· Brent Wilson's Answer
· Hi Victoria - I'm pretty sure the holes in your petunia flowers are being caused by bugs. It could be any number of bugs eating on them..though it's probably one of the bugs that feed at night. My first thought when seeing the picture is that it looks like damage from earwigs. These are those skinny, slithering, crawling insects that have horseshoe-shape pointed pinchers on their backend. Second thought was slugs. Both of these feed at night. If you go out just after dark and examine your plants you might see what bug it is. Slugs will be on the back of the foliage until it really gets dark outside. If you shake the plant you might see earwigs fall out. The earwigs look scary but are not harmful to humans.
The methods of control for slugs and earwigs is different.
Control slugs by using a Slug & Snail Bait or with jar lids filled with beer that are placed near plants being damaged.
First start with prevention. Adult earwigs overwinter in your soil and emerge in spring when the female lays eggs just beneath the soil surface. When planting in pots make sure to replace potting soil/mix between seasons. In beds, till the soil well to disturb the baby-making process.
Earwigs are attracted to lights so you should reduce lighting around doors, windows, and other entry points. Sodium vapor yellow lights are less attractive to insects. Earwigs need moisture. Try to reduce moist conditions around your water spigots, air-conditioning units, and along the foundation of your home. Keep your lawn and garden free of debris and rotting organic matter. Rake up your grass clippings, leaves, weeds and old wood.
As with slugs, earwigs like beer and will drink themselves to death if given the opportunity. Place a number of small jars on their side with beer in them. The earwigs will crawl right in and die.
I've read that setting out empty tuna cans filled with about a 1/2 inch or inch of cooking oil helps to significantly reduce their numbers. Don't wash the cans out prior to filling them with cooking oil as the smell of the tuna oil is what draws the earwigs in. Place the cans around plants that you know have been attacked or are at risk for attack. The earwigs will crawl in and drown in the oil.
Regarding chemical control, Sevin dust works quite well as a barrier and contact killer as does Malathion if sprayed on and around the plants at dusk. Products containing Acephate, Bifenthrin, Permethrin and Pyrethrin are also listed for use to control earwigs. Always check the label to make sure a chemical can used on the plant you want to spray and be careful to follow the instructions on product label for mixing and application.
My guess is that it is earwigs. If so, maybe try the non-chemical methods of control first and then move to chemical control if necessary. Whatever it is, hope you get them under control.