According to the Northeast Organic Farming Association (NOFA), “white grubs are the most important insect pests of lawns and turfs in our region.” At All Outdoors, we carry products used to both kill active grubs and prevent grubs from emerging. Dylox is used to kill active grubs. Merit is a systemic, preventative product. Grubs will die when they feed on plants that have been treated with Merit. However, it is only effective in preventing grubs and should not be used to kill grubs that are already active.
The following information regarding grubs comes from the “NOFA Organic Lawn and Turf Handbook” (NOFA OLC 2007), and is helpful in the identification and treatment of grub infestations.
“Damage Signs and Symptoms
White grubs damage turf by chewing off roots close to the soil surface. The voracious feeding of late second- and third-stage grubs, when combined with hot and dry condidtions, can result in quick and extensive loss of turf from late August through mid-October. In early spring, damage is less common; it usually occurs only under exceptionally warm and dry conditions. All cool-season and many warm-season grasses are susceptible to white grubs, but tolerance to damage varies. Being alert to the symptoms of white grub infestations helps avoid extensive damage. First signs of infestation include gradual thinning, yellowing, and wilting in spite of adequate soil moisture, and the appearance of scattered, irregular dead patches. The patches can grow together until large turf areas are affected. Infested turf feels spongy underfoot due to the larval tuneling and can be pulled up like a carpet, exposing the C-shaped larvae. Secondary, often more severe damage can be caused by vertebrate predators (e.g., crows, skunks, raccoons, moles) that tear up or tunnel under the turf to feed on the grubs, sometimes even at grub densities that don’t cause turf damage on their own.
Seasonal History and Habits
Adult beetles emerge between June and August. Adults either don’t feed, feed very little, or feed extensively on many different plants and fruit. After mating, the females return to the soil to lay eggs individually or in small batches over a period of two to four weeks, typically at a depth of one to four inches. The egg stage, first larval stage, and second larval stage each last about two to three weeks.
[…] When the soil is warm and moist, grubs may be found feeding throughout the root-zone. The majority are no more than one or two inches below the thatch. As the soil cools in October, the grubs move to deeper soil layers, where they overwinter in an inactive state. However, European chafer grubs continue feeding later into the fall and resume feeding earlier in spring than other species. As the soil warms in spring, the grubs return to the root zone to feed for another four to six weeks in April and May before pupating in the soil at a depth of two to eight inches. After one to two weeks, the new beetles emerge to restart the life cycle” (56).
Most common grub species:
Asiatic Garden Beetle (Maladera castanea)
European Chafer (Rhizotrogus majalis)
Oriental Beetle (Anomola orientalis)
Japanese Beetle (Popillia japonica)