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W i n e s & V i n e s s e P T e M B e R 2 0 1 4 53 and Canada fleabane are present in the Okanagan. While glyphosate resistance hasn't yet been observed in local populations of the weeds, Sapsford said that's no reason for complacence; in fact, the weeds are ideal candidates for developing glyphosate resistance. Where there's a problem Typically found on open, bare ground, these resistant species adapt well to hardy conditions with low competitive pressure. Roundup weakens them, but there are no competitors in these envi- ronments that can leverage that weak- ness to overtake the weeds. And so the weeds thrive. "Where glyphosate is applied as a pre- seed burndown and a crop is planted, the crop provides competition to any weeds that may survive the treatment and helps to control the weed," Sapsford explained. But "when glyphosate is applied to an area to control all weeds and keep the ground bare, there is nothing to compete with any weed that may survive the treatment." This makes kochia and Canada flea- bane especially problematic in vineyards, where they're often found on bare soil within the rows. The canopy doesn't shade them, giving them the light needed for photosynthesis in an environment with little competitive pressure. This is where Roundup comes into play, keeping the vineyard floor clean and reducing competition for resources such as water. Glyphosate doesn't impact the vine as long as the spray doesn't touch the leaves, Sapsford said, leading grapegrowers to apply it at rates of as much as 5 to 7 liters (1,800 to 2,500 grams acid equivalent) per acre. By comparison, grain growers apply glyphosate at rates closer to 1 liter (360 grams acid equivalent of glyphosate) per acre. Bigger isn't always better But just because a regular dose of glypho- sate does a good job doesn't mean a stronger dose will do a better job, Saps- ford said. Rather, it ultimately inures the weed to the herbicide. "The higher the rate of application, and the more frequent it is, the sooner resis- tant weed strains are likely to emerge," he said. "I've seen it on the prairies, and it's only a matter of time before grapegrowers are facing resistant strains of these weeds." Kochia responds by producing more of the protein that Roundup attacks, frus- trating the action of the herbicide, while Canada fleabane increases efforts to iso- late the glyphosate, preventing it from moving to where it can take effect. "Plants have developed different resis- tance mechanisms such as reduced trans- location, isolation of (the) herbicide and gene amplification to develop resistance to glyphosate," Sapsford explained. A smarter approach to weed control is combining herbicides to broaden the chal- lenges weeds face. Rather than battling one kind of poison, a species will face two herbicides with different modes of action. The double-headed challenge makes it harder for the weed to adapt to either one successfully. "Glyphosate has made it very easy to control the weeds under the vine. But easy is not always the answer, good manage- ment is required to avoid resistance," Sapsford said. Anecdotal evidence Sapsford's vineyard manager, Pierre Levesque of Earlco Vineyards Ltd. in Pent- icton, B.C., says his work for Sapsford has heightened his attention to signs of emerg- ing glyphosate resistance among weeds in the approximately 130 acres of vineyard he oversees in the southern Okanagan, primarily along the Naramata Bench. "I have a feeling that people are using too high a dosage of glyphosate," he said, acknowledging that even he has been using too much—2.5% versus a recom- mended rate of 1.5%. "But I know my neighbors are talking about 5% and 7%. That's deadly." Levesque is now combining herbicides from different groups. Glyphosate, a Group 9 herbicide, inhib- its amino acid synthesis, but Levesque combines it with Chateau, a moisture- activated herbicide belonging to Group 14, which inhibits a chlorophyll enzyme. It kills the seeds of weeds, preventing them from returning after mowing. "It's a different mechanism and a differ- ent active ingredient," he said. "That's defi- nitely made a difference. It's minimized the amount of weeds on your second round." Earlco has also invested in a Fischer GmbH mower that mows within the rows, between the vines, and is able to apply a focussed spray to the area around the trunks to ensure thorough, and tar- geted, suppression of weeds. vines, and they were swept clear of leaves before application. The treatments were mixed with 30 gallons of water per acre at various rates and combinations of herbicides. They were applied using a CO 2 backpack sprayer with two 8002 nozzles, each de- livering 700 ml per minute. Ron- coroni said that 30 to 50 gallons of water per acre seemed about optimum for adequate coverage. No weeds were visible at the time of treatment. All of the herbicides are reg- istered. Roncoroni works exclu- sively with registered materials in Napa, saying: "The grapes are too expensive to destroy! Those trials are made with lower priced grapes in the Central Valley." Glyphosate is widely used in vineyards, but some weeds have developed resistance to it, and others (some new to the region) are tolerant of it. He applies the treatments in January or February, as they re- quire rains to be activated, but they're only effective for four to six months. Vineyards may require mid-season spraying. Rely is a preferred contact herbicide for mid-season and post-harvest spraying after pre- emergent herbicides have become ineffective and can't be applied again, but it is in short supply be- cause of demand in the southeast for use with cotton and soybeans fighting glyphosate-resistant weeds. Rely won't kill the vines if it gets on suckers, just the suck- ers, while glyphosate can get into the vine and cause problems in the spring. "In the old days, they used paraquat," said Roncoroni. Para- quat is still registered for use in grapes but requires special permit- ting and safety equipment for use. Some of the new herbicides have some post-emergent proper- ties, but one of the longest last- ing, Alion (indaziflam), has none. In any case, Roncoroni empha- sizes that mixes of two or more herbicides are generally more ef- fective than a single product. The results Many of the herbicides did a pretty good job by themselves, notably Matrix (rimsulfuron), Chateau (flumioxazin), Goaltender (oxyfluo- rfen), and especially Alion at 5 ounces of product per acre. (Continued on page 54.) G R A P E G R O W I N G