Stevia is a perennial crop where in-season and dormant weed management is vital to successful production (Figure 1). In organic production systems, mechanical weed control methods (cultivation of row middles and hand hoeing) are the primary weed management options. In conventional systems, the development of herbicide programs, in conjunction with mechanical practices, will help growers reach optimal stevia yields.

Figure 1: Stevia Field with high weed pressure

Figure 2: Row that received a pretransplant herbicide application v. an untreated row

Being a relatively new crop in the United States, there are not many herbicides labeled for use in US stevia plantings. Currently there is one product registered, Select Max (clethodim), which will only control emerged grasses, but research is being conducted to pursue more registrations. The USDA IR-4 Program (ir4.rutgers.edu), which assists specialty crop growers with registration of pest control products, is currently working on three different herbicide projects in stevia (s-metolachlor, halosulfuron, and ethalfluralin). The eventual registrations of these will help growers control many broadleaf weeds along with both annual and perennial nutsedge species. Other products are also being evaluated to find safe and effective products to be used at different timings and methods (pretransplant, hooded/shielded in row middles, broadcast over the crop, dormant stevia, etc.) (Figure 2). Some promising products have already emerged from these research trials and could possibly be in the IR-4 system in the near future (Figure 3), while some that have been screened will not be pursued (Figure 4).

Figure 3: Herbicide product with good weed control and no damage to the plant

Figure 4: Leaf bronzing and curl due to exposure of an herbicide with phytotoxicity