Harvest and Storage

Seed yield and quality losses can be minimized with proper harvesting and handling techniques. Harvesting is done when temperatures become cooler, days shorten and humidity increases with snowfall always possible. Urgency at harvest can sometimes lead to poor decisions and impact your bottom line.

Poor timing of harvest or poor storage can lead to downgrading of oat due to:

  • Green seed
  • Frost damage
  • Damaged by mechanical harvesting
  • Mildew
  • Sprouted seed


Considerable concerns about glyphosate have been raised, primarily in Europe. The International Agency for Research on Cancer (IARC) classified glyphosate a “probable carcinogen” while the European Food Safety Authority (EFSA) concluded that it was safe.

In Canada, the Canadian Food Inspection Agency (CFIA) along with the United States Department of Agriculture, and World Health Organization have concluded that glyphosate residues in food is safe at levels below its Maximum Residue Level (MRL).

The MRLs for glyphosate in grains, including oat, have been established by the CFIA and are set at 15 ppm, lower than the 30 ppm established in the USA. In a recent survey of grain, residues of glyphosate has been identified in grain and other food products, but usually at levels below the MRL:

In Canada, glyphosate continues to be a valuable product for pre-seeding, pre-harvest weed control and harvest management and weed management for glyphosate resistant crops. However, in several European countries, glyphosate use may soon be restricted. This issue warrants vigilance as it may affect grain marketing in the future.


Depending on product choice, or combinations, pre-harvest herbicide applications have two purposes: control of perennial weeds and harvest management benefits (desiccation) (Table 5.1).

Desiccation helps to make plants within a field more uniform and thus hastens the harvest process. For harvest management, drier straw will increase the speed and efficiency of harvest, especially when: yields are high; if seeding rates were low; or if the crop was seeded late. Application timing for herbicides is critical. Early application of a desiccant herbicide such as diquat on an immature crop will stop the crop from maturing.

Glyphosate is the only herbicide applied pre-harvest that will effectively control many perennial weeds and accelerate the dry down of the crop. However, it will not speed up grain maturity. Glyphosate applied too early can result in reduced crop yield and quality, and leave unacceptable herbicide residues in seeds (Table 5.1).

Only three herbicides and four products are registered for pre-harvest crop management in oat (Table 5.1). They differ in the speed of dry down, and their level of weed control.

There are special considerations for glyphosate because of the potential for herbicide residues in grain (see below). Glyphosate use restrictions can vary with the market. It is critical to talk to your buyers in advance of applying glyphosate.

Table 5.1 Herbicides registered for pre-harvest use on oat.
Aim* (carfentrazone) Rapid No Not specified
Glyphosate (several suppliers) Slow Yes <30%
CleanStart* (carfentrazone /glyphosate) Intermediate Yes <30%
*Higher water volume increases efficacy


Glyphosate residues in oat grain can occur when glyphosate is applied pre-harvest when grain has not dried down sufficiently. The glyphosate label specifies that grain must be less than 30% moisture prior to application (Figure 5.1).

A recent study conducted in Saskatchewan led by Christian Willenborg, addressed the question: “Does application of pre-harvest glyphosate adversely impact oat yield and quality?” Trials were conducted at two locations in SK, 2016-2017. They compared glyphosate pre-harvest (900 g ae ha-1) with direct cut (no glyphosate) and swathing at 60% to 20% seed moisture content. They measured oat physical and functional quality, and glyphosate residues, including yield, plumpness, test weight, ß-glucan, flaking, groat %, etc. There were no significant differences in yield between the pre-harvest, direct cut oat, and swathed crops at 20%, 30%, and 40% moisture content (Figure 5.2). However, there were significant differences in yield at higher (40% – 60%) seed moisture content (Fig. 5.3).

The authors found that the use of glyphosate in 2016 did not exceed the Canadian or USA MRLs, but in 2017 seed with glyphosate applied early at 50% moisture, exceeded the MRL’s (Figure 5.3).

The glyphosate label specifies that glyphosate should only be applied when seed moisture is less than 30%.

Glyphosate applied pre-harvest did not negatively influence yield, residues, or any physical quality parameters when applied at the appropriate rate and timing.

Harvest and Storage
Harvest and Storage
Figure 5.1. Oat seeds at 30% SMC (seed moisture content). (Photo curtesy of Shawna Mathieson).
Figure 5.2. Application timing of glyphosate at different seed moisture content (SMC) levels impacts seed yield (2016-2017, SK). Willenborg et al., unpublished data, used with permission.
Figure 5.2. Application timing of glyphosate at different seed moisture content (SMC) levels impacts seed yield (2016-2017, SK). Willenborg et al., unpublished data, used with permission.
Figure 5.3. Glyphosate residues at various seed moisture content (SMC) levels. In 2017 but not 2016 glyphosate residues exceeded the Canadian and USA MRLs at > 40% moisture (Willenborg et al., unpublished data).
Figure 5.3. Glyphosate residues at various seed moisture content (SMC) levels. In 2017 but not 2016 glyphosate residues exceeded the Canadian and USA MRLs at > 40% moisture (Willenborg et al., unpublished data).

An agronomic practice that increased glyphosate residues was low seeding rates (presumably through uneven crops with more or greener tillers) (Figure 5.4).

Harvest and Storage
Harvest and Storage
Figure 5.4. The effect of seeding rate on oat dry down. Variety Pinnacle planted at 250 seed/m2 (First image) and 500 seeds/m2 (Second image). Notice the change in color and increase in uniformity evident in the second photo. (photo curtesy of Christian Willenborg).


Timing of harvest is critical to avoid damage to oat hulls, thereby reducing quality and yield. Oat should be swathed when kernel moisture content is between 30% to 36% to avoid negative impacts on groat yield and test weight (May et al 2005).

Oat is ready to swath when the panicle has turned yellow or brown and the least mature kernels have turned a cream colour (Figure 5.5). Oat left too long in the field can weather, lose quality and shatter during storms.

Figure 5.5. Harvest management issues in oat can be reduced by early seeding and higher seeding rates.
Figure 5.5. Harvest management issues in oat can be reduced by early seeding and higher seeding rates.

Research Paper: Canadian Journal of Plant Science (2005) 85: 839-846
“Oat quality and yield as affected by kernel moisture at swathing”

William E. May, Ramona M. Mohr, Guy P. Lafond, and F. Craig Stevenson.

“Oat grown in western Canada is typically swathed and then combined. If the oat crop is swathed too early, seed yield and quality decline; however, if swathing is delayed, harvest losses increase.”

In this study, conducted from 1997 to 2000, 2 locations were used: one in Manitoba and one in Saskatchewan. The locations were: Brandon and Indian Head. Calibre and AC Assiniboia were the varieties examined, and the oat crop was swathed at 5 levels of seed moisture content: 50, 41, 32, 23 and 14%.

Results And Discussion:
“There was an increase in yield as swathing was delayed with most of the yield increase occurring between a kernel moisture of 50 and 41%. Therefore, a kernel moisture content of 41% or less resulted in highest yields.”

“Kernel weight, plump seed and groat yield were optimized when kernel moisture was between 36 and 30% moisture content.”

“After 30% kernel moisture was reached, no improvement in oat yield and quality occurred when swathing was delayed any further.”

Straight combining oat may be an option but growers should ensure no green hulls are present at the time of harvest or the oat will not make milling grade. If the oat crop is left too long in the field before straight cutting, weather may cause the stems to break down and reduce yield.

Prevent damage to oat hulls by reducing cylinder speeds to around 900 r.p.m. and allowing wider concave clearances. Oat buyers discount oat with a high percentage of de-hulled kernels, so growers should aim for less than five per cent de-hulled kernels through harvest, storage and delivery.

As mentioned previously, growers should be cautious about using a pre-harvest glyphosate application on oat. Not all buyers accept oat that had an application of pre-harvest glyphosate Some markets also have strict limits on the allowable glyphosate residues in oat, which could affect their saleability.


Once the grain is in the bin, the next step is to ensure that quality is retained (Figure 5.6). Several factors during storage can lead to downgrading, including heating, mildew and excreta (see below)

Figure 5.6. Oat in the bin
Figure 5.6. Oat in the bin

If the grain is tough or damp it must be dried to prevent spoilage. Oat spoilage occurs when initial temperatures range from 0 C to 21 C with respective moisture levels from eight to 17 per cent. The Canadian Grain Commission has safe storage guidelines for storing grain on its website (Fig. 5.7).

Considerable information is available on efficient and effective grain drying. For a detailed understanding of grain drying, the following is a link to the Ron Palmer YouTube video:

or a shorter version here from Ron Palmer: 

Figure 5.7. Safe storage chart for oat.
Figure 5.7. Safe storage chart for oat.


All samples are visually inspected to determine if they are commercially clean prior to dockage assessment. Dockage is assessed to the nearest 0.1%.

For example:

  • 95.0% Oat, No 1. CW
  • 4.0% domestic mustard seed, No 1 CAN Oriental
  • 1% dockage

Dockage is defined under the Canada Grain Act as “any material intermixed with a parcel of grain, other than kernels of grain of a standard of quality fixed by or under this Act for a grade of that grain, that must and can be separated from the parcel of grain before that grade can be assigned to the grain.”

Oat grading factors (not in order of importance):

  • Barley
  • Cereal grains other than barley and wheat
  • Colour
  • Contaminated grin
  • Covered smut and false loose smut
  • Damaged
  • Earth pellets
  • Ergot
  • Excreta
  • Fertilizer pellets
  • Fireburnt
  • Foreign material
  • Frost damage
  • Fusarium damage
  • Green
  • Heated
  • Hulled and hulless
  • Large seeds
  • Mildew
  • Odor
  • Rotted
  • Sclerotina sclerotiorum
  • Soft earth pellets
  • Sprouted
  • Stones
  • Test weight
  • Total damage and foreign material
  • Treated seed
  • Variety (hulless)
  • Wheat
  • Wild oat

A complete list of grading factors for No. 1-4 CW can be assessed at the Canadian Grain Commission. Please note, most oats are graded at a 2CW in Western Canada.