Having decided to plant a large amount of irises this year, I decided to take on what has been killing my past iris plants. Besides the drought, fire ants, and moles, I've discovered I have way too many grubs in my garden and decided they are my root problem(pun intended). Drip lines should take care of the drought and the hormone ant killer finally has the ants at bay. So that leaves the moles and grubs, and I've learned it's the grubs that attract the moles.
This is a medium sized grub which I just found by turning over a bark bag, but I've seen several in more organic matter that get up to 3" long! That size could do a lot of damage to plant roots and I suspect is a different type of beetle grub besides the common Japanese Beetle or June Bug. My guess is the large ones hatch into Rhino Beetles which also live here.
I know many growers use insecticides over their plants during summer which many be a temporary solution, but having used Bacillus thuringiensis(bt) in the vegetable patch for cabbage loopers and tomato hornworm, I was glad to find another strain for grub control. Here's what many garden stores have to offer, called Milky Spore Powder. It is said to last 10 years but may be longer than that since infected grubs will burst and release millions of spores to continue infecting for years.
It's not hard to apply, just one teaspoon on top of the soil in a 4x4' grid, then just wait for the rain to wash it in.
If this destroys the moles' food source, they should also leave where they won't do so much damage, but I've also found a gadget that may encourage them to leave. It's called an solar powered ultrasonic mole chaser. I don't have as much faith in it as the BT but I figure it couldn't hurt.
