Golf Course Management

JUL 2017

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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68 GOLF COURSE MANAGEMENT 07.17 most effective if the active ingredient remains in the thatch and upper soil and then either stays there a long time, or there are repeated applications over time. Nematode numbers decline over time as multiple generations of nematode juveniles exit the roots and get ex - posed to the nematicide. Pacific s ot-gall nematodes Pacific shoot-gall nematodes (Anguina pacificae) are primarily endoparasites; only the second-stage juveniles occur outside plant tis - sues. They have a very limited host and distri- bution range. For all practical purposes, they occur only on annual bluegrass (Poa annua) in coastal Northern California. In contrast to the previously mentioned species, these nema - todes feed on aboveground plant tissues (9). Infective juveniles need a thin water film to move from the soil up the surface of a young shoot to its tip. There, they penetrate the plant tissues and induce a cavity-containing gall that develops at the base of the grass shoot. Inside the cavity, the nematodes molt twice and develop into adults. Sexual reproduction is required for fertile offspring. The next gen - eration hatches from the eggs, but it requires decomposition of the galls and perhaps their destruction by mowing for the juveniles to be released. Again, a water film is necessary for the juveniles to move to the next shoot tip or into the soil. Nemacur used to be the only ne - maticide registered in California that provided superintendents with useful activity against Pacific shoot-gall disease. Its efficacy seemed to decrease, however, during the years just be - fore it was withdrawn from the market. New nematicides Divanem Abamectin is the active ingredient in Syn - genta's new turf nematicide Divanem. Abam- ectin is not new chemistry; in fact, it has been a common active ingredient in insecticides and miticides for decades. The nematicidal properties of abamectin have also been long recognized. It is closely related to ivermectin, used to rid nematode parasites from animals and people. Abamectin is broadly effective on all kinds of nematodes and will kill any kind of nematode it contacts at very low con - centrations. Despite this, abamectin has only recently been adopted for nematode man - agement, mostly because of its major limita- tion: It does not move well in soil. Its water solubility is very low, while the soil adsorption value for abamectin is extremely high. It binds rapidly to organic matter and clay minerals. When sprayed onto the turf surface and irri - gated, very little abamectin makes it through thatch. Abamectin has excellent contact activ - ity on nematodes, but it is not systemic. The half-life in soil is about two weeks to a month. Abamectin is rapidly broken down in sun - light, so it should be watered-in immediately after application. Divanem has the same ac - tive ingredient as Avid, a Syngenta insecticide that was labeled for use against nematodes on greens in several states a few years ago. How - ever, the Divanem formulation is specifically designed for application to soil, which makes it an improvement over Avid for management of turfgrass nematodes. Root-knot nematodes tend to proliferate in the thatch and upper 1.5 inches of soil. This is exactly where most of the active ingredient in Divanem stays. In Florida, this makes Diva - nem an excellent product for management of root-knot nematodes on greens. As the juvenile nematodes exit the root, they are exposed to abamectin and die. About the time the abam - ectin starts to break down, another application needs to be made. Successive generations of nematodes are therefore impacted over time. Sting, lance and other nematodes occur - ring in the upper soil profile also are affected by abamectin, but timing can be important. Just before breaking dormancy in the spring, bermudagrass will slough off many of the pre - vious year's roots. At that time, a much higher percentage of lance nematodes are in the soil and exposed to contact nematicides. Therefore, initiating the Divanem application sequence before spring green-up will increase the chance of success in controlling lance nematodes. Be - cause sting nematodes move higher up in the soil profile during the cooler months, applica - tions made during that time will be more ef- fective than applications made in the heat of summer. Interestingly, University of Florida research has found that ring nematodes (Me - socriconema ornatum) move up in the soil pro- file during summer, so summer applications will work better for those nematodes. In Florida, the best results with Diva - nem have been from four applications of the maximum labeled rate (12.2 fluid ounces/ acre [0.89 liter/hectare]) at four-week inter - vals. It is important to go through the entire sequence, because one or two applications are usually not sufficient to give the desired Bermudagrass field plots at the University of Florida severely infested with root-knot nematode. Arrows indicate the two plots that were treated with Divanem.

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