Morning glories can be pretty when they flower, as long as they're not in your corn field, growing up your stalks of corn. They are powerful enough to bring a stalk down and lay the ear on the ground. That's lost yield – the ear will never see the combine.
If there are just a few escapes and a few stalks affected, it most likely isn't a big deal. If you're in bottom land or other areas where morning glories run rampant, they can grow up on several stalks down a row, and take down a whole section of a row. If you can still harvest the crop and get the ears, morning glories can still be a menace during harvest, even with some of today's modern equipment. It all depends upon how thick they are.
Dow AgroSciences' Damon Palmer classifies morning glory as a hard-to-kill weed for certain herbicides. Glyphosate can control it, but only at high rates. Lambsquarters falls in the same family. In both cases, the weeds aren't resistant to glyphosate, Palmer says. These two weeds are just harder for glyphosate to control than many other weeds. If you skimp on rates or if conditions for spraying aren't the best, or if you didn't set your sprayer to get the best coverage on weeds that you could get some will likely escape control. Whether or not you need to deal with it depends on how many are escaping control.
As you harvest this fall, keep an eye out for morning glories. If the infestation is bad enough, you won't miss it – it will slow you down. If you have patches that are more virulent then you like, then consult with your ag chemical retailer before deciding how to handle these tough weeds in upcoming crops.