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Four Tips For Better Spray Application Timing

Choosing the right application timing for crop protection products isn’t always a straightforward decision. The difference between getting it right or not can mean economic losses from wasted product, crop damage or poor control. One of the factors that complicates the decision making process is different timing recommendations for different pests. The following tips will help get application timing more accurate and improve efficacy of crop protection products.


When deciding between pre-seed or pre-emerge timing, consider that if you are planning to spray with a non-selective product like glyphosate prior to crop emergence your window of opportunity closes very quickly. Every year there are fields that don’t get the planned burn-off application because time just gets too tight. Getting back into the field before the crop emerges doesn’t always happen and that all-important weed removal opportunity is lost.

Planning for pre-seed timing for burn-off is the safer bet. The recommendation is to spray the field no more than three days ahead of seeding it. Plan to go pre-seed compared to pre-emerge, unless the sprayer is in the field ready to spray as the seeder leaves the field. When scouting fields for pre-seed burn-off brush away the layer of chaff and crop residue from the soil surface and chances are you will see weeds in “the white” just ready to poke through. These very tiny weeds are the target weeds early in the spring.


In-crop herbicide application timing recommendations are based on the stage of the crop and the stage of the weeds. Spray too early and the target weeds may not be there and you risk crop injury. Too late and target weeds are beyond the size for successful control and the farmer again risks crop injury. The window of application for in-crop spraying is dependent on the

rate of growth and environmental conditions.

Herbicide labels explain in detail the recommended stages of the weeds and the crop for product application. The weed and crop sizes on the label give a range of sizes based on the number of leaves on the plant or with an actual measurement of the size of the plant. The leaf stage and size is what the herbicide company determined during registration trials what the limits were of product effectiveness. Spraying beyond label recommendations of weed and crop size and control rates results in less than satisfactory control and crop injury may result.

The recommendation is to plan herbicide application when the weeds present are at the minimum size listed on the label. By targeting weeds at that early stage chances are there will be weeds already at the limit of what the label recommends when the sprayer actually gets to the field. In-crop application product rate ranges show products can be lower if smaller weeds are targeted; bigger weeds mean more product is required (which adds to costs). An early-as-possible application also sets you up the possibility of a second application before the crop is too advanced.


Farmers ought to give consideration to crop stage when applying herbicides to reduce the chance of injury. Spraying canola during the budding stage or at bolting stage can cause undue injury; these are critical times for the plants. Cereals at filling or past the flag leaf stage is too late for most products. Chances are if you are spraying past the flag leaf stage it is revenge spraying, and the weed population has already reduced the yield potential of the crop.

As for the impact of what time of day you spray — we’ve seen a difference in performance with products applied early in the day or towards evening. For most herbicides spraying, during the day gives the most consistent results compared to spraying at night.

Herbicide application on smaller weeds does not guarantee performance, but there are important benefits to treating small weeds. Spraying when weeds are small reduces the risk of yield losses due to competition with the crop. It is also difficult to get uniform coverage of large weeds or in situations with high weed densities or a thicker crop canopy. Finally, delaying initial applications may complicate secondary control options if the weeds survive the first treatment.


For pre-harvest and post-harvest burn-off considerations, it really depends on the target weeds. With thistles, pre-harvest is the way to go; getting glyphosate on the tops of the plants is best. If you wait until after harvest you need three to six inches of regrowth from the stems to be as effective. Dandelions are better targeted post harvest because their leaves are flat on the ground and you will get improved coverage with the crop canopy removed.

Look at the factors involved in accurate spray application timing and have a plan for improved product efficacy. These tips will help improve the decision making process and get it right the first time.


withDunveganAGSolutions,Inc.(, atRycroft,Alta.


Be ready to go in and spray when the weeds present are at the minimum size

listed on the herbicide label

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