Keeping on Our Toes
by Rita Perwich, Consulting Rosarian, San Diego Rose Society
You gotta love a rose garden for keeping us on our toes. Pest damage on our beautiful rose blooms rankles deeply. It affects us vividly and viscerally. It also spurs us on to find the culprits to put them to rest. There are several beetles and weevils that are rose pests. In San Diego there are three that can cause problems in our rose gardens. This is what you need to know.
Our first task is to look at the damage and follow it until we find the culprit.
ABOVE: Hoplia Beetle
Know the Enemy:
The Hoplia Beetle
In the early spring, chewed up petals and holes in our rose blooms lead us to suspect that either hoplia beetles or caterpillars are at work. If the blooms damaged are mostly our light colored roses, the whites, yellows and pinks there is a good chance that the pests we are dealing with are hoplia beetles. There is mercifully only a single generation of these beetles each year and these beetles are easy to spot because of the contrast of their dull brown-gray color against the light-colored roses. The hoplia beetle (Hoplia callipyge, family Scarabaeidae) measures about 1/4-inch long. The adult is brownish-gray with brown wing covers and a slightly iridescent silvery underbody. Female beetles lay glossy, white eggs in the soil. The whitish larvae are C-shaped and feed on decaying vegetation and plant roots but do not feed on roses’ roots. They develop slowly, remaining in the larval or pupal stage throughout the winter. In early spring the adult beetles emerge from the soil and fly to gardens where they feed on the blooms of roses and other flowers. They do not feed on leaves. When the hoplia beetles are not feasting on my roses, I find heaps of them taking a siesta within the deep comfortable funnel blooms of my calla lilies. In San Diego adults generally are active from late March to early May. After feeding for several weeks, adults fly back to their egg-laying sites.
The Fig Beetle (also known as Green Fruit Beetles)
In the summer, metallic iridescent green Fig beetles (Cotinis mutabilis, family Scarabaeidae) loudly announce their arrival with buzzing sounds. They zoom into our gardens to feast on the ripe fruits on our fruit trees and our roses. The adults are large easy-to-spot metallic green beetles that measure from 1 to 1 and 1/3-inches long. Their habitat is the southwestern United States and Mexico. Some people mistakenly think they are Japanese beetles or June beetles, pests that are found in the eastern United States. After mating, the females lay oval white eggs in the soil. The eggs hatch in a week. During spring, larvae mature and pupate in a cell of soil particles. The larval stage is the longest period of their life cycle. The adults are present from late June through to the early fall. They are active during the day and feed on soft-skinned ripe fruits such as peaches, apricots, plums, figs and apples. Their gourmet tastes also include rose petals. Removal of ripe and mushy damaged fruit from trees and from the ground can help prevent these pests from being attracted to your garden. There is mercifully only a single generation of these beetles each year. ABOVE: Fig beetles
The Fuller Rose Beetle
Pale brown adult Fuller rose beetles (Asynonychus godmani) are actually weevils. They are all females that reproduce and lay eggs without mating. Larvae chew and feed on roots, but generally this does not seriously damage roses’ roots. Adults emerge from pupae mostly during summer and fall. They hide during the day in organic litter on the ground and feed at night chewing blooms and leaving jagged edges along the margins of leaves. They are 1/2-inch long and flightless. If you spot this type of damage, look for this pest in the evening with a flashlight. Thankfully, these weevils have only one generation per year. More information on these pests and others can be found here. ABOVE: the Fuller Rose Beetle, photo credit Regents of the University of California.
ABOVE: Fig beetles love ripe fruit
Controlling These Pests
In the rose garden, insecticides are of little value against these pests and are not recommended. Hand picking is very effective for controlling the adults of all these pests. Here are some options for what to do next:
The Bucket Method: Add a few drops of detergent soap to a bucket half-filled with water. Drop the beetles into the bucket. Once in the soapy water bath, the beetles are captive. They cannot get out.
Crush or Clip: I have a lot of experience with hoplia and fig beetles. They are slow and focused on feeding so they are easily captured in your hand and can be crushed underfoot, or clipped in half with your pruners. But do remember these beetles can fly. I rarely see Fuller rose beetles in my garden so I can’t attest to how fast they are but our advantage is that they are flightless. ABOVE: Hoping it's not Hoplia sex.
Rose growers cannot be passive in their rose gardens. Stopping the desecration of our rose blooms takes action on our part but it is a battle we can win with handpicking and the disposal method of our choice. The birds and beneficials in our garden can be counted on to take care of the remaining pests we miss.
ABOVE: All photos by Rita Perwich unless otherwise stated.