**5. Crop response and weed control**

Treatments were applied at times typically occurring in Georgia soft red winter wheat production (**Table 1**) and are thus representative of producer practices and label recommendations for the PRE herbicides evaluated. For AE and POST herbicide treatments, applications that included surfactants when needed were made based on label recommendations.

An important factor for any PRE-applied herbicide in soft red winter wheat is stand establishment. Crop injury or stand reduction can lead to weed infestations, promote disease proliferation, and thus reduce yield and quality. Three herbicides were PRE applied over the course of these experiments: pyroxasulfone (40 to 160 g ha−1), pendimethalin microencapsulated (ME) (1064 g ha−1), and saflufenacil (60 g ha−1). There was no stand reduction in any of the experiments for any PRE herbicide treatment where the average wheat stand was 21 (**Table 2**), 21 (**Table 3**), 22 (**Table 4**), and 24 (**Table 5**) plants per meter of row (data not shown). Even when pyroxasulfone was applied 12 days PRE (12 DPRE), no reduction in stands occurred (**Table 3**) (data not shown). These data indicate the crop safety which these herbicides, pyroxasulfone, pendimethalin ME, and saflufenacil PRE, have toward soft red winter wheat in this region. The AE and POST for these herbicide applications did not affect wheat stand.

Soft red winter wheat injury ranged from 0 to 20% across PRE treatment timings for all studies when evaluated at 14, 15, or 30 DAP (**Tables 2**–**5**). Pyroxasulfone PRE at 160 or 120 g/ha injured wheat 20 and 11% (**Tables 2** and **3**), respectively. This injury was in the form of stunting. Some stunting from pyroxasulfone was still visible at 90 DAP for the 80 and 160 g ha−1 rates (**Table 2**). However, this injury was transient by the end of the season and not observed. Metribuzin applied alone or in combination with pendimethalin ME at emergence resulted in significant injury, 18%, at 30 DAP (**Table 4**). The soils for the present studies were a sandy loam, loamy sand, or sandy clay loam with less than 2.0% organic matter. Hulting et al. [52] noted 3% or less wheat injury from pyroxasulfone rates up to 100 g ha−1 on a silt loam soil. Previous research indicated decreased pyroxasulfone injury with legumes grown in soils with greater clay contents [19]. Canadian dry bean research indicated that pyroxasulfone injury at 210 g/ha was 11% or less [55]. These data indicate that at rates up to 160 g ha−1 wheat had tolerance in sandy loam, loamy sand, and sandy clay loam soils of the Southeastern United States. When pyroxasulfone was POST applied at Feekes scale 1.0–1.9 (**Tables 2**, **4**, and **5**), no injury was ever observed. Pyroxasulfone has limited POST activity but can be applied after wheat emergence per label recommendation [47–49]. This will provide growers an opportunity to incorporate a residual herbicide to promote weed control. When pinoxaden, diclofop, or mesosulfuron was POST applied, wheat injury did occur but was consistently less than 9% (**Tables 2**–**4**).

Wheat yield varied by location and by year (**Tables 2**–**5**). There were no differences for yield when pyroxasulfone was PRE applied (**Table 2**) or 12DPRE and PRE (**Table 3**) as compared to AE or POST applications of diclofop, pyroxsulam, mesosulfuron, or pinoxaden. For these experiments, yield exceeded 4000 kg ha−1 for all pyroxasulfone treatments and was always greater than the nontreated control. There was no rate response for wheat yield for pyroxasulfone rates of 40, 60, 80, 100, or 120 g ha−1 (**Tables 2** and **3**). There were no differences in wheat yield as compared to the nontreated control when pyroxasulfone was applied alone or in combination with saflufenacil PRE, AE, or POST (**Table 4**). Wheat yields in this set of experiments (four totals) were consistent with early season injury, in that metribuzin alone or in combination with pendimethalin ME-applied AE had significant injury 30 DAP, and this translated into reduced yields of 5670 and 5350 kg ha−1, respectively. Previous research indicated that metribuzin reduced yield demonstrating the risks growers take when using this herbicide for weed control [16, 31, 33].

Early-season Italian ryegrass control for pyroxasulfone application at 40 to 160 g ha−1 12DPRE or PRE was 72 to 99% when evaluated at 30 DAP (**Tables 2**–**4**). However, by 175 DAP Italian ryegrass control began to decline to 83% and less for the 40 and 60 g ha−1 rates of pyroxasulfone. Pyroxasulfone at 80 g ha−1 or greater provided 87% or greater season-long control (**Tables 2**–**4**). Previous research has noted similar Italian ryegrass response to pyroxasulfone at 50–150 g/ha with control ranging from 63 to 100% [52]. Bond et al. [1] noted a significant difference of 37 versus 99% control of glyphosate-resistant Italian ryegrass for pyroxasulfone at 50 versus 160 g ha−1, respectively. These data indicate that for season-long Italian ryegrass control, pyroxasulfone at 100 g/ha will be required in the Southeastern US soft red winter wheat production. As a PRE herbicide, soil dissipation of pyroxasulfone will occur over time [45, 46], thus requiring the appropriate rate to be utilized for season-long weed control. Applying pyroxasulfone 12DPRE prior to wheat planting resulted in 74% and less Italian ryegrass control. This could be potentially contributed to soil disruption in the planting process via the tractor wheels and planter disk blades.

Although no attempt was made to quantify the level of herbicide resistance in these Italian ryegrass populations, ACCase resistance is suspected in the Griffin GA population (unpublished data). Diclofop and pinoxaden are ACCase herbicides that failed to control Italian ryegrass effectively (**Tables 2**–**4**) when POST applied. Similarly, the ALS herbicide pyroxsulam exhibited variable Italian ryegrass control at 86 and 49% at 175 DAP (**Tables 2** and **4**, respectively) indicating potential ALS-susceptible and potential ALS-resistant populations. This was established even further when the ALS herbicides thifensulfuron plus tribenuron were used as sequential POST applications following AE or POST pinoxaden applications in that Italian ryegrass control was 54% at 175 DAP (**Table 5**). Multiple herbicide-resistant Italian ryegrasses to ALS and ACCase herbicides have been confirmed in Georgia [4]. Previously, growers relied on AE or POST herbicide combinations for weed control, but the addition of pyroxasulfone for PRE application in soft red winter wheat will provide much greater potential for successful crop production. However, pyroxasulfone must be applied prior to Italian ryegrass establishment, as noted by AE and POST applications in **Tables 4** and **5**. Italian ryegrass control declined significantly to 72% and less for any rate of pyroxasulfone AE or POST alone or when used with other POST-applied herbicides at 175 DAP.

Pyroxasulfone PRE controlled henbit 91% and greater (**Table 3**) or provided suppression (**Table 4**). Combinations with other herbicides improved control of this winter annual species (**Table 4**). These data indicate that henbit can be controlled with currently registered herbicides for wheat production. There is limited information about pyroxasulfone winter weed species control in wheat, other than Italian ryegrass, in the literature.

The complexity and difficulty of managing winter weed species in soft red winter wheat have increased with the discovery of herbicide-resistant weeds, specifically ACCase- and ALS-resistant Italian ryegrass [4]. Additionally, glyphosate-resistant Italian ryegrass is now an issue in this same region [1]. Successful management of Italian ryegrass resistant to multiple mechanisms of action will require diligent control programs utilizing PRE residual herbicides prior to wheat emergence, during the cropping season, and after crop rotation, in order to extend the use of pyroxasulfone's mechanism of action, which is different from all other previous wheat herbicides.
