Pest Managers on Green Roofs: Think Before You Jump

This 24,000 square foot green roof in Houston, Texas reduces energy consumption and minimizes effects on water resources. Source: Jacob White Construction Co.

The vertical height of a building doesn’t pose much of a problem for pests. They find their way onto the roof just fine, no matter the size and height. Once there, it may be unclear who has the responsibility for managing them.

This warning comes from academic and industry experts who attended the National Conference on Urban Entomology in San Antonio, Texas in May of 2014. A session on pest management in the green roof environment was moderated by Allison Taisey, board certified entomologist and program coordinator at the Northeastern IPM Center.

A green roof, that “growing” trend in sustainable living, attracts both urban and agricultural pests. Managing them safely requires knowledge of both structural and agricultural pest management. Attendants at this session began working out some of the nuances. When faced with a green roof, a pest management professional (PMP) might find the pest problem out of the contract scope, license category, or pesticide label restrictions.

A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems.

Presenters at the sessions identified several research questions needing further study. What are the potential pests that might be new to the urban PMP? Which have potential to damage the membranes that protect the building from moisture in the soil? The starter list includes adelgids, grubs, crane flies, overwintering insects, and vegetable garden pests. Add these pests to the list that structural experts already know, including roof rats, mosquitoes, fire ants, termites, pigeons, and carpenter ants. They also identified a need for a pest identification guide for rooftop gardens and green roofs.

For now, PMPs should contact their local cooperative extension office for identification and insights on controlling agricultural pests. Visit http://npic.orst.edu/mlr.html to find your nearest office. The Northeastern IPM Center plans to add literature on green roof pest management to its resources database when it becomes available. Experts say urban and structural PMPs will need training on identifying agricultural pests, working safely around beehives, and applying materials on a green roof.

Another concern for pest managers: A structural applicator’s license may not qualify a PMP for pesticide application on a green roof. PMPs must be clear about the scope of their abilities (legally-speaking) when promising to manage pests in and around structures with green roofs. Session presenters suggested a turf and ornamental license may be more appropriate for this setting. In the same vein, PMPs should contact pesticide manufacturers to make sure a rooftop setting is a legal site for application. If a contract does include a green roof, PMPs must be able to access the roof for inspections—this can be difficult in the more self-sustaining extensive green roof systems.

Another topic that came to light in this session was water quality. Water runoff is a major component of green roof planning. How pesticides break down in the green roof media is an area that needs to be researched.

“Green roofs are now part of the building ecosystems that PMPs are trying to protect from pests,” Taisey said. “The green roof topic is full of opportunities for industry-extension partnerships that would help people manage pests on green roofs while posing the least risk to health, property, and the environment.”

The title “Think Before You Jump” was inspired by the presentation given at the meeting by Gil Bloom, president and entomologist at Standard Pest Management in Astoria, New York.