Scarab beetles lay eggs within the garden which hatch into grubs. The grubs go through three pupate stages of growth with the third stage being the most damaging to gardens. Grubs can cause large dirt mounds within the garden and consume the roots of turf grass. The adults of certain grub species cause damage by feeding on tree, shrub or plant leaves. Timing control properly can limit the grubs' damage to the landscape.
Grubs cause turf lawns to thin out and yellow. Brown patches begin to occur as the grass root system suffers if control is not gained. over the grubs The death of the root system makes the grass unable to absorb needed nutrients or water, according to the University of Florida. Grubs of the Japanese beetle enjoy feeding on plant roots, vegetable gardens and other plant life. They gradually cause the decline of the overall plant's health.
All gardens and lawns suffer a limited number of grubs and can tolerate the infestation. These areas do not warrant control measures. Dig up a patch of soil that is 6 inches around by 3 inches deep and count the grubs to determine the extent of infestation and decide if control is warranted. If more than three grubs are found on the patch, the gardener should begin control measures, according to the University of Rhode Island. Continue to dig up patches of the garden to pinpoint the exact locations of the heaviest infestation prior to beginning grub control treatment.
The highest concentration of grubs occurs in August because most beetles begin to breed and lay their eggs in July. The grubs of Japanese beetles, Asiatic beetles, Oriental beetles and European beetles are all common species in a garden. Identify the type so proper control measures can be successfully undertaken. Many county extension offices or garden nurseries will help gardeners identify problem insects.
Spring grub control normally proves unsuccessful because the insects have pupated and are rarely effected by insecticides. Treating areas with imidacloprid and halofenozide in late June or early July proves successful at killing the eggs of the beetles which produce the grubs. Fall treatments using carbaryl or trichlorfon can help prevent the insects from overwintering and causing spring damage. When treating for grubs, water all the insecticides into the soil thoroughly to be effective.
Milky spore bacteria can be safely used to kill grubs naturally. One treatment can last up to 30 years, according to the University of Illinois Extension. The grubs that come into contact with the bacteria develop the disease and die, but beneficial infects are immune. The milky spore bacteria can be spread over lawns and gardens in the form of a dust or light powder. As the infected grubs die they disperse the bacteria back into the soil through decomposition which can again infect other grubs, according to the University of Illinois.