Grub Control for Ohio Turfgrass – April and May are Generally Too Soon

April 22, 2009 at 7:30 am

In the April 16 BYGL Newsletter there was a brief mention of indirect grub damage occurring this time of year. I use the word ‘indirect’ because the grubs themselves are not doing the damage. Grubs have moved back up close to the surface to do superficial feeding. The feeding from grubs, this time of year, does not do much (if any) damage so long as there is ample moisture in the spring. However, damage is coming from animals looking for an easy food source. From the recent BYGL newsletter:

Both raccoons and skunks have excellent memories and will return to areas that had a good crop of grubs in prior years . . . the process of the animals tearing and rolling the turfgrass can kill portions of it. To prevent damage from the varmints, spread Milorganite or a similar fine graded composted sewage sludge on areas that had grubs last fall.

So, what about controlling the grubs? In the April 17 edition of Purdue’s Turf Tips Timothy Gibb wrote a straightforward article on the best timing for grub control applications. In almost every outdoor retail store and garden center you will see grub control products prominently displayed this time of year.  Applying grub control products in April or May is too early for effective control with today’s current technology.  Gibb provides four reasons why you should not make grub control applications in April/May:

  1. The goal of white grub insecticides is to prevent turf damage, not eradicate grubs. Grub damage in the spring is very minimal and only seen in the driest of years. Since there is a limited chance of significant grub damage, why apply?
  2. Grubs found in the turfgrass right now are the stage that passed the winter. These feed very little and are extremely difficult to kill. Insecticides applied now will not be very effective.
  3. Even if you could control grubs now, it will have no effect on the population of grubs come next August when the really damaging generation hatches.
  4. Insecticides applied now will biodegrade over time and may not remain in the soil at high enough concentrations to be effective in August when we really need them. (Certainly, they will be more effective if applied closer to the egg hatch date in early August).

White grub populations should be assessed beginning in early-August.  Populations of annual grub species that are less than six grubs per square foot can usually be masked by water and fertilizers, unless it is a dry year then treatment may be warranted. Populations between 10 and 15 per square foot can cause significant turf damage and treatment should be applied. If your lawn has had a perennial problem with grubs, then a treatment may be warranted. White grub control insecticide treatments are best applied July through mid-August.

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