Get results from your pre-seed herbicide application

Your most frequently asked questions, answered
*Contributions from Brett Teetaert, Michelle Thompson and Simon North

So you’ve decided to do a pre-seed herbicide application to combat pesky, yield-robbing weeds this spring. Check √

You’ve made sure to choose products with multiple modes of action. Check √ 

Now, to help you get the results you’re seeking, we’ve answered some of the most common questions our farm customers are asking about spray effectiveness.

Q: How little water can I get away with?

A: First and foremost, follow the product label. Recommended water rates have been optimized by the manufacturer to ensure you get the most out of the product, and many add-ins are contact herbicides, which means coverage is king. Most glyphosate add-ins recommend 5 gallons/acre and we can’t say it enough: Use the recommended water rate. Increase the rate IF there is higher weed density or crop residue to ensure sufficient product coverage.

Q: Can I use water from my dugout to spray?

A: It’s very common for water from sources like dugouts to be hard or to have an undesirable pH level. If you plan to do this, it’s critical you get the water tested for hardness and pH. 
#Pro-tip:  If you don’t have a reliable way to test for water quality, check with a local hot tub dealer. Most of them have the equipment to do this correctly. Here’s what you’re looking for:

• Water hardness < 350 ppm.
• Ideal pH = 5-6 (4.5-7 is tolerable)

Q: I have a few old jugs of glyphosate in the shed. Can I throw them in with my Roundup?

A: In general, we recommend that you do not mix glyphosate products because of the differences in salts. Different products have different salts and different loads of grams per active ingredient. If the salt in your leftover product is unknown or different, avoid mixing the products.

For more on mixing glyphosate products, check out our #FarmHack video here:

Q: When can I start spraying?

A: Hopefully soon! Keep these tips in mind to make sure you get the timing right:

• You can typically start spraying when overnight low temperatures are 5°C or warmer and daytime temperatures reach 8-10°C. Annual weeds are just like your newly seeded crops in that they need similar conditions to germinate, i.e. warm soil with moisture.
• Spray when the sun is shining.
• Get the most out of your day. As spring temperatures warm up, you might be able to complete a pre-seed herbicide application in the morning, followed by seeding on a different field in the afternoon as soil temperatures increase.

Q: How soon can I spray after getting frost?

A: Overnight temperatures of 0 to -4°C, are considered a light frost. These temperatures shouldn’t affect perennials too much. Wait to spray until the daytime temperature is AT LEAST 8°C for a couple of hours, and there must be no risk of frost the night you spray.

If overnight temperatures drop to -5°C or colder, wait for two frost-free days and check weeds for regrowth. You will likely see some signs of life. A fog or light rain can alleviate damage from frost. Wait for daytime temperatures to reach 8°C for a couple of hours, ensuring no risk of frost the night you spray.

If you’ve got any more questions about your pre-seed herbicide application, contact your Cargill location. And always read and follow label directions for any product you apply.