will spray residue kill mature pine trees

[Hendrix]

I have sweet gum growing right next to pines and have been hand spraying to kill them. They are in the one foot to 15 foot stage. Will residue from sprayer have any negative affect on the pine trees. I used roundup but I don't think that is going to work. Any suggestions would be helpful.

[Furu]

Impossible to know without complete information. 
What concentration was your spray 1% 1.5%, 2% etc? 
Did you ensure that here was no drift of the spray? 
Were the pines pruned up or did they have lower branches that could get spray on them?
How did you direct the spray on the sweet gum and was it directed towards the lower boughs of the pines?

In general you should be OK but without knowing all the conditions it is impossible to know.  Glyphosate was not your best choice to take out trees of any type in the 1-15 ft stage, however that does not mean that it won't be effective just not to the degree that you hope for.  There are appropriate chemicals for that purpose that are much better, however the other questions still stand and have to be evaluated.

[Hendrix]

Thanks, I think I have enough info from your answer to make a decision and I will be more specific next time

[WDH]

Garlon 4 will nuke sweetgum.  As long as you don't slop it on the pines or get the spray on the needles, you will be fine.  The generic version of Garlon 4 is Element 4.  If you are using it as a foliar spray, a 3% solution is fine.  If you are basal spraying the bark, you can mix 25% Garlon and 75% diesel fuel.  Read the label for specific instructions.  Just keep the chemical off the pines.  Garlon is not soil active, so as long as you don't get the chemical on the pines, you are good.   

[Furu]

Garlon 4, Element 4, Triclopyr 4 all the same thing.
Triclopyr Ester formulation. 
Use it all the time. 
The Amine (Garlon 3A, Element 3A) version works, but IMO, not as well for the described prescription.

[Wudman]

Give your Roundup time to act.  Glyphosate at the appropriate rate is death to sweetgum in that size range.  Be aware that Garlon 4 has some volatility issues at higher temperatures and humidity.  I haven't used it in years, but its label used to carry a temperature restriction above 85 degrees Fahrenheit.  It will volatilize in hot weather.  It also has restrictions around sensitive crops like tobacco or grapes.  On the other hand, glyphosate is a user friendly product.  It stays where you put it.  If you don't get it on non-target plants, they will be fine. 

Wudman 

[RjMaan]

I think it totally depends on the composition and characteristics of spray chemicals. There are some spray chemicals which do not last longer and usually decompose after application.