How do I get rid of lawn grubs?

Question

My lawn is progressively getting worse every year.

I've got large bare patches that just won't take seed, and in the spring and fall I've got racoons and skunks digging up grubs. There is also a large Norway Maple that isn't helping matters.

My plan is to completely redo the lawn in a couple of weeks by roto-tilling a truckload of soil in, and regrading. However, I figure that anything I do is useless if I don't get rid of the grubs first. What's the best way to do this?

Region: Toronto, Ontario (Etobicoke) Clay soil

Answer 1

There are a less and less ways to do this fast since the 2009 ban on using pesticides in Ontario. Your goal is get your lawn to grow roots faster than the three different species of grubs can eat them.

• nematodes can provide some control but are fussy to apply and should be reapplied yearly. Best recommended way to apply is:

  • applied with a hose end sprayer. Their effectiveness is not 100% but it is typically effective enough to strike enough of a balance that the grub population is reduced to the point your lawn suffers little to no damage.
  • the soil needs to be 15 degrees Celsius or else they will die.
  • they need lots of water to get into the ground.
  • they are killed by ultra-violet light from the Sun.

Stand out in the rain on a warm June day and water your lawn with Nematodes. Oh, and once you buy them you have to keep them in the fridge until you use them. This does not always thrill other people who have to use the fridge.

Longer term cultural controls are effective as well.

• try and have at least 6 inches of topsoil over the clay base. Top dress spring and fall every year with about one half inch of compost or top soil
• raise your summer mowing height to 6 to 8 cm (2.5 to 3 inches)
• Leave lawn clippings after mowing because their slow release of nitrogen favours the decomposition of thatch by microorganisms
• if possible do not let your lawn go dry and yellow during the hot summer months. The stress on the turf hinders regeneration of the root systems which the grubs are eating. Water thoroughly during dry times.
• aerate with spikes or a plug machine regularly (yearly or every other year)
• over seed with grass seed spring and late fall when you top dress. Choose varieties adapted to the light levels
• some grass seed is available with endophytic fungus that grubs find unappetizing and repels them
• consider sowing clover seed. This is not something you can undo so be sure you don't mind a less than perfect lawn. Grubs don't eat the clover and it will provide some nitrogen to the soil.
• my experience is that grubs prefer lawns that have been regularly fertilized with a high nitrogen fertilizer. This formulation offers a quick spring green up so the homeowner is happy right away at the expense of stressing growth of grass blades over root growth. By leaving the clippings on and top dressing you can use less fertilizer. Slow release fertilizers also assist in steady growth instead of the "pop" of a high nitrogen fertilizer.