I have experience in controlling mealybugs on the shoot system, but not as much on the roots of plants! I was able to find some helpful information though, which I will summarize below:
- Apparently the mealybug destroyer (Cryptolaemus montrouzieri) will go to the root-shoot interface and still prey on root mealybugs! These are small, gray beetles that feed on mealybugs at all life stages (larval and adult). Be careful not to kill the larvae, they look a lot like mealybugs, but are gray (not white).
- Before transplanting, inspect roots thoroughly for eggs (little white specks) as they can easily come from your greenhouse.
- Before planting you can increase the temperature around the root ball of the plants between 110-120 degrees F for about 10 minutes to kill root mealybugs. This has been shown to even kill eggs!
- Plant on time! Dense root balls encourage feeding by root mealybugs
- Sterilize all pots and garden tools with hot water and soap after working in infected soils
- neem soil drench (there are different reports of rates to use and amounts of plant material depending on if you use leaves or seeds). OISAT has several different formulations you could try. I’ve had success with their leaf extract. Does anyone else have experience using a specific neem pesticide formula?
- Mixing diatomaceous earth into the soil when prepping a bed or potting mix
- Insecticidal soap soil drench. I’m the most skeptical about this one - I’m sure the soap will kill a lot of beneficials in your soil as well. Has anyone else in the community tried this?
There are lots! I don’t know what you may have available, but the synthetic pesticides that are labeled for mealybugs are almost all effective against root mealybugs as well. I looked up 4 and they all were able to be used for either pest. Your local agrodealer or agricultural store hopefully has information and a label for pesticides that are available in your region.