Most of the weeds that are present in your pastures as we approach summer will probably be perennials plus some annuals that you missed with your initial chemical application (if there was one). The transition from spring to summer is the right time of year for brush control, as long as the weather is good.
Some of the brush control herbicides we recommend during the late spring-early summer period can move in the soil during wet conditions, so keep this in mind when spraying near desired trees and plants. Remedy is a brush control herbicide that doesn't have soil activity, so we don't worry about it moving in the soil. For the weeds in the pastures, the spring-summer transition is the time to consider herbicide applications on horsenettle, silverleaf nightshade, bull nettle, blackberries, Johnsongrass and sericea lespedeza. Sericea lespedeza should be controlled as soon as you discover it in your pastures. Oklahoma State University has shown that Remedy or Pasturegard applied to actively growing plants in June or early July when soil moisture was adequate for plant growth provided excellent control. Another option would be Cimarron applied in September during midbloom of the sericea, again where plants are actively growing. Remember that the blackberries, horsenettle and silverleaf nightshade should be sprayed when they are in the bloom stage of development since these are perennial plants. The highest flow of carbohydrates from the shoots to the roots occurs during the bloom stage. The goal is to move as much herbicide as possible to the roots, killing them and preventing them from visiting our pastures next year. By the beginning of summer, any annuals you have in your pastures have already done most of their damage for the year and are likely to be too mature to control.
By June, you've probably missed controlling weeds for the year, except for those listed above. Take a summer "weed census" of your pasture so that you know what you'll need to control next spring.