Pesticides to Kill Grub Worms

Preventative Pesticides

• Preventative pesticides are used prior to the beetle eggs hatching in the grass. Recommended chemicals include imidacloprid or halofenozide. Preventative chemicals have an extended residual activity in the soil and offer greater flexibility in terms of time of application. Apply the chemicals two to three months prior to the expected hatching time of eggs. Ingestion of even small doses of the pesticides is lethal for any hatching grubs. The University of Kentucky Extension suggests using the chemical between mid-June and mid-July.

Curative Pesticides

• Curative pesticides help to control grubs after their emergence and include products containing diazinon, carbaryl, bendiocarb or trichlorfon. Curative pesticides are most effective when timed precisely for very young grubs that are actively feeding. This is generally in August and early September. The rule of thumb is to apply the chemical four weeks after the adult beetles are seen as this is when the eggs also start to hatch. Curative pesticides have a shorter residual activity in soil as compared to the preventative products and often require repeat application.

Preparation

• Preparing insecticide application area prior to using the chemical helps to optimize effectiveness. Mow infested lawn to a short height and rake away the clippings. Dethatch grass if required as this will help the insecticide, especially the granules, penetrate to the grass roots properly. Using insecticide on thatched grass binds the product to the excessive organic matter on soil surface, reducing efficacy.

Pesticide Use Suggestions

• After applying any type of insecticide to grass, water immediately and deeply in order to leach the chemical into grass roots, the main site of infestation. Water also helps to attract pests to soil surface and maximizes their contact with the applied chemical. Do not allow the pesticide to dry on the grass blades as irrigating later will not wash it into the root zone. In case immediate irrigation is not possible, it is better to use granular formulas. Handle all pesticides and equipment rinsing on grass areas as this reduces chances of chemical runoff in other landscape areas.