Scientists Pursue Biological Control for Turfgrass Pests

No one will deny the pressures often placed on turfgrass managers to achieve perfection. Placing a dollar figure on the aesthetic quality of turfgrasses is difficult, and damage thresholds are usually low. As a result, many turfgrass managers rely on conventional pesticides. These pesticides, although effective, are often costly and require caution during application because of their chemical nature. By definition, pesticides are meant to kill the targeted pest. Unfortunately, some insecticides have the potential to cause deleterious effects to nontarget arthropods, wildlife or even humans.

Figure 1: B. bassiana spores and hyphae on a mole cricket setae (hair).

Recently, the public has become more vocal over the potential risks involved with pesticide use and called for change. In Canada, for example, numerous cities will soon decide if pesticides should be banned when applied solely for cosmetic purposes. Isolated communities in the United States have followed suit.

Those who support these bans feel chemicals should only be applied when human or animal health is at risk. Overall, societal concerns have increased because of greater awareness of pesticide use, combined with increased media coverage of the occasional problems.

Turfgrass managers are also plagued by the restricted use and loss of many of the older classes of chemicals. These products often provided broad-spectrum control quickly for little expense. The broad-spectrum nature of these chemicals posed problems for off-target organisms, and some of them contaminated groundwater sources. The newer products are typically more expensive (due to the long and rigorous research-and-development processes), may not have as long of a residual period and have a much narrower control spectrum.

Never before have turfgrass managers been asked to reduce or eliminate their pesticide choices more than now. As a result, all of the above factors support the need for research on biological control, which means using living organisms for pest management.

Quick Tip

A number of biological control agents are available for insect management in turfgrass, including bacteria, fungi, nematodes and others. Historically, many of these agents showed promise under controlled laboratory conditions, but have failed to deliver in the field.

At North Carolina State University, we feel our resources are well spent exploring the factors that contribute to the lack of success of biological control agents in turfgrass. By determining why some biological control agents have not been successful in the field, we hope the limitations can be overcome. One area of recent research has focused on the evaluation of an entomopathogenic fungus, Beauveria bassiana, for mole cricket control.

Mole crickets are extremely damaging pests of turfgrasses in the southeastern United States. There are two major species of concern, introduced from South America around the turn of the 20^th century (Walker and Nickle, 1981). Damage is caused when the crickets feed on the roots of turfgrass and produce surface tunnels. The root feeding can lead to total plant loss and eventual weed invasion. The production of surface tunnels and large megaphone-shaped calling chambers (in the spring) are unsightly, but also lead to desiccation and plant stress.

Most superintendents and sod farmers in the Southeast will agree that mole crickets are their No. 1 insect pest. We feel they make a great model insect for our studies because they are so large, mobile and damaging.

A number of studies conducted since 2001 explore the factors that may contribute to the disappointing results seen with entomopathogenic fungi in the field. Beauveria bassiana kills insects when the spores attach to the insect cuticle (Figure 1), penetrate into the body cavity and proliferate within the pest's body. Mortality results from toxemia from fungal metabolites or when the insect becomes depleted of nutrients (Jaronski and Goettel, 1997). Eventually, the fungus exits the cadaver and produces additional spores, capable of infecting other nearby crickets (Figure 2). Based on this mode of action, the spores need to come into contact with the pest for infection to occur.

Figure 2: Mole cricket sporulating with Beauveria bassiana.

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