturally minimize YHSS impacts. Our conclusions and recommendations are aimed primarily at white spruce stands in the Great Lakes region, where most research has been conducted. However, these recommendations should be generally appropriate for other regions and spruce species where YHSS problems exist.

Site evaluation YHSS management begins with estimating the risk of buildup by the sawfly on a particular site. Potential impacts of YHSS can be minimized by establishing new stands on appropriate sites. The available hazard rating system should be used to determine the likelihood of defoliation and damage.

Further, insect problems are typically more frequent and more severe when trees occur on sites not suited for spruce. Selecting appropriate sites for growing spruce can be difficult. However, ecological classification systems, such as the habitat type system developed for Wisconsin (Kotar et al. 1988), may provide an excellent tool for locating sites where spruce are well adapted. Resource managers should become aware of regional ecological classification systems and integrate them into forest pest management activities whenever possible.

Management guideline No. 1: Do not plant white spruce on steep south-facing slopes or on poorly drained sites where the risk of YHSS damage is high.

Management guideline No. 2: Grow spruce on ecologically appropriate sites.

Competing vegetation - White spruce are generally considered tolerant of overhead shade. Therefore, forest managers can take advantage of shade to reduce YHSS defoliation. For example, Rauscher (1984) found that a nurse-canopy of aspen or white birch, which reduces full sunlight by 25 to 30 percent, permits maximum height growth of young spruce while protecting them against spring frost damage.

Management guideline No. 3: Delay release of established white spruce stands until trees are 10 to 12 feet tall, at which point they are less susceptible to YHSS defoliation. In some stands, use a light overstory of aspen or other species until trees outgrow their susceptibility to YHSS. Maintaining an overstory would be more important on high-hazard sites such as south-facing slopes.

Management guideline No. 4: Plant fast-growing shrubs with roadside spruce plantings for several years to provide shade and reduce susceptibility to YHSS.

Natural enemies - Certain predators and parasites help maintain YHSS populations at low levels. Many management practices can either encourage or discourage predators and parasite abundance. Small mammal predators would benefit from hiding places such as an abundance of large woody material on the ground. Many adult parasites would benefit from nectar sources, such as flowering plants. A diverse ecosystem with spruce as a component would likely provide for many of the special needs of parasites and predators.

Management guideline No. 6: Discourage site disturbance, especially windrowing, when establishing spruce plantings. Allow some woody material to remain on the site to provide habitat for predators such as small mammals and insects.

Management guideline No. 7: Encourage white spruce as a component of stands rather than as a single species plantation.

Direct control - Insecticidal control of YHSS can be selectively used in forest plantations. However, reported tree mortality levels of only 2 to 3 percent are likely to be acceptable in most white spruce plantations. Pockets of mortality as high as 15 percent may occur on high-hazard sites. In these areas, and where growth loss is a concern, direct control measures using insecticides could be used.

YHSS may be a more notable concern in Christmas tree plantations, and on ornamental, roadside, and shelterbelt trees. Frequently, trees in these situations may be exposed to full sunlight for many years, increasing the likelihood of YHSS infestations. This, combined with the inherent high value of these trees, may justify direct control measures. Insecticides should be applied to early instar larvae, before defoliation becomes significant. Regular scouting and monitoring should be done to detect YHSS populations before significant damage occurs.

Management guideline No. 8: Carefully consider costs and benefits of using insecticides to control YHSS.