Phyllopertha horticola, commonly known as the garden chafer, is a beetle belonging to the Scarabaeidae family. While natural components of many ecosystems, their presence can become problematic in gardens and lawns. The garden chafer is prevalent across various regions, including Europe, Asia, and parts of North America where it has been introduced. Understanding this common garden inhabitant is crucial for effective management.
Recognizing the Garden Chafer
Adult garden chafers are relatively small, typically measuring about 10 to 12 millimeters (approximately 0.4 to 0.5 inches) in length. They have characteristic reddish-brown wing cases, slightly hairy and outlined with dark edges. Their head and thorax display a metallic green to shiny black coloration. They also have distinct fan-like antennae.
Adult garden chafers are often observed flying low over lawns during May and June, particularly on warm, sunny mornings. Their smaller size and specific color patterns help differentiate them from other common beetles, such as the larger May bugs or Japanese beetles.
Understanding Its Life Cycle
The garden chafer completes its life cycle within approximately one year. Adult beetles emerge from the soil in late spring or early summer, typically May or June. Males engage in low-level swarming flights to locate and mate with females, who remain closer to the soil surface.
After mating, females burrow into the soil, often 5 centimeters deep, to lay eggs. A single female can lay between 15 and 25 eggs. Eggs hatch into larvae, known as grubs, within two to six weeks.
The grubs are white, C-shaped, and have brown heads with three pairs of legs, growing to about 15 to 18 millimeters long. These grubs feed on plant roots throughout the summer and autumn months. As temperatures drop in late autumn, the grubs move deeper into the soil for overwintering, though they may continue feeding during mild winters. In early spring, generally between March and April, the grubs pupate in the soil, transforming into adult beetles that emerge to restart the cycle.
How It Harms Your Garden
Most damage from garden chafers occurs during their larval, or grub, stage. These grubs primarily feed on the roots of grasses, leading to visible yellowing patches in lawns. Heavily infested turf may develop a spongy texture and can often be easily lifted or rolled back, revealing the grubs as the root system becomes compromised. Beyond turf, grubs can damage roots of vegetables like potatoes, strawberries, and lettuce, and ornamental plants.
Adult chafers feed on tree foliage (oak, hazelnut, birch) and plant flowers/fruits (roses, cherries), but this damage is less severe than grub feeding. Secondary issues arise from predators seeking grubs. Birds (crows, magpies, jays) and larger animals (badgers, foxes) dig up turf to access grubs, often causing more visible lawn disruption than the grubs’ feeding.
Strategies for Management
Managing garden chafer populations involves a combination of strategies to minimize their impact. Cultural controls focus on maintaining a healthy lawn, which can naturally deter infestations. Proper irrigation and keeping grass blades longer, around 7.5 centimeters (3 inches), can make the lawn less appealing for adult beetles to lay eggs. Regularly aerating and de-thatching the lawn also disrupts the grubs’ habitat, making it less conducive for their survival. Adequate fertilization and, if necessary, liming acidic soils, further contribute to overall lawn resilience.
Pheromone traps can also attract and capture adult beetles, reducing mating and egg-laying. Biological controls offer environmentally friendly solutions.
Entomopathogenic nematodes, specifically Heterorhabditis bacteriophora, are microscopic worms that infect and eliminate chafer grubs. These nematodes are applied to moist soil when temperatures are between 12 and 20 degrees Celsius (50-68 degrees Fahrenheit), typically from mid-July to early August or extending into October, when the young grubs are actively feeding. Another biological option is Bacillus thuringiensis galleriae (BtG), which also targets grubs. Natural predators like birds, badgers, and foxes also help reduce grub numbers. An integrated pest management approach, combining these cultural and biological methods, provides the most comprehensive and effective strategy for controlling garden chafer populations.