Crossbow should do a good job on English Ivy, but trichlorpyr by itself does the great job too. Garlon 4 is the best product IMO applied spray to wet but not to runoff. Be careful not to spray on tree trunks or exposed buttress roots directly as the product can be taken up. Check the label for legal sites and be careful of high temps as they are both esters as you know. Garlon 3A is the amine formula and although not as quick, it's a good alternative and best to use with a surfactant for penetration. We like Syltac by Wilbur-Ellis Co. for the surfactant combined with InPlace, also a Wilbur-Ellis product. If you haven't heard of that product yet, check into it. It encapsulates the herbicide so more stays on the target and only the water evaporates. The combination enhances control for a few pennies per gallon.
Neal