Insect Problems in New Beds

Insect Problems in New Beds

Part of Ep. 602 Back to Basics

Meet with UW-Madison Extension Entomologist Phil Pelliteri as he tackles the common white grub and the wire worm. Learn new ways to minimize insect problems in new vegetable and flower beds.

Premiere date: May 31, 1998

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley:
Meet our special guest. This critter can cause a lot of problems for many gardeners. However, since he can't talk, we've asked UW-Madison Extension Entomologist, Phil Pelliteri to join us. Phil, introduce us to your friend, please.

Phil:
This is the common white grub. Most people are very familiar with it if they work in the soil very much at all. It is from a june beetle family that we see quite commonly. We see them very commonly associated with sod.

Shelley:
Now do we see them this big?

Phil:
This species comes from wood but the species that we get look almost the same, but they're about half the size.

Shelley:
And how are they a problem for gardeners?

Phil:
Well, what we see is, if we work sod open we can find the little white grubs feeding on the roots of the sod plants. The adult stage of this insect is the june beetle that you see in may and june flying around. And she lays her eggs in grassy situations. It's a three year life cycle and the grubs come up and down during the winter and spring. If we plant into this new garden, the only roots that these insects have to feed on are potatoes or carrots, some of the root crops where they cause big gouges in the plants. And then for the other plants, they'll feed on the tiny roots and so we'll get the plants wilting in june or july.

Shelley:
Because there's no root under the soil.

Phil:
There's no root and the unfortunate thing is that once you discover that in a new garden, you've already lost; there's no way that you can rectify. So you have to catch these before that.

Shelley:
Well then, what are the solutions for something like that?

Phil:
Well, one of the things is that when you work the soil over, if there's no grubs, there's nothing to worry about.

Shelley:
So actually you're counting them.

Phil:
Right, anything above about one per square foot are the kind of numbers that can be damaging. We've got two options then. If there's lots of grubs there, you can let the ground remain fallow for a year and the grubs that will come up in the spring will starve to death.

Shelley:
Okay.

Phil:
The other option is to work insecticide in and there we would have to work it in the spring before we plant our crops.

Shelley:
And is that a common, do we get those high numbers here in Wisconsin?

Phil:
Well, I would say probably four out of five times you're expanding your garden, there is not the number that is going to hurt you. It's just that one out of five, if you're not careful and looking for it, you will have some unpleasant surprises.

Shelley:
Okay. And do the high numbers ever bother the turf itself?

Phil:
Well, one of the ways you know you've got grubs in your lawn are when the skunks come in. If the skunks are tearing your lawn up, what they're after are the grubs that are in the lawn.

Shelley:
Okay, Then it's time to concern ourselves.

Phil:
Definitely.

Shelley:
Okay, Are there other insects that are a problem in a new bed like this one?

Phil:
Yeah, there's one other insect particularly that we associate with sod and this one is called the wire worm. The life cycle is rather similar. These larvae here are the immature stage that causes the damage. They'll feed on the seeds that we put in the ground. They'll also feed on the young seedlings. The adult stage are these click beetles. And these click beetles lay their eggs in the spring in sod situations. In this case, though, the life cycle is seven years long in some cases. And so these wire worms keep coming up and down. And again, if you plant carrots or potatoes, unfortunately when you harvest those crops, you'll find that those insects have drilled and caused damage that way.
Shelley:
And again it's too late once we've seen it.

Phil:
Right.

Shelley:
Thy look a little harder to see. Is there a way we can count these also? Are numbers again the factor?

Phil:
Right, and one of the ways we can assess how many wire worms are around is with a wire worm trap. And this is what we have placed here. Wire worm traps we put out in the spring, usually about the middle of april. We dig a hole in the soil about 12 inches deep and I put some popcorn in there, but we can use whole grain corn, we can use meat. As the water percolates through, it diffuses chemicals that will attract the wire worms and they'll come up here. Now we put the black plastic around it because it warms the soil and it speeds this process, but after a week or two we can come check it. And anything above one wire worm per trap suggests the populations are high enough to cause damage to our crops.

Shelley:
And again, the solution is to wait.

Phil:
We've got two options. We can let the ground remain fallow and again starve them out. We've got to do a good job of weed control because the weeds that survive would provide food for both of these insects or again, if we have to plant, then we can use insecticides.

Shelley:
Okay. Are there any insects we're likely to confuse with these problem ones?

Phil:
A real common mistake that people make is for an insect we call a millipede and they incorrectly call it a wire worm. The way we tell the difference is that millipedes have large numbers of legs, rather than the three pairs of legs like any true insect does. The good news about millipedes is they just feed under decaying organic matter so they're not harmful to our plants at all. In fact, they're often an indicator of good organic matter levels in the soil.

Shelley:
Okay, Great! Thanks, Phil. So if we see these, we shouldn't worry but we need to plan ahead and know our insects.

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