Ricardo Ramirez: Hi, I'm Ricardo Ramiriez, entomologist at Utah State University.
Today, we're here at Greenville Research Farm, where we're standing in an alfalfa
field that's on its second cutting.
One component of an integrated pest management program is the sampling and
monitoring of insect pest populations.
In this video, factually I'll cover how to use a sweep net to sample for insect pests
and how to use these sweep samples to make an informed decision about when
to manage these pests.
When people are sampling for insect pests in their fields, one of the problems is
that they use their hats, which vary in size from one person to the next, so as
you go to collect samples, what you're collecting in your hat is different from
one person to the next.
So sweep nets consist of a 15 inch diameter ring, a canvas bag which fits
over that ring, and a wooden handle or metal handle that varies in length and
also thicknesses.
Now, you'd want to choose a handle that is going to be comfortable to your height
and also for your hands. This one happens to be two feet by one inch in diameter.
When you're selecting your net, just be aware that--not to buy a butterfly net.
They're not as durable, they don't have the canvas bag, they can rip easily, and
the other thing is when you're sweeping through alfalfa, there are a lot of thick
branches that could potentially damage the net.
Sweep net sampling consists of swinging the sweep net from one side of the body
to the other in a 180 degree arc, keeping the net below the tops of the alfalfa
plants. And so we'll take 10 sweeps in a series.
[Net brushing plants.]
Ramirez: Take a series of 10 sweep samples in different parts of the field to get a
representative sample when alfalfa is 10 inches or taller.
Consider using a Z, M, or U pattern in the field so that way you get a
representative sample throughout a field.
Also, avoid the edges of the field where insect pest populations tend to be a
little bit more variable and aren't representative of what's going on in
the entire field.
Once you collect your sample, you'll want to transfer your sweep sample into
a plastic baggie by slipping the plastic baggie over the opening of the canvas bag,
pushing the canvas bag so that the insects will fall out into your bag sample.
[Bag rustling]
Ramirez: Seal the bag and this is when you'll be able to count the average number
of larvae, aphids, or any other insects per 10 sweeps.
To monitor the insects of concern, in particular for alfalfa, alfalfa weevil and
also aphids, you want to count the number of weevil larvae or aphids and take the
average number of these insects on a per sweep basis.
For example, with alfalfa weevil larvae, when we find more than 19 larvae on
average per sweep, this is when we would consider an active management strategy to
control them before they cause economic loss.
Another benefit to sweep netting is that you not only collect the pest insects, but
you also collect beneficials.
These are the insects that can feed on pest insects and that'll give you some
information, too, as to how healthy the field is and whether or not beneficials
can be incorporated into your pest management program.
Once you've collected your insect samples, you can go to our website and look at fact
sheets to identify the insect pests and also to look at threshold numbers that
are available for each of the insect pests that I've talked about today.
When sampling for insect pests, you want to start at the very beginning of the
season before pests become a problem.
That's what the monitoring is all about.
And so once you do your first sweeps when the alfalfa is 10 inches tall--or
10 inches or more, then you'll want to continue to monitor throughout the season,
referring back to the fact sheets and the threshold data that's available for each
of the insect pests.