I just got done with a my Growing Cool Season Crops class today and someone asked about those white grubs in the soil when they were turning it over. So I dug out this post I wrote in 2012 about what are those white grubs in the soil. I told the class I would put pictures up of the grubs and cutworms so you can know how to ID each of them. One is harmless and the other can be a real problem. Read on.
This time of year when you are adding amendments and turning your soil, you may notice some white fat grubs with brown heads. I noticed they were in soil that I heavily amended with horse manure and would freak out when I saw them. I took all of them (sometimes a lot) and give them to the chickens. I use to think were cutworms but they are not.
They are Scarab beetle larvae and will NOT harm your vegetable plants or vegetable roots. They are also known as the ‘dung beetle’ larvae. In fact they are beneficial because they help break down the manure by eating it, hence you will find them where you use manure. Just leave them alone as they are kind of like worms, adding nutrients to the soil as they process the manure. I have never seen any damage to vegetables but if they are in your lawn (what lawn?! LOL) they will eat grass-roots (but not vegetable roots).
On the other hand, here is a picture of cutworms which are HARMFUL to your plants. They come out of the ground at night and chew the base of your transplant stem off leaving you with a decapitated plant (so to speak). They attack baby plant stems because they are tender. After the plants get older, they don’t bother them. If you see these, get rid of them. I look for them in the soil around the hole I dig just before I put my transplants in the ground. But there is something else you can do to protect your plants.
You can protect your plant by putting a ‘cutworm collar’ around your newly planted transplants. I use a paper towel roll or toilet paper row cut into 2 inch increments. I cut the tube lengthwise to get them around the plant stem and tape the cut seam.
Then I sink the tube about 1 inch into the soil. They won’t crawl up the tube. After your plants get a little older, take the tube off-they only like young stems. In this picture the collar is filled with dirt but I just leave the collar on without filling it with dirt.