ISSUE 10   July 15, 2010


The 2010 growing season has changed from cool and wet to warm and sunny growing conditions. Heat injury to canola plants may occur on hot sunny days, when air temperatures range from 85 to 95 F and soil temperatures rise to 100 F. Heat injury is most common when the plant is already under drought stress. When canola is in the bloom stage, heat blasting and/or flower abortion are possible. The start of flowering and the duration of bloom can vary from field to field and is related to the seeding date, variety, soil moisture and humidity during the hot periods. The duration of flowering can last up to 3 weeks. High temperatures during flowering shorten the time the flower is receptive to pollen, as well as the duration of pollen release and pollen viability. This can decrease the number of pods which develop, and the number of seeds per pod, resulting in lower yields. Because the flowers and pods develop sequentially on the stem, you may see no pods or limited pod growth in certain regions of the stem. This is a result of reduced pollination during extreme hot conditions. With good soil moisture, the flower abortion in canola will usually be minimized as compared to canola under drought stress. High temperatures at flowering will hasten the plant's development, reducing the time from flowering to maturity.

Once pods are formed, canola is more tolerant to high temperatures. Cool night temperatures may help the plant recover from extreme heat or dry weather. However, during the pod formation stage, a combination of heat and extreme drought will severely affect the pod development including formation of seeds, seed size and oil content. Canola plants will maintain the number of pods they can support through the process of plant photosynthesis under the given growing conditions. If there is stress during the time of the pod development some of the pods may abort. The seed oil content is highest when seeds mature under lower temperatures (50 to 70 F). High temperatures, drought and long days will accelerate maturity.

Canola hybrids differ in when they start flowering. This hybrid
flowered 46 days after seeding in Minot (2009), which was significantly
earlier than the mean of the trial. This photo was taken on July 15, 2009
at the Minot Research Extension Center.

Hans Kandel
Extension Agronomist broadleaf crops



There are substantial acres in ND that were not planted this spring due to excessive moisture.  Planting winter wheat this fall on this land may be a viable option.  However, winter wheat survival is enhanced when it is planted into fields that catch and retain snow that will insulate it during the coldest winter months.  Fields that have standing stubble are ideal for direct seeded winter wheat.  In these fields, however, carefully manage weeds and volunteer crop plants prior to planting.  Volunteer wheat plants and other grassy weeds can harbor the wheat curl mite that is the vector of the wheat streak mosaic virus.  These plants must be control well in advance of planting winter wheat in order to “break” the green bridge and reduce the risk of wheat streak mosaic virus infections.  For fields that were previously tilled or that have little or no stubble, establishing an effective residue crop can significantly improve the probability that there will be adequate snow cover for successful winter wheat production.  To be effective, a residue crop must remain erect during the fall and winter.  Cereal crops that do not reach the boot stage before being killed by frost or herbicides, for example, will lay flat on the soil and will not capture much snow.  The most effective residue crop is probably flax. Flax can be established as a lightly seeded solid stand, in wide rows (i.e. 3-4 feet spacing) or as strips.  Strips of flax 3 to 5 feet wide and 15 feet apart have been found to effectively trap snow while minimally depleting soil moisture.  When seeding flax in strips or in wide row spacings, the drill should be set at a high seeding rate (40-60 pounds per acre) and drill spouts should be taped shut to obtain the desired spacing.  Strips of flax more than 20 feet apart can be risky as they do not catch sufficient snow in most years.  Flax should be seeded in late July or early August, depending on the region of the state.  Though some additional weed management will be needed prior to planting, flax planted in late July or early August followed by winter wheat could be a viable and profitable option for dealing with land that was too wet to plant this spring. 

 Joel Ransom
Extension Agronomist - Cereal Crops

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