The Japanese beetle (Popillia japonica) is a highly destructive and invasive garden pest in North America that can cause significant damage across hundreds of different plant species. While they are known for their preference for certain ornamental plants, the answer to whether they consume tomato plants is a definitive yes. Tomato foliage is included in the broad diet of this beetle, though it is generally not their first choice. This insect’s presence signals a need for immediate attention to protect susceptible plants from defoliation.
Identifying Japanese Beetles and Specific Tomato Damage
Confirming the presence of the Japanese beetle requires recognizing the adult insect’s distinct physical characteristics. Adult beetles are roughly half an inch long, with a striking metallic green head and thorax. The wing covers, known as elytra, are a coppery brown or bronze color, creating a noticeable contrast. A series of small, white hair tufts line the sides of the abdomen, which is a key identifying feature of this species.
The damage they inflict on tomato plants is highly specific and easily recognizable. Japanese beetles are classified as “skeletonizers” because they systematically consume the soft leaf tissue between the veins. This feeding pattern leaves behind a delicate, lace-like network of leaf veins. Severely injured leaves often turn brown and may drop off, reducing the plant’s ability to photosynthesize.
Although the beetles will occasionally feed on soft fruit, they primarily target the foliage of the tomato plant. This focused defoliation can weaken the plant and reduce its yield, especially if the infestation is heavy. The presence of this distinct skeletonization pattern, coupled with sightings of the metallic-colored beetle, confirms the pest responsible.
Understanding the Beetle’s Feeding Preferences and Life Cycle
Japanese beetles are considered generalist feeders, capable of consuming over 300 plant varieties, but they exhibit clear preferences for certain species. Plants like roses, grapes, linden trees, and ornamental shrubs are typically much more attractive than nightshades like tomatoes. Attacks on tomato plants often serve as an indication of a particularly heavy infestation or a scarcity of their more preferred host plants.
The adult beetle’s destructive feeding period is relatively short, typically lasting about six to eight weeks, beginning in late June and peaking through July. During this time, they feed, mate, and lay eggs, which restarts their annual life cycle. Female beetles lay up to 60 eggs in the soil, usually in moist, sunny turf areas.
The larval stage, commonly known as white grubs, spends underground, primarily feeding on the roots of turfgrass. These C-shaped grubs are the overwintering stage, burrowing deeper into the soil as temperatures drop. Understanding this one-year life cycle is important because controlling the subterranean grub population can help reduce the number of emerging adult beetles the following summer.
Immediate Control and Long-Term Prevention Strategies
Managing a Japanese beetle infestation requires a two-pronged approach, targeting both the adult beetles causing immediate damage and the grubs in the soil. The least invasive and most effective immediate control method for adults is simple hand-picking. The beetles are often sluggish in the cool early morning hours, making them easy to collect by knocking them into a container of soapy water to drown. This method should be done daily to reduce the population.
Using commercial Japanese beetle traps is generally not recommended, as they employ powerful attractants that can draw significantly more beetles to your garden than they capture. For small or young tomato plants, physical barriers like floating row covers can be used to prevent adults from landing and feeding on the foliage. These barriers must be secured around the plant base and removed during the tomato blooming period to allow for pollination.
For a long-term strategy, managing the grub population in the lawn is a proactive measure that reduces the next generation of adults. Biological controls, such as beneficial nematodes (Heterorhabditis bacteriophora or Steinernema riobrave), are microscopic worms that attack and kill the grubs. Another option is milky spore disease, a naturally occurring bacterium that specifically targets Japanese beetle grubs, though it can take up to three years to establish a noticeable level of control.
If the infestation is severe, a targeted application of certain horticultural products may be necessary. Organic options like neem oil act as a feeding deterrent and can disrupt the beetle’s life cycle. Another effective organic insecticide contains spinosad, which can be sprayed on foliage. When using any insecticide, follow the product label directions and avoid application during peak bee activity, typically mid-day, to protect pollinators.