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.

Thank you VERY MUCH for your post, Ivan! My DD lives in Austin and I was maybe going to bring her some bearded irises this summer. I didn't realize that grubs would be a problem down there, so thanks for the heads-up AND a solution!

I have looked for milky spore around here, have not found it yet, but have a couple more places to check. I have not tried the ultrasonic mole chasers and have heard different opinions. I would love to know if it works for you. I don't really have many grubs, very few Japanese beetles. A few years ago we were covered in Japanese beetles, then the moles moved in. They did some damage, but frankly, the moles annoy me less than the beetles. I keep thinking the moles will move on now that they have less food, but must be more than I realized.

Yucky, yucky, yucky! No grubs for me, please. Hopefully the spore powder works for you, to get rid of the grubs....AND the moles.

I got mine off of Amazon, but I saw it on Ebay and several other websites for about the same price. The ultra sonic mole repellers came off of Ebay and I hope they do work, since the only alternative is poison, which leads to poisoned pets which nobody wants. Well, taking that back, I have heard of traps but who has time for that?

https://www.domyown.com/milky-...
a possible source.

hmmm timothy, checkedyour link, and unfortunatelythere are shipping restrictions to many states, mine included.😕

however, not that we have borers here, but something has been making small craters (round holes) on the tops of the rhizomes.

daphne, those might be " sow * bugs (spoken, as if a piggy momma) , pill, or roley poley (sp.?) bugs are common names, for this pest.. They can chew rhizomes & may come out at night & find the root to be a delicacy & return nightly for more tasty treats . They are grey in color & if you locate a hoard in the day, they make a mad dash for it.. Some curl up in a ball & others go running off...
I have used a, cheap peeled cucumber, as bait & grab the cucumber later at night, quickly & dump them into a receptacle, to help reduce numbers & eventually you won't have nearly as many, to contend with to do as much damage, by repeating the procedure.
You may also try to locate a "cool damp spot", under which they may hide out, during daytime. Just be ready to take quick action, as they will try to quickly disperse & escape, after uncovered & get into difficult areas, to hide from you ! They can even be tunnelled, in holes, near the bottom of plastic pots, or hiding out near the base of the crown, of nearby leafy plants,....

Just to be clear, Milky Spore may also work on Iris borers but only in the pupae stage when they are in the soil later on in the Summer.

A better solution for Iris Borers appears to be an organic bacterium solution called Spinosad. I haven't tried it but it appears to last 4 months and not only treats borers, but sowbugs, thrips, slugs, spider mites, fleas and a host of other predators. It should be sprayed before blooming but not on blooms, to avoid killing pollinators. Here's a link from Texas A&M and I see it is also for sale on Amazon:

https://aggie-horticulture.tam...

Now, I don't have them here but since iris borers start out as moths, I think a bug zapper would help alot if it was put out in April and May to get a lot of these before they start laying eggs. I've used it for tent caterpillar moths, but be prepared to clean it out daily because it can really clog fast this time of year.

thanks shawnsteve. i know what sow bugs are. but the damage was done mostly to rhizomes in one area where not too many sow. bugs live. thanks for the tip on how to capture and get rid of them. they might be the culprits

do crickets and grass hoppers eat rhizomes?

i was blaming the gouges on this 3 1/2 in. monster, brown grasshopper that i couldn't catch https://pbase.com/markb249/ima.... it looked very much like this one but browner in color.

but i couldn't tell for sure, i never saw it feeding; only saw the chewed hole. i caught it one night feeding on the ti leaves, and didn't see more holes after that. ( but not before it shredded the cordyline fruticosas😤) i just hope it didn't leave eggs for another crop to hatch.

I just wanted to leave an update on the grub situation a year later. Seems they are a lot scarcer now after only using one treatment of milky spore. Funny thing last summer I even saw one grub on top of the ground running as fast as he could. First time I'd ever seen one do that and just thought to myself he must be infected. But not really sure.

I also used about 6 of the solar mole repellers and they also have seemed to help. Moles are still around but it looks like they migrated to the woods. There was one place I neglected to set up repellers and they totally devoured a couple of clumps of rhizomes. Will have to add more there when I replant.

Ivan, do you know the distance the repellers work?

barbara, the ones i put in, said they have a 25' radius, but i've overlapped mine a little closer than that. they differ by manufacturer, i think.

Thank you Daphne. I think I'll try to get some for a problem area here. Does anyone know if they sell them at Home Depot or Lowe's?

It is not that difficult to trap moles either, should they get used to the mole repellers over time.

The difficult part is to find the tunnels they actually use. If you put a trap in their meandering feeding tunnels it will be of little use, since they will just use them once and rarely return.
There are plenty of YouTube videos to learn how, and more importantly where, to set mole traps.

I can personally recommend the claw type traps, they are excellent, but it can perhaps also depend on which type of soil you have. Here I have loose sandy soil, and some type of traps do not work at all with that.

I trapped moles several years ago, and they have not come back. It took some practice and time to learn to do it right, so one shouldn't loose fate if it doesn't work right away.
If you don't succeed, most likely you just haven't found the main tunnels.

I just wanted to leave an update on the grub situation a year later. Seems they are a lot scarcer now after only using one treatment of milky spore. Funny thing last summer I even saw one grub on top of the ground running as fast as he could. First time I'd ever seen one do that and just thought to myself he must be infected. But not really sure.

I also used about 6 of the solar mole repellers and they also have seemed to help. Moles are still around but it looks like they migrated to the woods. There was one place I neglected to set up repellers and they totally devoured a couple of clumps of rhizomes. Will have to add more there when I replant.

Not all soil living grub larvae eat living tissues you know. So unless you're able to exactly identify the species you're just guessing.