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You must Log In to use the Mite Yield Loss Estimator.
Spider mites are an important pest of cotton They are small arthropods that feed on the undersides of cotton leaves.
High populations can effect the yield and quality of Cotton. They use piercing mouthparts to
suck out the contents of leaf cells. This removes chlorophyll from the leaves and causes reduced photosynthesis.
The degree to which photosynthesis is reduced depends on how many mites are on the leaf and for how long.
In general mite populations which develop earlier in the cotton season and which develop to high densities more quickly will
cause the greatest losses.
Using on-going and regular presence/absence mite counts (refer to the IPM guidelines or Cotton Pest Management Guide for
sampling protocol), the Mite Yield Loss Estimator calculates an estimated yield loss percentage based on time of the season
and rate of increase of the mite population. This allows the need for control to be accessed.
The analysis page presents information about all mite samples taken for a selected crop, charts which show mite population
change and average rates of change over the season and comments to assist with managing this specific mite population.
This information helps in looking ahead to see where mite populations might be in the next week, providing a strong basis
for sound control decisions.
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Mite Species
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Several mite species are present in cotton, the most common of which is the two-spotted spider mite, see pictures below.
These species differ in potential to affect yield; the two-spotted spider mite and bean spider mite are equivalent but the
strawberry mite rarely if ever affects yield. So it is important to identify which species are present.
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Figure 1: Two spotted spider mite, Tetranychus urticae, showing characteristic green spots on either
side. Also note the relative size of the mite egg above adult.
Photo: Lewis Wilson
Size – 0.5mm
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Figure 2: Bean spider mite, Tetranychus ludeni – similar in size to T.urticae but deep red. Note the
translucent mite egg in upper right of photo and pale adult male in foreground.
Photo: M Hill (NSW DPI)
Size – 0.5mm
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Figure 3: Strawberry spider mite, Tetranychus lambi – note the smaller size and characteristic spots (6) along sides.
Photo: C Mares (CSIRO)
Size – 0.3mm
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Mite Sampling
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Mites should be sampled about 40m into the field – not on the field edge. Mite sampling is often carried out
as the checker is walking into or out of the field after a normal crop inspection and can be combined with sampling for
aphids and whitefly.
Leaves inspected are from the third, fourth or fifth main-stem node below the terminal. This is a random
selection until you have inspected 50 leaves. If the plant has less than three leaves, sample the oldest.
Leaves are scored as infested if any stage of mites (eggs or motiles) is present on the underside of the leaf.
A hand lens may be needed to see mite eggs.
Depending on the size of the field, 4-6 sites are needed to obtain a good estimate of mite abundance. For
further information about mite sampling refer to the IPM guidelines.
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How to use the Mite Yield Loss Estimator
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A simple relationship has been developed which allows prediction of yield loss from mites based on knowledge of
the rate of increase in the mite population and the time of the season (time remaining until defoliation).
The rate of increase is quantified as the increase in the percentage of plants infested over time. For
instance, if you sampled this week and found 4% of leaves infested (using the technique described below) and 7 days
later found 18% of leaves infested, then the rate of increase is the change in the % of leaves infested (14%) divided
by the number of days between samples (7 days) which yields a rate of increase of 2% per day.
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Before entering a mite sample
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Before a mite sample can be entered, farm(s) and crop(s) must be set-up unless they have already been set-up for
other CottASSIST tools. This is done through Your Farms and Crops in the CottASSIST main menu.
As mite thresholds change depending on crop stage – it is important to update the crop development status of your
crops. This is done through Crop Development > Crop Status in the CottASSIST main menu.
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Entering mite samples
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Select Your Mite Samples through Mite Yield Loss in the CottASSIST main menu.
Select a crop.
Create new sample data by selecting the sample date and entering the totalnumber of leaves sampled and the total
number of leaves infested. If you have sampled mites from a number of sites in the crop – total the number
of leaves sampled and the number of leaves infested before entering the sample data.
Tick the box if the crop has been sprayed recently with a product that controls mites.
Click on the save observation button.
You can then either select the next crop to enter more mite samples or analyse your last entry.
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Analysing mite samples
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Select Mite Analysis through Mite Yield Loss in the CottASSIST main menu or use the analyse button
on the Your Mite Samples page.
Select a crop from the drop down box and the tool will automatically analyse your mite sample(s) for that crop.
The table and charts display
- Mite Population % - This is the percentage of leaves infested with mites (e.g.number of leaves
infested x 100, divided by the number of leaves sampled). This is presented in the 1st chart.
- Recently sprayed – Shows a ‘yes’ if you have ticked the box indicating that the crop has been
sprayed recently with a product that controls mites. If not the table will display a ‘no’.
Sprays are presented in all charts.
- Average rate of change (increase/decrease) – This is an average of the rates of change recorded for
successive mite samples. This is plotted in the 2nd chart and compared with the rate of change
that you would expect if the yield loss from the mite population was 4%. This value (4%) is
roughly when yield loss from mites would justify control – based on loss of revenue and cost of control
– however this may need to be adjusted for your particular situation
- Yield Loss % - The yield loss calculation is based on the current percentage of plants infested
with mites, the rate of change of the mite population and the number of days remaining in the season
depending upon the region. Yield loss % is presented in the bottom chart and compared with
4% yield loss. In general zero or negative change in mite populations indicates that something
as adversely affected population development such as (1) a mite spray (2) beneficials eating mites (3)
heavy rainfall, which dislodges mites or (4) a combination of these factors.
Note: You will notice as the season progresses that the font used to display the older mite samples will be
black and the newer samples will be blue. This is an indication that the older
samples are no longer used in the yield loss calculations. They become invalid if there is more than 10
days between samples or if they are more than 16 days old.
Mite analysis comments
Various comments are presented just below the table. These will vary depending on the crop development stage;
the figures presented in the table and if there are any invalid samples in the table. These
comments provide the user with information to assist with sound mite control decisions.
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