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When the time does come to check, growers should look at the growing point of the plants, determine the percentage of plants killed verses recovered, and assess the weed population, says CCC senior agronomy specialist Doug Moisey.
"The extent of the damage can be determined only by waiting several days following the frost," says Moisey. "If an initial inspection suggests the remaining plant population is questionable, but growing conditions since the frost have been cool contributing to slow plant recovery, producers may need to revisit the field in another three to four days to accurately determine the extent of the damage and the surviving plant population. As well, after a frost any herbicide applications should be delayed until recovery of the plants as well as the weeds has occurred."
If there is any green colour at the growing point in the centre of the frozen rosette, or the centre stem is exhibiting turgor pressure and does not appeared pinched off, the plant will recover and yields will be higher than if the field is re-seeded. Canola seedlings will usually recover from a light spring frost that does not damage the growing point of the plant. A light frost that wilts the leaves but does not cause any browning will not injure the plants. There may be some discoloration of the leaves, usually a yellowing or whitening especially under drought conditions.
When a frost does blacken the cotyledons and/or leaves, no action should be taken for at least four days, advises Moisey. Under good growing conditions, green re-growth from the growing point should occur in four to five days. Under poor growing conditions; cold and/or dry, this can take up to 10 days.
When evaluating frost damaged seedling fields, growers should consider the percentage of plants killed, the percentage recovered, and the weed population.
To evaluate a frost damaged field, Moisey suggests walking a diagonal path across the field, evaluating all plants in a 1/4 m2 (3 ft2) every 20 paces. This should result in 50 to 100 samples. If, for example, 80 per cent of the field has a minimum of 20 to 40 recovering healthy plants per m2 (2 to 4 per ft2 ) and a light and/or easily controlled weed population, while the remainder of the field has fewer plants, then this field probably still has a higher yield potential than one that is reseeded. That’s because only the 20 per cent with less than two to four plants per square foot likely will benefit significantly from reseeding.
Canola can compensate for lower plant populations because surviving plants can take advantage of reduced competition for light, moisture and nutrients. Plants will grow larger, producing more branches, pods and seeds per pod. While the surviving plants will require longer to mature, a re-seeded crop would require an even longer frost-free period and have a greater risk of fall frost damage.
Contact:
Doug Moisey
780-645-9205
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