In my yard was a patch of strawberries. About half were the June-bearing Hood variety, and the rest were Tristar day-neutrals. Two years ago, I was given more day-neutrals, of an unknown variety.
Last spring, several of the berries had soft spots as they ripened. When the berries were cut open, there was a tiny worm inside.
Because it was unlike any I had seen before, I quickly took some of the affected berries to the Master Gardener Plant Clinic. There, with the help of Rick Hilton, OSU research entomologist, the culprit was identified as the larva of the spotted wing drosophila, or SWD.
This insect, drosophila suzukii, is an invasive fruit pest that has appeared in our area rather recently. Although known in its native Japan since 1916, as well as in many other Asian countries, it was not observed on the mainland of the U.S. until 2008, in California. Since that time, it has become widespread in the Western states, including Oregon. It has done tremendous damage to fruit crops, as it attacks cherries, and sometimes grapes, as well as all kinds of berries.
The SWD resembles the vinegar, or fruit fly, but prefers to eat ripe fruit right on the vine or tree, unlike fruit flies, which eat already-decaying matter. The female SWD lays its eggs inside the almost-ripe fruit, where they hatch, forming small larvae. This process leaves a soft area in the fruit, rendering it inedible — unless you like extra protein with your fruit. Only the male has a dark spot on its wings.
A single female can lay several hundred eggs in her lifetime, which is three or four weeks. The larva, or worm stage, then pupates into adulthood inside the fruit, and in about 10 days, the new adult SWD adult emerges, mates and begins the process all over again. It is estimated that in a single season, three to seven generations may be produced in Oregon's climate.
These rascals can overwinter in soil, leaf litter and in unpicked, end-of-the-season berries. Dryness, or hot or freezing weather, may help limit this. Spraying with spinosad has provided some control.
As if an invasion by these pests wasn't enough, earlier this spring I noticed several strawberry leaves looking like they were folded in half. Upon close inspection, it became obvious that there was webbing and a larva or caterpillar inside that folded leaf. Again, something new to me, so back to the Plant Clinic!
This time, the culprit was identified as a strawberry leafroller. These pale-green or gray-brown caterpillars have dark heads and are only about a half-inch long, and the adult, brown or buff-colored moths are about the same size.
While leafrollers, in small numbers, may not do a lot of damage to the family strawberry patch, in larger numbers they can affect the growth and health of the plants, especially the formation of runners.
If you see small numbers of rolled strawberry leaves bound with silk webbing, you many be able to control them by simply picking off the affected leaves and putting them in the garbage (not the compost pile). However, if they get a head start, as mine did, there is not much you can do to control them, as they are protected inside their little rolled leaf shelter. Bt and spinosad are both effective if you catch the young larvae soon enough, before they roll up in the leaves, pupate and wait to become adult moths.
I learned that I must keep all leaf and mulch litter out of the bed, as that's where they hide. I did not think that my strawberry bed was a littered mess, but I began to wonder about some mulch I'd purchased in bulk, as well as about those "new" plants that had been given to me, as possible sources of the infestation.
So what's the end of this sad tale? The strawberry bed got ripped out and sent away with the rest of the garbage. I did not want to be a neighborhood incubator for these pests. I will let the ground lie fallow for the rest of the year, with every scrap of strawberry litter gone so there will be no place for them to spend the winter.
Next year, I'll start over again. And this time, I'll use straw between the rows, not mulch. Wish me luck.
Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. Email her at firstname.lastname@example.org.