Weed Science Research Update: <<< Turf Tips
Pylex – A new Carotenoid Inhibiting Herbicide By Clebson G. Gonçalves, Ph.D., Graduate Student at Auburn University and Scott McElroy, Ph.D., Professor, Auburn University
T
enacity (mesotrione) was the first carotenoid-inhibiting herbicide introduced to the turfgrass market. It has developed into a niche herbicide due to the need for repeat applications and potential for bleaching green tissue to a white color, even in tolerant species. Despite these issues, it still remains a viable weed control option, especially in cool-season grasses and centipedegrass. Carotenoids are lipid soluble pigments integrated into light-harvesting complexes (LHC) along with chlorophyll and perform physiological roles of photoprotection and lightharvesting. Photoprotection is the prevention of oxidative damage, or photoinhibition, to the LHC, allowing plants to maintain efficient rates of photosynthesis. Carotenoids function as photoprotectants by sequestering free radicals before oxidative damage can occur to the chlorophyll and the larger LHC. Carotenoids function as light-harvesting pigments by channeling photons unabsorbed by the chlorophyll molecule to the reaction center for photosynthesis. Thus, two things happen when carotenoids are inhibited — the LHC is destroyed due to light stress and light is not channeled to the chlorophyll for photosynthesis. Pylex (Topramezone) is a new postemergence herbicide that controls susceptible species by inhibiting carotenoid biosynthesis; specifically, it inhibits the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD) (Shaner, 2014). Topramezone (Pylex) is labeled for use in turfgrasses for the control of both grass and broadleaf weeds (Anonymous 2006; Smith et al., 2013). The characteristic symptoms of susceptible weeds by HPPD inhibitors is bleaching because of chlorophyll loss.
Weed management
results showed that Pylex in combination with Turflon Ester provided an increase in bermudagrass control compared to Pylex alone, and reduced visual bleaching. This effect would be beneficial since it is always desired to control weeds with minimal reduction of turf aesthetics and quality from the strong bleaching effects of Pylex. Although Pylex in combination with triclopyr has provided excellent control of bermudagrass, this species is very aggressive and has a high capacity for new infestation by the regenerative underground organs, so reapplication is required for long-term control (Figure 1).
Pylex Application
Pylex is registered for use in most cool-season turfgrasses such as fescue (Festuca sp.), bluegrass (Poa sp.), bluestem (Andropogon sp.), and centipedegrass (Eremochloa sp.) (Haller et al., 2017). Although creeping bentgrass injuries caused by Pylex have been reported (Elmore et al., 2015), reduced rates can reduce injury, opening the door for possible future use of Pylex. Creeping bentgrass injury can be influenced by different factors such as application rate, tank mixes, growing season, soil/air temperature, precipitation, and other environment conditions. The specifics of such factors remain poorly understood. Turfgrass managers have commonly used low Pylex application rates (<0.5 fl oz/a) and re-applied (weekly or every two weeks) to control crabgrass and goosegrass. This strategy aims to decrease bleaching injuries in creeping bentgrass. Currently, studies at Auburn University have investigated the optimal growing season for Pylex application and also the integration of field programs with paclobutrazol
19
Ala bama T urf Tim es >>> S ummer 2019
Pylex has become an important tool in turfgrass systems as it effectively controls crabgrass species (Digitaria spp.) and goosegrass [Eleusine indica (L.) Gaertn.] with a low application rate of 12.3 to 36.8 g ai ha-1. Among the HPPD inhibitors, sequential applications of Pylex have potential for bermudagrass suppression (Brosnan et al. 2011). However, researchers showed that Pylex alone cannot effectively control bermudagrass, suggesting that tank mixtures with other herbicides may be required to provide effective long-term control. Previous research shows that Pylex combined with triclopyr (Turflon Ester) may be used for bermudagrass control (Brosnan and Breeden 2013; McElroy and Breeden 2006). Researchers at Auburn University seek to determine better Pylex plus Turflon Ester rates for bermudagrass control. The first
Figure 1
