News

getting the most from your spray

By Harry Brook

We are in the middle of spray season. Some canola producers are using insecticide on their canola and others are trying to spray the emerging crop for weeds. It is a major crop expense, but how do you maximize the results from your spray dollar?

Let’s review the best way to get good results. You need to spray the intended target at the right rate, timing, coverage and environmental conditions. Spraying when it is too cold, too wet, too windy or the wrong stage is a recipe for poor results. Let’s look at the crop first.

Research in the 1960s and '70s found that weeds germinating before the crop germinated can severely damage crop yield. However, if the crop germinates at the same time or before the weeds, yield losses were significantly reduced. You should closely follow the crop staging for pesticides as using it outside the recommended growth stages can lead to crop damage and/or yield loss. This also applies to the problem insect staging compared to the crop. With weeds, they usually have to be vegetative and not flowering.

Weather conditions are always challenging, especially while spraying. Wind is a common problem during spraying season. The need to cover many acres over a limited time can lead to spraying in poor conditions. Every year, people living on adjoining crop fields find their trees or gardens are hit by spray drift. Spray with wind conditions at 15 km/h or lower. It could be the adjoining crop was sprayed under windy conditions or the other extreme of complete calm and vapour clouds drifting off the field.

Remember, pesticides have a critical temperature at which they are effective. If you’re spraying herbicide, the plants must be actively growing. That means they are most effective when there is water for growth and temperatures that allow photosynthesis to occur.  Spraying any pesticide when it is 5˚ C or colder is mostly a waste of money and time. Best temperatures for good results should be above 12˚ C. Spraying when it is too hot can also be a problem. Most crops grown in Alberta grow best from 15 to 28˚ C. When temperatures are in the 30+ range, they shut down, as they do in drought conditions. Spraying when it is too hot can lead to poor control and vapour clouds due to volatilization.

Then there is the false economy of cutting rates. The recommended rates on the label are set to ensure good activity on the target weed or bug. By cutting rates, you may get good control if everything works out perfectly or you may only get partial control. Cutting rates can be a shortcut to developing resistance in the problem disease, weed or insect.

Finally, the most important thing to consider is the economic threshold of the pest compared to the crop. Many common pests, especially insects, have fairly, well defined economic thresholds. That cannot be said for weeds. Our tolerance for weeds is low in some crops, as we have many herbicide tools to use for control. However, using those same tools year after year has resulted in serious problems controlling weeds, which have become resistant to the herbicides. Two examples of this are wild oats and kochia. There are wild oats in the county that have herbicide resistance to two or three of our main herbicide groups. In some cases, we are relying on old chemistries to try and combat the problem.

As with the 4R fertilizer program, the same philosophy could be applied to pesticide application. Make sure weather conditions are good for success, rotate your pesticide groups, use the proper rates and make sure the pesticide you are using will provide you with a profitable return for your investment. For further information, click HERE and check out the videos below.


Harry Brook is Flagstaff County's Agricultural Fieldman. He can be reached via email at: This email address is being protected from spambots. You need JavaScript enabled to view it. or by phone at: 780-384-4138.