Weed management issues in corn, soybean and wheat in Ontario

Principal Investigator: Peter Sikkema

Scientific Summary:

Disclaimer: The information presented here does not constitute a recommendation by the researcher or Grain Farmers of Ontario. Always read and follow the pesticide label before use. Always ensure that you have the most current label.

Weed control is the single most important aspect of pest management in corn. Seventy-one studies conducted in Ontario over a nine-year period found a 102 bu/ac or 49% yield loss in corn where no weed management tactics were implemented. Every year there are new issues to address in respect to weed management in corn, soybean and wheat in Ontario. These issues arise as a result of a) changes in nutrient deficiencies due to changes in crop production systems, b) new herbicide resistance traits (e.g. Roundup Ready Xtend, Enlist), c) new tankmixes of herbicides plus fungicides plus micronutrients, and d) new crop production systems including cover crops. Ontario growers and crop consultants are demanding local data to determine the main reasons for the extreme variability in corn responses with the addition of a tankmix of fungicide plus glyphosate. With the recent registration of Roundup Ready Xtend soybean, local data is needed to determine if the addition of Xtendimax to Group 1 herbicides antagonizes volunteer corn control. Winter wheat producers are interested in minimizing the number of trips across the field with their sprayers, especially to reduce tramping; some growers have combined their herbicide, fungicide and foliar fertilizer with mixed results. One aspect of cover crops that needs further research is the effect of residual herbicides in soybean and wheat on the emergence and growth of oilseed radish.

This project aimed to provide Ontario grain growers with additional information on how to manage their crops that result in excellent weed and disease control, minimal crop injury and allow for the successful establishment of cover crops. In corn there were experiments conducted to determine on the effect of fungicide plus Roundup, and the tolerance of corn to Group 1 herbicides. Six field studies were conducted to determine if the addition of Xtendimax (dicamba) in RR2 Xtend soybean antagonizes the control of volunteer corn with Assure or Select. Twelve field experiments were conducted to determine the effect of herbicide (Buctril M, Refine M, Infinity or Estaprop), fungicide (Quilt, Stratego or Twinline) and/or ammonium thiosulfate applied alone or in combination on winter wheat. Twelve field experiments were conducted to determine the effect of herbicides in soybean and wheat on cover crop establishment. Two field studies were conducted to determine the establishment of annual ryegrass in corn.

The results from this project have been added to the Pest Manager app and have been used to update information in OMAFRA Publication 75, Guide to Weed Control.

Summary of Lessons Learned:

  • This study concluded that in most situations there is no economic return to Ontario corn producers when they add a fungicide to the their last in-crop application of glyphosate. Ontario data indicates that there is a greater potential economic return when a fungicide is applied at VT-R1 than at V3-5.
  • This study concluded that the addition of Xtendimax to either Assure or Select antagonizes volunteer corn control in soybean. The activity of Assure is reduced more than Select. The antagonism can be overcome by increasing the rate of Assure or Select but this will be an added cost to Ontario farmers.
  • This study concluded that the addition of ammonium thiosulfate (ATS) to a herbicide/fungicide tankmix resulted in increased injury in winter wheat. Ontario wheat producers are advised to apply their herbicide/fungicide combination and then make a second application to address sulfur deficiency. There was a trend to increased yield in winter wheat with the application of each of the inputs evaluated.
  • This study concluded that the application of Classic, FirstRate, Lorox, Sencor, Valtera, Dual, Frontier, Zidua, and Prowl applied PRE, and Blazer, Reflex, Basagran, Pinnacle, and FirstRate applied POST can be safely used for broadleaf weed control in soybean with minimal effect on oilseed radish stand and biomass. In contrast, the application of Broadstrike, Pursuit, and Command applied PRE and Pursuit applied POST for weed control in soybean caused unacceptable oilseed radish injury. In addition, the 2,4-D ester, MCPA ester, Target, Estaprop, Lontrel, Buctril M, Refine Extra, Trophy, Infinity, and Peak + Pardner applied POST in winter wheat had no negative effect on oilseed radish stand and biomass.
  • This study concluded that annual ryegrass can be successfully established in grain corn at the 3- and 5-leaf stage of the corn, but later planting timings (ie. 7-leaf and later) did not allow for successful establishment of annual ryegrass in corn. 

Project Related Publications

a) Roundup + fungicide in corn

Soltani, Nader, David C. Hooker, Jonathan Brinkman and Peter H. Sikkema. 2018. Effect of the addition of a fungicide to glyphosate applied postemergence on crop injury, disease control, and corn yield. Canadian Journal of Plant Science.  98: 971-974.

b) Xtendimax antagonizes Assure and Select

Underwood, Matthew G. Nader Soltani, David C. Hooker, Darren E. Robinson, Joseph P. Vink, Clarence J. Swanton and Peter H. Sikkema. 2016. The addition of dicamba to POST applications of quizalofop-p-ethyl or clethodim antagonizes volunteer glyphosate-resistant corn control in dicamba-resistant soybean. Weed Technology 30:639-647.

c) ATS accentuates injury in wheat

Hooker, David C., Nader Soltani and Peter H. Sikkema. 2018. Response of winter wheat to herbicide plus fungicide plus ammonium thiosulphate tank-mixes. Canadian Journal of Plant Science 98: 1357-1364.

d) Soybean and wheat herbicides on oilseed radish

Cholette, Taiga B, Nader Soltani, David C. Hooker, Darren E. Robinson and Peter H. Sikkema. 2017. Effect of soybean and winter wheat herbicides on oilseed radish establishment and growth. Canadian Journal of Plant Science 97:1175-1184.