Scouting
for Thrips in Cotton
This
past week I have received quite a few questions about scouting for thrips in
cotton. The questions have not revolved
around so much ‘how’ to scout for thrips as most have already watched our how
to scout for thrips in cotton video. If
you have not and would like to do so, the link is here:
These questions have
dealt more with, “How many plants do I check per field for thrips?” Mostly this is an open-ended question most
entomologist in extension do not usually answer directly. If we do, we must give the answer that guarantees
the scout will absolutely know exactly what the pest population in the field is
and be able to scientifically defend their findings to a publication review
board. For those that have looked at our
new thrips guide you have found this type of answer there: “Randomly select 25 plants from 4 regions of the field and closely go
through the plants looking for adult and immature thrips.”
If you have not given the new thrips
guide a once over, I encourage you to do so now at: http://lubbock.tamu.edu/files/2017/05/Thrips_ENTO-069.pdf. There are a
lot of helpful tips to be found there.
Meanwhile, for those of us
scouting lots and lots of fields, that level of pest population precision is not
always needed. Rest assured that for all
our research plots and other cases where that level of precision is needed, we
are getting it and more. But for day to
day field scouting, I find it to be overkill and too time consuming to practically
cover all the acres we must on a weekly basis.
We just need to know if this pest is over economic threshold and at what
level are the beneficials helping us out.
So, we need a decision now, based on solid scouting but derived as
quickly as possible about whether to spray or not.
To help fill you in on how our
scouting program generates these answers, I have asked our 2017 Plains Pest
Management Intern, Trey Buxton, to fill you in on what data I expect of him when
he scouts a typical cotton field in Hale, Swisher, & Floyd County. Trey made a picture perfect scouting in a 30-acre
drip field trip last week that gave us great data. Here is what that path looked like as tracked
by his GPS active Strider Tablet:
Here is Trey in his own words:
My name
Is Trey Buxton and I am a summer intern under IPM Agent Blayne Reed out of
Hale, Swisher, and Floyd county. I started working for the Plains Pest
Management Association in the summer of 2016 as just a summer job and I had no
idea what I was doing at first. After working under Blayne for a full summer I
feel pretty good about knowing what it takes to scout cotton, corn, and sorghum
fields in West Texas and get good data.
When
scouting cotton fields early in the growing season the first thing that I do is
walk good distance into the field to avoid edge issues, say 50 to 100 steps or
so. These edge areas can catch drift
from a neighboring farmer and always have an edge effect with pest, disease and
weed populations that do not represent the full field. When I get to an area that I think is
consistent to the rest of the field I start gathering data. We call each stop we make a data set. Each data set consists of a stand count (how
we calculate plants per acre), record the plant stage in the vicinity, record any
weed populations, and conduct 2 whole plant inspections where all thrips, any plant
disease, and beneficial populations are recorded. After I have finished
recording all my data I start walking to my next data set. You want to make
sure that you space your data sets out across the field so you can cover more
portions of the field and know what problems you have in those spots of the
fields.
Blayne
tells me the question is how many plants do we need to get in each field. Blayne always points to the Texas A&M
AgriLife Extension guide. It says,
“Randomly select 25 plants from 4 regions of the field and closely go through
the plants looking for adult and immature thrips.” This would be very accurate. Blayne coaches us that, “More data is always
better, but not every field is a research plot.
In day to day scouting, we do not have that much time.” So, I was trained to scout for thrips on 2 randomly
selected plants at each data set and to get them from at least 5 regions of the
field. So, in most fields, I am only inspecting 10 total plants throughout the
field versus inspection 100 like the Texas A&M AgriLife Extension Handbook
says to. This should not be more
accurate than what the handbook says, it just helps to get in and out of fields
quicker and allows us to get the minimum amount of data that we need for a field.
In many fields, there is a need to get
more data. Larger fields are a good
example. On really big fields I can
easily get 10 data sets. Another example
of needing to get more data in the field would be when thrips populations are
very close to averaging around 1 thrips per true leaf stage or when we start
seeing thrips larva in the field. In
either of these cases, more data is required to give the producer the best data
to help them make tough decisions about spending more money on additional
spray.
I would
also like to say that when you are scouting for thrips, you must do a really
good job of scouting your 2 plants per data set. If your data is no good, it does not matter
how many plants you check, you have no idea what is happening in that
field. Thrips like to hide on the bottom
of the Cotyledon leaves and attach to the veins on the leaves and suck the plant
juices out of the leaves. They also like to crawl down into the growing point
terminal of the cotton plants and feed down in there which can really turn into
a problem because they will damage the terminal and stunt the plants growth. So,
whenever I get down check for thrips I make sure that I look the plant over
real good and open up the unfurled leaves with my pen or knife. Thrips are really
little tan colored insects that have the shape of a grain of rice but they are
way smaller. So, when you are searching
for thrips it can be easy to mistake some dirt of a piece of plant that is
stuck to the bottom of the cotton leaves for a thrips. To make sure that I
don’t get confused I get my pocket knife out and I will poke what I think is a
thrips, and if it’s a thrips it will start to crawl around on the leaf.
In the
picture shown reveals the path that I took through the field in Swisher County.
My boss, Blayne Reed, considers this a
perfect path through a field. It is
considered perfect because I covered enough ground to make sure the data was representative
and I didn’t take too long in the field. In this field, all 5 of my data sets were
consistent in weed control, thrips control, and stand count numbers. Because of the consistency of the thrips,
weeds, stand counts, and lack of disease pressure or other issues, the minimum
amount of data required from this size field was all that was required and I could
move quickly on to my next field to check.
Thanks
Trey!
Blayne
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