August 6, 2013

Agronomist Notes

Hello Reader

While the rains tapered off last week, the mild weather continues with temperatures in the low to mid twenties. The 14-day trend looks like a continuation of cool weather in the low 20’s with the odd shower. We’re now at 995 growing degree days since May 1st, which is right on track with the 5-year average. Crops planted in late May could be pushed into a frost risk scenario should the cool weather continue. Yield potential in this corridor is well above average.

In this issue of Beyond Agronomy News, we’ll look at how to estimate yield loss from disease in wheat and barley. Next, I’ll show you how to calculate yield potential in six major crops and I’ll pass along scouting and control tips on Berth Armyworms in canola. We’ll end with technical grain market news.

Photo: Crop scouting from the cab in our wheat, August 3rd, 2013. S. Larocque

Crop Staging

(Calgary to Drumheller to Three Hills)

Seeded May 1-7 May 8-15 May 15-22
Wheat Soft dough Milky dough Watery ripe
Canola Mid podding Early pod Early pod
Barley Soft dough Milky dough Milky dough
Peas Late pod Mid pod Mid pod

Steve's tips & tricks of the week

Follow me on Twitter for in-season updates @BeyondAgronomy

Continue sweeping for lygus bugs in canola.
Scout for Bertha Armyworms in canola.
Purchase glyphosate for pre-harvest before preferred products are sold out.

Estimating Yield Loss from Crop Diseases

By now we've made the decision to spray or not to spray for leaf diseases in cereals. We are quickly approaching the point to which you can actually estimate whether your decisions were correct or, sadly, not.

Leaf diseases
To estimate yield loss from Net Blotch, Scald, Tan Spot or Septoria, examine crop at the milky dough stage. Assess at least 25 main stems two diagonals from one corner to the opposite corner of the field. Then assess the average percentage of the top two leaves affected.

The calculation for percent yield loss is: 0.66 × % area of flag leaf infected + ½ × % area of second leaf infected ÷ 2.

For example, you find disease present in wheat on 20% of the flag leaf and 30% on the leaf below. The percent of yield loss would be:
0.66 x 20 + ½ x 30 ÷ 2 = 6.66% + 5% ÷ 2 = 14.1%

Therefore, your calculated yield loss is 14.1%. At $7.05/bu wheat and a yield potential of 60 bu/ac, you have lost 8.4 bu/ac (60 x 14.1%). That loss translates to $59.22/ac (8.4 bu/ac x $7.05/bu). The cost of a fungicide is roughly $12.00/ac plus $8.00/ac for application for a total of $20.00/ac. So, the return on your fungicide investment is $59.22/ac - $20.00/ac = $30.76/ac or 196%.

Proper disease scouting pays dividends especially when conditions are mild and humid like we've experienced this year. With more than 10 inches of rainfall in most areas and yield potentials in the 60-90 bu/ac range, a fungicide investment provides a very good return on investment. SL

Photo: Septoria on wheat. S. Larocque

Calculating yield potential

At this time of year many producers have an idea of what they think crops will yield. The number they come up with may vary by 20% which makes calculating grain storage and off combine movement difficult. To assist you this fall I've included some quick calculations to help you estimate yield. In my experience, the actual number is somewhere in between your own estimate and the calculated amount. Good luck!

Wheat: Heads/ft/row × #seeds/head ÷ row width (inches) × 0.48 = bu/ac
Example: 60 heads/ft/row × 26 seeds/head ÷ 12 × 0.48 = 62.4 bu/ac

Barley: Heads/ft/row × #seeds/head ÷ row width (inches) × 0.60 = bu/ac
Example: 72 heads/ft/row × 22 seeds/head ÷ 12 × 0.60 = 79.2 bu/ac

Canola: plants/ft2 × pods/avg/plant × seeds/avg/pod × 10.7 ÷ 86,000 × 44.1 = bu/ac
Example: 8 plants ft2 × 60 pods/plant × 20 seeds/pod × 10.7 ÷ 86,000 × 44.1 = 52.6 bu/ac

Peas: Pods/ft2 × peas/pod × 4840 × 9 ÷ 3600 × 0.036744 = bu/ac
Example: 40 heads/ft2 × 4 peas/pod × 4840 × 9 ÷ 3600 × 0.036744 = 77.1 bu/ac

Oats: heads/ft2 × kernels/head × 10.7 ÷ 129 = bu/ac
Example: 40 heads/ft2 × 35 seeds/head × 10.7 ÷ 129 = 116 bu/ac

Flax: plants/ft2 × bolls/avg/plant × seeds/boll × 10.7 × 0.000023 × 39.368 = bu/ac
Example: 35 plants/ft2 × 15 bolls/plant × 8 seeds/boll × 10.7 × 0.000023 × 39.368 = 40.6 bu/ac

Bertha Armyworm identification, monitoring & control

I haven’t found any bertha’s in my travels and moth trap counts have been low, but just in case I thought I would give you the low down on bertha armyworm monitoring, description and control.

Description Mature larvae are green, brown or black with a light brown head and an orange stripe along each side. They are 1" to 1.5" long. The most damaging larval stages are when worms are 0.5" long and larger. Small larvae feed on the underside of leaves, but usually cause little economic damage even when population levels are high.

Threshold At a canola price of $12 per bushel and application costs of $12 per acre, the economic threshold is 17 bertha armyworms per square metre. At that number, bertha armyworms can reduce canola yields by roughly one bushel per acre. Counts of 200 per square metre can reduce yields by 50%.

Insecticide Timing It is important to ensure that the larvae are up on the middle to upper parts of the plant and feeding on the pods. If the larvae are still feeding on leaf material in the lower canopy or the leaf litter on the ground, there will be poorer control. Avoid spraying during high temperatures (above 25C), as the larvae are likely to be in the lower levels of the canopy. Use rates appropriate to the stage of the larvae. Most insecticides recommend a range of rates. Use higher rates when faced with high populations and/or larger stages. Also at the latest stage, ensure that the larvae are actively feeding. Larvae at the latest stage may be inactive on the ground as they prepare to pupate.

Registered Products

Lorsban: 485 ml/ac: preharvest interval 21 days

Decis: 60 ml/ac: preharvest interval 7 days

Coragen: 50-150 ml/ac: preharvest interval 1 day

Matador: 34 ml/ac: preharvest interval 7 days

Provincial forecast

map

More info

Photo source

Vertical tillage equipment recap

The No-Till farmer magazine has put together an ironic but good overview of vertical tillage machines in their latest update. Vertical tillage units have been useful to some of my clients who grow peas to cut vines properly or to manage heavy residue that impairs germination and emergence. Like all things, everything in moderation and the same applies to vertical tillage in our direct seeding systems. Here is the summary:

Vertical Tillage Summary

Photo source: www.producer.com