What looked like an early spring for seeding small grains has turned into an average to late spring for sowing. A question that has come up again this year is whether HRSW producers should switch varieties if planting is delayed to mid-to-late May in northwest Minnesota and North Dakota.

For a number of other crops (e.g. soybean, corn, sunflower), producers are encouraged to switch to earlier maturing varieties or hybrids when planting is delayed and the growing season is shortened. For each of these three crops, the shorter maturity is needed to ensure that maturity is attained before fall frosts kill the crop and reduce both grain yield and grain quality.

For HRSW, the story is a bit different. Delayed planting shortens the growing season but in a very different way. It is not the potential of frost, but the high temperatures in July and August that will hurt the yield and grain quality most. HRSW, as all small grains, is a cool season annual. This means that around 85ºF the balance of photosynthesis (the conversion of light energy into sugar) and respiration (the use of the sugar produced during photosynthesis for growth and maintenance) is zero. When temperatures reach above 85ºF, this balance will actually become negative, and the crop basically goes on a weight loss program. When temperatures reach above 92ºF, this process accelerates because the photosynthesis shuts down completely.

So, what should a HRSW producer do? In general terms, if planting is delayed, switch to earlier maturing HRSW cultivars if possible. This will help the odds of escaping those high temperatures of 85ºF and above. If this is not practical or possible, what can you expect for grain yield and grain quality? Also, do all cultivars respond similarly to heat stress?

As a rule of thumb, you can assume that, on average, for each day past the optimum planting date, grain yield will be reduced by a minimum of 0.5 bu/A.

You can partially reduce the impact of delayed planting by increasing your seeding rate by about 1-2% for each day planting is delayed. The increased seeding rate will result in more plants with fewer tillers. This is important because with delayed planting, the plants will form fewer tillers, a result of the  higher temperatures that usually occur while the crop is tillering (June tends to be warmer than May, although around here one never really knows).

Are there varieties that have more tolerance to heat stress? Yes, varieties like Ingot, Russ, and Alsen seem to handle heat stress during grain fill better than, for example, Gunner, Marshall, and AC Barrie. Research at Langdon has shown that planting Gunner and AC Barrie late will result in a larger decrease in grain yield relative to varieties like Ingot and Russ

The Langdon Research Extension Center has had a late planting trial for the last two years. The two year average yield for AC Barrie was 26.6 bushels per acre while Gunner averaged 30.9 bu/acre. All other varieties in the trial average yields were at 40 bu/acre or above. The varieties Alsen, Russ, and Parshall had average yields of 43 bu/acre. In a similar trial planted the first week of May, Gunner and AC Barrie had yields similar to the other varieties.

When should one consider switching varieties? While each year is different, general farmer experience and research data suggest that Gunner and AC Barrie and perhaps varieties with similar genetics should not be planted after May 20 in northern N.D./ MN and perhaps earlier in southern portions of ND.