what's chomping off the heads of my plant starts?
This happened last year too, especially to all the sunflowers I tried to grow (tried 3-4 times, kept finding the tops lopped off when they were about 2 inches tall). THis year it's also happening to my little arugula starts. See photo. Another question - how can I get rid of this little green caterpillar that's devouring my azalea leaves. See photo - the caterpillar is at the edge of one of the leaves.
Multnomah County Oregon
The sunflower looks more like damping off https://pnwhandbooks.org/plantdisease/pathogen-articles/common/fungi/damping-vegetable-seedlings
Which is caused by a fungus within the soil. We are still having cool wet weather which is perfect for the fungus to take hold. I'm a little surprised about the arugula because it is a cool-weather plant as opposed to the sunflowers. you might be able to mitigate this by using a thin layer of seed starting mix (not more than an inch) over the native soil where you want to plant.
For the azalea it looks like https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/azalea-rhododendron-azal... (there are additional links for controls in the link)