[From the May 2015 issue of the UC IPM Green Bulletin]
For landscape professionals: Turf areas, such as residential lawns, commercial landscape features, municipal rights-of-way, sports fields, and golf courses, can be challenging to manage since they often require substantial inputs and may be expected to always look clean, green, and uniform by clients. Insect pests, though actually quite rare in well-managed turf, can sometimes jeopardize a flawless appearance (Figure 1), leading to further inputs in the form of pesticide applications. With proper monitoring, however, pest infestations can be detected when pest populations are still small and can be dealt with using cultural tactics and other nonchemical methods. Initially, some important preventive measures can be taken to ensure that the turf areas you manage never become infested in the first place.
Figure 1. Patch of turfgrass killed by billbugs.
Pest management for turf areas begins during the design and installation of the site, with species selection, grading and drainage, irrigation systems, and the maintenance plan. Choosing the appropriate turf species for the site by considering regional climate and water availability is the single best way to reduce overall stress and to ensure longevity and resiliency of the grasses planted. The University of California's Division of Agriculture and Natural Resources (UC ANR) has published some excellent online resources to help choose appropriate turf species based on tolerance to key stressors such as temperature, salinity, drought, and foot traffic.
Once established, turf needs to be properly managed for health, considering aspects such as mowing height, appropriate watering and drainage, and periodic thatch removal. Thatch removal can be especially important since many pests take shelter in thatch and because monitoring is more difficult when thatch has built up.
Next, realize that an integrated approach to pest management will require regular monitoring and some knowledge of the key turf pests in the region. In most of California, the major insect pests of turf fall into one of several categories: beetle larvae (grubs) feeding on roots, caterpillars feeding on grass leaf blades, true bugs with piercing-sucking mouthparts feeding on leaf blades, and nuisance pests disturbing the soil. Blade-feeding pests may be active at odd hours and are usually hidden within the thatch layer, so it is necessary to bring them to the surface to confirm their presence and to monitor population changes. One way to do this is by using the ‘drench test', where a soap and water solution is applied to saturate the thatch and soil in an area suspected to be infested (Figure 2). This test works well for caterpillars such as cutworms, armyworms, webworms and the larvae of fiery skippers and lawn moths. It also will work for highly mobile piercing-
Figure 2. Performing a drench test.
sucking pests such as leafhoppers and chinch bugs. Unfortunately, this simple monitoring procedure will not work with pests that live deeper in the soil profile feeding on roots. For these pests, including the potentially damaging white grubs (C-shaped larvae of scarab beetles), billbug larvae, and crane fly larvae, it will be necessary to undercut a section of turf in order to inspect the root zone (Figure 3). Utilizing these monitoring practices in problem areas or in high value landscapes before damage occurs can help reduce management costs later in the season. The spring months, when grass is growing rapidly and when moisture is more available, are ideal for weekly or bi-weekly monitoring (Table 1).
Figure 3 Pull back turf to inspect root zone.
Often times, damage due to insect pests in turf only becomes apparent during late summer and fall, when low soil moisture and heat stress take a visible toll on areas with damaged roots or tattered blades. Unfortunately, it is difficult or even impossible to mitigate the damage at this point since pests may already be gone or dormant and because grasses are no longer vigorously growing. For example, the larvae of masked chafers (the most common and most damaging of the ‘white grub' species, having only one
generation per year in California, Figure 4) have largely stopped eating roots and stopped growing in size in autumn (the season when they and the damage they cause are most observable). The most effective treatments for this pest should be made in June or July, when grubs are small and damage has not yet appeared. Without a spring monitoring program, landscape managers in areas where masked chafers are common can easily find themselves in an autumn situation where turf has been irreparably damaged and where few management options remain.
Figure 4 Masked chafer larvae (white grubs).
Learn more about prevention, monitoring, and treatment of turf pests by accessing UC IPM's newly revised Lawn Insects Pest Note.