Which condition is known to predispose woody ornamentals to borers?

Sunscald is a condition that can predispose woody ornamentals to borers because it creates wounds or stress on the plant. When trees or woody plants experience sunscald, typically occurring on the south or southwest side of the trunk where the bark may become damaged, it can lead to the formation of cracks or weakened areas. These wounds can attract borers, which are insects that lay their eggs in the damaged areas.

As the larvae hatch and begin to feed on the inner tissues of the tree, they can cause more significant harm, ultimately leading to decline or death of the plant. The physical damage from sunscald not only makes the plant more susceptible to pests such as borers but can also leave it vulnerable to other pathogens that could exploit the compromised tissues.

In contrast, the other conditions mentioned, such as excessive humidity, high soil pH, and frequent rain, do not directly create wounds or stress that are typically associated with increased borer activity. While they may affect plant health or growth, they do not have the same direct impact on creating entry points for borers as sunscald does.