Since Classic was first introduced into the peanut herbicide market in 1989, there has been much controversy over its use for the late-season control of Florida beggarweed.
Classic is labeled for use in Alabama, Florida, Georgia, North Carolina, South Carolina and Virginia and can be applied on peanuts from 60 days after emergence until 45 days before harvest.
Extensive, region-wide research trials have validated the tolerance of peanuts to Classic when applied in this manner.
Although Classic can provide very effective control of Florida beggarweed, growers have been somewhat uncomfortable with its effects on the crop. Additionally, field observations suggest that Florida beggarweed plants, previously treated with Cadre, may be more difficult to control with Classic. It also has been discovered in recent years that Classic may have a variable influence on the expression of tomato spotted wilt virus (TSWV)
In this research, Classic caused a 10 percent or more increase in TSWV about a third of the time.
Peanut fields must be kept weed-free of Florida beggarweed for at least four to six weeks after emergence to avoid competition. Beggarweed plants that emerge after this time period do not directly reduce yields. However, these late-emerging plants can severely impede fungicide applications and harvest efficiency, which, indirectly, can negatively impact yields.
Unfortunately, the peanut weed science research community has not put much effort into this area. Research has shown that it takes roughly six Florida beggarweed plants/m2 to reduce peanut yields by 25 percent, but I do not know the exact number of beggarweed plants that it takes to significantly influence fungicide deposition or peanut digging. I would be willing to bet that most seasoned peanut growers probably have a good idea.
Other effective herbicide options exist for the control of Florida beggarweed in peanuts such as Valor, Strongarm, Gramoxone, and Cadre (beggarweed less than 2 inches tall).
If these have failed to do the job, Classic should be used for late-season Florida beggarweed control if the population of beggarweed is high enough to impede digging and fungicide spray deposition.
In my opinion, the fungicide deposition and digging problems related to excessive Florida beggarweed populations outweigh the potential for Classic to increase the expression of tomato spotted wilt virus, cause crop injury, and reduce peanut yields.
The only other legal alternative for late-season Florida beggarweed control in peanuts is to mow just prior to harvest. But, who has the time and interest to do that with current diesel fuel prices?