Long-Term Benefits of Protecting Table Grape Vineyards
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agronomy Article Long-Term Benefits of Protecting Table Grape Vineyards against Trunk Diseases in the California Desert Carmen Gispert 1, Jonathan D. Kaplan 2, Elizabeth Deyett 3 and Philippe E. Rolshausen 3,* 1 Division of Agriculture and Natural Resources, University of California Cooperative Extension, Indio, CA 92201, USA; [email protected] 2 Department of Economics, Sacramento State University, Sacramento, CA 95819, USA; [email protected] 3 Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA; [email protected] * Correspondence: [email protected] Received: 3 October 2020; Accepted: 27 November 2020; Published: 30 November 2020 Abstract: Grapevine trunk diseases (GTD) are caused by several fungal species and are major limiting factors to vineyard productivity and profitability in all viticulture areas. This study is aimed at addressing the gap in the knowledge with regards to measuring the long-term benefits of post-pruning fungicide application on trunk diseases incidence and crop yield in grape production systems. It also calculated the net economic benefit of implementing such practice over the vineyard lifespan. We selected a newly planted commercial table grape vineyard in the California desert and divided it in two blocks. In one block, the registered fungicide thiophanate-methyl was mechanically applied on pruning wounds for six consecutive years, while the other half remained untreated. Our results showed a significant lower GTD incidence and vine replants in treated blocks combined with a significant increase of total and marketable fruit. Potential annual economic benefits of applying fungicide on pruning wounds appear to be in the range of $8500–$12,500 per hectare annually in a 50–75% disease control scenario. Keywords: Vitis vinifera; table grapes; grapevine trunk diseases; cultural practices; pruning wound protection; economics 1. Introduction According to the International Organization of Vine and Wine, 77.8 million tons of grapes were produced in 2018, with 57% wine grapes, 36% table grapes, and 7% dried grapes [1]. The US is the 8th largest producer of table grapes worldwide with about 1 million tons and 49,000 bearing hectares [2]. California produces over 95% of the nation’s table grapes [3]. A substantial fraction of table grapes is being produced in the California desert, where local growers have adapted the viticulture practices to the hot and dry summers and mild winters in order to reach optimal fruit yield and quality for early market access and high dollar crop value. To that end, they have implemented a hydro-cooling system using overhead sprinkler irrigation during the winter months to add chilling units and increase bud fruitfulness. In addition, a plant growth regulator (i.e., Dormex®; Hydrogen cyanamide) is applied after pruning to break bud dormancy and stimulate more uniform and earlier bud break. Another practice that is common for the new planted vineyards in the desert is to leave the old stumps from the previous vineyard and re-train the new vines on the already established trellis system (Figure1). However, previous studies have raised concern that these practices would favor incidence of severity of grapevine trunk diseases (GTD) caused by fungal vascular pathogens [4]. Agronomy 2020, 10, 1895; doi:10.3390/agronomy10121895 www.mdpi.com/journal/agronomy Agronomy 2020, 10, 1895 2 of 12 Agronomy 2020, 10, x FOR PEER REVIEW 2 of 11 FigureFigure 1. 1. VineyardVineyard with with new new vines vines inter-planted be betweentween old vine stumps (white arrow). GTD areare major major factors factors limiting limiting the the profitable profitable lifetime lifetime expectancy expectancy of vineyards of vineyards [5,6]. Standard [5,6]. Standard business businessmodels for models vineyards for vineyards are based are on 25based years on or 25 more years of or optimal more of productivity. optimal productivity. First GTD symptomsFirst GTD symptomscommonly commonly manifest in manifest 8–10 years in old8–10 vineyards years old by vineyards a loss of spurby a positions loss of spur [7]. Aspositions vineyards [7]. age,As vineyardsthe diseases age, progress the diseases causing progress cordon/trunk causing dieback cord andon/trunk eventually dieback vine and death. eventually The drop vine in productivity death. The dropis also in accompanied productivity with is also a decrease accompanied in fruit with quality a de andcrease marketability in fruit quality [8]. This and disease marketability condition [8]. implies This diseasethat for growers,condition the implies break-even that pointfor growers, is reached the at abreak-even later time than point projected is reached in their at businessa later time model, than or projectedin worst case in their scenario, business not at model, all, and or that in overallworst case profits scenario, are diminished not at all, [6]. and that overall profits are diminishedGTD are [6]. caused by a set of taxonomically unrelated fungi that are soilborne (e.g., black foot causedGTD by areCampylocarpon caused by a, Dactylonectriaset of taxonomically, and Ilionectria unrelatedspecies, fungi that and Armillariaare soilborne root (e.g., rot black caused foot by causedArmillaria by mellea Campylocarpon), airborne, (e.g., Dactylonectria Eutypa dieback, and causedIlionectria by Eutypaspecies,species, and Armillaria Botryosphaeria root rot canker caused caused by Armillariaby several taxamellea in), the airborneBotryosphaeriaceae (e.g., Eutypafamily), dieback or both caused (e.g., by esca Eutypa caused species, by Phaeomoniella Botryosphaeria chlamydpospora canker, causedPhaeoacremonium by severaland taxaCadophora in the Botryosphaeriaceaespecies) [4,9–17 ].family), Fungi useor both wounds (e.g., (natural, esca caused mechanical, by Phaeomoniella pruning) chlamydposporaas a point of entry, Phaeoacremonium to the plant vascular and Cadophora system, colonize species) the [4,9–17]. host and Fungi decay use the wounds wood, causing (natural, an mechanical,irreversible losspruning) of function as a point of theof entry xylem to andthe plant phloem vascular elements system, that colonize results in the the host dieback and decay and wilt the wood,symptoms causing [18]. an To irreversible ensure that loss vines of function remain pathogen-free, of the xylem and one phloem must adopt elements preventative that results practices in the diebackin order toand limit wilt the symptoms risks of infection, [18]. To such ensure as pruning that vines during remain dry weatherpathogen-free, when airborne one must inoculum adopt preventativeis low [4,19]. practices In addition, in order adoption to limit of pruning the risks wounds of infection, protection such with as pruning biological during and conventionaldry weather whenagrochemicals airborne earlyinoculum on at is the low establishment [4,19]. In additi of aon, vineyard adoption remains of pruning the safest wounds practice protection to ensure with low biologicalinfection risks and andconventional extended agrochemicals vineyard longevity early [ 6on,20 at]. However,the establishment experimental of a vineyard studies implemented remains the safestto evaluate practice efficacy to ensure of pruning low woundinfection protectants risks an ared extended limited in vineyard scope mainly longevity because [6,20]. of the However, relatively experimentalshort time frame studies of these implemented studies in comparisonto evaluate efficacy to the incubation of pruning period wound required protectants by those are pathogenslimited in scopeto cause mainly symptoms. because The of challenges the relatively of conducting short time trials frame in commercialof these studies vineyards in comparison over several to years the incubationthat clearly period links adoption required of by preventative those pathogens practices to cause to increased symptoms. productivity The challenges and positive of conducting economic trialsreturn in hinders commercial the positivevineyards perception over several of theseyears practicesthat clearly and links the adoption broad adoption of preventative among practices industry tostakeholders increased [productivity21]. The goal and of this positive research economic was to address return this hinders gap and the assess positive the long-termperception e ffiofcacy these of practices and the broad adoption among industry stakeholders [21]. The goal of this research was to address this gap and assess the long-term efficacy of adopting preventative management practices at the establishment of vineyards on GTD incidence, measure its impact on grape yield, and calculate the net economic benefits. Agronomy 2020, 10, 1895 3 of 12 adopting preventative management practices at the establishment of vineyards on GTD incidence, Agronomymeasure 2020 its, impact 10, x FOR on PEER grape REVIEW yield, and calculate the net economic benefits. 3 of 11 2. Materials Materials and and Methods 2.1. Experimental Experimental Design Design The fieldfield experiments experiments were were conducted conducted in a 3.8in haa 3.8 own-rooted ha own-rooted table grape table vineyard grape cv.vineyard “Sugraone” cv. “Sugraone”located in the located desert in of the Coachella desert of Valley, Coachella California. Valley, TheCalifornia. vineyard The was vineyard planted was at aplanted vine density at a vine of density3.7 m between of 3.7 m rows between and 1.5 rows m betweenand 1.5 m vines between (1800 vines vines (1800 per hectare). vines per Vines hectare). were Vines planted were in 2012 planted and werein 2012