Tropical soda apple (TSA) continues to be a problem in Florida pastures, but other weeds are often present in significant numbers. Dogfennel is the most widely encountered weed in Florida pastures, and it is commonly found growing along with TSA (Figure 1). Although Milestone is highly effective on TSA, it provides little or no dogfennel control. Likewise, GrazonNext HL (a mixture of 2,4-D and Milestone) is more effective than Milestone, but still fails to control large dogfennel plants. To illustrate, UF/IFAS research has shown that GrazonNext HL applied at 1.5 pints/acre was excellent on TSA, but highly inconsistent (30%–95% control) when dogfennel was 30 inches or greater in height. Increasing the rate to 2.0 pints/acre improved the consistency of control for 30 inch-tall dogfennel but failed to control plants that were 40 inches tall or greater. Since TSA and dogfennel of all sizes are common throughout Florida, GrazonNext HL tank-mixed with another herbicide will be required to effectively control both species.
Many combinations were tested to determine what herbicides could be tank-mixed with GrazonNext HL to provide adequate control of both dogfennel and TSA. The ultimate goal was to maximize weed control without adding more than $8/acre to 1.5 pints/acre of GrazonNext; the total cost of the final tank-mix should not exceed $20/A. The most promising combinations were 8 fl oz/acre of Pasturegard HL, 2 pints/acre of 2,4-D + dicamba (WeedMaster, others), or 3 pints/acre of 2,4-D amine. Each of the herbicides, when mixed with 1.5 pints/acre of GrazonNext HL, provided at least 88% control of 40-inch dogfennel 60 days after treatment (Figure 2). TSA control with these tank-mixtures was approximately 90% at 60 days after treatment.
In Figure 2, the addition of $4–$7/acre increases dogfennel control from 60% with GrazonNext HL to at least 88% with GrazonNext HL and one of the three tank-mix partners. Therefore, as you scout your pastures for TSA, be sure to also look for other weeds as well. If you have pastures with both dogfennel and TSA, consider one of these tank-mix options to get the most for your money.
The tank-mix treatments in Figure 2 were applied on a large scale to demonstrate the success of these tank-mix treatments. All treatments performed similarly (Figure 3), but at the time of application dogfennel was at least 6 feet tall. Therefore, these tank-mix combinations can be used for both dogfennel and TSA control at any growth stage.