Break the cycle

Photo © Brian Kunkel, University of Delaware

In recent years, the red-headed flea beetle has become an issue for nursery growers, especially those growing woody, flowering ornamentals like hydrangea, rose or loropetalum, which are all susceptible to the beetle.

The damage is two-fold: first, the pests feed on roots, stunting the growth of the plants. Second, the adult beetles feed on the leaves, causing aesthetic damage. When populations are small, they are selective about their plant hosts. But when populations grow larger, the beetles become more generalistic, feeding on many different types of plants. OHP senior manager of technical services Carlos Bográn says growers should follow this action plan.

“There is a three-step approach: identify the most susceptible crops to target, go after the larvae in the spring and do foliar sprays in the summer,” Bográn says.

The first step is to identify the most susceptible crops and varieties in your operation. Next, in spring, when there is a history of beetles damaging crops, treat plants with an insecticide targeting young larvae in the roots of the plant.

It is an extra expense for the grower to perform drench applications, depending on the equipment they have. However, Bográn believes that when there is a history of the pest and populations have been large in prior years, that growers need to address the larvae in the soil to minimize populations that will emerge from the containers to cause damage during the growing season.

Fortunately, there are several types of conventional and biological insecticides that have shown effective in fighting this pest.

“Some of the most effective conventional products that have been tested in the nursery against the larvae include neonicotinoids like Marathon,” Bográn says. “We have a formulation of Marathon G which is a granular formulation that makes it a little bit more practical to apply relative to drenching with a liquid.”

Marathon G can be either top-dressed, broadcast or incorporated in the soil media at planting.

For growers looking for alternatives, OHP offers Sarisa, a cyclaniliprole (MOA 28) formulation that targets larvae in the soil or adults on the foliage. Bográn recommends rotating Sarisa foliar sprays with Azatin O, a botanical insecticide with the active ingredient azadirachtin.

Depending on your geography, the red-headed flea beetle will have 2-4 generations per year.

“What you want to do is minimize the population of the first generation so that further generations don’t become large and outbreak and cause significant damage,” Bográn says.

Often the spring soil treatment won’t stop all of the beetle larvae, so foliar spray applications may be warranted to handle emerging adult beetles, especially with sensitive crops.

Growers can easily tell if they have a red-headed flea beetle infestation. The leaf injury is very prominent, which typically leads to further inspection. The adults often drop to the ground, which can make them harder to find.

“More knowledgeable growers can look at the roots of the plants and find the larvae there,” Bográn says.

When there are moderate populations, growers may see the larvae when they pull a plant out of its container. The challenging part is recognizing them, because they are relatively small and white, so they could be mistaken for the plant’s thicker roots.

If a grower detects an infestation of flea beetles in their operation, the next steps they should take depend on the size of the pest population. If it is low to moderate, foliar sprays on susceptible plants will prevent some of the damage, Bográn says, but if the population is large, even contact insecticides may be too late to handle all the adults. That’s why suppressing larvae in the spring is so crucial to break the cycle and prevent adult damage during the growing season.

For more: www.ohp.com