Today, more than ever, maximizing weed control while minimizing cost is critically important. This means that the right herbicides must be sprayed at the right time and in the right way.
A weed control failure can be devastating since it will result in lost crop yield as well as additional herbicide and application expense. This is especially true for annual grasses that can cause tremendous pod loss during the digging process.
Not All Herbicides Tankmix Well
Multiple herbicides are often sprayed in combination in an effort to save time and broaden weed control. However, not all herbicides perform well when tankmixed.
Of particular concern is the grass herbicide clethodim (Select Max, Trigger, Arrow and others). Imazapic (Cadre, Impose, others) and clethodim are considered to be complimentary herbicides with respect to the weeds controlled when applied in combination.
When tankmixed, imazapic can potentially control most all broadleaf weeds present while clethodim will control grasses. Although logic tells us these two herbicides should work well together for broad-spectrum weed control, experience tells us something else.
In many research trials over many states, the combination of imazapic and clethodim will often lead to decreased grass control.
In a study conducted recently in Florida, clethodim was applied alone and with imazapic to control goosegrass, crowfootgrass and crabgrass. Clethodim applied alone provided 100 percent control of all grass weeds present. However, when tankmixed with imazapic, control of goosegrass and crowfootgrass dropped to 60 percent.
Two Trips Vs. Maximum Yield
Since imazapic is particularly weak on Texas panicum and goosegrass, the need for additional grass control is common. Therefore, research was conducted in North Carolina to closely examine ways to use these two herbicides to their greatest potential.
In these studies, they found that applying imazapic alone, followed by clethodim three or more days later, greatly improved grass control verses applying the two herbicides together.
Applying clethodim followed by imazapic in three days was also effective. Although the addition of adjuvants such as ammonium sulfate was found to improve grass control with a tankmix, nothing was as effective as applying the two herbicides separately.
• Tankmix clethodim with imaza-
pic and live with the control received.
• Apply one product followed by
the other product three days later.
• Increase the rate of clethodim in
Knowing Compatibility A Challenge
Granted, making two trips across the same field in three days is time consuming and frustrating. However, maximizing peanut yield and getting the most out of your herbicides will be well worth the added effort.
One other option includes increasing the rate of clethodim in the tank mixture as this can alleviate some of the antagonism. This is also expensive, but may be more convenient to the grower.
The potential interaction of clethodim and imazapic is but one example of why understanding compatibility of herbicides or compatibility of a single herbicide with other crop protection products such as fungicides, insecticides and micronutrients is important but very challenging.
Conducting research to define potential for interactions among products used in peanut is an important part of many research programs across the peanut belt. Information on these interactions can be found through your local Cooperative Extension office. PG