Oats
Crown Rust is Intensifying on Oats
We reported that crown rust was evident on oat crops as
much as two weeks ago. It should be no surprise that it is
both intensifying and pustules are evident on upper leaves
in the crop canopy. Propiconazole-based products may be used
up to the time that heads (panicles) are half emerged. They
have a pre-harvest interval (PHI) of 45 days. Stratego,
which is now registered on oats and barley, also has a PHI
of 45 days. Furthermore, if the crop is to be grazed or
silaged, this should not occur within 30 days of
application. |
Figure 1. Crown Rust on Oats |
|
Figure 2. Soybean Aphids |
Soybeans
Soybean Aphids Beginning to be Detected in
Manitoba
Soybean aphids were found in several soybean
fields in the eastern and central parts of the province last
week. These were the first confirmed findings of soybean
aphid in Manitoba for this year, and numbers were very low
in all cases. Economic threshold for soybean aphid are quite
high: when the field average is 250 aphids per plant and
populations are actively increasing. A minimum of two field
visits are needed to determine if populations are actively
increasing. Crop scouts and soybean growers should monitor
levels of soybean aphid when scouting soybean fields over
the next few weeks.
Soybean aphids are quite small and when
numbers are small can be easily missed while field scouting
(it is easy to think the small yellow specks that are not
moving are debris or pollen). Note in Figure 1 the size of
the soybean aphids in relation to the hairs on the leaves,
and the difference in size between the younger and older
aphids in this picture. This is one of the insects where the
magnifying glass in the scouting kit may be useful to help
in the identification, particularly for those who have not
seen soybean aphids before.
|
Insect Monitoring Programs Update
Bertha Armyworm Trap Counts High in Northwest
The risk of
an economical infestation of bertha armyworm larvae later in the
season is based on cumulative counts of moths in traps over a six-week
monitoring period from mid-June through July. The following risk
levels are based on cumulative moth counts over the six week trapping
period: low = 0-300; uncertain=301-900; moderate=901-1200; high=
>1200. Depending on the region, traps have been up anywhere
from one to three weeks now. As the table below shows, some traps in the
Northwest have caught 1500 moths in just two weeks, putting this
region at high risk. Some trap counts from the Killarney/Somerset
area are currently in the uncertain range. Below is a summary of
some of the higher counts that we have been getting:
| Nearest Location |
Number of Weeks of Trapping |
Cumulative Count |
Risk |
| Durban |
2 |
1,500 |
High |
| Minitonas |
2 |
1,500 |
High |
| Birch River |
2 |
715 |
Moderate |
| Roblin |
1 |
309 |
Uncertain |
| Killarney |
2 |
404 |
Uncertain |
| Cartwright |
2 |
314 |
Uncertain |
| Somerset |
2 |
296 |
Low |
Agronomists and farmers in the high and uncertain risk areas
should begin to familiarize themselves with biology, identification
and thresholds for bertha armyworm. This information can be found
at:
http://www.gov.mb.ca/agriculture/crops/insects/fad03s01.html.
Moths Other than Bertha Armyworms in Traps
There are
moths other than bertha armyworm that can appear in bertha armyworm
traps. Alberta has a
Guide to Bertha Armyworm Monitoring that shows some of the other
moths that can end up in bertha armyworm traps.
It is important to make sure that only the bertha armyworms are
being counted.
If there are a lot of moths in the trap, and counting each one
would be very time consuming, dump them into a wide container where
you can spread them out fairly evenly, then count a portion of the
tray and multiply by the appropriate number to get an approximate
value for the weekly count. But, if you notice that a certain
proportion are not bertha armyworm, then it is important to make
sure these are not included in the counts.
Timing of Control for Bertha Armyworm
One of the
questions that came in this week was whether it would be a good
decision to add in an insecticide when spraying for sclerotinia if
there are a lot of bertha armyworm moths being caught in the region.
This is not something I would advise. With profit margins already
being tight in canola, the chances of the being economical are
unknown at best, and there is potential for this to do more harm
than good by killing parasites and predators of the eggs and larvae.
It is best to wait and monitor the development of the larvae and
how many are present. There have been years before where large adult
counts did not materialize into high larval numbers. If you do get
high numbers of larvae, applying insecticide once hatch is done and
before they move onto the pods to feed would give you the best
results. Insecticides generally don't kill insect eggs, and spraying
for adult moths is likely to give poor results. So best to wait and
keep an eye on what develops.
Disease Forecasting
Fusarium Risk Forecasts Now Online
Last week, we sent
subscribers to the Insect and Disease Update a couple of maps to show
the current risk of infection to
Fusarium Head Blight. The forecast is based on temperature and
rainfall over the seven days leading up to the current date. This
forecast changes very rapidly as you’ll see once we have the
animated risk-over-the-last-week posted. You can also get an idea
from the archive how rapidly things change. As of last Friday, most
of the province was green (low risk) because of the combination of
cool night temperatures (often dropping below 10C) and lack of
significant rainfall. Some areas did have substantial
rainfall on Friday; (Minnedosa’s station recorded
approximately one inch, Birtle
recorded almost two inches), however, it fell in a short period. The
model is influenced by the number of hours in which rain fell
over the seven days. Today’s map shows only a few areas where the
risk is still moderate.
Sclerotinia Risk Forecast Will NOT be Posted
Many folks
have called or mailed to ask if and when a risk map for Sclerotinia
in canola will be posted. The short answer is that we cannot
confidently forecast risk (which is based primarily on top soil
moisture estimation) with the current density of weather stations.
We rely on growers and local agronomists to assess the soil moisture
situations in their own areas. Only if soils under a crop canopy
have been moist (field capacity to saturation) for seven days or more
can you have ascospores blowing about. In many areas, agronomists
report that surface soils have been dry.
Insects and Diseases in Vegetable Crops
Information on insects and diseases in vegetable crops in
Manitoba can be found at:
http://web2.gov.mb.ca/agriculture/mwvr/index.php
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