Annual Weeds and Control

Annual Weeds and Control

Part of Ep. 302 It's Planting Time!

Hoe and mulch to rid your garden of weeds like galinsoga and common purslane.   Herb Hopin, UW-Madison horticulture professor, discusses garden problems associated with annual weeds and offers tips to control them.

Premiere date: Apr 30, 1995

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley Ryan:

It's a great time of year to be planting in your garden. It's also a good time a year to start being on the lookout for some plants you may not want in your garden. I'm with UW-Madison horticulture professor Herb Hopin. We're at Arlington Horticulture Research Farm to take a closer look at weeds. Herb, earlier you mentioned that we were going to talk about annual weeds. Let's start out with the definition of what those are.

 

Herb Hopin:

An annual weed would be a weed that the seed would germinate and the plant that it germinates from would complete its life cycle during one growing season.

 

Shelley Ryan:

So from seed to seed in the entire season.

 

Herb Hopin:

Correct.

 

Shelley Ryan:

And what weeds are we going to talk about?

 

Herb Hopin:

There are many weeds that are a problem in the small home garden, but we're going to talk about two today. One is Galinsoga, and the other is common purslane.

 

Shelley Ryan:

They're both annuals that are problems in Wisconsin?

 

Herb Hopin:

That's correct.

 

Shelley Ryan:

Let's start out with the Galinsoga. I think I actually recognize this one.

 

Herb Hopin:

This is galinsoga. It has the yellow and white flowers, as you can see.

 

Shelley Ryan:

And a hairy stem.

 

Herb Hopin:

A hairy stem is one of the determining characteristics.

 

Shelley Ryan:

How is it a problem?

 

Herb Hopin:

It's a problem because the seed that drops from the plant really doesn't have any dormancy. You can see on this plant that there are flowers and there's also mature seed here. When this seed drops in the soil, it can germinate immediately. Once you have the start of this problem, it can rapidly explode and become a serious problem in a short time.

 

Shelley Ryan:

So we don't want to wait until it's this large to deal with it.

 

Herb Hopin:

It's probably best to control galinsoga when it's in a young seedling stage. This is a seedling of galinsoga. This would be the correct time, or slightly larger than this, to control it.

 

Shelley Ryan:

Now I know that one of the problems is that these compete with sunlight with my plants. Are there other ways that this is actually a problem for my vegetable crop?

 

Herb Hopin:

It can compete for moisture and nutrients. That would be the primary problem that these plants would cause.

 

Shelley Ryan:

Once we've identified it in the young stage, what is the best way to control it?

 

Herb Hopin:

Probably the best way to control it is he use of cultivation and hoeing, mechanical removal, and combining this with mulching. A mulch will exclude the light from the young seedlings and will cause them to die as young seedlings.

 

Shelley Ryan:

So mulch and then just physically get them out of the garden when they're young, before they've reseeded.

 

Herb Hopin:

Right.

 

Shelley Ryan:

Okay, and what about herbicides for something like this?

 

Herb Hopin:

As you have an individual patch of, let's say tomatoes, then herbicides, if you choose to use them are an all right option. But in the small home garden, where you talk about selective herbicides, this is not the best choice, because you will harm one plant that you're trying to grow and not harm the other.

 

Shelley Ryan:

Okay, so physically just pulling this stuff out is the best solution.

 

Herb Hopin:

Correct.

 

Shelley Ryan:

What about this one here? Again, I recognize this. I have a lot of it in my garden.

 

Herb Hopin:

Again, a common problem for home gardeners. This is common purslane. We start to see this weed during the middle part of the growing season. It requires a high soil temperature for the seed to germinate. So, during the middle part of the season, we start to see this common purslane.

 

Shelley Ryan:

It competes with most of the crops in my garden?

 

Herb Hopin:

Again, it doesn't like low light levels, so if you have shade it's not a problem. But if you have a crop like onions, let's say, that doesn't have intense foliage, or beets, then it would be a problem in high light levels.

 

Shelley Ryan:

Again, here we've got a mature plant. These are the young ones here. That's the best time to start worrying about getting it out?

 

Herb Hopin:

Again, any weed, it's best to control it at a young stage. But if we do control this weed by cutting it off, we need to get the weed out of the garden area. Because if you cut the weed off, and let's say you cut it into several pieces, it will re-root itself. So remove it from the garden, or you'll have several weeds.

Shelley Ryan:

Don't leave any pieces behind when you hand hoe this.

 

Herb Hopin:

That's correct.

 

Shelley Ryan:

Again, you're saying that hand hoeing and mulch are the best solutions for purslane, as well.

 

Herb Hopin:

For all the weeds in a small garden.

 

Shelley Ryan:

You said there was another method for purslane that didn't involve our activity at all.

 

Herb Hopin:

Right, we have a naturally occurring insect, and that is the purslane sawfly. This plant has the purslane sawfly in it. It's a leaf miner. It's an insect that feeds only on purslane, so it's a very selective control. It is very sensitive to pesticides, but if you're an organic gardener and you see this insect working your purslane, leave it alone and it will control the weed.

 

Shelley Ryan:

We can just sit back and enjoy it then.

 

Herb Hopin:

Correct.

 

Shelley Ryan:

Great, thanks Herb.

 

Shelley Ryan:

So, physical control is the best way to deal with weeds like these. But coming up next, when is a weed not a weed? Sometimes weeds like these are not only good in your salad, they're good for you, too.

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