Staying one step ahead of dynamic pest populations
Two species of European crane flies have now been identified in the U.S. Northeast since its first sighting there in 2004.
Photo courtesy David Cappaert, Michigan State University, www.bugwood.org.
Pests, including insect pests that destroy turfgrass, continually change, whether in number, kind or status. If they weren’t in constant sway to the rhythm of shifting environments (like all living organisms), we would have them figured out by now. We would know precisely when and how to manage them. However, insect pests represent moving targets. Tracking that dynamism remains a challenge for pest management practitioners.
As our action, tolerance and economic thresholds are pushed lower and lower the status of pests can change. Elevated standards and risk adversity call new challenges to the forefront, among them insect pests.
Another reason for change is pesticide release. This can come about from the collateral damage posed to non-target organisms. These include the predators and parasitoids that would have helped to suppress pest populations in their own right. Also, pesticide release may occur through a shift from broad-spectrum insecticides to products with a narrower spectrum, wherein secondary pests that might have been controlled along with the target pest, are no longer kept in check, with outbreaks as one possible outcome.
Ecological release is another way pests change. This can occur when shifting cultural and agronomic practices end up making the habitat more favorable for the growth of insect populations.
Finally, the starkest way is through the arrival and establishment of invasive exotics. Invaders may establish and spread in new territory when they arrive without the pathogens and predators that kept them in check in their native range.
Emerging pest complexes
For example, both the annual bluegrass weevil and the leatherjackets are notable for their increasing pest status in the eastern United States. The annual bluegrass is an emerging native threat of golf course playing surfaces. The European crane flies are recently established exotic threats to amenity and production turf. As part of efforts to alert and arm the turfgrass industry, each merits a thorough summary of their distribution, expansion and pest status.
Six main insect pest complexes can outbreak in cool-season turfgrass and severely affect turf quality and maintenance for its intended aesthetic, recreational or environmental purposes.
European crane flies: Tipula oleracea and Tipula paludosa are native to Europe, but each has established in three geographic areas of North America. In the West, both occur from British Columbia south to California. In the East they occur in northern Maine to the Canadian Maritimes, and in the broader Great Lakes from Michigan to Massachusetts. In the eastern United States the first areas of establishments were western New York (2004), eastern Michigan (2005) and Long Island (2006). In the eastern United States T. oleracea is now known from six states, and T. paludosa from three.
The more restrictive range of T. paludosa matches its biology wherein gravid females are extremely poor fliers and moreover deposit the majority of their eggs the first day after emergence. Contrast this to the more dispersive T. oleracea whose gravid females are capable fliers and deposit their eggs over several days.
While the range of T. oleracea is shaped by points of original establishment and natural dispersal, the range of T. paludosa may be more set by introductions through the movement of infested soil media, such as sod. Based on their known native range in Europe, climate-matching models indicate that spread is inevitable across broad regions of the northern and central United States.
Crane fly larvae attack both aboveground and belowground portions of their hosts, which includes all species of managed turfgrasses, in all types of management habitats from home lawns to sports fields, golf courses and sod farms. Late-stage T. oleracea will encroach onto putting greens where they cause damage akin to black cutworms by chewing around the entry of their burrows. Late-stage T. paludosa can cause extreme thinning damage as they graze on foliage, and they may also cause damage akin to white grubs by pruning belowground portions of the plant. Outbreaks are favored under continually humid conditions given that eggs and early stage larvae are extremely susceptible to desiccation.
The European crane fly, an established lawn pest in the Pacific Northwest, is now spreading in the Northeast and Midwest, too.
Caterpillars, another of the six turf-damaging complexes, are the larvae of moths. They have a series of prolegs and well-developed head capsules with mandibles for chewing foliage. Caterpillars can be grouped into three classes based on general differences in behavior.
The cutworms chew through stems above the crown of turfgrass plants and consume the foliage. The black cutworm, Agrotis ipsilon, is among the most problematic species because of its affinity for bentgrass greens in golf course settings. Late-stage larvae will settle into holes on the playing surfaces and forage out at night to scalp half-dollar sized depressions around the entrance.
The webworms incorporate webbing into their burrows. There are a number of species that can infest low- to high-maintenance turf from home lawns to sports fields to golf courses. The armyworms are prone to move across the edible landscape shoulder to shoulder once local food runs out.
Chinch bugs comprise a third class of turf insect pests, although cool-season turf largely contends with only one species. The hairy chinch bug, Blissus leucopterus, is a small fast-moving insect favored by full sun, well-drained sandy soils and thick thatch. They can become a big pest in home lawns. Adults and nymphs ingest plant sap with piercing sucking mouthparts, which inevitably introduce enzymes into the plant that promote a tissue-killing chlorosis.
The white grubs are the quintessential pest complex, well-known and diverse. At least eight species can outbreak in turfgrass. The most problematic are four invasive species, the Asiatic garden beetle (Maladera castanea), European chafer (Amphimallon majale), Japanese beetle (Popillia japonica) and Oriental beetle (Anomala orientalis).
Four native species can sometimes erupt, namely the black turfgrass ataenius (Ataenius spretulus), Green June beetle (Cotinis nitida), May or June beetle (Phyllophaga spp) and Northern masked chafer (Cyclocephala borealis).
A crane fly egg and four larvel instars.
Images courtesy Dr. Daniel Peck.
The main form of damage caused by subterranean white grubs is pruning of the roots, which can lead to die-off of the foliage after disruption of water and nutrient flow.
The weevil complex consists of beetles that have long snouts tipped by chewing mandibles that the females use to drill into the stems of host plants for egg laying. Larvae begin life as stem borers, and then later move out to feed on the crowns.
The bluegrass billbug, Sphenophorus parvulus, is a main species of billbug that is favored in stands of Kentucky bluegrass in the high-mown form. Another high-profile species, the annual bluegrass weevil, Listronotus maculicollis, is favored in stands of short-mown annual bluegrass.
The annual bluegrass weevil is a native insect known to occur as part of the local fauna in at least 40 states and four Canadian provinces. First documented as a pest in Connecticut in 1931, outbreaks of the annual bluegrass weevil now challenge turf pros in 15 states throughout the greater U.S. Northeast. It is spreading west and south as it was reported as a pest in Delaware and Maryland in 2002, Virginia 2006, Ohio 2007 and North Carolina 2012. It is not known as a native insect south of North Carolina.
The likely reason for its spread probably involves pesticide or ecological release. However, to date, there is no clear explanation for its expanding impact. Nothing is known of annual bluegrass weevil in its native habitat before the introduction of Poa annua and its management as a golf course playing surface. Its westward trajectory across the cool-season zone is probably inevitable while its southward march might be limited by the conditions of warm-season turf
The annual bluegrass weevil is a specialist of short-mown annual bluegrass. This grass species, at a low height of cut, provides favorable conditions for population build up and outbreaks on susceptible surfaces. Early-stage larvae are stem borers where they live relatively insulated from the impacts of adverse weather, natural enemies and contact insecticides. Grown too large for their neonatal stems, late-stage larvae move out to the soil surface where they feed on the crowns.
The annual bluegrass weevil is an emerging threat to turf in the U.S. East.
Ants comprise yet another of the turf pest complexes. One of main culprits is Lasius neoniger, which is most common in the U.S. Northeast. Colonies of this ant throw up multiple entrances around the main nest, small volcano-shaped mounds. The main nest is usually situated in native soil adjacent to affected surfaces. Ants, which nest underground, vigorously tunnel as they scavenge for meals. The mounds they create are more of a problem for golf course maintenance than they are for home lawns or commercial properties.
Turfgrass professionals should keep these insect pests on their radar screens. All have the potential to rear their ugly heads on customers’ lawns or on sports fields or golf courses. Moving targets indeed, but knowing what they are and how they’re moving and adapting from location to location will gives the knowledgeable turf specialist good valuable information for managing them.
Daniel C. Peck is lead scientist at Grass Systems Entomology LLC, an independent consulting firm that helps clients get a grip on their turf-infesting, grass-feeding and soil-dwelling insect challenges. To learn more about their services, and more about new and emerging insect pests, visit http://www.grass-systems-entomology.com or email [email protected].