One of the most effective techniques for managing resistance is the early detection which can help growers choose novel herbicides and manage resistance already in their fields. Assessing herbicide resistance in weedy species can be a time- and space-consuming task for MSU Plant and Pest Diagnostics (PPD). For a thorough herbicide resistance test, clients need to submit seeds from mature weeds which were not controlled with herbicides. Many seeds are initially dormant so species-specific techniques must be utilized to break such dormancy. Upon successful germination, the diagnostician must grow several dozen plants, treat with the herbicides of interest, wait for symptoms to appear, and report back to the client. Once seeds reach the clinic this screening process can take two or more months, depending on the species. That means it could take 6 or more months from the initial herbicide failure in the field until potential resistance is confirmed (Figure 1). It also risks introducing more potentially-resistant seed into the seedbank as the grower waits to collect mature seed.

Objective 1: Gather a diverse sample-set from the five most commonly herbicide-resistant weed species in soybean fields across Michigan using a network of professional crop scouting agribusinesses as well as focused sampling of resistance hotspots.

Objective 2: Deploy already developed molecular diagnostic assays for EPSPS and ALS inhibiting chemistry resistance.

Objective 3: Communicate results to soybean growers and streamline the process of sample submission, assay running, and reporting.

Data about the type and extent of resistance of these keys weed species will be delivered to soybean growers and crop scouting companies in a short (<1 week) turn around allowing for growers to alter herbicide applications if necessary. Furthermore, the assays data will be discussed at MSU extension meetings and shared with MSPC to gage the extent of herbicide resistance issues in Michigan soybean fields as well as the viability of offering molecular diagnostics and/or expanding to other modes-of action.

The availability of in-season diagnosis of herbicide resistance has the potential to reduce weed competition with the crop thereby increasing yield potential and it also can help prevent the spread of resistance both within the farm and the larger community, helping to preserve critical modes-of-action. Furthermore, when resistance issues are known, resistant plants can be rogued and/or those fields can be harvested last and extra equipment cleaning measures can be taken.