CropWatch, Feb. 18, 2010: Asssessing Winter Wheat Stands Still in Dormancy | CropWatch

February 18, 2010

The cool summer and fall precipitation delayed maturity and harvest of many crops as well as seeding of winter wheat. Many winter wheat fields were seeded late last fall, especially those seeded after a fall-harvested crop. In many of these fields winter wheat development was limited.

Several factors determine the survival of winter wheat.

Determining Whether Wheat is Dormant or Dead

The following method can be used to determine if dormant wheat plants are alive and likely to resume active growth in the spring:

Remove the top 3 inches of soil containing the plant crown (typically located 1 to 2 inches below the soil surface).

Thaw the samples and warm to room temperature.

Remove soil from the roots and wash with cool water to remove attached soil.

Cut off fall growth to within 1 inch above the crown and 1 inch below the crown in the roots.

Rinse the crowns with cool water.

Place 10 wet crowns in a labeled plastic bag, inflate the bag and tie shut.

Place the bags in a lighted room, but not in direct sunlight.

Check the crowns in two days, rinse with cool water and re-inflate the bag.

After four days, the crown should show about two inches of new growth.

Plants that are not growing after six days should be considered dead when estimating survival.

Remember, winterkill can be a localized event, so select sample areas carefully and don’t try to extrapolate results too widely. If winterkill is a problem, visit with the appropriate government agencies before destroying your wheat crop and carefully plan your alternatives.

Root System Development

When winter wheat is seeded after the suggested range of seeding dates, poor root development is a concern. Plants have adequate winter hardiness if they have two or more tillers and a good crown root system. Also, plants that are in moist soil are less likely to suffer from desiccation.

In Nebraska, winter injury to winter wheat plants is common because of dry soil. Dry soil warms up and cools down six times faster than moist soil. This alternate freezing and thawing of the soil subjects the plants to injury. It also can cause the plants to break dormancy early.

Plants with few secondary roots and no tillers are more susceptible to winter injury. To determine the development of secondary roots, dig up plants and examine the secondary roots. Poor shoot and/or root development can be caused by poor seeding depth, lack of soil moisture, poor seed to soil contact, insects and diseases.

Seeding Depth

Seeding depth is critical to the survival of the winter wheat plants. The recommended seeding depth is usually 1.5 to 2 inches if firm moist soil is present at that depth at the time of planting. Some winter wheat varieties may be seeded deeper. Those varieties should be selected if one needs to seed deeper to reach firm moist soil.

Seeding the wheat at the proper depth in firm moist soil protects the crown from the effects of cold temperatures. Crowns that develop too close to the soil surface are more susceptible to winter injury because the growing point is close to the soil surface.

Seed Bed Preparation

Seeds planted in loose, dry soil or in soil with crop residue mixed in increases the possibility of the crown and roots being more susceptible to cold temperatures and desiccation. Snow cover helps protect the young winter wheat plants from winter injury.

Insects and Diseases

Also check for injury by insects such as mites, army worms and crown and root rot diseases. These pests and diseases also can cause injury.

Fertilizers and Herbicides

Winter wheat plants that were seeded late and have limited growth will be subject to additional stress from fertilizers and herbicides. Table 1 illustrates the potential for injury to early seeded winter wheat compared to winter wheat seeded during the recommended time. For example 2,4-D amine + Banvel with UAN fertilizer only lowered yields 2% in wheat planted at the recommended time on soil that had adequate fertility when the field was weed-free. Alternatively, yields were 15% lower for the combination of 2,4-D amine + Banvel and UAN on winter wheat seeded early.

Early seeded winter wheat needs additional nitrogen to meet the needs of a larger plant in the fall. We suggest that UAN and herbicides not be combined for top dressing this spring on late seeded winter wheat.

Table 1. Relative winter wheat grain yield for two planting dates, fertilitizer application, and herbicide application. North Platte, 1989.
		Planted Sept. 25		Planted Sept. 10
Treatment	Rate	UAN		UAN
		No	Yes	No	Yes
		---- % ----
No herbicide	----	100	98	86	100
2,4-D ester	1 pt	96	93	65	83
2,4-D amine + Banvel	0.5 pt + 0.25 pt	99	98	85	85
Ally¹	0.1 oz	97	98	88	91
Ally¹ + 2,4-D ester	0.1 oz + 0.5 pt	96	95	80	77

¹X-77 surfactant was added at 0.25% v/v

Nitrogen application may be made as soon as the ground has thawed and soil conditions permit. The herbicide should be applied for the correct timing of the weeds being controlled. For example, blue mustard must be controlled early in the spring.

Robert N. Klein, Western Nebraska Crops Specialist
Greg Kruger, Cropping Systems Extension Specialist
Tim Shaver, Nutrient Management Specialist
All at the West Central REC in North Platte

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