Horseweed/marestail in soybean:
There are populations in PA that are both ALS- and glyphosate-resistant; in these cases, here are some suggestions. For varieties that have the LibertyLink trait, including Enlist E3 and XtendFlex platforms, glufosinate (Liberty, others) at higher rates (32-36 fl oz) is a viable option and more so if tankmixed with 2,4-D choline (Enlist One/Duo) in an E3 system. If your populations are not ALS-resistant, then FirstRate (0.3-0.6 oz/A) can still provide adequate control of marestail. In a Roundup Ready system, a 2x rate (1.5 lb ae) of glyphosate or a couple of in-crop applications of glyphosate usually stunts marestail. In a Plenish system, a combination of FirstRate, Classic/Synchrony, and glyphosate tends to provide some suppression of these populations. It is always best to treat them soon after they start regrowing from the burndown application. This will not control them but might suppress them somewhat if they are sprayed early enough. Keep in mind, marestail plants are generally not very tolerant of shade and most soybeans will begin to canopy over the marestail and outcompete them. In general, the post PPOs (Reflex/Flexstar, Cadet, Cobra, Ultra Blazer, etc.) are not effective on marestail, but the pre's (Valor, Authority, etc.) are.
Palmer amaranth and waterhemp in soybean:
Populations of these weeds continue to spread around the state. Make sure to scout fields early to determine what kind of pigweed species are in your fields. The sooner you ID them the easier it is to manage them.
Source : psu.edu