Spraying Tips for Tough Conditions

Rain, wind, sun, dust; six months into 2024, and the Peace Region has already seen it all. How and when should we spray in these tough conditions?

When to Spray Weeds After a Frost?

After a light frost, spraying could resume when the following conditions are met:

• A minimum of one night with a minimum temperature of 5 degrees Celsius.
• A minimum of one day of good growing conditions i.e.. warm and sunny, has passed.
• Good growing conditions are present at the time of spraying.
• No evidence of frost damage is visible, such as blackening or a water soaked appearance, on the crop or weeds. 

Tips for Spraying in the Wind

Spraying with wind speeds higher than 15 km/h will increase drift. Please ensure that the wind is blowing away from high risk areas, such as a neighbour's yard or recently emerged crops, before commencing spraying. To help reduce drift in windier conditions, consider the following:

• Use low-drift nozzles.
• Increase water volumes to improve coverage with larger droplets.
• Find a nozzle that can achieve a coarse spray at a wide range of pressures. 
• Aim for 100% overlap nozzle to nozzle, to provide equal coverage across the whole boom width.
• Keep the boom low.
• Travel slower to reduce the amount of fine droplets. Please ensure it is safe to drive with the boom lower before commencing.
• Spray at night if the winds are calmer, as inversions can lead to unpredictable drift.

Tips for Spraying in Dusty Conditions

Dry conditions and wind can cause dust to build up on weed leaves, which may limit herbicide uptake. Most products are not overly affected by dust, but both glyphosate and diquat (Reglone) are very dust-sensitive.

Active ingredients in these products are highly 'charged' and bind readily and strongly to soil particles, including not only the dust on plant surfaces, but also suspended soil in spray water. This is the same reason why hard water affects glyphosate.

Tips for Spraying Before Rain

As most producers know, spraying in the rain is not advised, as the product washes off before it gets absorbed. However, spraying just before rain - allowing time to satisfy label requirements for rain-fastness - can provide effective control, especially if rains are forecast for a few days and weeds are growing strong. 

Please note that rain-fastness is different for each herbicide, so always check the latest product labels for any updates.

Efficacy when Spraying in Cool Conditions

Herbicides generally tend to work best in sunny conditions when weeds are actively growing and cycling nutrients, with performance being on a sliding scale. 

• Cloudy days with highs of 10 degrees Celsius after a night of near 0, will tend to result in low herbicide performance.
• Sunny days with highs of 15 degrees Celsius after a night of 3 degrees, will provide improved control.
• Sunny days with highs of 20 to 25 degrees Celsius after a night of 10 degrees, will provide optimum control.

Efficacy when Spraying in Hot Conditions

Weeds: Warm, sunny days when weeds are actively growing are generally the best for herbicide spraying, although hot weather reduces efficacy, especially if conditions are also dry. 

Flea Beetles: Flea Beetle activity is lower under extreme heat and, perhaps more importantly, so is insecticide performance.

When to Spray Post-Emergence if you Missed Pre-Seed Burnoff?

Seeding and then spraying means that winter annuals and perennials will be much larger and harder to control, making it even more important to apply in-crop application early. 

Want more tips on spraying? Join Tom Wolf at our Spraying Workshop at the Cotillion Hall, on July 10, 2024.

Information in this article taken from an article by the Canola Council of Canada.