đ
Using Degree-days to Time Insecticide Applications in Fruit and Nut Orchards - YouTube
Channel: unknown
[10]
This presentation is about using
a tool, called degree-days, to
[14]
help you better time insecticide
treatments and other pest
[17]
management practices in your
orchards. Use degree-days to
[21]
predict when susceptible pest
stages are present so you
[25]
can maximize control.
For example, you need to apply
[29]
an insecticide for peach twig
borer after the majority of
[33]
larvae hatch but before they
bore into the ends of twigs
[36]
where insecticide wonât reach
them. Use degree-days to
[40]
pinpoint the best time to kill
the most peach twig borer larvae
[44]
with a single application.
[47]
Although degree-days are used to
manage pests in many crops, we
[51]
will focus on its application in
stone fruits and nuts. In these
[56]
crops, degree-days are useful
for the management of several
[59]
insects and for this
presentation we chose different
[63]
insect examples to show how
degree-days can be used.
[68]
At the end of this presentation
you will know what a degree-day
[72]
is, what information you need to
collect to calculate degree-days,
[77]
where to find resources for
calculating degree-days, and how
[81]
degree-days can optimize pest
management in your crop.
[87]
Letâs define a few terms
important to understanding
[90]
degree-days. The first is
phenology, the study of an
[93]
organismâs development and how
itâs influenced by weather.
[98]
Ambient temperature influences
the development times of
[101]
cold-blooded animals and plants.
For example, as temperature
[106]
warms in the early spring, trees
start to bloom. Being cold-
[110]
blooded, insects and mites do
not regulate their internal
[114]
temperature; instead their
development is dependent on the
[118]
temperatures they are exposed
to. Because of this, temperature
[122]
affects when an insect will go
through its various life stages:
[126]
in other words, when it
becomes an egg, caterpillar,
[130]
or adult moth.
Humans are warm-blooded
[134]
and so regulate their internal
temperature. Human development
[138]
doesnât change based on ambient
temperature. For example, a
[142]
human pregnancy is 9 months
whether a woman is living in
[146]
the Arctic Circle
or at the equator.
[151]
So letâs take a little quiz.
How long does it take for a
[154]
peach twig borer egg to hatch?
Is it 5 days, 10 days, 11 days,
[161]
or all of the above?
[163]
Thatâs right, all of the above,
because how long it takes for
[167]
the caterpillar to get ready to
hatch out of the egg depends on
[171]
the temperature it
is exposed to.
[176]
This graph shows the average
development time from egg to
[180]
adult for different batches of
obliquebanded leafroller also called
[185]
(OBLR) raised at different temperatures.
As the temperature increases,
[190]
the development time decreases.
At fifteen degrees Celsius it
[194]
takes approximately one hundred
days for an egg to develop to an
[197]
adult. But at twenty-five
degrees Celsius it takes
[201]
only about forty days.
[204]
In the previous graph, it seems
that if the temperature kept on
[208]
increasing, the development time
would continue to get shorter
[211]
and shorter. But this doesnât
happen. Below a certain
[215]
temperature insects cannot
develop. And above a certain
[219]
temperature their development
slows and will eventually stop.
[223]
These critical temperatures are
referred to as the lower
[226]
threshold, or base threshold,
and upper threshold, and
[230]
represent temperature limits
on insect development.
[235]
When temperatures fall between
the upper and lower thresholds,
[238]
the insect will develop.
Depending on how long these
[242]
temperatures occur we get so
many units called degree-days,
[245]
which can be used to
measure development.
[252]
A degree-day is a unit combining
temperature and time used to
[256]
measure development
of an organism.
[259]
One degree-day is a single
degree of temperature above an
[262]
insectâs lower temperature
threshold, maintained for
[265]
twenty-four hours, or in other
words, one degree above the
[268]
lower threshold
maintained for one day.
[272]
For example the lower threshold
for navel orangeworm is
[275]
fifty-five degrees Fahrenheit.
If the temperature is maintained
[279]
at fifty-six degrees Fahrenheit
for twenty-four hours, a
[282]
single degree-day accumulates.
[285]
But temperatures are not
constant in the real world.
[288]
So how do we measure degree-days
with temperature fluctuations?
[294]
Here is a graph of degree-days
accumulated over two twenty-
[297]
four-hour periods. The red solid
line shows the temperatures over
[302]
two days and the dashed lines
mark the upper and lower
[305]
thresholds. The yellow area,
showing when the temperatures
[308]
are between the upper and lower
thresholds, represents the
[312]
accumulated degree-days for
each day. Adding the areas under
[317]
each dayâs curve gives the
total number of degree-days
[320]
accumulated for the two days.
Once we know the number of
[324]
degree-days required for each
development stage of an insect
[327]
we have a phenology model.
[331]
Recall the example of
maintaining navel orangeworm at
[334]
fifty-six degrees Fahrenheit, or
one degree Fahrenheit above its
[338]
lower threshold, for twenty-four
hours. We said that one
[342]
degree-day would accumulate.
Then the next question is: At a
[347]
constant temperature of
fifty-six degrees Fahrenheit,
[350]
how many days would it take for
navel orangeworm to develop from
[353]
an egg to an adult? The navel
orangeworm phenology model says
[357]
that they require, on average,
one thousand fifty degree-days
[361]
to complete their life cycle.
Therefore, if maintained at
[365]
fifty-six degrees Fahrenheit,
meaning an accumulation of one
[369]
degree-day per day, navel
orangeworms would take one
[373]
thousand fifty days to develop.
[379]
Now letâs say that navel
orangeworms are placed at
[382]
fifty-seven degrees Fahrenheit,
or two degrees Fahrenheit above
[385]
the lower threshold. Development
would be twice as fast as
[389]
compared to rearing them at
fifty-six degrees Fahrenheit.
[393]
So it takes the navel
orangeworms only five hundred
[396]
and twenty five days, or half
the time, to develop.
[401]
As the temperature increases,
more degree-days accumulate in a
[405]
day, and less time is required
for development, until the upper
[409]
threshold is reached.
When temperatures are above
[412]
the upper threshold,
no degree-days accumulate.
[417]
Also remember that development
time represents an average for
[420]
a population! So the majority of
navel orangeworms will develop
[425]
in one thousand fifty
degree-days, while some
[428]
individuals take less
and others take more.
[433]
Now for an important question:
How do we know when to start
[437]
accumulating degree-days?
Accumulation starts either on a
[441]
particular date, for instance,
January first or on the biofix
[446]
date. A biofix is an observable,
biological event such as the
[451]
first pheromone trap
catch or egg laying.
[456]
The biofix for omnivorous
leafroller is the date when
[459]
traps start consistently
catching moths. For navel
[462]
orangeworm it is when
fifty percent of
[465]
the egg traps have eggs.
[468]
So now that youâve got a good
understanding of the terms
[471]
commonly used and the basics of
how degree-days are calculated,
[475]
letâs take a closer look at what
it takes to use them in the
[478]
field to manage your pests.
[481]
You can effectively predict
population trends of
[484]
an insect if the insect has
discrete generations, you know
[489]
the developmental thresholds
(upper and lower), and the
[493]
degree-day accumulation needed
for a particular event.
[497]
You know when to begin
accumulating degree-days,
[500]
and if itâs a biofix that
signals the start, you have
[503]
the tools to detect
when this occurs.
[506]
If all these are known, a
phenology model can be used
[509]
to manage your pests.
[513]
If a phenology model has been
developed in a location far from
[516]
yours, you should test the model
for one or more seasons in your
[520]
area to verify it will
predict biological events
[523]
accurately. A different location
presents different conditions an
[528]
insect is exposed to, which may
influence the development of the
[532]
insect. This also applies for a
phenology model developed for an
[537]
insect in one crop that youâd
like to use for the same insect
[541]
in another crop.
[543]
For example, at one time we
didnât have a phenology model
[547]
for obliquebanded leafroller in
California, but one was
[550]
developed in New York.
We performed a field test to
[554]
verify if the New York model
could predict timing of OBLRâs
[559]
growth stages in California.
[561]
According to the New York model,
one generation of OBLR takes two
[565]
thousand degree-days using lower
and upper thresholds of
[569]
forty-three degrees Fahrenheit,
and ninety degrees Fahrenheit,
[572]
respectively. The biofix is
the date the first moth is
[575]
caught in a trap.
[578]
To see how well the New York
model would predict California
[582]
populations researchers recorded
the number of obliquebanded
[585]
leafroller males caught in traps
throughout the season in a
[589]
California pistachio orchard.
This graph represents the
[593]
results of a field test.
Obliquebanded leafroller is an
[596]
easy insect to follow because it
has distinct generations that
[600]
donât overlap. In other words,
at the end of the first flight
[604]
there is a period of time with
no trap catches until the
[607]
second flight begins.
[611]
You can see that the first moth
of the first flight was trapped
[614]
in the orchard on May eighth.
The first moth of the second
[617]
flight was trapped around July
fifteenth, and the degree-day
[621]
accumulation between these two
dates is one thousand, nine
[624]
hundred and eighteen degree-days.
According to the New York model
[629]
we saw that one generation of
obliquebanded leafroller takes
[632]
two thousand degree-days
for one generation.
[636]
Although there is a discrepancy
of eighty-two degree-days
[638]
between the New York model and
our California results, it is
[642]
not uncommon in June and July to
accumulate twenty to
[646]
twenty-five degree-days each day.
This means the difference between
[650]
the values is only about three
calendar days. A three-day
[655]
discrepancy will not influence
whether an insecticide
[658]
application is successful or not.
So, after several years of
[662]
similar results, we accepted the
New York model for predicting
[667]
obliquebanded leafroller
generations in California.
[672]
In addition to monitoring traps,
it's important to keep records
[676]
of other production and
management activities in the
[678]
field. Here is an example
of why: see this dip in the
[683]
population on August seventh?
Without records of orchard
[687]
practices or events, the
population drop could lead to
[690]
unnecessary speculation. As it
happened, this particular
[695]
orchard was treated with an
insecticide targeting another
[698]
pest on that day.
[701]
So, what do you need to
accumulate degree-days in the
[704]
field to predict treatment
application dates? You need the
[709]
minimum and maximum field
temperatures for each day.
[714]
Weather stations or data loggers
like this one record rainfall,
[718]
temperature, relative humidity,
solar radiation, wind speed, or
[724]
soil moisture and send
information directly to
[727]
computersâincluding yours!
[731]
You may not need your own
weather station.
[733]
There are many located
throughout the state and there
[736]
may be one in your area.
To find out go to the UC IPM
[741]
website, the California
Irrigation Management System,
[744]
(or CIMIS) website, or to
a commercial network.
[749]
On the UC IPM website, when you
select the county of interest,
[753]
you will be linked to the
information about sites that are
[757]
recording temperatures.
Choose the site that is closest
[760]
to your farm.
[763]
Now that you know how to get
weather data, letâs look at
[765]
another bit of information you
need to haveâwhen to start
[769]
accumulating degree-days
if thereâs a biofix.
[774]
Grower Bill Chandler is looking
for obliquebanded leafroller.
[779]
Traps are checked twice weekly.
[784]
When he gets multiple moth
catches, meaning more than one
[786]
moth within one week, he will
designate that date as the
[790]
biofix and start
accumulating degree-days.
[795]
It is critical to correctly
identify the insects in your
[798]
traps because they can look very
similar to each other. The big
[802]
moth, is an obliquebanded
leafroller.
[805]
You may think, âBut Iâm using a
pheromone trap that will attract
[809]
only OBLR.â Although pheromones
are pretty selective to species,
[814]
in the case of some tortricids,
like obliquebanded leafroller,
[817]
this is not always so.
[821]
A very similar, but smaller
moth, the garden tortrix, has
[825]
very similar wing patterns.
People have mistaken garden
[829]
tortrix for obliquebanded
leafroller and begun
[832]
accumulating degree-days based
on the wrong insect;
[836]
garden tortrix emerges almost one
and a half months before OBLR!
[842]
The advantage of using
degree-days to time treatments
[845]
is that they allow you to reduce
insecticide use by targeting the
[849]
most susceptible insect stage,
attaining maximum control and
[854]
reducing costs. Monitoring and
using degree-days allows for the
[857]
correct application timing of
reduced-risk products preserving
[862]
many of the parasites and
predators that control
[865]
other orchard pests.
[869]
There are many benefits to
using phenology models. The
[871]
highest level of control is
achieved, pesticide applications
[875]
are minimized, and beneficial
insects are preserved.
[879]
But getting a workable phenology
model takes a lot of research.
[883]
Because insects and mites are
cold-blooded, the temperature
[886]
around them influences their
development and so their
[889]
developmental times vary as
daily temperatures vary.
[894]
Phenology models are developed
in the lab for pests by
[896]
determining their upper and
lower development threshold
[899]
and the rate of growth at
different temperatures.
[903]
However, temperatures arenât
constant in the real world, so
[907]
phenology models are refined in
the field to estimate
[910]
developmental times. One
degree-day accumulates when the
[913]
average temperature is over the
minimum threshold for
[916]
twenty-four hours. The
accumulation of degree-days is
[919]
used to predict when an insect
will reach a certain stage
[923]
in its life cycle.
[926]
Phenology models for
obliquebanded leafroller,
[929]
omnivorous leafroller, peach
twig borer and others, plus more
[933]
information on calculating
degree-days and using
[936]
degree-days in your orchard can
be found on the UC IPM website.
[941]
[No audio]
Most Recent Videos:
You can go back to the homepage right here: Homepage