Roundup Weed and Grass Killer Ready to Use Plus will kill poison ivy. You may need to make several applications. You may also want to consider Bonide Poisin Ivy and Brush Killer BK-32 Concentrate. This is formulated specifically for brush and ivy. Please see the product label for complete application instructions.
You can replant 2 to 4 weeks after Roundup Weed and Grass Killer Ready to Use Plus applications.
You could spot treat the grass with Roundup Weed and Grass Killer Ready to Use Plus. Be sure not to contact the trees directly, and apply when it is not windy to avoid drift.
Roundup Weed and Grass Killer Ready to Use Plus is a non-selective herbicide and will kill weeds or grass sprayed directly with this product. Quackgrass generally is a hard to kill weed and may need to make multiple applications to completely control it. The yellowing of the weed is a good sign and for harder to kill weeds, it could take more than two weeks to fully see the results.