White Grub Control in Lawns
Dead spots in an otherwise healthy lawn may be a sign of root damage caused by white grub feeding. In late summer or fall, homeowners with large infestations of grubs, may find small patches of turf torn out or flipped over from skunks or raccoons foraging for the grubs at night.
Grub Life Cycle
The annual white grub is the most common grub pest in Kansas and is the larval stage of the Masked Chafer beetle which completes its life cycle in a single year. There are six different chafer beetle species known to be found in Kansas and all have similar life cycles.
Masked chafer beetles begin emerging from the soil in mid-June. After mating, the female burrows back into the ground and deposits eggs. Small, first-instar grubs emerge in two to three weeks. Larvae begin to develop during mid-summer and mature by mid- to late-September. Cooler weather and soil temperatures drive the larvae deeper in to the soil, where they remain dormant until spring.
As warmer temperatures return the following spring the larvae move back up to grass root zones. Most grubs will have reached full size the previous fall and will not feed much in the spring. They pupate in late May and within two weeks beetles emerge to repeat the cycle.
Root feeding by the first- and second-instar grubs may not cause serious problems until September or October when the larger, heavier feeding third-instar grubs consume large amounts of grass roots. Damage may be more severe when turf is dry or insufficiently fertilized, or in lawns where grass must compete with weeds.
May beetle (June bug) larvae can do similar damage in lawns. The June bug has a three-year cycle with the heaviest grub feeding occurring on grass roots the second year of the cycle from May to September.
Grub Control Timing and Products
Annual white grubs in turf can be managed by either using preventative or rescue treatments. If perfect turf is the goal than a preventative treatment should be applied as part of a regular maintenance program.
Summer Recue Treatment
Applying systemic insecticide to an entire site may be an unnecessary expense when pest populations are low. It may be more cost effective to apply short-acting contact insecticides when grubs are most susceptible, ideally when 90 percent are in the first and second developmental stages. This occurs 30 to 40 days after peak flight of the masked chafer beetles. However, cycles may vary somewhat from one location to another.
Since peak beetle flights are generally between July 1 and 10 in Kansas, the ideal treatment time is typically August 10 to August 20. For this treatment products containing carbaryl or trichlorfon (Dylox) are recommended.
Spring Preventative Treatment
For more lasting effects and greater flexibility in timing, consider products containing the systemic active ingredients imidacloprid, chlorantraniliprole, clothianidin, thiamethoxam, or halofenozide. Although labeled for late April through August applications, to ensure adequate protection systemic insecticides should be applied during mating and egg-laying, typically from mid-June and late July.
Watering before and after treatment improves product performance. Watering beforehand encourages grubs to move up in the soil, bringing them closer to insecticides. Irrigating immediately after treatment removes insecticide residue off the grass and moves the insecticide down into the root zone where the grubs are located.
Each product will have specific instructions on it’s label to provide the best control.
