What impact can rotation have on winter wheat yields?

As reviewed in a previous post on Crop Chatter, the most common rotation is seeding winter wheat into canola stubble.   However, what impact can rotation have on winter wheat yields?  Once again we can use Manitoba Agricultural Services Corporation’s (MASC) database to help try and answer this question.

The table below is a crop rotation chart, one planting season at a time, using data from MASC’s database.  It shows the potential yield of winter wheat on various stubbles, as compared to the average yield for winter wheat on all stubble types from 1998 to 2007.

The data illustrates a winter wheat on canola rotation where farmers see a relative yield response of 104% compared to the average yield of winter wheat in Manitoba.   Perhaps this is one reason why 51% of farmers reported a winter wheat on canola rotation.  If we look at a winter wheat on spring wheat rotation, yield potential drops to 91%.    We could speculate that the yield decrease may be due to increased disease pressure but can’t say for sure as yield-limiting factors are not collected in the harvest production reports.

Table 2:  Relative yield response (per cent of 1998 to 2007 average) of winter wheat sown on large acreage fields (<120 acre) of various previous crops (stubble) in rotation.

Previous Crop

Winter Wheat

Spring Wheat

Barley

Oat

Canola

Flax

Pea

Relative  Yield of Winter Wheat

76

91

91

97

104

102

90

 

The above table and all of the combinations are to provide farmers and agronomists with an additional tool to determine crop sequences and their yield benefits or risks.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

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What stubble do Manitoba farmers prefer to seed their winter wheat into?

In Manitoba, the most common rotation is seeding winter wheat into canola stubble.  This is for a variety of reasons:  early availability of stubble, rotational considerations in managing disease, and the excellent snow trapping potential of canola stalks.  However, farmers also seed their winter wheat into various other types of stubbles, depending on availability.  How often does that happen? 

This question can be answered by using Manitoba Agricultural Services Corporation’s (MASC) database.  The database contains information submitted by producers in their harvest production reports and can provide additional insight into what rotations farmers are using, the frequency of those rotations, and yield potential of various rotations.

The table below shows the frequency that winter wheat is grown on various stubbles.  As we can see, 51% of farmers reported using a winter wheat on canola rotation, followed by oat (4%) and barley (3%). We don’t recommend seeding winter wheat into wheat (spring or winter) stubble for a variety of reasons but as you can see it is a rotation used by some producers in the past. 

Table 1:  Previous crop (stubble) distribution (%) of large acreage fields (>120 acres) sown to winter wheat in Manitoba during the period 1998 to 2007).

 

Previous Crop

 

Winter Wheat

Spring Wheat

Barley

Oat

Canola

Flax

Pea

Frequency (%) of Winter Wheat Seeded

1

2

3

4

51

1

2

 

Submitted by:  Pam de Rocquigny, MAFRI Cereal Crops Specialist

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I had a lot of blackleg in my canola in 2012, what should I be doing to manage the problem in the future?

Identifying that you have blackleg in your canola and it is a problem is a critical first step.

If you have had canola in tight rotation (canola every year or every other year in same field) for a number of years, that will have helped to slowly build up the level of disease inoculum in your field.  As well, potentially allowing for selection of blackleg races that your past variety did not have resistance to. 

Going forward:

1. Increase the time between canola in the same field by adding another crop for additional break year (instead of canola-wheat-canola, try canola-wheat-pea-canola or canola-wheat-flax-canola).

2. Grow an R-rated blackleg tolerant variety.  If you have already been growing a variety with the R rating and still have high levels of blackleg, consider changing to another variety.  R-rating is a blackleg tolerance rating, and does not mean immunity.  Your affected field, may have blackleg races that are different than the races your current variety has tolerance to.

3. Control volunteers from the past crop in break years. Also control weeds like wild mustard, stinkweed, flixweed and shepherd’s purse, which are all hosts and sustain blackleg in non-canola years.

4.  Consider a fungicide. Using a fungicide on high pressure fields can assist in reducing the incidence and severity of blackleg infection. But, using a fungicide to control blackleg on fields where no blackleg has been seen in the past is not economical.  Save this option for when you need it.

 Keep record and continue to track the level of blackleg in those fields when planted back to canola.  As well, watch other fields on your farm in 2013 and onwards for the signs of blackleg infection.

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Can I seed winter wheat into spring wheat stubble?

The recommendation is “No”.  Does that stop producers from seeding winter wheat into spring wheat stubble?  The answer again is “No”.

If rotation limitations have you considering seeding winter wheat into spring wheat stubble, here are some management tips and key things to keep in mind.

  1. If seeding into wheat stubble, diseases can become a big issue.  Diseases such as tan spot and septoria survives on wheat stubble and straw.  Both can be severe and begins earlier where winter wheat has been planted into wheat stubble.    Fungicides can be used to help control these diseases so make sure to pencil in a fungicide application early in the season.   Even more important though here in Manitoba is fusarium head blight (FHB).  Like tan spot and septoria, FHB overwinters on cereal stubble so a break of at least one year – preferably two years – is advised between cereal crops.  Most winter wheat varieties are either susceptible or moderately susceptible to FHB.  However, there have been advances made and there are varieties coming to the market place with improved resistance to FHB, including Emerson (Resistant or R rating) and AAC Gateway (Intermediate or I rating).  Plus there is CDC Buteo which is rated as moderately resistance or MR.
  2. Seed into weed free conditions to manage another disease – Wheat Streak Mosiac.  This recommendation actually applies to any type of stubble but is more critical when seeding winter wheat into spring wheat stubble.  Eliminate any green cereal growth prior to seeding in order to reduce the ‘green bridge’ that can transmit the wheat curl mite and the wheat streak mosaic virus it carries.  At least 10 days between the dry-down of spring cereal crops and the emergence of winter wheat is necessary to prevent problems with the disease, as the wheat curl mite needs a live cereal plant for a host at all times.
  3. Make sure straw has been properly managed during the spring wheat harvest to reduce interference with seeding and stand establishment.  Light harrowing can help spread straw and chaff around.  Cereal stubble will provide lots of stems to catch snow and reduce the risk of winter injury; however, you must be careful in managing straw and chaff as the stubble needs to remain standing to be of benefit.
  4. Volunteer spring wheat in the winter wheat crop next year can cause problems.  If any spring wheat volunteers produce grain, this may increase the possibility of downgrading of the winter wheat crop due to mixing of wheat classes.  Result can be marketing problems and price discounts.

So, if seeding winter wheat into spring wheat stubble is the only option available, manage your yield and quality expectations.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

 

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