May 2, 2000
Get A Grip on Grub Control             

             As usual this spring, there’s a lot of interest in how to kill those nasty grubs that have had a hand (along with last year’s drought) in wiping out lawns.  And, as usual, I have to tell folks that, if they had treated their lawn when the grubs were hatching last August and September, they could have saved their lawn from all this damage.  There’s so much confusion about grub control that garden centers will sell a much larger percentage of grub control in the spring than in fall when, logically, it should be the other way around.  I’m sure that much of this has to do with the fact that the damage that the grubs do in late summer and fall isn’t visible until the following spring.  So the purpose of this column is to help you GET WITH THE PROGRAM. 

                The first step is to understand the life cycle of the Japanese Beetle.  Let’s start at the beginning.  The female Japanese Beetle, after feasting on you beans and rose bushes all summer then lays her eggs into warm sunny areas of healthy grass.  The healthiest grass around is probably the sunny areas of your beautiful lawn that you’ve worked on all summer.  She won’t lay her egg in the shade since soil temperatures are too low to keep the eggs alive.  Each female is capable of laying a couple of hundred eggs.  These eggs will all hatch within four days after they they’re laid.  Are you listening?  There are no grubs hatching in the spring.  None.  They ALL hatch in late August or September.

                After the grubs emerge from their eggs in late summer, they must eat and what they eat are the roots of your lawn.  They eat and eat and eat and eat until they are the size that you are familiar seeing them when you find them in your garden while you’re planting. 

                As the soil’s temperature drops in the fall the grubs must burrow down below the frost line to avoid being frozen over winter.  Naturally, there is nothing for them to eat down that deep in the soil so they survive on all that body fat that they put on by eating the roots of your lawn. 

Finally in spring, the soil’s temperature begins to rise and the grubs (who are ravenous after months in hibernation) burrow their way back to the root zone of your lawn.  Now the feast begins all over again.  After putting on another round of body fat (compliments of your lawn) they pause and pupate; that is: they form a hard shell and begin the transformation into the adult or beetle stage of their life.  They will enter this pupae stage during Early to mid-June.  In mid-July the beetles emerge from the soil and the cycle begins again.

                If you’ve been paying attention, you’ve realized that by the time you get out there in spring with your grub killer three quarters of the damage the grubs cause has already occurred.  This is a classic case of closing the barn doors after the horses have run off.

                There’s no way we’ll ever convince the Japanese Beetle to change their habits so, we must try to change ours.  The best time to wipe them out is during the hatching period in late August or early September.  If you have a severe grub problem you may need to treat this spring just to save your lawn from extinction but you should try to GET WITH THE PROGRAM so you can prevent the situation from happening again.

                If you find that you need to apply a grub control as an emergency measure in spring, you should pick one that is fast acting.  The best choices for spring applications would be Dylox or Diazinon.  They kill quickly and on contact.  Both break down quickly once they’ve killed the grubs but, since there are no new grubs hatching in spring, it is of no concern.  As with all grub controls, it is imperative that they get watered-in for a couple of hours IMMEDIATELY after application.  DON’T COUNT ON RAIN TO DO THE JOB!   Rainfall is never hard enough to get the chemical off the surface of the soil and down to the roots where the grubs are.  You must realize that these chemicals begin to break down as soon as they are out of their bag.  Sunlight and air both begin to strip these chemicals of their potency the instant they’re out of the bag.  If Diazinon is left on the surface of the soil, it will lose about 33% of its potency every 24 hours.  As soon as you put your spreader away after you apply you grub control, get the sprinkler out and soak the area for at least an hour.

                O.K. now you’ve treated for grubs in spring for the last time in your life and you’re ready to GET WITH THE PROGRAM.  What’s the best thing to use?  In my opinion it will be one of two products.  Either the chemical Imidacloprid (sold as Merit Season Long Grub Control) or the biological control (non-chemical) Milky Spore Disease.

                Let’s start with Merit: Ideally, you’ll want to apply Merit in mid to late July and WATER IT IN.

By now you must think I’m totally nuts.  I just explained how there aren’t any grubs in July because they are all in the beetle form eating the beans and roses.  Rest assured, I’m not nuts.  The reason Merit needs to be applied so early is that it needs some lead time to get absorbed into the roots of the grass where it remains waiting for the grubs.  As soon as the grubs hatch they begin to eat the roots of the grass.  POW!  They die.  That’s the beauty of Merit.  It can’t miss since it’s in the food of the grubs.  Properly applied and watered-in Merit will kill 98% of the grubs that hatch.  No need to lose your lawn…no need to treat again in spring either.  Don’t worry, your neighbors grubs will stay in his yard.  Grubs aren’t much for traveling.

                Better yet there’s Milky Spore Disease.  Milky Spore is a disease that only affects white grubs.  It won’t hurt earthworms or even a bird that eats a grub that has the disease.  Milky spore needs to be applied

two or three times a year for three years to reach “epidemic” proportions in the soil.  After that the grubs that hatch into your lawn will contract the disease then die reproducing the disease and spreading it throughout the soil.  Milky Spore is more expensive up front but will last at least 20 years once it takes hold.  Not a bad investment really.  Over the years it will actually save you money to say nothing about the time you won’t need to spend spreading chemicals and running sprinklers. 

                I hope I’ve helped make this the last spring you’ll need to kill grubs.  Thanks for the read.