Golf Course Management

AUG 2018

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08.18 GOLF COURSE MANAGEMENT 65 and mostly not noticeable, makes P. annua control easier. Combining pre-emergence and post-emergence herbicides removes the first regular pre-emergence application and thereby reduces the herbicide load being ap - plied, making this practice a sound compo- nent of a resistance strategy. Another sound component of resistance management is tank- mixing products with different modes of ac - tion, which should also delay resistance, as ex- plained earlier. Northern and transitional zone use strategies Table 1 lists the products most often used for pre-emergence and post-emergence Poa annua control in nonoverseeded bermu - dagrass and zoysiagrass in areas that experi- ence total dormancy each year. In order to implement this control strategy, we suggest a three-year rotation of tank-mixing different herbicides with three modes of action. One component of this mixture should be a pre- emergence herbicide as shown in the left-hand column of Table 1. Simazine should be added to this pre-emergence herbicide. Isolated pockets of P. annua are resistant to simazine, but because simazine has a different mode of action and good activity on small P. annua plants, is relatively cost-effective and has some broadleaf activity, it possesses a lot of positives. Another post-emergence herbicide with a dif - ferent mode of action should also be included with the pre-emergence and simazine combi - nation. In the fall, when the turf is still green, we suggest either pronamide or an ALS (ace - tolactate synthase)-inhibiting product such as foramsulfuron, trifloxysulfuron, flazasulfuron or rimsulfuron. Once the turf goes completely dormant, one of the nonselective products could be considered. is holistic strategy ac - tually incorporates four different modes of ac- tion and has proved very effective. e following year, a pre-emergence her - bicide with a different mode of action should be tank-mixed, again with simazine and either pronamide or an ALS product not used the first year. If a nonselective product is needed once the turf is dormant, then choose a mode of action that is different from the one used the first year. Again, using products with four different modes of action should significantly delay the occurrence of resistance. In the third year of the rotation, a third different pre-emergence herbicide should be used along with simazine and the accompa - nying post-emergence herbicide used the first year (either ALS inhibitors or pronamide). If an additional product is needed on dormant turf, then rotate to a herbicide with a mode of action different from that used the first two years. Note that oxadiazon and flumioxazin have a similar mode of action (PPO inhibitors) and therefore should not be used together or concurrently in a year. Use strategies for tropical areas Turfgrasses that are not normally fully dormant present an extra challenge in Poa annua control. Obviously, herbicides used only in dormant turf are now off-limits, at least, at normal use rates. In addition, using simazine on green bermudagrass causes some apprehension. However, such is the serious - ness of this problem that some concessions must be discussed. Rotating the pre-emer - gence herbicides, as discussed earlier, is the first component in the herbicide program. We still suggest adding simazine to the pre-emer - gence herbicides. Adding simazine in mid-fall makes sense as problems are rarely seen when either bermudagrass or zoysiagrass is treated in fall. Most simazine issues occur when applica - tions are made in spring when the turf is start- ing to grow aggressively. To the combination of simazine and the pre-emergent, add either pronamide or an ALS inhibitor, and then al - ternate the products on a yearly basis. Some Pre-emergence Post-emergence Dormant or nondormant turf Dormant turf only MOA Mitotic Cellulose biosynthesis PPO PSII ALS* Mitotic EPSPS Glutamine synthase PSI PSII PPO Common names prodiamine, dithiopyr indaziflam oxadiazon simazine sulfonyl- ureas pronamide glyphosate glufosinate diquat amicarbazone flumioxazin Trade name examples Barricade, Dimension + others Specticle Ronstar + others Princep + others * Kerb, Pronamide Roundup Pro + others Finale Reward + others Xonerate SureGuard Year 1 X Year 2 X Year 3 X *ALS (acetolactase synthase)-inhibiting herbicide examples with activity on Poa annua include Katana (flazasulfuron), Revolver (foramsulfuron), TranXit (rimsulfuron), Certainty (sulfosulfuron), and Monument (trifloxysulfuron). Abbreviations: MOA = mode of action; PPO = protoporphyrinogen oxidase (aka, protox); PSI = photosystem I; PSII = photosystem II; EPSPS = enolpyruvylshikimate-phosphate synthase. Table 1. Cross-listing of herbicides based on their modes of action used in non-overseeded bermudagrass and zoysiagrass fairways and roughs for Poa annua control. As discussed in the text, we recommend combining herbicides with at least three modes of action and then rotating them on a three-year basis. Empty boxes indicate the herbicide(s) chosen for each year during a three-year rotation. The X's in column 5 indicate that simazine should be used annually. Modes of action of herbicides for Poa annua control

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