Cereals: Other Problems

Excerpt from Agronomy Guide for Field Crops (Chapter 6)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Winterkill
2. Frost Heaving
3. Ice
4. Cold Injury
5. Herbicide Injury
6. Updates on Cereals: Other Problems
7. Related links...

Winterkill

lWinter cereals can be destroyed during the winter and early spring period by frost heaving, ice, low temperatures and snow mould. Varieties differ in their ability to withstand these different winter stresses. This explains the regional adaptation of some varieties that may not perform well across the province.

Growers should select varieties to address the winterkill concerns of their area. Varieties grown in the Ottawa Valley need ice tolerance; those grown in the Lake Huron snow belt need snow mould tolerance, while those grown in the heavy clays of Essex, Lambton and the Niagara peninsula need resistance to frost heaving.

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Frost Heaving

The freeze/thaw cycles of early spring are one of the main reasons for winterkill in Ontario. As frost goes into the ground, it works under the crown and "lifts" the plant up.

Plate 124. Frost heaving of winter wheat is caused by freeze/thaw cycles of early spring lifting the crown up.

If these freeze/thaw cycles are repeated enough times, the plant is ejected or "jacked" out of the soil. Roots are broken and left exposed above the soil, causing death of the plant due to desiccation. This process is referred to as frost heaving.

Deep-seeded wheat is not more resistant to frost-heaving injury. The primary root system does not anchor the plant in the soil. The secondary root system anchors the wheat plant in the soil, protecting against frost-heaving injury. The secondary root system of the wheat plant cannot develop deeper in the soil than the depth of the seed (See Figure 6-1, Days to Emergence at Various Seeding Depths). When wheat is seeded deep, the plant develops the crown and secondary root system at about 2 cm (3/4 in.) deep, as the crown develops in response to light. Regardless of planting depth, the secondary roots will not develop below 2 cm (3/4 in.). To maximize resistance to frost heaving, wheat plants need an extensive secondary root system developed as deep as possible.

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Ice

When a rapid snow melt or winter rain is followed by below-freezing temperatures, ice can form as a thick sheet across ponded areas. Even when the water is able to drain away below the ice sheet, the ice itself will prevent oxygen from getting to the plants and the wheat will essentially suffocate and die below the ice.

Surface and subsurface drainage can help reduce the ponding, which leads to this problem. Should an ice sheet form (for example, during January and February), dormant wheat will only survive for approximately 2 weeks. Break the ice surface to allow gas exchange and to keep the wheat alive.

Cold Injury

Wheat will survive extremely cold temperatures before plant death occurs. Plants that have "hardened off" (gone dormant) will survive temperatures down to -24°C (-11°F). Snow cover acts to insulate the crop from extremely cold temperatures, and even 7^1/2cm (3 in.) of snow is sufficient to protect the crop from colder temperatures. Leaf tissue on plants that have not hardened off will withstand -9°C (16°F), making late spring frosts of little consequence. There was only 1 year in the last century when cold temperatures in Ontario destroyed the wheat crop.

While the wheat crop survives cold temperatures well, cold injury can sometimes reduce vigour and final yield.

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Herbicide Injury

All herbicides have the potential to cause crop injury. A significant cause of herbicide injury in cereals is from residues persisting from herbicide applications in the previous crop. For post-emergent herbicide products used in the cereal crop, most injury results at or shortly after application. Spray drift from the target crop onto neighbouring non-target crops can also cause injury when the non-target crop is susceptible to the herbicide being applied. Spray overlaps are also common places to find crop injury from herbicides.

Stage of growth, crop stress, weather conditions, variety, tank mix partners and adjuvants will all affect the amount and severity of crop injury. When the target crop is under stress, its ability to metabolize a herbicide is reduced and injury may result. The type of herbicide (mode of action) is a major factor in how herbicides affect crops; in general, while contact herbicides may look worse, systemic herbicides will have longer lasting injury, which is often more severe. Late herbicide applications occurring close to heading time can interfere with pollination and reduce yield. Fungicide or insecticide applications that have herbicide residues in the spray solution may impact the crop in this way. Always read the label for information on how to reduce herbicide injury.

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Updates on Cereals: Other Problems

No updates available at this time.

Related links...

• Cereals
• Field Crop Protection Guide - Publication 812

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