Crop Report – Week of September 18th, 2023

The headlands of this field received a fall application to control dandelions, making for a nice seed bed to plant into. The rest of the field had no fall management, and the dandelion pressure is significant and will take much longer to control now.

Three tips for weed management this fall.

Reflecting on some of the weed control issues that came up this past spring, below are three key items where management activities this fall can significantly improve control and/or financial return next season.

1. Fall management provides better dandelion control.

In the fall, resource allocation of perennial weeds shifts and carbohydrates move towards the root system, building root mass for overwintering. When dandelions are managed in the fall, whether it be by tillage or herbicides, resource allocation to the roots is disrupted and control is significantly better when compared to management in the spring (Table 1). A better seed bed is also established when dandelions are managed in the fall since all the vegetative growth has been desiccated by planting time (Figure 1).

Figure 1. The headlands of this field received a fall application to control dandelions, making for a nice seed bed to plant into. The rest of the field had no fall management, and the dandelion pressure is significant and will take much longer to control now.

Figure 1. The headlands of this field received a fall application to control dandelions, making for a nice seed bed to plant into. The rest of the field had no fall management, and the dandelion pressure is significant and will take much longer to control now.

Table 1. Control of dandelions at four different herbicide application timings (Adapted from Franssen and Kells, 2007).

DandelionLate fallEarly fallEarly springLate spring
Control (%)80%74%65%55%
Source: A.S. Franssen and J.J. Kells. Weed Technology 2007 21:18–22

When using glyphosate to manage dandelions, if they are larger than 6” (15 cm) in diameter, a higher rate is required according to the product label. Efficacy work conducted by the University of Guelph and presented in Table 2, is consistent with the labelled guidance.

Table 2. Comparing the average and range in control of dandelion over multiple trials evaluated at eight weeks after the application of glyphosate at two rates.

ProductRateControl (%)Range (%)# of Trials
Glyphosate (540 g/L)0.67 L/acre6554-988
Glyphosate (540 g/L)1.34 L/acre8365-958
Source: Dr. P.H. Sikkema, Dr. C.J. Swanton and F.J. Tardif, University of Guelph

2) Consider fall management in winter wheat if Canada fleabane is present.

Although winter wheat yield loss from weed competition is typically small, there are exceptions. High densities of weeds that emerge with, or shortly after the crop will have the most impact on yield loss. A recent study conducted by the University of Guelph (Ridgetown Campus) found that Canada fleabane interference reduced winter wheat yield by as much as 27%. Managing Canada fleabane in the fall, improved winter wheat yields by 10-15% when compared to waiting until the spring to manage Canada fleabane (Table 3).

Table 3. Control of Canada fleabane at different application timings and impact on the yield of winter wheat (Adapted from Soltani et al., 2023).

ProductApplication TimingCanada fleabane control (%)Winter wheat yield (bu/acre)
No weed control045
InfinityFall8359
Fall + Spring10061
Spring9953
PixxaroFall9761
Fall + Spring10057
Spring10052
Source: Soltani et al., 2023. Journal of Agricultural Science; Vol. 15, No. 5

A complete list of herbicide options that are labelled for application to winter wheat in the fall can be found at the Ontario Crop Protection Hub.

3. When killing off an old stand of alfalfa with herbicides, make sure that the two-week weather forecast after application has warm air temperatures.

A study conducted at the University of Guelph (Elora Research Station) demonstrated that warm air temperatures after herbicide application, quantified by growing degree days, appeared to negatively effect the control of alfalfa. Since alfalfa has a base growing temperature of 5°C, when air temperatures following herbicide application rarely exceeded 5°C, alfalfa growth was stagnant, thereby reducing herbicide uptake and movement within the plant, and leading to unacceptable control (Table 4).

Table 4. Alfalfa control as affected by growing degree day accumulation in the two weeks following application.

TreatmentApplication DateGrowing Degree Days (14 days after application)Alfalfa Control (%)
Glyphosate + 2,4-D ester Oct 38498
Glyphosate + 2,4-D ester Oct 30930
Source: https://fieldcropnews.com/2019/11/killing-off-roundup-ready-alfalfa/

Weather DataWeekly September 11 – 17, 2023

LocationYearHighest Temp (°C)Lowest Temp (°C)Rain (mm)Rain (mm) April 1stGDD 0C April 1stGDD 5C April 1stCHU May 1st
Harrow202323.07.46.5587286720333134
202227.210.625.1412305222293467
10 YR Norm (11 – 20)23.910.123.2527309422163527
Ridgetown202324.05.98.5513273619102937
202227.89.98.0285290020853220
10 YR Avg. (2011-20)23.98.421.8479291820453285
London202322.65.616.3561271618922926
202227.26.515.2333282020153136
10 YR Avg. (2011-20)23.48.923.3505288820203258
Brantford202324.34.21.1446269618702891
202227.36.223.3311283320173075
Welland202324.36.11.4507275619242982
202225.57.415.3380288520603223
10 YR Avg. (2011-20)24.19.216.8447290720383284
Elora202322.94.433.9478249816892653
202226.53.72.7256260518012827
10 YR Avg. (2011-20)22.57.321.7498261017542904
Mount Forest202321.54.711.1417249216882656
202225.34.55.0379259617992870
10 YR Avg. (2011-20)22.17.919.6508260117542930
Peterborough202325.11.519.6430256117392686
202224.11.818.6342260117832824
10 YR Avg. (2011-20)23.85.013.2440263717802889
Kemptville202323.55.56.4516271819022895
202224.66.032.3488276119243041
10 YR Avg. (2011-20)23.06.419.7497277219173094
Earlton202322.04.220.6408231715482459
202220.63.460.1412233315642568
10 YR Avg. (2011-20)20.65.424.2448226214902538
Sudbury202321.96.514.5530235615882527
202222.60.027.9347239416172695
10 YR Avg. (2011-20)20.96.331.3483242716332753
Thunder Bay202321.1-0.64.9305215414072320
202223.60.778.9556212913882326
10 YR Avg. (2011-20)18.74.317.7435217713932389
Fort Frances202318.9-3.11.1312231015562508
202225.62.146.7622221714782491
10 YR Avg. (2011-20)20.33.919.7438230315012540
Report compiled by OMAFRA (Ontario Ministry of Agriculture, Food and Rural Affairs) using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.

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