### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D.C., 20460 

## JUN 18 2015

MEMORANDUM OFFICI:: OF CHEMICAL SAFETY AND POLLUTION PREVENTION



### SUBJECT: Isoxaben Qualitative Benefits Assessment (PC Code 125851) 

### FROM:

THRU: Leonard Yourman, Plant Pathologist

## ~ Biological Analysis Branch 

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# ~·~V//Ct**>---** 1 ism, emor 10 og1st**/~ ~**  Biological Analysis Branch Derek Berwald, Economist Economic Analysis Branch Biological and Economic Analysis Division (7503P) Arnet Jones, Chief Biological Analysis Branc



### TO: Christina Scheltema, Chemical Review Manager Risk Management and Implementation Branch III Pesticide Reevaluation Division (7505P) BEAD Product Review Panel date: June 13, 2015


### SUMMARY Isoxaben is undergoing registration review. The Biological and Economic Analysis Division (BEAD) conducted a qualitative assessment ofthe benefits ofisoxaben. Isoxaben is a benzamide chemical (WSSA Group 21) that inhibits cell wall biosynthesis. Isoxaben is the only herbicide ofbenzamide chemistry (Group 21). The largest use ofisoxaben is to manage preemergent broadleafweeds in ornamental nurseries and on golfcourse turfalthough there is use for managing pre-emergent broadleafweeds in bearing and non-bearing fruit and nut orchards and vineyards. Much ofthe orchard and vineyard use is in California. It appears to be particularly effective for difficult to control nursery weeds such as bittercress, common groundsel, creeping woodsorrel, pearlwort, and spurge and appear to be effective for up to 18months in container plantings. Preemergence herbicides are also used to control annual weeds of turf. Isoxaben has beenrecommended onturffor managing black medic, cudweed, dandelion, henbit, knotweeds, and others. Isoxaben is primarily used on golfcourse roughs (it is not permittedto be used on golfcourse greens and tees). In orchards and vineyards, isoxaben is applied in the fall or winter and can provide 4-5 months ofweed control. Isoxaben is effective on hairy fleabane, common mallow and marestail, which are important orchard weeds.

BACKGROUND The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) requires EPA to register pesticides before they canbe distributed and used and to re-evaluate the registrations at least once every 15 years. FIFRArequires EPAto regulate the use ofa pesticide to the extent necessary to prevent unreasonable adverse effects onthe environment, including human health, where 'unreasonable' is defined as taking into account the economic, social, and environmental costs and benefits ofthe use ofthe pesticide.

APPLICATION CONSIDERATIONS The primary concern for isoxaben use is risk to non-target plants, primarily from spray drift. Since spray drift after isoxaben application is a major consideration for risk boom height and droplet size are key factors to reduce the potential for drift. Isoxaben is absorbed by plant roots (very little is absorbed by leaves), which is optimally accomplished by a low boom height. Preemergence herbicides that are taken up by the plant roots should be applied with large droplets since they will roll offthe leaves into the soil where they can be taken up by weed roots. Fine droplets can collect on leafsurfaces and never reach the soil or weed roots. Proper application and sprayer calibration ofpreemergence herbicides in orchards will maximize efficacy and reduce drift (Doll, 2013; Sumner, 2007). Preemergence herbicides often require 0.5-1.0 inch ofrain or irrigation for optimal incorporation. Some current labels indicate application of"mediumto coarse" droplets. Mitigation ofrisk due to drift might be achieved through restrictions on boom height and droplet size.
QUALITATIVE BENEFITS GolfCourse Turf On turf, isoxaben is used for the preemergence control ofa number ofdifficult to control annuals and perennial weeds (Yelverton, 2001). The unique mode ofaction and effectiveness of isoxaben may provide a particular benefit for the userin a weed control program. Isoxabenhas been recommended for managing black medic, cudweed, dandelion, henbit, knotweeds, and others (e.g., McAfee and Baumann, 2012; Pfeiffer, 2011). It is primarily used ongolfcourse roughs (the label prohibits its use on golfcourse greens and tees). Two other chemical groups canbe used to target similar weeds. Alternative preemergence herbicides include Group 3 herbicides dithiopyr, prodiamine, and pendimethalin (Reicher, 2013) and a Group 8 herbicide ethofumesate (McAfee and Baumann, 2012).
Page 2Nurseries Benefits ofisoxaben are its effectiveness against difficult to control weeds and long-term weed control. For container-gro\\'.Il production isoxabenhas been recommended for control of bittercress, common groundsel, creeping woodsorrel, pearlwort, and spurge (UC, 2009). Itis considered an "excellent" material for broadleafweed control and some weeds may be controlled for up to 18 months (UC, 2010). It is commonly combined with herbicides active against annual grasses. Disadvantages include possible injury to susceptible crops such as lilac, snapdragon, and Euonymus, and cost. There are limited chemistries used as preemergence herbicides in nurseries. Alternative preemergence herbicides that are used include oxyfluorfen (Group 14-- use only around conifers), oxadiazon (Group 14--residual activity of 12-16 weeks, although not very effective onpearlwort,·chickweed, and horseweed), and oryzalin and pendimethalin (Group 3-nothighly effective on bittercress, fleabane, and groundsel) (UC, 2010).

Orchards and Vineyards In orchards and vineyards isoxaben appears to be particularly effective for managing weeds that have been difficult to control with other chemical groups. Fleabane is difficult to control with the available preemergence herbicides registered for almonds and is susceptible to postemergence herbicides when weeds are small (UC Pest Management Guidelines, 2009). Applied in the fall or winter isoxaben can provide 4-5 months ofweed control. Because isoxabenhas a unique mode ofaction it a good rotational herbicide with other herbicide modes ofaction to manage weed resistance (Canevari et al., 2014). Isoxaben targets a wide range of weed pests (e.g., UC Pest Management Guidelines, 2012; UC Pest Management Guidelines, 2014). Limited preemergence chemistries are available for orchards and vineyards. Alternatives that target a similar range ofweeds include Group 14 herbicides flumioxazin and oxyfluorfen. Weeds such as hairy fleabane, common mallow and marestail are important orchard weeds effectively managed by isoxaben. For example, the prolific production ofwindborne hairy fleabane seeds allows this weed to quickly grow in orchard tree rows. Integrated weed managementprograms that include preemergence herbicides canbe effective for orchard and vineyard cropping systems (Hanson, 2014).

CONCLUSION Isoxabenprovides a unique chemistry as a preemergence herbicide where there are limited modes ofaction available for controlling more problematic weeds. For difficult to control weeds ofthe three main use sites (nurseries, turf, and orchards/vineyards) extension information suggests that isoxaben is among the most effective. Isoxaben is optimally applied with larger droplets and lowboom height to maximize exposure ofthe chemical into the root zone. This would have the advantage ofreducing drift.

Page 3REFERENCES Canevari, M., Holtz, B., and Hanson, B. 2014. Dormant weed control in tree nut crops 2014. The Almond Doctor, Jan. 27, 2014. http://thealmonddoctor.com/2014/0 1/ 27/dormant-weedcontrol-tree-nut-crops-2014/ Doll, D. 2013. Pre-emergent herbicide use in perennial crop orchards. The Almond Doctor, Dec. 14, 2013. http://thealmonddoctor.com/2013/12/14/pre-emergent-herbicide-use-perennialcrop-orchards/ Hanson, B. 2014. Preemergence herbicide concepts for orchard crops. The Almond Doctor. http://thealmonddoctor.com/2014/11/24/preemergence-herbicide-concepts-orchard-crops/ McAfee, J. and Baumann, P.A. 2012. Herbicides for weed control in turfgrass. AgriLife Extension, Texas A&M University, Publ. SCS-2007-13. http:/!publications.tamu
.edu/TURF LANDSCAPE/PUB turf Herbicides% 20for%20We ed%20Control%20in%20Turfgrass.pdf Pfeiffer, M. 2011. Control ofweeds inturf. Pesticide Training Resources, Arizona. http://ptrpest.com/pdf /turf weed.pdf Reicher, Z. 2013. Pre-emergent herbicides for golfturf. Golfdom, Jan. 6, 2013. http://www.golfdom.com /pre-emergent-herbicides-for-golf-turf / Sumner, P. E. 2007. Weed control sprayers. University ofGeorgia. http://www.ent.uga.edu/peach/peachhbk/pdf /weedcontroI.pdf UC. 2009. Special weed problems for container nurseries. Floriculture and Ornamental Nurseries, UC Pest Management Guidelines, University ofCalifornia Extension. http://www.ipm.ucdavis.edu/PMG/r2807004l l.html UC. 2010. Treatment for container nurseries. Floriculture and Ornamental Nurseries, UC Pest Management Guidelines, University ofCalifornia Extension. http://www.ipm.ucdavis

.edu/PMG/r280700511.html UC Pest Management Guidelines. 2014. Susceptibility ofweeds to herbicide control-pistachio. University ofCalifornia Extension. http://www.ipm.ucdavis.edu/PMG/r6057003l 1.html#SPRING UC Pest Management Guidelines. 2012. Susceptibility ofweeds in almond to herbicide control. University ofCalifornia Extension. http://www.ipm.ucdavis.edu/PMG/r3700411.html#WINTER UC Pest Management Guidelines. 2009. Integrated weed management-almond. University of California Extension. http://www.ipm.ucdavis.edu/PMG/r3700111.html
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### WSSA. 2014. Herbicide Handbook, Weed Science Society ofAmerica, Tenth Edition, 2014. Yelverton, F. 2001. Strategies for turfgrass weed control with 

### preemergence herbicides. North Carolina State University. http://www.turffiles.ncsu

.edu/PDFFiles/000071/Preemergence Herbicide Strategies for

Turfgrass Weeds.pdf

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