To safely control grubs in a vegetable garden, work the soil frequently and deeply to discourage the pest. If the infestation is moderate or severe, apply beneficial nematodes or beneficial bacteria to the soil. Remove adult beetles that are in the garden, and use an organic pesticide such as food-grade diatomaceous earth in the affected area if necessary.
Remove leaf litter in the autumn, and till the ground to a depth of 7 inches. After two weeks, till the ground to a depth of 2 inches to further reduce grub populations in the soil.
To remove adult beetles, prepare a bucket of soapy water, and shake heavily infested plants over the bucket so the beetles fall into the water, or pick the beetles off the plant manually. Place them in the soapy water after picking them off the plant.
When applying beneficial nematodes, water the soil to a depth of 1/4 inch before applying the nematodes. Choose Heterorhabditis or Steinernema nematodes to ensure the application effectively kills grubs. Allow beneficial bacteria two to four years to completely control the grub infestation, and avoid applying commercial insecticides to the soil after spreading the bacteria.
To use diatomaceous earth, place a thin ring of the powder around the base of each plant. Reapply the powder after heavy rains.