Pinoxaden

By John Peppers (Graduate Research Assistant) Scott McElroy (Alumni Professor) and Jim Harris (Research Associate)

Pinoxaden is a new active ingredient that was released by Syngenta for turfgrass use in September of 2018 under the trade name Manuscript. Pinoxaden is a member of the phenylpyrazolin chemical family, the third family in the group that includes the aryloxyphenoxypropionates (FOPs) and the cyclohexanediones (DIMs). This herbicide group makes up the ACCase inhibiting herbicides (HRAC Group 1) which are also known as the graminicides because they are only active on grass species. These herbicides kill grasses by preventing the production of lipids. Pinoxaden was previously sold in the U.K. until June 2018, under the trade name Rescue for control of Poa trivialis and Lolium spp. within fescue systems.

The current label for Manuscript allows for use in bermudagrass (Cynodon dactylon) and zoysiagrass (Zoysia spp.) in all areas except putting greens. It is also labelled for St. Augustinegrass (Stenotaphrum secundatum), but only in sod production where turfgrass injury can be tolerated. The label claims that Manuscript can control tropical signalgrass (Urochloa subquadripara), crabgrass (Digitaria spp.) and bahiagrass (Paspalum notatum). Dallisgrass (Paspalum dilatatum) is also labelled for control with Manuscript, but it is recommended that applications be made in the late spring or early fall while the dallisgrass is actively growing and not under drought stress. Manuscript can also be used to suppress torpedograss (Panicum repens) and seashore paspalum (Paspalum vaginatum). The maximum broadcast spray rate is 19.2 fl. oz/a and the maximum spot spray rate is 83.6 fl. oz/a. No more than 10,000 ft 2 per acre can be treated with Manuscript. The addition of the adjuvant Adigor, at a 0.5 % v/v rate, is recommended for all applications of Manuscript.

At Auburn, we have screened nine different grassy weed seedlings in greenhouse experiments to determine Manuscript efficacy on these weeds. These species include yellow foxtail (Setaria pumila), annual bluegrass (Poa annua), roughstalk bluegrass (Poa trivialis), large crabgrass (Digitaria sanguinalis), dallisgrass (Paspalum dilatatum), goosegrass (Eleusine indica), southern sandbur (Cenchrus echinatus), bahiagrass (Paspalum notatum) and perennial ryegrass (Lolium perenne). Good control (>80%) was found at maximum labeled rates and lower for yellow foxtail, Poa trivialis, large crabgrass, dallisgrass, bahiagrass, southern sandbur and perennial ryegrass. Notably, Poa annua and goosegrass were very tolerant requiring much higher rates to show injury. The weed species examined can be ordered from most to least susceptible as such: perennial ryegrass, yellow foxtail, dallisgrass, southern sandbur, large crabgrass, roughstalk bluegrass, bahiagrass, goosegrass and annual bluegrass.

In the field, preliminary results indicate that there is a differential response between cultivars of St. Augustinegrass to Manuscript. The cultivars Floratam and Raleigh are less susceptible to injury than Palmetto and Classic. We have focused on making Manuscript safer for use on St. Augustinegrass by using it in combination with several other pesticides. Potential safeners include the ALS inhibiting herbicides halosulfuron (Sedgehammer) and metsulfuron (Manor), along with the fungicides chlorothalonil (Daconil Weatherstik) and propiconazole (Banner Maxx). In 2018, halosulfuron, metsulfuron and chlorothalonil reduced Manuscript injury when combined in a tank mixture. Manuscript tank mixed with Banner Maxx injured St. Augustinegrass the same as Manuscript alone did. However, in 2019, halosulfuron, metsulfuron, chlorothalonil and propiconazole all reduced Manuscript injury to St. Augustinegrass when applied in combination. Unfortunately, combinations of Manuscript with Sedgehammer, Manor and Daconil Weatherstik all antagonized Manuscript control of smooth crabgrass when applied as a tank mixture. Manor tank mixed with Manuscript was the most antagonistic with virtually no smooth crabgrass control or injury noted two weeks after application. Halosulfuron and Daconil Weatherstik combinations with Manuscript partially controlled smooth crabgrass, but Manuscript applications alone were much more effective.

Another research question that is being examined concerns application timing for optimal control of crabgrass. Results in 2018 indicated that Manuscript, applied at the 1–3 tiller stage, effectively controls smooth crabgrass with either one or two applications at 41.8 fl. oz/a. However, a single application made at the 4–7 tiller stage barely injured smooth crabgrass. Two applications of Manuscript at the 4–7 tiller stage injured the crabgrass more than the single application, but still resulted in virtually no control of the smooth crabgrass. In 2019, both single and sequential applications made to 1–3 tiller stage smooth crabgrass resulted in complete control. Single applications made at the 4–7 tiller stage were also ineffective in 2019. However, sequential applications to 4–7 tiller smooth crabgrass controlled the smooth crabgrass much more in 2019 than they did in 2018.

More research is needed to fully understand how application timing effects Manuscript’s control of crabgrass.

Also, more research is needed to determine if Manuscript is antagonized by other ALS inhibiting herbicides and what the physiological basis for the antagonism is. Work needs to be done in order to determine why Daconil Weatherstik reduces Manuscript injury. For end users, the best course of action to take with Manuscript is to avoid tank mixtures that have not been confirmed safe-to-use.