By Darren Hefty

This spring, the 1000th episode of Ag PhD TV aired.  That’s 1000 weeks of a new show every week.  That’s also a whole lot of “Weed of the Week” weeds we discussed controlling.  Guess what?  Even if we stopped every one of them, there will still be more weeds!  Nature finds a way to get around things.

The challenge at this time of year, in terms of weed control, is knowing when to stop.  If you’re like me, you don’t want to see any weeds in your fields EVER.  At the same time, though, you have a few things holding you back from making that (hopefully) last application of the season.  You may have a legitimate concern about spraying, but you can’t forget the reasons why you really do need to kill the weeds in your fields.

Avoid analysis paralysis! The only thing that pays your bills is YIELD this year and YIELD every year after.  Weeds hurt yields A LOT.  Look at the return on investment you get with herbicides.  If you ever miss a strip with your pre-emerge or post-emerge herbicide application, estimate what that area will yield.  It’s often a 25 to 50 percent yield loss, and possibly worse.  If a herbicide costs $5/acre and the alternative is to lose $50 or $100, the answer is clear.  You need to kill the weeds.

Here’s where it gets tricky.  Let’s say you can’t increase your yield much with weed control because it’s late in the season.  Should you still spray?  Since one waterhemp or one Palmer pigweed plant can produce over 1 million seeds, you know you will have to face a lot of weeds in the future if you let just a few go today.  Many other weeds produce a lot of seeds.  Kochia, for example, can produce up to 30,000 seeds.

Spraying late in the year is a judgment call.  If you decide to do it, make sure you check the pre-harvest interval (PHI) first.  The PHIs for many of the herbicides you may consider are around 60 days, but some are as little as a few days.  This can really vary by product and the state where you live.  Check the label to be sure.

I encourage you to keep scouting your fields all the way up until harvest.  Even late in the season, you can still influence yield in some crops, and you can definitely stop weeds from going to seed IF you spray before those seeds are viable.