Is Your Green Roof a Pest Paradise?

By Jennifer Brumfield, Training and Technical Specialist, Western Pest Services

Green roofs are steadily sprouting across the country, with the North American green roof industry experiencing 10.3% growth between 2015 and 2016. This form of living architecture helps buildings reduce their water runoff, increase their insulation and even attract more renters.

Green roofs aren’t just appealing to building management and renters, however. This treat for residents could also become a paradise for pests due to the abundance of food, water, and shelter. This could ultimately result in damage to your property – and your bottom line.

By understanding the potential pest threats and implementing proper prevention techniques, your green roof can remain an oasis for people, not pests. Just remember to stay “GREEN”!

G: Get to Know the Pest Threats – Pests don’t have to fly to enjoy a spot on your rooftop. From rodents to ants, meet the pest threats that you could be up against.

• Roof Rats: These excellent climbers are capable of breeding year-round, making them a threat to no matter the season. Roof rats feed on ornamental plants, burrowing their way through vegetation and mulch.
• Stinging Insects: Bees, hornets, wasps, and yellow jackets are attracted to the flowers and water fixtures on green roofs. Once on site, these pests can build nests inside gutters, within trees, in bushes, or on the corners of the building walls.
• Birds: Enticed by the landscaping, birds often make green roofs their nesting site. Pigeons, starlings, and sparrows are known to hang out on roof ledges and form nests under plantings.
• Plant-feeding insects: Beetles, caterpillars, and aphids can’t refuse a good plant stem, whether it’s located in the ground or on top of a building. In fact, these pests feed on the liquid within plants, producing a honeydew-like sap that also attracts ant colonies. 

R: Redesign your Roof – Many of these pest threats can be deterred by properly designing – or redesigning – your green roof. When thinking through the layout of your roof, plan to position vegetation away from roof entrances or exits. In addition, avoid placing plants by the ledge of your building, as pests can easily move from vegetation to open windows.

Ponds and/or fountains are a common feature for green roofs. While beautiful, be warned –standing water can also be a breeding ground for pests, including mosquitoes.  Ensure that all water is constantly circulated, to help deter mosquitoes from laying their eggs on the surface.

E: Evaluate Vegetation – Oftentimes, preventing pest threats can be as simple as choosing the right vegetation. Plants that produce nuts, seeds, or fruits are particularly appealing to flying pests who are looking for a quick meal. Instead, opt for one of these varieties:

• Succulents: These plants are green roof essentials, as they can survive with virtually no water and require only 3 to 4 inches of soil. Stonecrops and houseleeks tend to grow particularly well in these conditions.
• Ornamental Grasses: While most grasses would fail on a living roof, there are a few “grass-like plants” that are able to thrive. Armeria maritima and Carex nigra are two such varieties.
• Wildflowers: Looking for a little color? While wildflowers require deeper soil, they are accustomed to intense weather conditions. Asters and yarrows can be great choices to add some variety among the green. Although these will attract some bugs, most – like ladybugs – are beneficial.

In addition to vegetation, it’s important to evaluate mulch options. Cedar mulch is recommended over organic mulch because it’s considered a natural insect repellant and can help prevent the spread of ants.

E: Exclusionary Practices – Exclusion is an essential element of any integrated pest management (IPM) strategy. IPM aims to prevent pest activity before it occurs through assessment, implementation of prevention tactics, and ongoing monitoring of pests.

Exclusion is a proactive technique that entails sealing all possible pest entrances, essentially “excluding” any pests from moving into your facility.

While it is impossible to fully seal off a green roof, eliminating any cracks, holes and other voids around the exterior of your building is essential. This includes gaps around doors, pipes and fixtures, which can be convenient entranceways for insects or rodents – rats can fit through holes as small as a quarter and cockroaches can squeeze into cracks measuring just one-sixteenth of an inch. Use water-resistant sealant, copper mesh and caulking to close gaps around utility connections and outlets.

N: Next Steps – IPM is not a one-time job. It’s an ongoing cycle that requires the involvement of all building stakeholders. Moving forward, be sure your green roof incorporates the following preventative measures:

• Inspection: Regularly inspecting plants, dining areas and water fixtures for signs of pest activity should be a priority for your team.
• Maintenance: Frequently emptying trash receptacles and minimizing any water build-up from storms or leaky taps can help reduce the presence of pests.
• Communication: Keeping open lines of communication between your maintenance staff, building administration and pest control provider is critical. Be sure staff are educated on early warning signs of pest activity and know who to contact to report any pest problems. Informing residents about your pest control program and how they can play a role should also be considered.

As green roofs continue to grow in popularity, it’s essential to remain vigilant about potential pest threats. By staying G.R.E.E.N, your building can reap the benefits of your living roof – and say so long to pests.

Jennifer Brumfield is a Training and Technical Specialist and Board Certified Entomologist for Western Pest Services, a New Jersey-based pest management company serving businesses and homeowners in major Northeastern markets.

Originally featured at Multifamily Executive.