Spikes of Deat h:
Cover Story
Can Turfgrass Cultivation Effectively Control White Grubs? By Ben McGraw, Ph.D. and Kevin Trotta
W
hite grubs, or scarab beetle larvae, may be the one common pest that plague all turfgrass systems around the globe. Larvae feed directly on roots, which impedes water and nutrient uptake. If left unchecked, grub feeding may cause a separation of root tissue from aboveground plant material (Figure 1). This is particularly problematic on athletic fields where large populations of actively feeding grubs can create footing and other safety issues. Additionally, the mere presence of the larvae can attract predators (e.g. skunks and raccoons), which in turn may cause even more severe damage. To avoid these issues, many turfgrass managers choose to control white grubs with preventive (prior to egg laying) or curative insecticides. However, over the last decade many municipalities, several states and Canadian provinces have limited, if not banned the use of synthetic insecticides for “cosmetic” purposes on public or school grounds. Given the increasing public demand for less-toxic alternatives to chemical controls and the tighter governmental scrutiny placed on pesticides used in turf, the Turfgrass Entomology Laboratory at Penn State has conducted studies over the last decade to determine whether turfgrass cultivation is a viable alternative to controlling white grubs with insecticides. Grubs are present near the soil for much of the year and likely to be affected by cultivation
8 Pennsylvania Turfgrass • Spring 2019
practices. Here we report findings from multiple field and simulation studies aimed at determining the expected levels of control provided by cultivation.
Equipment evaluation:
Preliminary field trials were initiated to determine which cultivation equipment/practices were most effective in controlling white grubs. Treatments consisted of plots cultivated with a hollow-tine aerifier (Toro ProCore® 648; 0.5" tine, 2" forward spacing; Figure 2a), a solid-tine, vibratory cultivator (First Products UA-60 Aera-vator®; Figure 2b), and a below-ground injection system (Cambridge® Liquid/Air Injection
Figure
1
System; Figure 2c). Plots were roughmown (> 1.5 inches) Kentucky bluegrass/perennial ryegrass/fine fescue mixes and arranged in a randomized complete block design. Hollow- and solid, vibratory-tine treatments were applied as either one or two passes over the replicate plot. In treatments with two passes, the second pass was conducted perpendicular to the first pass, immediately following the initial application. Cambridge injection treatments consisted of six injections per plot of either pressurized air (125– 150 PSI) or air plus a solid material (Turface®). Each treatment was replicated eight times. Grub control was
White grub larvae feeding near the soil surface
