Organic pest management: Earwigs
Earwigs, Dermaptera, are perhaps more well-known for their freakiness than for their capacity to be destructive in the garden- but trust me, they are both. These lovers of water in the desert are common in dry climates where water is present- i.e. irrigated gardens and farms. In fact, they look like miniature aquatic crawdads. They are nocturnal so you may not even know you have them until you go out with your headlamp and see them feeding on tender corn silks, the leaves of young fruit trees, or zinnia leaves and petals. Luckily the tell-tale signs of earwig damage are easy enough to spot in the daytime.
Signs and symptoms:
Earwigs are omnivores that eat insects in addition to their favorite plant parts. Though their plant preferences seem widespread, they are luckily pretty predictable and specific feeders once you get skilled at identifying their typical, lacey leaf damage. I have seen them most commonly feed on corn silks, zinnia leaves and petals, petals of other flowers such as daisy and cosmos, tender leaves of young fruit trees, young hollyhock leaves, celery stems, and boc choi.
Feeding trails look lacy like this:
There may also be a great deal of dark brown frass (poo) where earwigs have been feeding. If you have any doubts about the damage you are seeing, head outside at night with a headlamp. You will find them feeding at night in creepy crawling clusters of sometimes dozens of earwigs.
Earwigs mate in the fall, and male and female overwinter together in leaf piles or similar environments. The main damage phase of earwigs in the adult phase. You will start to see active feeding adults in the heat of midsummer, around June or July, and they will continue until cooler fall weather. Watch for them and start reducing their population before their a problem though with these simple steps.
Coping with earwigs organically:
First, decide what amount of damage is acceptable: For some of the plants that earwigs like to feed on the damage is negligible and I choose to do nothing about it. For other plants, including corn, young fruit trees, boc choi, and celery, damage is best controlled with preemptive attempts to reduce the population before it gets out of control.
Limit organic debris: Leaf piles and the like are perfect hiding places for earwigs during the winter and during the daytime. They love cool, dark, and moist places. Limiting the amount of this type of undecomposed organic matter in the garden, especially around new seedlings, is one excellent way to prevent earwig damage.
Attracting and trapping: Because earwigs are omnivores and are attracted to meat as well as plants, we have developed a homemade meat-based trap that traps earwigs in the hundreds. We start with a cat food can (dog food, tuna, or other canned meat will do just as well) that has most of the contents removed but the residual smell and a small amount of meat on the edges remains. To that we add water and just a dash of vegetable oil (to beak up the surface tension on the water) and place it near where earwigs are a problem. Better yet, strike preemptively and place it where they are expected to be a problem, that way you can start to get the population in check before explosion. Slightly bury the trap so it is near soil level. Check the trap the following morning, if you have earwigs there will be some (if not hundreds) that have drowned in there.
This trap is really simple and effective, but it will only help quell the damage if put out early and changed often. You might have to change the trap every day as it fills up with earwigs and becomes less and less attractive to live ones.
Sticky traps: When we first planted our young orchard, we were dismayed to see earwigs aggressively attacking the young leaves. Left without treatment, this could easily kill and definitely stunt a young fruit tree. One effective way to reduce this sort of damage is a sticky trap around the trunk of the tree. This is easily done using the backside of duct tape wrapped in one round around the small tree trunk. Earwigs have to climb the trunk to get to the leaves, so climbing onto the trap gets their feet stuck, where they die.
These traps need to be changed every couple weeks or they lose their stickiness and/or fill up with earwigs. Be absolutely sure to remove the tape a the end of the season, as it will restrict the expansion of the trunk, ultimately becoming embedded in the expanding layers of bark. This kind of foreign object inclusion can damage the vascular and support structure of the trunk, often fatally.
Spinosad certified organic pesticide spray:
Spinosad is a short-lived systemic spray that causes a plant feeding insect to die. Applied at nightfall, the short-lived nature of this spray makes it so that daytime feeding insects and pollinators are unharmed. This also means it needs to be reapplied nightly when used as a control method.
I use Spinosad when attempting to control earwigs on corn silks. Earwigs eat the tender, newly pollinated corn silks, damaging the pollen or pollen tube as it is growing. The result is under-pollinated corn cobs filled with holes where kernels should be. Because the time period where a corn plant is "silking" is finite, there are only a handful of days I need to spray. Watch the small corn ears closely so you can catch the time when they will begin silking. Sprayed on the corn silk, earwigs will die upon ingestion.
Spinosad is approved for use in certified organic systems. As always, read and follow the directions thoroughly.
Read more about earwigs and cornsilks here.