In this video series we discussed bait-and-wait for ants,
we caught cockroaches on sticky boards, we tried to think like a rodent, and we took a look
inside the tunneling system of a toothy gopher. Now we’ll deal with something stationary,
but something that’s still a challenging pest: turfgrass weeds. Dandelions! Crabgrass! Clover! Why are they a problem? First of all, most people would say a weed-free
turf looks better. So it’s mostly aesthetics! But weeds can also be a safety hazard… safety hazard. Slipping on broadleaf plaintain
can cause sprained ankles, and some weeds, like
star thistle, have sharp spines. Clover and other flowering weeds in turf
attract bees, and bees can sting students! If a student or staff is allergic, weed and bee
management will become a big issue fast. Weeds. They’re just plants that grow really well
in places where we don’t want them to. Weeds do well in places that are hard for turfgrass
to live in, such as in dry, salty or compacted soil. They love open areas and disturbed sites, like those old
gopher mounds or that area in the center of the football field. Incorrect irrigation, fertilization, or mowing can
weaken turfgrass and is likely to bring on a weed invasion. Weeds can either be annuals, or perennials and the type of weed you have will
decide your management strategy. If you have spotted spurge, crabgrass, annual blue grass,
or burr clover in your turf, you’re up against annual weeds. Control them when they are at their
smallest before they produce seeds. If you’re fighting kikuyu grass, dandelions, or white clover,
you’re up against perennials which are the bullies of weeds. Perennials may seem to die during the winter,
but come spring, they pop-up again even stronger and bigger from their roots
and underground stems. Stop them while they are young and remove the parts of the weed below the
soil surface so they don’t pop back up or spread. So let’s grab our clipboards and head back outside and meet up with our landscape IPM
professional Phil to see what we have. Hey Phil! Hi, how are you doing? Good. Looks like we’ve got some weeds out here. Sure do. All right. So what is the best way for us to
look for them that makes sense for IPM? What I like to do is about once a month I want
to come out and do a transect in the field. That is a careful, systematic evaluation of what the
condition of the field is and what weeds are growing. If I do it on average once a month
and if I do it in a systematic way, then I can evaluate whether the
problem is increasing or decreasing, whether I have to make any kind
of significant management changes. Makes sense. What have we got here? Well one way to do it is a line transect. There are a lot of different ways to do a transect.
The important thing is that you do it consistently each time. This is one method, it is a 15 foot line and
what we would do is just throw the line out… do you mind bringing that over here,
I’m going to pull this line over here. Right here? That’s just about right.
Exactly perfect. I would lay that out. I’m going to grab my clipboard. Now what I’m going to do, I’ll do this multiple
times through the field, at least three times. And what I’ll do is look down
here at foot number one. I don’t see any weeds.
Okay? So one is zero. Two, no weeds, that’s a zero. Three, aha! We’ve got something here and to be
honest with you I don’t exactly know what it is. So I’m going to take a sample
and we’ll identify it inside. So we brought the weeds in from the
outside and we’ve identified them and in that area that we were sampling what we had primarily were clover and knotweed and this wild Heliotrope. So what’s the underlying problem out there? Well the goal is to make the soil healthy. What this tells us is that the soil conditions are
better for these weeds then it is for the grass. So we need to turn it around and make
the soil a healthier for the grass then it is for the weeds through aeration and
better fertility and better irrigation management. Now if we had found Dallisgrass or Nutsedge
or other plants that like wet soil, that would have told us that we needed to change
those conditions to make the grass healthier. So the underlying problem
is underlying: it’s the soil. It’s the soil. That’s punny. Thanks a lot Phil. It’s my pleasure. Turf has it hard. It gets stressed by
too much use, not enough rest, and not enough maintenance. Stressed turf
is susceptible to invasion by weeds. Karrie is a University of California environmental
horticulture advisor and turf management expert. Karrie, we’ve just heard from Phil that
soil problems can encourage weeds. So to keep our turf healthy and competitive
against weeds we need to make sure that our soil and turf are properly
managed. How do we do that? Well the first thing you want to do is
start with the right amount of water. You want to make sure that you
water deeply and infrequently. And you want to apply the water either
very late at night or really early in the morning. That way you avoid the wind and the heat
and the sun that can evaporate the water. It’s better for the grass and you save water. Okay, so we need to set
irrigation timers. For how long? Well there’s no magic number for how
long you run an irrigation timer. What we need to do is match the amount
of water that your system delivers with how well your soil infiltrates water,
the turf type that you have, and of course the weather. And it’s really important that the water
gets applied evenly over the turfgrass so you need to walk around and look
for dry spots or look for soggy areas. If you walk across the grass and your footprints
stay in the grass, that’s drought stress. But if your foots sinks into soft soil, then
you’re probably overwatering that area. So a really good way to analyze
that is through a catch can test. So you take a large number of cans, same size, and you distribute them all over your
field and then you run the sprinklers. And walk around and see how much water–
after the sprinklers are turned off–is in each can. And you’ll see pretty quickly how little
and how much you’re putting down. That’s a neat trick. Alright so now our turf
is properly watered. What do we do now? Well, you’re probably going to need to fertilize. Most turfgrass needs fertilizing and the best time
to do it is in the spring and again in the fall. In the spring you get the grass
growing and then in the fall you replace the nutrients that the grass used to grow
and that you removed when you were mowing it. So for turfgrass mostly that is nitrogen, but it
could also need potassium or phosphorus or iron. Okay so how do we know what we
need to add when we fertilize? Well you’re going to have to have
your soil tested by a soil lab. That test will tell you exactly which nutrients
you need and how much you need to add. So we check the soil. Right. And then after you add the right type of fertilizer
and the right amount, you’re going to need to water. This will carry the nutrients down into the root zone.
You may also need to aerate any compacted areas. Aerate? What’s that about? Over time soil gets compacted and that makes it really
difficult for air and water and nutrients to move through the soil into the root zone. Weeds don’t seem
to mind this, but turfgrass has a tough time. So it’s a really good practice to aerate
your turfgrass at least once a year. OK, so we irrigate, check the soil, fertilize
appropriately, and aerate. Anything else? Well there is one more practice you can
use to really help suppress weeds. And that is to overseed. Overseed doesn’t
mean to use too much seed. What it means is to spread seed over
the grass that is already there so that you fill in any holes that have
come up with new fresh grass. You want to make sure that you use high quality fresh seed
and the best time to do it is in the spring or in the fall. But anytime you notice bare spots you’re going to want to come
in and overseed so that the weeds don’t come in instead. And there it is: the keys to a healthy and good
looking lawn or turf without a pesticide in sight. Thanks a lot, Karrie. You’re welcome. Is she gone? OK. So what happens
if you follow all of Karrie’s advice, but you don’t get Karrie’s results?
What else should you be doing? Well, are you mowing regularly? Mowing makes the
turf look well groomed, removes weed flowers, and reduces the chance of a student tripping or slipping.
Just follow the one-third rule: no more than one-third of the grass
blade is to be removed at one time. And leave the grass clippings right where you cut them.
Recycling the grass puts valuable nutrients back into the soil. You should hand-weed regularly.
Remove the weed while it’s still young, before it sets seed. Be sure to remove
the entire weed: roots and all. The last choice is herbicides. Use them only after weed prevention, fixing irrigation
issues, soil improvements, overseeding, aeration, and other management methods have failed.
No single herbicide controls all turf weeds, so you have to choose carefully based on the season,
the weed type, and the turfgrass species. That’s where your monthly
transect line monitoring will help. Herbicides can be: pre-emergent; used before weeds come up, post-emergent; used when weeds are young, selective; used to kill specific types of weeds, like broadleaf, and non-selective; which kill most plants. Read the label carefully, and follow instructions
precisely. In fact, if you do use herbicides, strike early! Remember, new, young weeds
take less herbicide and are easier to manage. And apply herbicides when school is not in session
to reduce potential exposure. Turfgrass IPM comes down to a few simple points: Set acceptable levels for weeds in
each of your school’s turf areas. Keep the turf healthy with good watering,
fertilizing, mowing, and aerating. Hand-pull weeds or use
other mechanical methods first. And reach for herbicides only as a last resort
after all other methods have failed. So now you know how to manage turfgrass weeds. But what if your pest problems are bigger
than you can tackle on your own? Hire a pro! We’ll talk about that next.