Grape phylloxera, Daktulosphaira vitifoliae (Fitch) seasonal biology, predictive model, and management in the Ozarks

Grape phylloxera (GP), Daktulosphaira vitifoliae (Fitch), is often a serious pest of wine grapes. In order to develop a management program for GP in vineyards of the Ozarks, studies were conducted on seasonal biology of GP, field validation of a GP degree day model, a study of the effects of applying compost tea to vineyard soil on plant root pathogens, and timing and efficacy of insecticides against GP crawlers. Experiments were conducted in St. James and Purdy, MO and Altus, AR. Aerial sticky traps, cane and trunk tape traps and soil emergence sticky traps were used record weekly or biweekly changes in GP crawler and alate populations. The reported cumulative degree-day (DD) value for development of foliar GP from oviposition to adult was 303 DD (base 6.4, upper limit 36 °C) in the laboratory. It was confirmed in the 2006 field studies where second generation crawlers were already present in 'Norton' leaf galls in Purdy, MO on 11 May with 454 DD accumulated since 21 Mar. In 2008 in St. James, MO, 'Norton' vines had third generation crawlers already forming new galls on terminal expanding leaves on 30 May at 580 DD. In 2007 in Altus, AR and Purdy, MO, no stem mother galls appeared due to a defoliating freeze on 6 to 7 April. However, fourth generation crawlers appeared in sticky tape traps on canes of 'Vignoles' on 13 June (1,034 DD) or 26 June (1,205 DD), respectively. In addition, alates were first detected on sticky tape traps on canes by 7 Aug. (2,013 DD). Given a 303 DD generation period, foliar GP in the Ozarks completed more than nine generations per year. A biologically-based biofix (starting date for DD accumulation) for this species may be the date of first expanding grape leaf rather than the current calendar-based biofix of 21 March, the equinox.;Two insecticide efficacy studies were conducted against foliar crawlers. Insecticide applications were delayed until second or third generation crawlers were detected in leaf galls at an accumulation greater than 303 or 606 DD, respectively. In 2006, one application against second generation crawlers on 11 May (454 DD) of Danitol (fenpropathrin) and applications on 11 and 25 May (637 DD) of Assail (acetamiprid) allowed < 3 galled shoots per vine, which was significantly less than the 6.4 to 8.8 galled shoots per vine for soil drench (11 May) by Admire (imidacloprid) or two applications (11 and 25 May) of BAS 320 (metaflumizone). All treatments prevented damaging levels of leaf galling compared to the check (15.8 galled shoots). In 2008, Movento (spirotetramat) and Danitol (fenpropathrin) applied to foliage against third generation crawlers on 30 May (580 DD) and a soil drench treatment of Admire (imidacloprid) applied on 17 March each had significantly fewer galled leaves per shoot than did acetamiprid, Esteem (pyriproxyfen), and HGW86 applied to foliage on 30 May. All treatments had significantly fewer galls and galled leaves than did metaflumizone, but all these treatments had at least 1.8-fold fewer galls than the check, including metaflumizone.;Keywords: grape, cultivar, degree-day, compost tea, soil biomass, insecticide;The second experiment, which looked at the effects of compost tea on grape vine soils, found significantly more fungal colony forming units in unpasteurized than pasteurized soil from potted grape vines and a doubling of fungal units in all treatments after three months. The most common potential root pathogens found were Pythium spp., Fusarium spp., and Rhizoctonia spp. with significantly more Rhizoctonia root infection in 'Norton' than 'Vignoles'. The soil microbial biomass assay showed significantly more total biomass C in 'Norton' than 'Vignoles' vines and significantly more of both biomass C and biomass N in unpasteurized than pasteurized soil with no differences in soil microbial C/N ratios among any of the following treatments; compost tea added, filtered compost tea added, or no compost tea added.