Black willow scale

The black willow scale (Chionaspis salicis-nigrae) is an insect pest belonging to the family Diaspididae within the order Hemiptera. It is a well-known sap-sucking pest that primarily targets various species of willow trees, significantly impacting their health and vigor.

Besides willow species, the pest has been recorded on various other deciduous trees, including cottonwood, poplar, ash, and tulip trees. These insects are often found on the bark of twigs and branches, where they remain stationary throughout most of their adult life cycle, protected by a hard scale covering.

The life cycle typically includes one or two generations per year depending on the local climate. Adult females overwinter under their scales and deposit eggs in early spring. Once the eggs hatch, the young nymphs, known as crawlers, move to new areas of the host plant to begin feeding.

The damage caused by the black willow scale is primarily due to nutrient loss from sap feeding. Infested trees often display symptoms such as stunted growth, yellowing foliage, branch dieback, and in extreme cases, the overall decline and death of the host tree if the infestation remains unmanaged.

Effective management and control strategies for the black willow scale include:

• Applying horticultural oils in early spring while the tree is dormant to smother overwintering females.
• Timing systemic insecticide applications to coincide with the crawler stage for maximum efficacy.
• Pruning and destroying severely infested branches to reduce the overall population pressure.
• Monitoring the tree regularly and encouraging biological control agents like predatory beetles and parasitic wasps.