Last fall’s wetter-than-normal conditions may not have been the best for harvesting, but were good for winter wheat seeding and establishment. Most winter wheat fields were seeded in September, allowing for good establishment and over-winter survival. Few winterkill problems were observed this spring.
“Producers were very optimistic and looking forward to good yields with winter wheat, due to the favourable moisture conditions going into the spring of 2005,” said Ross McKenzie, a research scientist with Alberta Agriculture in Lethbridge.
“Winter wheat got off to an excellent start in the first three weeks of April, with warmer than normal temperatures and fairly good early spring soil moisture conditions. Unfortunately, late April and May 2005 were less than kind to winter wheat. Problems with frost injury, nitrogen deficiency, very low rainfall and the brown wheat mite have all been causes for concern.”
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Frost injury: In the last week of April, frost between -6 and -12 C occurred for six consecutive nights and, coupled with another frost in the second week of May, set winter wheat back. At the time of the first frost, winter wheat was actively growing. Although the crop was set back, soil moisture conditions were still adequate and, in most areas, winter wheat grew out of the injury.
Low rainfall: After the first week of April and until the last week of May, little significant precipitation had fallen in most of southern Alberta. Although the region is not in a drought situation, the drier than normal conditions were starting to show drought stress on winter wheat that was seeded on stubble land.
Nitrogen deficiency: Drier conditions have had a compounding effect on fields where nitrogen fertilizer was broadcast on the soil surface and no significant precipitation had fallen to move the fertilizer into the soil to benefit the plants. This has resulted in nitrogen deficiency symptoms showing up in fields with low soil nitrogen levels. Symptoms include lower leaves turning pale green or light yellow.
Brown wheat mite: The unusually dry weather has provided excellent environmental conditions for the brown wheat mite, which was first identified on winter wheat near Foremost, Alta., in mid-May.
“The brown wheat mite is only 0.5 millimetre in size, has a brownish body with yellow front legs. They are so small that identification really needs to be done with a microscope,” McKenzie said.
“The mites thrive and multiply rapidly in dry weather and cause significant crop damage in dry years. They reproduce very rapidly and feed primarily on cereal crops and grasses by removing the plant sap from leaves. The damage they cause is similar to the effects of drought, even though soil moisture levels may be adequate. Symptoms include yellowing or bronzing of leaves or a mottling of the leaves.”
The mite is also a vector for the yellow streak mosaic virus in barley and fields should be watched closely. Spraying is warranted when mite numbers reach 200 per foot of row. Several products are registered for use, but a seven to 10 mm rain is also reported to be effective.
“Producers observing yellowing of lower leaves in winter wheat or other cereal crops need to determine whether these symptoms are caused by drought, a lack of nitrogen, the brown wheat mite or a combination of these factors,” McKenzie said.
“Check the leaves for feeding damage and observe the plants carefully for high numbers of mites. If numbers are high, spraying may be required. It is advisable to factor in the growing conditions and the crop yield potential to determine if spraying is warranted. Also, dig up plants and check the soil moisture conditions to see if the symptoms are related to moisture stress. Do remember that if no rain fell after N fertilizer was broadcast, the effects may be partly related to nitrogen deficiency.”
