Palmer amaranth continues to be a troublesome weed in corn, soybeans, cotton and even sometimes rice. Fortunately corn and soybeans appear to have a fair amount of competitive ability to "shade out" Palmer amaranth and in rice, Palmer does not tolerate a flood. However, Palmer amaranth is especially difficult in cotton- especially the first-generation Roundup Ready cotton as the pigweed can grow 12" a week and can quickly ruin a height differential.

Flex cotton has offered our best Palmer amaranth control in recent years. While herbicide resistance is a concern- in our programs, only one or two additional glyphosate applications were needed. When compared to hooded applications of glyphosate this can sometimes mean no net change in the number of glyphosate applications.

Reflex received a full federal label for post directed and preemergence use. For post-directed use, Reflex has been much like Valor, providing good contact and residual pigweed control. Careful application is critical as both Reflex and Valor are damaging if they contact cotton leaves. Preemergence Reflex has provided outstanding pigweed control; however, there is some risk of severe crop injury if a heavy rainfall occurs shortly after cotton emergence. The Reflex label limits this application to coarse textured soils only. While preemergence Reflex may be something we want to avoid- it could become more of a necessity if glyphosate resistance develops.

The Dual-type mixes with glyphosate (Sequence, Dual and Stalwart) have improved Palmer amaranth control- as long as an activating rain occurs. Syngenta has been stating that Stalwart is less active than Dual Magnum, and it is correct that pint for pint- Dual magnum is more active. However reduced Dual rates have provided additional pigweed control- so the Full Stalwart rate (equal to approximately 2/3 of the Dual activity) can provide additional pigweed activity.)

We have extensively tested post-directed herbicides and more often than not, they all provide good residual control. Sometimes Valor appears to be slightly better than Direx. Also we have found that using Dual or Prowl in a post-directed mix with glyphosate may improve Palmer amaranth control

2006 Field Day Report