Last column we discussed inputs that build yield: varieties, cultivars and nutrients. This column deals with inputs that protect yield.
A later herbicide application may result in optimum weed control, but earlier applications will achieve maximum yields.
Previous research has found that canola in which herbicides were applied three weeks after crop emergence yielded more than 25 percent less than plots with early herbicide application.
Spraying early will almost always be better than delaying applications.
Research has also shown that a properly timed, reduced rate of herbicide on a vigorous cultivar or hybrid that is seeded at a higher plant population may be as successful as a full rate of herbicide applied to a less vigorous, lower populated crop.
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Farmers should also consider the balance between controlling a weed and the economic control of a weed.
Many acres are treated with a wild oat herbicide in which a positive economic return is not achieved.
Research that assumed $14 per acre for a wild oat herbicide and $7 per bu. prices on a 50 bu. wheat crop found that it takes a wild oat population of four wild oats per sq. metre to break even and six wild oats per sq. metre to give a $2 return for $1 invested.
I have walked fields in which two-thirds of it were below the economic threshold. However, the difficulty is to spray the areas where the populations are high.
Maximum return may be achieved by using high target seeding rates, seeding into conditions that will result in rapid emergence and spraying early to remove weeds. This should be accompanied by a good pre-seeding weed control package.
A reduced herbicide rate may still be effective in controlling weeds if the crop gets a good start and the leaf stages are beyond the weeds.
Controlling diseases with fungicides has increased exponentially over the last decade.
This increase has resulted in new products as well as new ways to use them, including some that may not produce economic returns.
Many growers have told me that they mix a reduced rate of fungicide with their herbicides and apply them at the herbicide stage (three to five leaf stage).
An extensive review of research on using a half rate of fungicides at herbicide staging has found that the practice rarely shows a yield increase, let alone an economic return.
The exception is when a cereal crop is grown on its own stubble.
The use of foliar fungicides should be restricted to two situations:
- when cereal leaf disease symptoms are observed in the crop (cereal leaf diseases)
- when conditions are present that indicates a disease such as fusar-ium head blight
Scouting is the only effective way to find cereal leaf disease symptoms in the field.
Before scouting, it is important to know what symptoms to look for and the stage at which the symptoms must be scouted. The threshold of disease presence must also be decided.
Fungicide should be applied only if scouting discovers the presence of a disease at levels at or above thresholds set by industry research. Don’t spray just because your neighbour is spraying.
However, it’s not as simple with diseases such as fusarium in cereals or sclerotinia stem rot in canola or beans. There are no symptoms with these diseases until it is too late, which means we must rely on disease forecasts based on weather to predict their presence.
We must also rely on personal experience.
A fungicide application is warranted if weather models are high for these diseases, if neighbours have had problems with these diseases and if the crop is in the proper stage.
Scouting is also important when deciding when to apply insecticides:
- know what the insect or its damage looks like
- scout at the proper stage for the disease
- consult economic thresholds
When considering seed treatments, remember that they usually contain a fungicide to control soil or seed borne diseases.
Most products are wide spectrum and control the major diseases. However, consult the label to ensure that the treatment controls the targeted disease. Seed treatments can also control insects.
Insecticides are contained in all canola seed treatments but are an “add in” for cereals and pulses.
These products are expensive so economic thresholds must be considered.
Some products promote their growth enhancement properties. I have seen the visual response from these products, but farmers should test the economic benefit on their own farms by using replicated strips.
