By John Ippolito, Regional Crops Specialist, Ministry of Agriculture, Regional Services, Kindersley
There are a few weeds that were particularly troublesome in the 2016 crop. Two of real concern are Canada thistle and Narrow-leaved hawk’s beard. Part of the solution for these weeds is to start control measures in the previous fall.
Narrow-leaved hawk’s beard is both a summer annual and winter annual. It is a very prolific seed producer with some seeds maturing as early as mid-July. Seeds have no dormancy and can germinate readily in late summer and early fall. The plants that germinate at this stage act as winter annuals and are difficult to control with spring herbicide applications. As a result fall herbicide applications are a recommended practice.
One of the most cost effective fall applications is an October application of 2,4-D ester 600 at 0.57 to 0.9.0 litres per acre. Other formulations can be used at appropriate rates. This application is effective on the fall seedlings but producers must keep in mind that with these application rates they should only plant cereals on those fields the following spring.
Fall and late summer applications of tribenuron formulations are also very effective at control of narrow-leaved hawk’s beard seedlings as well. Often these may be combined with post-harvest glyphosate applications. Producers should consider spring planting plans when considering this application as there may be cropping restrictions as well.
Canada thistle is very difficult to control prior to seeding due to its late start in the spring. Also we are currently growing a number of crops with limited or no in-crop herbicide options. As a result, control in the previous fall is essential. The most effective herbicide application is a pre-harvest application of glyphosate to registered crops.
Post-harvest glyphosate applications can also be used but there are a few complications with this application. Regrowth of the plants after harvest is required to ensure translocation. With abundant moisture this summer regrowth should occur provided we do not have killing frosts prior to application occurring. The other challenge with post-harvest applications is the higher rate of herbicide application required and the fact that results are not as consistent.
Prior to harvest operations starting producers should evaluate weed populations in the fields and determine what should be done in anticipation of controlling these two weeds prior to planting of crops in the spring of 2017.
For more information on control of weeds in the fall contact your regional crop specialist.
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