Mitigating The Risks Of Delayed Seeding

With excessive moisture in some areas of Manitoba, farmers face the possibility of delayed seeding. Late seeding can still produce a decent crop.  If seeding is pushed back into late May or early June, farmers may need to consider changing their cropping plans.  

Data from Manitoba Agricultural Services Corporation (MASC) shows that earlier seeding generally results in higher yields.  The chart below shows the relative yield of various crops as seeding date moves from late April to mid-June over a 10-year period from 2012 to 2021.  Average relative yields were highest for spring wheat, oat, peas, and sunflowers when seeded in late April, while barley, grain corn, soybean, canola, and flax had the highest yields when seeded the first week of May.  Delayed seeding until the fourth week of May resulted in average relative yields of 87 to 89% of the 10-year average for soybean, canola, and flax.  Cereal crops, grain corn, field peas, and sunflower showed average relative yields of 66 to 76% when seeded the last week of May. 

Seeding Date Effect on Crop Yields (2012-2021)

Data Source: Manitoba Agricultural Services Corporation


Keep in mind that MASC has seeding date deadlines that must be met in order to be eligible for crop insurance coverage.  To view seeding deadline dates, please refer to the MASC website at: Note that these seeding deadlines are generally considered the outside dates for successful crop production.  

Cereal Crops

Yield potential in small grains is a function of three components: number of heads per unit area, kernel number per head and kernel weight. A decrease in any of the components may result in reduced yield. When crop planting is delayed, yield components can be affected since a number of risks can increase. A shortened growing season (reduced number of frost-free days) increases the risk of damage by fall frost affecting both yield and quality. Increased risk of high daytime temperatures can affect crop development. For example, hot temperatures during early vegetative development can result in fewer heads per plant and fewer spikelets per head, and thereby lowering yield potential. Flowering when daytime temperatures are high can increase the probability of floret abortion. Delayed seeding may also increase potential of yield loss due to disease and insects.

Farmers should increase their seeding rates to target the high end of the recommended plant population range when seeding is delayed in order to shorten the time to maturity. To optimize yield potential, target plant populations should be: 

Crop Type Target Plant Population (plants per square foot)
Spring Wheat 23-28
Oat 18-23
Barley 22-25
Corn 30,000-36,000 plants per acre

To calculate optimum seeding rates using plant population, please refer to the following link:  

If facing a late planting scenario, farmers will have to consider crop type and variety selection with a focus on maturity and disease package. Barley does not do well if planted late so, if planted after June 1, the earliest maturing varieties should be used. Wheat may be planted later but the chances of fall frost damage increase considerably. For grain corn, if wet conditions continue for an extended period of time, farmers should either consider switching to a lower corn heat unit (CHU) hybrid or consider planting shorter season crops instead.

If seeding is delayed beyond late May, farmers should consider selecting an earlier maturing variety which may reduce the risk of damage from fall frost or excess weathering. The days to maturity presented below are for varieties listed in Seed Manitoba. 

Crop Type Maturity
Spring Wheat 96-108 days
Oat  92-99 days
Barley 86-91 days
Corn 2000 - 2625 CHU

Increased disease pressure often associated with delayed planting needs to be considered by farmers when selecting a variety. Late-seeded oats will be more susceptible to barley yellow dwarf (BYD), a viral disease carried and spread by aphids, and crown rust. If your crop plan includes oats, select oat varieties with some resistance to those two diseases.

Late-planted (after June 1) fields of wheat may be more susceptible to fusarium head blight (FHB). Choose hard red spring wheat (CWRS) varieties with some resistance to FHB if planting late. Late planted wheat is also more susceptible to leaf rust so farmers should try to plant varieties that have some resistance. Farmers may have to consider foliar fungicides applied at the correct stage if either rust is observed or conditions are conducive for fusarium head blight infection.

Seed Manitoba is an excellent source of information to assist farmers with selecting varieties. It is available online at

Oilseed Crops

Target appropriate seeding rates to overcome issues with weedy fields, poor emergence conditions, or crop pests.  As recommended with cereal production, choosing a seeding rate on the higher end of the seeding range is suggested in early and adverse conditions.  Higher seeding rates can also be used to combat soil conditions if prone to crusting or there is heavy weed pressure at the time of seeding. As well, growers could target shallower seeding to facilitate rapid plant emergence. To optimize yield potential, target plant populations should be:

Crop Type Target Plant Population (plants per square foot)
Canola 5 - 8
Flax 37 - 56
Sunflower - confectionary 16,000 - 20,000 plants per acre
Sunflower - oilseed 20,000 - 32,000 plants per acre


To calculate optimum seeding rates using plant population, please refer to the following link:

The general recommendations for seeding dates of oilseed crops for optimum yields are May 1 to May 31 for flax, canola, mustard and oilseed sunflowers.  Confectionary sunflowers should be sown by the third week of May. When seeding is delayed, farmers may want to consider selecting earlier maturing varieties within the crop type to reduce the potential of fall frost damage or excess weathering, especially for sunflowers.

Crop Type Maturity
Canola 92-102 days
Mustard 80-95 days
Flax 95-125 days
Sunflower 115-130 days


The above days to maturity are based on the information collected from registration and post-registration variety trials conducted in Manitoba. Within each crop type there is a range of varieties with different maturities. Maturity varies depending on environmental conditions, especially heat accumulation.  For more specific details on varietal maturity, the Seed Manitoba guide is available at  

Canola - If seeding is delayed into mid-June, earlier maturing varieties should be selected, and sown at a heavier rate to increase plant uniformity, and reduce branching, which in turn, reduces days to maturity. A frost in early September with a June seeded crop could mean immature seeds with frost damage, and have high green seed (chlorophyll) counts.  This is a quality concern and prices will be discounted accordingly. Additionally, yields will be reduced as frosted seeds will lose bushel weight and potentially be too light and blow out the back of the combine when harvested. Recognizing that delayed seeding in canola can mean the crop will flower during very hot July and/or August days, with little chance of overnight cooling.  This can result in heat blast and flower/pod abortion in the crop if environmental moisture is limiting.  

Sunflower - If seeding is delayed past the last week of May and the first week of June, the risk of frost in the fall becomes much greater. A frost in early September could result in immature sunflower seeds with reduced bushel weights and the possibility of an unmarketable product. When forced to plant late, a very early confection type sunflower or oil-type sunflowers are recommended.

Flax - Late seeding of a flax crop is not as much of a concern as other oilseeds.  Delayed seeding can result in longer straw, and greater green stem issues at harvest, but can be managed via swathing or use of a crop desiccant.  In an open fall, flax can stand and ripen without much shelling while other crops such as canola are being harvested.

For more information, contact the department:

Phone: 1-844-769-6224