In September 2017, after doing some preliminary screening (Figure 1), we collected yellow nutsedge tubers from a peanut field that were a strong suspect for resistance to Cadre (imazapic). We sent the tubers to BASF for further greenhouse testing and just got back the results.
Unfortunately, it looks like this population of nutsedge has developed resistance to Cadre (Figures 2 and 3). On the positive side, it does not appear to have developed cross-resistance to Sandea/Permit (halosulfuron). In order to protect the grower’s privacy, I would prefer not to reveal the exact location of this field at this time.
Assuming adequate funding is obtained, I will be working very closely with our new teaching/research weed scientist on the main campus in Athens, Dr. Nick Basinger, to further investigate this issue. Dr. Basinger recently replaced Dr. Bill Vencill.
If you are already aware of or become aware of peanut fields where Cadre has been used for yellow nutsedge control with less than optimum results, please let us know so that tubers can be collected from the field. At this point in time though, I believe that this discovery of resistance is most likely an isolated case.
Here are a few things to consider in regards to this issue, especially how it compares to the herbicide-resistant Palmer amaranth problems that we have been dealing with since 2004:
1. At this point in time, only 1 case of herbicide-resistance in yellow nutsedge has been officially confirmed world-wide. In 2013-2014, researchers from Arkansas confirmed halosulfuron resistance in a yellow nutsedge population collected from a rice field. For comparison, 61 cases of herbicide resistance in Palmer amaranth have been confirmed.
2. In Georgia, Cadre was first commercialized for use in peanut in 1996 so it took more than 20 years for this resistance to occur in yellow nutsedge. It took roughly 3-4 years for glyphosate resistance to evolve in Palmer amaranth after the introduction of RR soybeans (1996) and RR cotton (1997).
3. The GA problem site is a dryland field where peanuts were grown for 5 continuous years and Cadre was used every year (for economic reasons). This is atypical of the normal crop rotation sequences used by most Georgia peanut growers. Unlike glyphosate, Liberty and PPO herbicides, Cadre is not applied to fields on a yearly basis.
4. Yellow nutsedge can produce a large amount of seed but seed is not the primary propagation mechanism. Some research has shown that <1% of yellow nutsedge seeds can develop into viable seedlings. Seed is the only propagation mechanism for Palmer amaranth.
5. The primary mechanism of yellow nutsedge propagation is through tubers. In Georgia, a single yellow nutsedge plant, growing without competition in a bareground area, produced 700 tubers after 6 months of growth.
6. The primary mechanism of yellow nutsedge tuber dispersion in fields is through normal field operations such as tillage/disking and equipment movement (i.e. human action).
7. Foraging and soil disturbance from feral hogs has been reported to promote the long-term population maintenance of yellow nutsedge.
8. There could be also be some slight dispersion from waterfowl that prefer yellow nutsedge tubers as a food source (i.e. ducks, geese). However, a recently published study from Missouri reported that no intact nutsedge tubers were recovered from mallard ducks in 8 feeding trials. In these same feeding trials, 26% of Palmer amaranth seeds were viable after feeding.
|Figure 1. Cadre and Sandea field screen on suspect resistant yellow nutsedge population in Georgia, 2017.|
|Figure 2. Suspect resistant yellow nutsedge population treated with Cadre 2AS @ 32 oz/A (8X rate), 21 DAT.|
|Figure 3. Susceptible yellow nutsedge population (left) and suspect resistant population (right) treated with various rates of Cadre 2AS – 28 DAT.|