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The potential of local EPN’s to control mealy bug

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By Lucinda Heyns
In this project, locally sourced entomopathogenic nematodes (EPNs) were assessed for their potential as a biological control agent for mealybugs. The intention is to determine if it could be used in an integrated pest management system and to provide an alternative for chemical control. PROJECT LAYOUT: Four local EPN species were screened for their efficacy against female mealy bugs;The most potent species were Heterorhabditis noenieputensis and Steinernema yirgalemense;Since S. yirgalemense was previously shown to be highly effective against a range of pests, the effects of temperature and humidity on the infectivity of S. yirgalemense to female mealybugs were also assessed;The project was carried out under optimal conditions in a lab.
RESULTS: The application of S. yirgalemense at 25°C yielded the highest mortality, of 72%, followed by 45% mortality at 30°C, and only 9% mortality when applied at 15°C;S. yirgalemense performed best at 100% relative humidity (RH), resul…

Effect of using winery wastewater for irrigation on chemical status of sandy soil

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By Lucinda Heyns
This field trial aimed to investigate the effect of re-using winery wastewater for irrigation, on the chemical properties of a sandy soil. A Cabernet Sauvignon vineyard grafted onto R99 on sandy alluvial soil in the Breede River Valley region, South Africa was used. Micro-sprinklers were used to apply irrigation. PROJECT LAYOUT: Vines were irrigated at 50% PAW;Winery wastewater was diluted with river water to different COD (Chemical Oxygen Demand) levels and used to irrigate the vineyard;The control was irrigated using river water;Soil pH, EC (Electrical conductivity), sodium (Na), potassium (K), carbon (C), magnesium (Mg) and Calcium (Ca) were measured before and after the treatments;Details about the cover crops and irrigation strategy can be found in the article.
RESULTS: The less diluted the wastewater, the more K+ and Na+ accumulated in the soil over the season. Increased K+ in the soil, if absorbed by the vine, can negatively impact wine color stability;The wastew…

Settling red juice improves colour and tannin content of final wines

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By Karien O'Kennedy
The aim of this study was to investigate if settling red juice before fermentation on skins can increase the phenolic content of the final wines. The reasoning behind this is because anthocyanins and tannins can form complexes with grape cell wall material, such as polysaccharides and proteins, which can precipitate during vinification. Pulp cell wall material has a high adsorption capacity and by removing such material from the must before extraction of anthocyanins and tannins from the grape skins and pips could theoretically increase final phenolic content in wines. Experimental layout: Monastrell (Mourvedre) grapes were harvested from a commercial vineyard in Jumilla (Spain).SO2 and tartaric acid was added at crushing for the traditional fermentation.For the settling experiment only SO2 was added.The experimental grapes were pressed at 2 bar in a 75 L membrane press and a pectinolytic enzyme as added to the free run juice. It was allowed to settle for 24 hou…

The effect of cap management techniques and extended maceration on Merlot

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By Karien O'Kennedy
The aim of the study was to evaluate the effect of nine different cap management and maceration techniques on Merlot’s chemical and sensory profile. Experimental layout: Merlot grapes were harvested at 27.4°Brix from the UC Davis Oakville Research station vineyard. Grapes were crushed and destemmed and transferred into 27 jacketed stainless steel 150 kg fermenters. Acidity and YAN was adjusted and musts inoculated with 20g/hl EC 1118. The following treatments were performed in triplicate: Pump-overs during fermentation and pressed at dry (no extended maceration)Pump-overs during fermentation and pressed 1 week post dry, 2 weeks post dry, 4 weeks post dry, 6 weeks post dry and 8 weeks post dry.Submerged cap during fermentation and pressed at dry.Submerged cap during fermentation and pressed at 8 weeks post dry.Punch-downs during fermentation and pressed at dry.Both pump-overs and punch downs were performed three times a day.Must and cap temperatures were contin…

Producing fructophilic Starmerella bacillaris as an active dried wine yeast

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By Karien O'Kennedy
Starmerella bacillaris, previously known as Candida Zemplinina, has received wide spread attention by wine yeast researchers as a result of its fructophilic nature and lower ethanol producing abilities. The yeast occurs naturally in spontaneous fermentations, but to date no commercially produced ADWY starter cultures are available. The aim of this study was to determine if Starm. bacillaris can be desiccated (dried) and rehydrated similarly to Saccharomyces cerevisiae and still have the desired effects in fermentations.For the purpose of this summary only some results of interest will be presented. Refer to the article for full experimental layout and all results. Experimental layout Cell suspensions of five strains of Starm. bacillaris were desiccated in the presence of different trehalose concentrations (10, 20, 30, 40, 50%), by exposure to dry air for 20 hours at 28°C.Cell rehydration was performed at 30, 40 and 50°C for 10, 20 and 30 minutes.Viability was de…

Nitrogen source preference of Starmerella bacillaris during fermentation

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By Karien O'Kennedy
The aim of the study was to investigate the uptake of nitrogen sources by Starm. bacillaris and how it compares to Saccharomyces cerevisiae. The effect on the central carbon metabolite production was also investigated. Experimental layout One S. cerevisiae strain, Uvaferm BC, and two Starm. bacillaris strains were evaluated in this study.Fermentations were conducted in synthetic grape must: SM200.The medium contained equal amounts of glucose and fructose but differentiating amounts of amino acids and ammonium, generating three different musts.Fermentations were conducted in 330 ml glass containers.Various analyses were performed on the musts during fermentation as well as after fermentation.
Main results Uvaferm BC fermented to dryness with a clear preference for glucose (depletion after 118 hours versus 142 hours for fructose depletion).The two Starm. bacillaris strains fermented slower and got stuck at approximately 340 hours. Glucose remained untouched but alm…

Microbial life in grapevines: elucidating the leaf microbiome

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By Lucinda Heyns
The goal of this project was to analyse the diversity and presence of members of the bacterial microbiome found on grapevines leaves. Essentially the aim is to identify if any of these organisms have the capability to protect vines against phytopathogenic organisms. Recent studies show that plants house complex bacterial communities which is known as the ‘microbiome’ of a plant. However, very little is known about these bacteria and their roles in nature. PROJECT LAYOUT: Three cultivars, in one location were used in the study: Pinot noir, Chasselas and Solaris (a variety with higher disease resistance than the other two);Leaves were sampled three times throughout the growing season;Epiphytic and endophytic bacterial communities were quantified and their numbers present determined.
RESULTS: Epiphytes were present in higher numbers and their communities were much more diverse compared to endophytes;The upper leaf surface areas were more densely colonised than the lower le…