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Weed Emergence in Winter Wheat
- Week of May 1, 2006

Author: Mike Cowbrough - Weed Management Specialist/OMAFRA
Creation Date: 03 May 2006
Last Reviewed: 03 May 2006

A number of crop scouts and agronomists that I have spoken with have commented that the wheat crop appears to be 10 days ahead of last year and scouting data from this week compared to last year during the same week would concur. This has significant implications for weed management in winter wheat.

Crop Staging and Weed Emergence

Crop Stage: All of the wheat fields are at Zadok's 30 (first node visible - see Figure 1), which is ahead of where last year's crop was at this time. Herbicide applications made after this growth stage will cause greater tramping damage. As the crop progresses to the flag leaf stage the potential for herbicide injury increases. Therefore, if weed populations are such that control is necessary then herbicide applications should be made as soon as possible.

Table 1. Growth stage, Zadok's Scale and Height of winter
wheat at 5 field locations on May 1st , 2006.

Location Growth Stage Zadok's Scale Height (cm)
1
First Node
31
30-32
2
First Node
31
28-31
3
First Node
31
23-24
4
First Node
31
27-29
5
First Node
31
28-30
Last Year -2005
Tillering
Zadok's 24
16-22

Weeds that Emerged this past week:

  • Dandelion
  • Canada Thistle
  • Field Horsetail
  • Wild Mustard
    (See Figure 2)
  • Wild buckwheat
  • Lady's Thumb
  • Lamb's-quarters
  • Ragweed
    (See Figure 3)
  • Common Chickweed

Weed Growth Stage Progression:


Table 2. Weed species and growth stage at 5 winter wheat
field locations on May 1st, 2006 compared to April 24th, 2006.

Weed Species Growth Stage
Last Week		 Growth Stage
This Week
Burdock 4-16 leaf
(20-30 cm diameter)		 20+ leaves
(40-40 cm diameter)
Carrot, Wild 10-15 cm diameter 15-20 cm diameter
Chickweed, Common 4 leaf to flowering cotyledon to flowering
Chickweed
(mouse-eared)		 2-4 cm tall 4-5 cm tall
Dandelion
10-15 cm diameter
bud stage		 15-30 cm diameter
flowering
Fleabane, Canada 4-8 cm diameter 8-10 cm diameter
Flixweed 12-15 cm tall 25-30 cm tall
Henbit 10-12 cm tall 12-14 cm tall
Horsetail, field 2.5 cm tall 2-5 cm tall
Lady's Thumb cotyledon cotyledon - 1 leaf
Lettuce, Prickly 6-8 leaf 8-12 leaf
Ragweed, Common cotyledon cotyledon - 2 leaf
Wild buckwheat cotyledon cotyledon - 1 leaf
Shephard's Purse 10 cm diameter 10-12 cm diameter
Stinkweed 15-20 cm
20-30 cm -f lowering
Violet, Field 6 leaf to flowering 10 leaf to flowering


Implications for Weed Management:

Of the winter wheat fields scouted, the weed populations in 3 of the 5 fields would justify an herbicide application as species type and density will most likely affect either yield, harvesting ease or straw quality. In fact one of the 5 fields received an application of dichlorprop/2,4-D on Monday May 1st, 2006. In the other 2 fields, weed populations are very low and it wouldn't appear that weed management would offer a net economic benefit.


Figure 1. First Node of Winter Wheat (Zadok's 31)

Note, on the main winter wheat stem pull back a couple of leaf sheaths to more clearly see the 1st node.

First Node of Winter Wheat (Zadok's 31)


Figure 2. Mustard species cotyledon - May 1, 2006

Mustard species cotyledon

Figure 3. Common ragweed at the 2 leaf stage - May 1, 2006

Common ragweed at the 2 leaf stage

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