Scarab beetle grubs in a raised bed are typically not numerous enough to cause significant plant root loss. As a comparison, in lawns, nearly a dozen grubs can be present per square foot of soil before noticeable plant damage occurs. If grubs are numerous in this bed, the simplest approach is to exclude the adult beetles this summer so they can't lay their eggs in the bed's soil. You can use either landscape fabric around crops to cover the bare soil, or use floating row cover over the entire bed. Any grubs found in the meantime can simply be tossed elsewhere for birds or other animals to eat; they won't be able to return to the bed. The row cover offers the bonus of excluding many other insect pests of crops, but could interfere with pollination of some blooms (depending on what crops you're growing), so may not be feasible to use all season long. The adult Japanese Beetles, if those are the types of grubs present, won't be flying and ready to lay eggs until midsummer.

A pesticide drench is not warranted in this situation, plus some products may be not be registered for use around edible plants or for use with this particular pest. At a minimum, they may simply may not work well. Neem as a soil drench is not one of the methods we recommend when controlling beetle larvae. Additionally, the ingredient azadirachtin in some neem-based products is a broad-spectrum pesticide (as is neem oil itself), meaning it can also impact beneficial insects that come into contact with the application. There are many beneficial insects which reside in the soil, for example. Azadirachtin's persistence in soil is relatively short (perhaps a few weeks) before it biodegrades, so grubs not within reach of the chemical seeping into the soil may not be impacted. Azadirachtin also has an inconsistent efficacy to begin with, since neem tree processing techniques can impact the potency of the finished product.

If you are finding only a handful of grubs in the garden boxes and the plants were struggling, there may have been other causes of their condition. Feel free to send us photos of ailing plants if it happens again and we'll try to diagnose the issue.

Miri