Murray Hartman: 2017 science-O-rama review

July 13, 2017

Murray Hartman’s science-O-rama was held in Lacombe, Alberta on April 5, 2017

Presentation summaries by Murray Hartman, Provincial Oilseed Specialist, Alberta Agriculture & Forestry

Action Thresholds for Lygus and Cabbage Seedpod Weevil – Dr. Héctor Cárcamo, Agriculture and Agri-Food Canada, Lethbridge.

The threshold concept in integrated pest management was outlined.  Economic injury levels are the pest abundance levels where control costs would be equal to value of crop loss.  Economic action thresholds are set near this level.  The relative price ratio of control measures and crop value will vary over time.  The relationship of yield loss to pest population is difficult to measure and highly variable over time and locations. Linear relationships are often assumed, but at low pest numbers the relationship can be resemble a curve due to plant tolerance and compensation.

There are 4 common lygus bug species in canola in Alberta: Lygus keltoni, L. lineolaris, L. borealis and L. elisus.  Lygus damage to canola include flower / seed abortion, and seed damage. Lygus bugs have a large host range.

A cage study on yield loss with various lygus densities was completed at Beaverlodge, Lacombe and Lethbridge in 2012-2015.  Lygus bugs were added to cages at late bud or early flower stages. Regression of yield and lygus densities at Lacombe in 2013-2014 (plots lost in 2015 to hail) revealed an economic injury level around 2 lygus per sweep.

Cabbage seedpod (CSP) weevils damage results mainly from larvae feeding within pods.  There is a low yield loss if less than 20% pods are infested. Large sprayed strip plots were conducted in 70 Alberta farm fields over 4 years in collaboration with Scott Meers.  Early seeded fields had higher CSP weevil numbers than late seeded, which was an opposite trend to lygus numbers. The relationship between CSP weevils and canola yield was weak and only for early seeded fields, with an economic injury level around 2 weevils per sweep.  There are several factors that create uncertainty on how much higher the action threshold should be than the economic injury level.  A recommended action threshold range is 25-40 CSP weevils in 10 sweeps.

Current insect pest thresholds are simplistic and do not account for natural enemies, canola compensation that varies under different weather scenarios, and caged studies are still artificial environments.  More farm levels studies are needed to validate thresholds.

Superior Crop Rotations Study – Dr. Kabal Gill, SARDA, Falher.

Results from a long term study to assess benefits of rotations versus continuous canola or wheat were presented.  The small plot replicated research was conducted south of Donnelly in the Peace River region.  Starting in 2009, twelve rotation treatments were seeded including canola, wheat, pea, barley and flax.  Continuous canola and wheat were compared to wheat – canola and various other crop combinations for 3 year rotations.  Due to large number of rotation comparisons, only one crop from each rotation sequence was grown each year (this was not a rotation study with all phases grown each year).  Each year, inputs were kept the same for each crop for all rotations.  There have been 4 years with less growing season rain than normal, and 3 years with near normal.

Each year, continuous canola had the lowest yield, ranging from 6 to 30% less than average of other rotations. The average rotation benefit over continuous canola for the 6 years was 0.65 T/ha or 11 bu/ac, and there was a trend to increasing benefit over time.   In contrast, continuous wheat had lower yield 4/6 years than other wheat rotations, and the average benefit was smaller than the canola response to rotation.

Wheat yields increased on pea stubble, whereas canola did not.  Wheat yields also were higher on stubble types other than canola.

With the higher price of canola than other crops, economic analysis showed that continuous canola had 3rd highest contribution margins in spite of the significant yield penalty.  C-W was 7th, and the two highest were diverse 3 crop rotations (C-P-W and W-B-C).

Detailed root measurements found that canola root growth (length, surface area, volume) was greater on wheat stubble than in continuous canola, whereas wheat root growth did not differ on wheat or canola stubble.

Bio-solution for Canola Green Seed Problem – Dr. Marcus Samuel, University of Calgary

The economic loss from green canola seed is due to lower oil quality from odor, reduced shelf life and additional costs of chlorophyll removal by bleaching clay.  A report in 2000 estimated this at $150 million annually.   The model plant Arabidopsis is a relative to canola and specific mutants have green seeds at maturity, which is useful for research. A transcription factor (ABI3-B3) is involved in the abscisic acid hormone signal pathway through 2 players – SRG1 and SRG2.  Research at this U of C lab has found that several genes controlled by ABI3-B3 are involved in the stay green mutant.  Genetically altering Arabidopsis lines to overexpress ABI3 rescues normal seed maturation and degreening. Since Arabidopsis is related to canola, this lab studied the green seed impact of overexpressing ABI3 in Brassica napus.   Increased expression of SGR2 was measured, and freezing studies found less green seed than the unaltered wild types.  Improved imaging techniques were developed to more accurately quantify the amount of green in the seeds.  Overexpressing ABI3 did not change canola yield per plant, but did increase pod mass and slightly reduced oil content.  The increased pod mass is partly due to a thicker replum and increased lignification in walls, both of which contributed to improved shatter resistance.

Managing Blackleg of Canola in Western Canada: Pathogen Population, Host Resistance and Fungicides – Dr. Gary Peng, Agriculture and Agri-Food Canada, Saskatoon.

The introduction briefly reviewed the blackleg disease cycle, symptoms, yield loss, incidence trend over time and impact on exports to China.  Blackleg resistant canola varieties have race-specific (major gene) and / or non-specific (quantitative) resistance.  Race specific resistance needs to match with corresponding avirulent (Av) genes in the blackleg population of the field to be effective.  Thus regional monitoring of the changes in Av genes is important to predict which variety resistance genes will be most effective, and which ones are being defeated (“breakdown”).   A study of 206 varieties and lines from several canola seed companies in western Canada found that 70% were using the same R gene (Rlm3).  Another study of 8 popular canola varieties found most used the same 2 genes together (Rlm1 and Rlm3).  The Triangle of U (canola relatives) was shown with the major resistances genes that have been found in each species. 

The changes in the blackleg population Av genes over time and provinces was shown.  The population genetics is complex on the prairies, with about 90 races identified. 

The Canadian system for blackleg resistance rating and identification was outlined, and the proposed new voluntary system to label varieties based on major genes was described.  Examples were given of the combined resistance label (includes both old and new system labels).   The utility of the additional resistance information to manage blackleg pathogen shifts was discussed.  Including quantitative resistance with major genes will help to reinforce resistance efficacy and durability. 

Several reports on the blackleg disease suppression and canola yield response to seedling foliar fungicides were presented.    Fungicides had little benefit when blackleg disease was low, and on varieties with R or MR resistance (that hasn’t been defeated). 

Recommended blackleg management strategies were discussed based on risk assessment (scouting, field history and other factors). 

Unmanned Aerial Vehicles for Agricultural Field Scouting – Dr. Chris Neeser, Alberta Agriculture and Forestry, Brooks.

Unmanned aerial vehicles (drones, flying cameras) are recent additions to technological tools for agriculture.  They are being tested / used for mapping hail and other crop damage, crop monitoring / mapping, field scouting, livestock inventory, building inspection and even spot spraying. Several pictures of various units with different capability were shown.  The process to map a field was described and an example of a field map for NDVI was shown.  Field inspections can be controlled by manual flight or by automated flight plan.  The images captured must be analyzed, stitched together to generate a report.  A research project at Brooks to assess UAVs for field scouting of diseases and weeds looked at 6 crops, 2 fields each at 3 times during the growing season.  Examples of distinctly different field patches picked out by UAVs were shown, and the ground truthing to determine the causes.   The ground resolution with camera pixels and associated file sizes was discussed, and attempts to detect /map small weed seedlings over large fields was not currently practical.  Methods to measure weed ground cover by identifying crop rows and removing them from calculations involving green pixels were outlined.  Intensively grid sampled fields can results in large file sizes.  The cost effectiveness of UAVs for agricultural purposes is under debate considering cost, time and changing regulations, but technology is rapidly evolving and costs will decrease.

Sclerotinia Disease Survey and Improving Sclerotinia Disease Control – Dr. Michael Harding, Alberta Agriculture and Forestry, Brooks.

The Blackleg survey 2016 target was 1% of canola fields in Alberta (378 fields).  The numbers for each county was proportionally weighted by the amount of canola grown (counties with most canola acres had more surveyed fields).  The survey was coordinated by AF out of Brooks in collaboration with AF at CDC North (Edmonton) and ARECA.  One hundred stems were collected from each field using a W pattern and 5 sample sites. Stem samples were shipped to Brooks for blackleg ratings. Positive samples had a stem portion sent to Saskatchewan for race ID.  All stems were sent for Verticillium testing even though no stem stripe symptoms were observed.

480 canola fields were sampled for blackleg in 2016, exceeding the target number.  Blackleg was detected in 90% of these fields, at an average of 21% stem incidence and severity of 0.42 (0-5 scale).

311 fields were rated for sclerotinia, and this disease was found in 81% of fields, 31% incidence in stems.  The north central and NE regions had the highest incidence.  At current prices and estimated yield loss of ½ the incidence, canola economic loss in 2016 due to sclerotinia was about $400 million.

The concept of priming plant resistance prior to pathogen exposure was outlined.  In some cases, certain micronutrients / compounds have been observed to improve resistance when seed coated.  Trials at Brooks have shown some primer effects with dry beans, but not canola.  Sclerotinia tolerant varieties lowered disease incidence by about 50%, but this rarely resulted in statistical higher yield than other canola varieties.  Predicting and controlling sclerotinia in canola remains a challenge.

Canola Midges and Bertha Armyworm Monitoring Study – Scott Meers, Alberta Agriculture and Forestry, Brooks.

Swede midge (Contarinia nasturtii) is a small fly of European origin that is a specific pest to Brassica species. The first North American report was in Ontario in 2000, and then in Saskatchewan in 2007. Damage to canola ranges from loss of main meristems leading to very delayed flowering from late branches, and stunting of main flowering raceme (palm-top or bouquet effect).   Midge damage observed on canola in the prairies results in flowers not opening properly and aborted pods, and thus does not resemble the severe damage in Ontario.  Slight physical differences in the female antennae were noted recently from prairie specimens and it has been concluded that this is a new species, not the swede midge.  The 2016 Alberta midge survey in 44 canola fields looked for flowers that were not opening properly (“bottle shaped”), and larvae in the damaged flowers. These larvae were sent to AAFC Saskatoon (Dr. Mori) who confirmed they were not swede midge by DNA barcoding.  This new midge was detected at trace levels in about 20 east central AB fields.  Although numerous locations were found with the midge, at each site only a few plants with part of a flowering raceme were affected. This may indicate that this new midge species may not be as severe as the swede midge, but time will tell.  Pictures of damages flowers showed visible brown to black feeding scars on the pistil and developing pod.

A study was conducted to validate the bertha armyworm monitoring model, and determine if trap height / location in field had an effect. Traps were modified to try to reduce inadvertent bumblebee catch.   Four sites in east central AB were used 2012-2014 to place pheromone traps, then nearby canola fields in the areas were sampled for larvae.  Several fields had sufficient numbers to justify insecticide control.  Although larvae numbers were highly variable between and within fields, the monitoring system was predictive of risk, especially at the start of an outbreak in an area.  Thus the pheromone trap system is useful, and more trap locations would be better in counties with high canola seeded acreage.   There were no changes needed to the trap height or location within field.  Modifying traps to close at specific times of the day was found to reduce bumblebee catch, and more research is needed.

Update on Trials for Canola Rotation, Seed Size and Weed Seed Destructor Trials – Dr. Neil Harker, and Breanne Tidemann, Agriculture and Agri-Food Canada, Lacombe.

Canola growers in western Canada have shortened rotations to capitalize on higher canola prices relative to other major crops, in spite of scientific evidence that pest risks will increase and yield will decrease.   Considering that adoption of short rotation canola is now well established and likely to continue, an interesting question is can the yield loss be reduced by mixing varieties, or higher agronomic inputs?

A study assessing the effect of 0, 1 or 2 break years between canola was conducted at 5 prairie locations (2 AB and 3 SK) in 2008-2016.   Varieties of Liberty Link and Roundup Ready in continuous canola was compared with canola-wheat, or 3 year rotations with barley and peas (or lentils in brown soil zone).  Every phase of each rotation was present in a plot each year.  Averaged over years and locations, blackleg disease incidence and root maggot damage declined with each additional year rotation break.   Canola yield increased with longer rotation breaks, but there was considerable variability over years and sites.  Averaged over all site-years, canola yield increased linearly 5 bu/ac (about 10%) for each additional rotation year break.  Net returns were estimated using average crop prices for each year, actual site yields, and average input costs for each soil zone from surveys.  Like yield, there was high net return variability between sites and years.  At the high canola yielding site Lacombe, continuous canola net returns tended to be high, whereas at Lethbridge and Swift Current, continuous canola net returns were lower than more diverse rotations.  On average over sites and years, there were no statistical differences in net returns between continuous canola and other rotations, with the lower yield offset by higher canola prices relative to other crops.  These short term net returns do not include an economic value for increased disease, insect or weed risks under long term continuous canola.

A study looking at the effects of alternating years (rotating herbicide tolerant systems) or mixing canola varieties together from different HT systems was conducted 5 locations (3 AB, 1 SK and 1 MB) in 2008-2013.  In the last year of this study (2013) blackleg incidence and severity was not affected by alternating or mixing varieties, but was lowest under rotations with canola grown after 2 break crops. Yield was statistically highest in the longer rotation also.  Although cultivar mixtures have reduced disease and increased yield in other crops, the major gene blackleg resistance of canola varieties in western Canada tends to be similar; therefore the mixtures probably did not provide any benefit.

The established continuous rotation plots from the previous study were then used since 2014 to investigate agronomic methods to recover some of the yield decline.  Higher fertilizer (+50% NPKS) was compared to soil test recommendation, and in combinations with higher seed rate (+50%), tillage, chaff removal or fungicide at 4 leaf stage.  The previous 2 and 3 year rotation plots were also maintained along with a C-W rotation.  The treatments began to show some yield differences in 2015, and most differences occurred by 2016 at Brandon.  Although extra fertilizer or fungicide at seedling stage occasionally increased yield of continuous canola, the most consistent yield increases were with longer rotations.

An experiment on canola seed size and rate was conducted at 8 or 9 locations 2013-2015.  Five seed sizes and 2 seed rates were included.  The emergence varied between sites and years, but overall more plants were established with the higher seed rate, and a trend to higher emergence with larger seed size.  Canola biomass increased with seed rate and larger seed size.  Days to flowering and maturity decreased a couple of days with higher seed rate, and green seed % also declined.  Average yield over sites and years was not affected by seed rate with large seed size, but decreased with small seed at the lowest seed rate.

The Harrington Seed Destructor, an Australian innovation, prevents viable weed seeds from being broadcast back across the field during combining. Several aspects of this method are being studied in western Canada.  The cage mill was used at Lacombe by hand feeding during stationary threshing with different seed species, canola seed sizes and chaff volume to measure efficacy of seed destruction.  The degree of weed seed destruction generally exceeded 95%.   Thus the key to this method will be how many of the weed seeds are retained on the plant and gathered into the combine.  Recent versions of the cage mill weed seed destructor include integrations into the combine rather than a tow behind unit.

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