Agronomist Notes

Yet another hectic week flies by with many producers pulling the trigger on late fungicide applications and some adding insecticide. There have been a few midge hot spots around Standard and south of Drumheller. All other areas in my territory have seen low midge emergence and with most wheat now flowering the critical stage has past. Stripe rust has shown up in the last seven days and has threatened early seeded wheat south of Calgary. If you’ve dodged the pests so far, heads up for the hail storms passing through almost every night.

This week’s newsletter looks the monitoring and control of stripe rust. We’ll also look at a new tool to help us improve pesticide application timings and I’ll give you some tips on how to assess hail damage in canola now that a few white storms have gone through. Last, we’ll look at potential harvest dates given our current accumulated growing degree days. We’ll finish with fundamental and technical grain market news.  

Crop Staging Area (Calgary to Drumheller to Three Hills)

Seeded	May 1-7	May 8-15	May 16-21	May 22-29
Wheat	watery ripe	flowering	head emerged	head emerging
Canola	late flower	mid flower	70% bloom	50% bloom
Barley	milky dough	watery dough	head emerged	head emerging
Peas	late flower	mid flower	early flower

Steve’s tips of the week

• Continue to watch disease movement up the canopy in cereals. A late fungicide application at heading in cereals can still provide a big yield bump.
• Continue to monitor wheat midge levels in the evenings for wheat that has not yet flowered.
• Most canola is now past the point where a fungicide is warranted for sclerotinia control.
• Monitor for stripe rust and leaf rust in wheat.

Agronomy

Stripe rust identification and control

The infection level and incidence of stripe rust has increased over the last two weeks in my territory. I've found trace amounts of stripe rust in the Beiseker area and severe stripe rust in the Airdrie and Okotoks area. It seems that varieties like AC Harvest and CDC Go have lost their tolerance to this strain of stripe rust. Most wheat crops in my territory are past the flowering stage and applying a fungicide is no longer economical but if crops are later in your area keep reading for more on this disease.

Identification and yield loss
Stripe rust can be identified as small orange-yellow coloured pustules forming in vertical lines along wheat leaves. This disease can result in yield losses of 10 to 70% in susceptible varieties and total yield loss has been reported when severe epidemics occur. Like other leaf and stem diseases, yield losses are roughly proportional to the plant area infected. Yield losses are generally most severe when the infection occurs prior to heading. Historically stripe rust has not been of economic significance in western Canada but incidences of the disease have been increasing over the past 4 or 5 growing seasons.

Conditions for development
The major source of rust spores in Alberta is carried by south winds from the Pacific North West. Wind direction and a specific range of temperatures are essential for the onset and development of stripe rust. For example, relative low temperatures and moisture favour development. Urediniospores germinate optimally between 5 and 15oC with limits near 0 and 20oC. Disease development is most rapid between 10 and 15oC with intermittent rain.

Monitoring
If you are growing a susceptible variety, it is important to scout every few days starting with the bottom leaves. Know the visual symptoms of stripe rust and monitor fields in the morning when new spores are distinctly yellow. See stripe rust tolerance ratings below.

Threshold
Spraying should be done when stripe rust reaches 1% of flag leaf area and before it reaches 5% of flag leaf area. Once this infection level is reached, stripe rust becomes very difficult to control. The period of infection to the release of spores is as little as 8 days, which can result in multiple generations per growing season.

Growth stage
Apply fungicide at flag leaf or before wheat has flowered. Fungicide treatments made past the flowering stage rarely provide an economical benefit.

Fungicide Options
Caramba: 283 ml/ac, $13.50/ac
Folicur 432: 118 ml/ac + 0.125% v/v Agral 90, $10.50/ac
Folicur EW: 200 ml/ac, $10.50/ac
Prosaro: 320 ml/ac, $15.50/ac
Quilt: 300 ml/ac, $11.50/ac
Headline: 160 ml/ac, $11.50/ac
Tilt: 202 ml/ac, $7.50/ac
Stratego: 200 ml/ac, $7.50/ac

The most effective fungicides on the market for control of stripe rust are Folicur EW, Prosaro, Quilt and Headline.

Stripe Rust Tolerance Ratings
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex4069/$file/100-32.pdf
(Scroll down to page 5 for hard red spring varieties and look for the stripe rust column for ratings.)

Delta T method measures ideal spray conditions

With the recent high temperatures coinciding with fungicide applications, most producers will shut down when temperatures reach 26 degrees Celsius to avoid high evaporation losses. That seems to be the rule of thumb that we all live by and don’t question. Unfortunately, temperature is just one half of the equation when it comes to determining evaporation losses. After doing some research I found out the Aussie’s use a method called Delta T to determine when to shut down spraying to avoid evaporation losses. The equation includes humidity and temperature to determine the lifetime of a droplet on a leaf.

Delta T is becoming one of the standard indicators for acceptable spray conditions in Australia. It is indicative of evaporation rate and droplet lifetime. Delta T is calculated by subtracting the wet bulb temperature from the dry bulb temperature. The diagram shown here relates air temperature and relative humidity to values of Delta T. As temperature increases, spraying conditions deteriorate unless humidity also increases. When applying pesticides, Delta T should ideally be between 2 and 8.

I can’t find dry bulb information but I did find wet bulb data on my Weatherbug weather station http://weather.weatherbug.com/AB/Morrin-weather.html?zcode=z6286&lang_id=en-c. However, based on the chart above we only need air temperature and relative humidity to come up with the appropriate Delta T value. For example, the daytime temperature has reached 28-30 degrees Celsius the last few days with a relative humidity in 70’s and 80’s. We would normally stop spraying at 26 degrees Celsius regardless of humidity levels but based on the Delta T values, we’d still be in the preferred range. We could have got a lot more spraying done in the last few days had we relied on an suitable measure of evaporation like the Delta T method offers.

I think most of us pay attention to temperature and wind speed when it comes to applying pesticides. Very few if any pay attention to humidity. I think the Delta T model is a more accurate tool to determine evaporation rates and allow us to spray during the optimum time of day and even beyond the rule of thumb we follow now. I can see the Delta T method improving the timing of foliar nutrients, herbicides and fungicides. With herbicides and fungicides costing most producers upwards of $40 and acre each year, it’s time we look at how to get the most of those dollars. The Delta T method might be one more tool to help us achieve better efficacy in our pesticide applications.  SL

Source: http://www.bom.gov.au/info/leaflets/Pesticide-Spraying.pdf

Hail damage in canola: What have you lost?

Yield loss in canola is always difficult to estimate when hail hits during flowering, especially when you're trying to come up with a fair estimate with the hail adjuster. Here are some facts to give you an idea of what to expect for crop loss after hail:

• Any leaf area destroyed will result in seed yield loss.
• Seed yield losses in canola are approximately 25% of leaf area lost. If leaf defoliation is 50%, then yield loss would be approximately 12.5%.
• Seed yield loss will depend on both percent leaves and branches lost. For example, if canola has 60% lost branches 7 days into flowering, seed yield loss is estimated at 18%, whereas 21 days into flowering, yield loss would be an estimated 60%.
• If hail strikes late, such as during pod filling or ripening, plant recovery is not possible. The time needed to develop new growth, flowers and mature is limited before a killing frost.
• If injury occurs at the ripening stage then it depends directly on the loss of branches, individual pods and seed knocked out of pods. Severe hail losses have occurred in canola swaths.

Source: Canola Council of Canada http://www.canola-council.org/

Predicted harvest dates for 2011

As I've mentioned in previous articles, all plant functions, such as evapotranspiration, photosynthesis, water and nutrient absorption and transport, enzyme activity, and other biological and chemical activities are regulated by temperature. For this reason, the development of the crop is more closely related to the amount of heat the crop is exposed to than calendar days. Other factors such as moisture, day length, nutrition and variety also play a role, but they generally have less influence.

Canola requires 1,432 to 1,557 growing degree-days (GDD's) to reach an optimum swathing stage of 40% seed colour change. Hard red spring wheat is similar to canola and requires 1,538 to 1,665 GDD's to reach maturity. Barley needs 1,269 to 1,522 GDD's. Surprisingly, peas need 1,527 to 1,686 GDD's to reach 90% seed colour change.

To predict harvest dates, let's do the math for wheat, barley and canola seeded near Three Hills, AB, on May 1. The climate data provided on http://www.farmzone.com/  shows we've received 754 GDD's since May 1. The average over the last 10 days has been 13.8 GDD per day. To calculate the predicted harvest date for our crops this fall, we'll add a few more GDD to compensate for the typically warmer, late July-August period to an estimated 15 GDD per day. Let's finish the calculation:
Canola: 1,432 - 754 ÷ 15 = 45 days until swathing (September 5)
Wheat: 1,538 - 754 ÷ 15 = 52 days until maturity (September 10)
Barley: 1,269 - 754 ÷ 15 = 34 days until maturity (August 23)
Peas: 1527 - 754 ÷ 15 = 51 days until 90% seed colour change (September 9)

So there you have it. I encourage you to keep track of growing degree-days to help you estimate swath and harvest timing this fall. Not everything was planted on May 1st so you could easily add one week to the harvest date of these estimates. Soil moisture will be a major factor in maturity. Once again, we’re going to need a decent September to avoid any yield or grade loss for most of our crops seeded past the first week of May. SL