Here is a way to control Yucca plants in pastures and it does not involve grass killing Roundup nor diesel fuel as advocated by the Nebraska Extension Service article in The Gazette 4-21-2017. We have used it for years to keep our pastures Yucca (Soapweed) free and get over 90 percent kill rates.
Apply it using a spray wand on a 4-wheeler and the key is to use it when the Yucca is at the bloom stage in the spring and to wet the spines of the plant. It does not harm the grass around the Yucca and cattle will eat the grass right up to the spiny Yucca. The Yucca will turn brown within 6 weeks and is dead in 3 months. The dead plants will continue to catch snow for a couple of years and help the other grass before completely deteriorating. Here is the recipe:
15 gal water
1# 2,4-D Esther (IE 22 oz of 2,4-D LV6)
Six-tenths of an oz (17 gm) of generic Metsulfuron 60 percent (Same as Ally)
1 cup (8 oz) of surfactant.
Mix thoroughly in the spray tank and spray as outlined above. The concoction is great for controlling Musk Thistle, Common Mullein and it will also kill Prickly Pear Cactus when sprayed at the bloom stage.
Hopefully, the Extension Service will add this remedy to their Yucca control list.
PS: Be wary of the buzz tails that come slithering out of the Yuccas when they are sprayed.