Commercial Strawberry Fields Research Articles

Meta-Analysis of a Web-Based Disease Forecast System for Control of Anthracnose and Botrytis Fruit Rots of Strawberry in Southeastern United States.

Strawberry production in Florida and South Carolina is affected by two major diseases, anthracnose fruit rot (AFR) and Botrytis fruit rot (BFR), caused by Colletotrichum acutatum and Botrytis cinerea, respectively. The effective management of both diseases traditionally relied on weekly fungicide applications. However, to improve timing and reduce the number of fungicide sprays, many growers follow the Strawberry Advisory System (StAS), a decision support system for forecasting fungicide applications based on environmental conditions and previously developed models. The objective of this study was to perform a meta-analysis to determine the effectiveness of the StAS for AFR and BFR management compared with a calendar-based spray program. Thirty-nine trials were conducted from 2009 to 2014 in Florida and South Carolina commercial strawberry fields. Meta-analysis was conducted to quantify the treatment effects on four effect sizes, all based on the difference in response variables for StAS and the calendar-based treatments in each trial. The mean difference in BFR incidence, AFR incidence, yield, and number of marketable fruit between the two treatments was not significantly different from 0 (P < 0.05). However, the number of fungicide applications per season was reduced by a median of seven when using the StAS, a 50% reduction in sprays compared with the calendar-based approach. Effect sizes were not influenced by location or the favorability of the environment for disease development. These findings indicate that use of StAS in commercial fields is effective in controlling fruit rot diseases with no reduction in yield while substantially reducing fungicide applications.

Sources of Primary Inoculum of Botrytis cinerea and Their Impact on Fungicide Resistance Development in Commercial Strawberry Fields

Strawberry transplants produced in nurseries across Canada, northern United States, and California are shipped annually to other strawberry-growing regions, including Florida. Botrytis cinerea, the causal agent of gray mold, causes latent infections on transplants which are suggested as a potential source of primary inoculum in strawberry fields. In this study, we investigated the survival of B. cinerea isolates over the summer in Florida, the presence of B. cinerea in transplants from 14 nurseries from Canada and the United States in 2011, 2012, and 2013, and the sensitivity of nursery population to several botryticides. Botrytis cinerea was detected on dead strawberry plants sampled from commercial strawberry fields between March and June but not in July and August, suggesting that the fungus does not over-summer in strawberry fields in Florida. Nursery transplants surveyed in 2011, 2012, and 2013 showed B. cinerea incidences of 20 to 37, 20 to 83, and 2.5 to 92.5%, respectively. In total, 409 isolates were tested for sensitivity to pyraclostrobin, boscalid, pyrimethanil, fenhexamid, iprodione, penthiopyrad, fluopyram, and fludioxonil. Overall, respective resistance frequencies were 91.7, 79.3, 33.2, 20.7, 2.4, 0.2, 0.2, and 0.0%. A majority of isolates tested were resistant to either 3 or 4 fungicides simultaneously. These findings reinforce the need for an integrated approach between strawberry nurseries and production fields to improve gray mold management and mitigate future risks of resistance development in B. cinerea.

Identification and Characterization of Botrytis fragariae Isolates on Strawberry in the United States.

Gray mold is a devastating disease on strawberry, and may be caused by several species of Botrytis. The goal of this study was to better understand and characterize the species of Botrytis with reduced sensitivity to the fungicide Polyoxin D, particularly Botrytis fragariae. In total, 78 Botrytis isolates of unknown species that were sensitive (28 isolates; S), moderately sensitive (22 isolates; MS), or reduced sensitive (28 isolates; RS) to Polyoxin-D were collected from commercial strawberry fields of five states in the United States, identified to the species level, and characterized. The majority (75%) of S isolates were Botrytis cinerea and the majority (79%) of RS isolates were the recently described species B. fragariae, indicating an innate ability of B. fragariae to tolerate Polyoxin-D. B. fragariae produced fluffy, white mycelium and was less likely to sporulate on potato dextrose agar than B. cinerea. Isolates from a commercial field recovered from blossoms in early spring were all B. fragariae, those from leaves of the same plants in late spring were a mixture of B. fragariae and B. cinerea, and those from fruit in early summer were all B. cinerea, indicating that B. fragariae may preferentially colonize blossom tissue. A polymerase chain reaction-based assay was developed based on NEP2 sequence variability to distinguish B. fragariae from other Botrytis spp. that have been reported on strawberry, including B. cinerea, B. mali, B. caroliniana, and B. ricini. None of the isolates collected from Canada, California, or North Carolina nurseries were B. fragariae, indicating that the newly described species may not exist or not be widely distributed in planting stock.

Resistance to the SDHI Fungicides Boscalid, Fluopyram, Fluxapyroxad, and Penthiopyrad in Botrytis cinerea from Commercial Strawberry Fields in Spain.

Gray mold, caused by the necrotrophic fungus Botrytis cinerea., is one of the most economically important diseases of strawberry. Gray mold control involves the application of fungicides throughout the strawberry growing season; however, B. cinerea isolates resistant to multiple classes of site-specific fungicides have been recently reported in the Spanish gray mold population. Succinate dehydrogenase inhibitors (SDHI) constitute a relatively novel class of fungicides registered for gray mold control representing new alternatives for strawberry growers. In the present study, 37 B. cinerea isolates previously characterized for their sensitivity to boscalid and amino acid changes in the SdhB protein were used to determine the effective concentration that reduces mycelial growth by 50% (EC50) to fluopyram, fluxapyroxad, and penthiopyrad. The present study was also conducted to obtain discriminatory doses to monitor SDHI fungicide resistance in 580 B. cinerea isolates collected from 27 commercial fields in Spain during 2014, 2015, and 2016. The EC50 values ranged from 0.01 to >100 μg/ml for fluopyram, <0.01 to 4.19 μg/ml for fluxapyroxad, and, finally, <0.01 to 59.65 μg/ml for penthiopyrad. Based on these results, as well as findings from a previous publication, the discriminatory doses chosen to examine sensitivities to boscalid, fluopyram, fluxapyroxad, and penthiopyrad were 100, 15, 1, and 6 μg/ml, respectively. Over the course of the 3-year monitoring period, the overall frequencies of resistance to the four SDHI were 56.9, 6.9, 12.9, and 24.6%, respectively. The frequency of boscalid-resistant isolates decreased from 73 to 41% over the years; however, the fluopyram-resistant isolates increased from 5 to 10% after 1 year of registration. Four SDHI resistance patterns were observed in our population, which included patterns I (30%; resistance to boscalid), II (13.8%; resistance to boscalid and penthiopyrad), III (5.7%; boscalid, fluxapyroxad, and penthiopyrad), and IV (7.9%; resistance to boscalid, fluopyram, fluxapyroxad, and penthiopyrad). Patterns I and II were associated with the amino acid substitutions H272R and H272Y; pattern III was associated only with the H272Y mutation; and, finally, pattern IV was associated with the N230I allele in the SdhB subunit. For gray mold management, it is suggested that the simultaneous use of boscalid and penthiopyrad should be limited to one application per season; however, fluxapyroxad and, especially, fluopyram could be used as valid SDHI alternatives for gray mold control, although they should be applied with caution.

Botrytis fragariae, a New Species Causing Gray Mold on Strawberries, Shows High Frequencies of Specific and Efflux-Based Fungicide Resistance.

Botrytis cinerea causes pre- and postharvest decay of many fruit and vegetable crops. A survey of German strawberry fields revealed Botrytis strains that differed from B. cinerea in diagnostic PCR markers and growth appearance. Phylogenetic analyses showed that these strains belong to an undescribed species in Botrytis clade 2, named Botrytisfragariae sp. nov. Isolates of Bfragariae were detected in strawberry fields throughout Germany, sometimes at frequencies similar to those of B. cinerea, and in the southeastern United States. Bfragariae was isolated from overwintering strawberry tissue but not from freshly infected fruit. Bfragariae invaded strawberry tissues with an efficiency similar to or lower than that of B. cinerea but showed poor colonization of inoculated nonhost plant tissues. These data and the exclusive occurrence of this fungus on strawberry plants indicate that Bfragariae is host specific and has a tissue preference different from that of B. cinerea Various fungicide resistance patterns were observed in Bfragariae populations. Many Bfragariae strains showed resistance to one or several chemical classes of fungicides and an efflux-based multidrug resistance (MDR1) phenotype previously described in B. cinerea Resistance-related mutations in Bfragariae were identical or similar to those of B. cinerea for carbendazim (E198A mutation in tubA), azoxystrobin (G143A in cytB), iprodione (G367A+V368F in bos1), and MDR1 (gain-of-function mutations in the transcription factor mrr1 gene and overexpression of the drug efflux transporter gene atrB). The widespread occurrence of Bfragariae indicates that this species is adapted to fungicide-treated strawberry fields and may be of local importance as a gray mold pathogen alongside B. cinereaIMPORTANCE Gray mold is the most important fruit rot on strawberries worldwide and requires fungicide treatments for control. For a long time, it was believed to be caused only by Botrytis cinerea, a ubiquitous pathogen with a broad host range that quickly develops fungicide resistance. We report the discovery and description of a new species, named Botrytisfragariae, that is widely distributed in commercial strawberry fields in Germany and the southeastern United States. It was observed on overwintering tissue but not on freshly infected fruit and seems host specific on the basis of its occurrence and artificial infection tests. Bfragariae has also developed resistance to several fungicides that is caused by mutations similar to those known in B. cinerea, including an efflux-based multidrug resistance. Our data indicate that Bfragariae could be of practical importance as a strawberry pathogen in some regions where its abundance is similar to that of B. cinerea.

Recovery of fungicide-resistant Botrytis isolates from strawberry nursery plants

In a four-year survey of strawberry nursery plants, 340 Botrytis isolates were collected and examined for fungicide resistance. High percentages of isolates with resistance to members of all fungicide classes registered on strawberries in Germany were found, i.e. trifloxystrobin (90.3%), boscalid (53.8%), cyprodinil (41.5%), fludioxonil (28.2%) and fenhexamid (15.6%). Of these isolates, 10.3% possessed multiple resistance to all compounds. At 5.0%, resistance to the recently registered fungicide fluopyram was low. Dutch nursery material harboured significantly higher proportions of isolates with resistance to any or all fungicides than plants produced in Germany. These data point to nursery plants as a possible route of introducing fungicide-resistant Botrytis strains into commercial strawberry fields.

Field assessment on the influence of RhizoVital® 42 fl. and Trichostar® on strawberries in the presence of soil-borne diseases

Strawberries are one of the most popular fruits in Germany. However, an expansion of the cultivation area, especially for organic strawberry production, is limited due to the high yield losses caused by diseases and arthropod pests. Therefore, the two soil strengthener RhizoVital® 42 fl. and Trichostar® were evaluated for their efficacy in stabilizing strawberry yields in the presence of soil-borne diseases.First, an integration of antagonists in an IPM strategy was proven by testing their compatibility with synthetic pesticides. When mixed for a maximum of four hours only few fungicides reduced germination of the antagonistic fungus contained in Trichostar®. The germination of the bacterial antagonist (RhizoVital® 42 fl.) was not influenced by any tested synthetic pesticide used in this study. Afterwards, the microbial based products were tested in two commercial strawberry fields in the Rheine-Main area, in which Verticillium-wilt was found. In one field, with just one treatment of Trichostar® in 2013, the yield increase in 2013 and 2014 was 8 and 9%, respectively. On the second field, RhizoVital® 42 fl. was applied both years and the increase was about 6% each year.Our results demonstrate that beneficial micro-organisms can promote health and can stabilize or increase yield of strawberries under field conditions. Integration of these organisms in IPM strategies seems to be possible.

Resistance to Increasing Chemical Classes of Fungicides by Virtue of "Selection by Association" in Botrytis cinerea.

Previous research has shown that Botrytis cinerea isolates with resistance to multiple chemical classes of fungicides exist in eastern strawberry fields. In this study, the fungicide resistance profiles of 2,130 isolates from flowers of commercial strawberry fields located in multiple states was determined over four consecutive strawberry production seasons. Producers were asked to alternate single-site fungicides that were considered low risk in their specific location based on resistance monitoring results in their fields. This recommendation led to an increase of chemical class diversity used in the spray programs. Results indicated that simultaneous resistance in individual isolates to two, three, four, five, six, and seven classes of fungicides increased over time. The increase in chemical class resistances within isolates was likely due to a process we termed "selection by association", where fungicide resistance traits were often linked to the trait being selected rather than the selectable trait itself. Data analysis also indicated that the odds were highest for isolates resistant to one chemical class (1CCR) to be resistant to thiophanate-methyl; for 2CCR isolates to be resistant to thiophanate-methyl and pyraclostrobin; and for 3CCR isolates to be resistant to thiophanate-methyl, pyraclostrobin, and either cyprodinil or fenhexamid. We hypothesize that the more chemical classes are used in a spray program, the faster isolates will be selected with increasing numbers of chemical class resistances by virtue of selection by association if such isolates preexist in the population.

Efficacy of Insecticides against Lygus hesperus Knight (Hemiptera: Miridae) in the California’s Central Coast Strawberry

ABSTRACTThe western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae), is an important insect pest of strawberry (Fragaria ananassa Duchesne) in the Central Coast of California. Because little is known about efficacy of new insecticides, especially sulfoxaflor and flupyradifurone, against L. hesperus, two replicated insecticide experiments were conducted in 2014 and 2015 in commercial strawberry fields naturally infested with L. hesperus. The insecticides, sulfoxaflor, flupyradifurone, flonicamid, thiamethoxam fenpropathrin, essential oils (rosemary and peppermint oils), and mineral oil, were compared with untreated check. Higher and lower rates of flupyradifurone and sulfoxaflor were tested. Higher rates of sulfoxaflor and flupyradifurone were effective in suppressing L. hesperus. The industry standard, thiamethoxam + fenpropathrin, was effective in 2014 but not in the 2015 experiment. Flonicamid provided a moderate level of efficacy against L. hesperus in both years. The number of predacious bugs was significantly lower in the higher rate of flupyradifurone than in other treatments, although the number of spiders was not significantly different among treatments.

Clopyralid Dose Response for Two Black Medic (Medicago lupulina) Growth Stages

Black medic is a troublesome weed in commercial strawberry fields in Florida. It emerges during crop establishment from the planting holes punched in plastic mulches that are installed on raised beds. Clopyralid is registered for posttransplant applications at 140 to 280 g ae ha−1but growers typically report suppression, not control. An outdoor potted experiment was designed to model the black medic dose-response curve and determine the effect of plant size at application on control. Two plant sizes were selected: designated small (0.5- to 1-cm stem length) and large (3- to 6-cm stem length). Dose-response curves were generated using a log-logistic four-parameter model. At 22 d after treatment (DAT), there was a significant interaction between clopyralid rate and black medic growth stage on both epinasty (P = 0.0022) and chlorosis (P = 0.0055). The effective dosage to induce 90% (ED90) epinasty were 249.5 and 398.3 g ha−1for the small and large growth stages, respectively. The ED90 for chlorosis was 748.2 for the small growth stage, whereas the estimated value for the large was outside the measured range. For necrosis there was no significant effect of growth stage, and the ED90 was 1,856.3 g ha−1. The aboveground dry biomass ED90 for the small growth stage was 197.3 g ha−1, and the estimated ED90 value for the large was not within the measured range. Results indicate that clopyralid adequately controls black medic when applied at maximum label rates when stems were 0.5 to 1 cm long but not when plants were larger. Poor efficacy typically observed in commercial fields is likely due to black medic plant size or lack of herbicide coverage via shielding by strawberry plants.

Managing Strawberry Pests with Chemical Pesticides and Non-Chemical Alternatives

ABSTRACTWestern tarnished bug or lygus bug (Lygus hesperus) is a major pest of California strawberries causing significant yield reduction. Other common insect pests include aphids (Chaetosiphon fragaefolii and Myzus persicae), greenhouse whitefly (Trialeurodes vaporariorum), and western flower thrips (Frankliniella occidentalis). Growers mainly depend on chemical pesticides for managing these pests. Limited control with some of the available chemical pesticides and the risk of resistance development due to their repeated use warrant a strong integrated pest management program where multiple tools can be utilized. Field studies conducted in commercial strawberry fields from 2012–14 in Santa Maria with an emphasis on managing L. hesperus demonstrated the potential of botanical and microbial pesticides. Replacing one or more applications of chemical pesticides with botanical and microbial alternatives and using them in different combinations can make a significant contribution to a sustainable management strategy.

Improving Strawberry Irrigation with Micro-Sprinklers and Their Impact on Pest Management

Overhead aluminum sprinklers, which are used during the early stages of strawberry crop development to establish transplants and to leach out salts from the root zone, deliver significant volumes of water. Micro-sprinklers, which are typically used in orchard crops, were evaluated in a commercial strawberry field in California as an alternative to conventional aluminum sprinklers to conserve water without any negative impact on yields. In addition to the water consumption, data were collected from multiple plots within each treatment to determine the impact on plant growth, disease incidence, and seasonal yield. Micro-sprinklers used 32% less water than aluminum sprinklers during a three-week period without affecting fruit yield. They also appeared to lessen the severity of powdery mildew and botrytis fruit rot. This is the first study reporting the use of micro-sprinkler system, which can be a good alternative to the aluminum sprinklers to conserve irrigation water.

Evaluation of damage, food attractants and population dynamics of strawberry sap beetle in strawberry

The strawberry sap beetle Lobiopa insularis (Castelnau) (Coleoptera: Nitidulidae) is one of the most devastating pests to commercial strawberry crops. In this study, the susceptibility of the strawberry fruit at different maturation stages to damage caused by the adult L. insularis and the baiting effect on the monitoring of its population fluctuation were evaluated in commercial strawberry crop fields using pitfall traps. ‘Camarosa’ strawberries at different maturation stages (G - Green, SM - Semi-ripe and R -Ripe) were exposed to adult L. insularis . Adult beetles preferred ripen fruits to green fruits. The attractants evaluated as bait were: (T1) ripe strawberries; (T2) cattle feed, granulated sugar and water; (T3) T1 and T2 attractants mixed at 1:1 ratio; (T4) fruit mix, granulated sugar, water and beer, sprayed with isoamyl-acetate; and (T5) control (no food attractants). Malathion 1000 ® CE insecticide was mixed to both attractive evaluated. Population dynamics of adult beetles were monitored during the production season of strawberry culture in the municipalities of Caxias do Sul and Bom Principio, Rio Grande do Sul State, Brazil. Ripe strawberries (T1) was effective for seven days in the field. The sap beetle adults were first captured in June in the municipality of Caxias do Sul and in August in Bom Principio and population peaks were observed during January in both sites.

First report of a ‘Candidatus Phytoplasma asteris’ isolate affecting a strawberry nursery in Cuba

Strawberry (Fragaria x ananassa) is traditionally multiplied in Cuba by vegetative propagation without phytosanitary certification. During November 2011, surveys for phytoplasma to strawberry nurseries revealed plants showing symptoms of leaf yellowing and reddening, fruit deformation and stunting in an orchard of ‘Ceiba del Agua’, Artemisa province (Fig. 1). Similar symptoms were previously described in strawberry associated with phytoplasma infections (Jomantiene et al., 3; Valiunas et al., 6). Leaves and midribs collected from symptom-bearing and symptomless plants were subjected to total DNA extraction (Murray & Thompson, 4). Total DNA was used as a template in a nested-PCR with generic primers targeting the phytoplasma 16S rRNA gene: P1/P7 (Deng & Hiruki, 1) and R16F2n/R16R2 (Gundersen & Lee, 2). R16F2n/R2 amplicons were purified, ligated in pGEM®-T Easy vector (Promega, Madison, WI, USA) and sequenced. The derived sequences were identified by comparison with phytoplasma reference sequences using BLAST (www.ncbi.nlm.nih.gov) and RFLP analysis (determined by comparing the digestion sites map for the endonucleases EcoRI, BfaI, HinfI, RsaI, AluI, MseI, HpaII and HaeIII using VECTOR NTI v.8.0 from Invitrogen, CA, USA). Phylogenetic trees were constructed using Mega 4.0. R16F2n/R2 amplicons of expected size (approx. 1200 bp) and similar to the reference control were amplified from 13/14 symptom-bearing plants. No amplification was yielded by symptomless plants (6/6). Two individual clones derived from four symptom-bearing plants were sequenced, and the partial consensus sequence of 1139 nt (GenBank Accession No. KC825053) exhibited 99% sequence identity with those of group 16SrI ‘Ca. Phytoplasma asteris’, closer to members of subgroup 16SrI-F, including the apricot chlorotic leaf roll-aster yellow phytoplasma, ACLR-AY (AY265211), aster yellows phytoplasma strain CVB (AY265212), Bajgah periwinkle little leaf phytoplasma (DQ266089), and macadamia phytoplasma (KC513772). Nucleotide comparison with strawberry phytoplasma sequences from Lithuania (DQ086423: Valiunas et al., 6) and USA (U96614, U96616: Jomantiene et al., 3) showed identities lower than 98%. RFLP profiles derived from the R16F2n/R2 amplicon sequence were identical to those of the subgroup 16SrI-F mentioned above used as reference. A phylogenetic tree based on the 16S rDNA sequence of the strawberry phytoplasma under study and those of reference sequences supported PCR and RFLP results, and confirmed that the phytoplasma is a member of the 16SrI ‘Ca. Phytoplasma asteris’ group, and possibly subgroup 16SrI-F (Fig. 2). This is the first report of a ‘Ca. Phytoplasma asteris’ isolate associated with symptoms in Cuban strawberry plants. Both RFLP and phylogeny analysis show the closest relationship between the strawberry phytoplasma (KC825053) and the previously phytoplasma identified from Cuban macadamia trees (Pérez-López et al., 5) in Artemisa province. This suggests complex epidemiological implications for the two ‘Ca. Phytoplasma asteris’ isolates in two different plant hosts within the same geographic location; indicating the possibility of significant risk of distributing possible phytoplasma-infected propagation material from strawberry nurseries to commercial strawberry fields. A more distant relationship was found between the Cuban strawberry phytoplasma sequence and those reported from strawberry in other countries, suggesting that this fruit crop supports the infection by a wide phytoplasma range. This research was supported by the Cuban Fruit Corporate Group (Grupo Empresarial Frutícola de Cuba, GEF) through national projects 0578 and 2004.

Determination of Strawberry Nutrient Optimum Ranges through Diagnosis and Recommendation Integrated System Analysis

Diagnosis and recommendation integrated system (DRIS) leaf blade and petiole optimum nutrient ranges were developed through tissue sampling in 53 commercial strawberry (Fragaria ×ananassa) fields in the coastal valleys of central California in 2010 and 2011. All fields were in an annual production system using the day-neutral cultivar Albion. Leaf blades and petioles were sampled five times from early flowering through the fruit harvest period. Data on soil nutrient availability and grower fertilization practices were also collected. DRIS analysis was used to develop nutrient optimum ranges based on nutrient concentrations observed in nutritionally balanced, high-yield fields. Blade nitrogen (N), phosphorus (P), and potassium (K) concentrations declined from the vegetative stage until the main harvest period, and stabilized thereafter. Blade calcium (Ca), boron (B), and iron (Fe) increased over time while magnesium (Mg), sulfur (S), manganese (Mn), zinc (Zn), and copper (Cu) decreased. The blade N optimum range was lower than previously published sufficiency ranges during the fruit harvest period, and the Zn optimum range was lower throughout the season. Other nutrients were in general agreement with previously established sufficiency ranges with the exception of Ca, Mn, and Fe, which were higher. Petiole nitrate-nitrogen (NO3-N) was highly variable among high-yield fields, was not correlated with soil NO3-N at any growth stage, and was therefore of limited value as an indicator of crop N status. Comparison of soil nutrient availability with grower fertilization practices suggested that significant improvement in fertilizer management was possible.

Strawberry yield efficiency and its correlation with temperature and solar radiation

The impact that future climatic conditions will have on agricultural productivity depends on the sensitivity to each environmental factor and relative changes in temperature, precipitation and UV-B radiation. The strawberry (Fragaria x ananassa) is a microclimatic crop cultivated almost worldwide and Spain is the world's second-largest strawberry producer after the USA. Strawberry production in Huelva has been affected by climate change in recent decades. Temperature and solar radiation are primary environmental factors controlling short-day strawberry plant growth and development. Temperature is a limiting factor in crop productivity. We assessed the effect of variations in temperature and solar radiation on strawberry production and crop cycle duration. The study was carried out in commercial strawberry fruit production fields in the province of Huelva (Spain's southwestern coast). Fresh plants of cv. Camarosa were cultivated from October to June. The resulting crop was recorded weekly in the production field: early and total strawberry productions (g/plant), were recorded from January to March and from January to May, respectively. Data revealed that between early production and temperature (R²= 0.86) and between early production and solar radiation (R²= 0.73) there was a linear relationship. However, total production and temperature (R²= 0.69) and total production and solar radiation (R²= 0.69) were related by a quadratic relationship. Our estimates suggest that strawberry production could be affected by climate change. Due to the relationship between yield and temperature, and between yield and solar radiation, climate change scenarios were found to result in reductions in crop cycle duration.

Fenhexamid Resistance in Botrytis cinerea from Strawberry Fields in the Carolinas Is Associated with Four Target Gene Mutations.

Botrytis cinerea, the causal agent of gray mold disease, is one of the most important pathogens of strawberry. Its control in commercial strawberry fields is largely dependent on the application of fungicides during bloom and fruit maturation. The hydroxyanilide fenhexamid is one of the most frequently used fungicides in the southeast of the United States for gray mold control. It inhibits the 3-ketoreductase (Erg27) of the ergosterol biosynthesis pathway and, due to this site-specific mode of action, is at risk for resistance development. Single-spore isolates were collected from 11 commercial strawberry fields in North and South Carolina and subjected to a conidial germination assay that distinguished sensitive from resistant phenotypes. Of the 214 isolates collected, 16.8% were resistant to fenhexamid. Resistance was found in three of four locations from North Carolina and in four of seven locations from South Carolina, indicating that resistance was widespread. Mutations in Erg27 (T63I, F412S, F412C, and F412I) were associated with resistance, with F412S the predominant and most widespread mutation. In this study, mutations T63I and F412C in field isolates of B. cinerea are described for the first time. Detached fruit studies showed that field rates of Elevate 50 WDG (fenhexamid) controlled sensitive but not resistant isolates carrying any of the four mutations. Resistant isolates produced the same lesion size and number of sporulating lesions on fruit sprayed with Elevate 50 WDG as on untreated controls, showing the fungicide's loss of efficacy against those isolates. A rapid polymerase chain reaction method was developed to quickly and reliably distinguish isolates sensitive or resistant to fenhexamid in the Carolinas and to determine the mutation associated with resistance. The presence of fenhexamid-resistant strains in B. cinerea from strawberry fields in the Carolinas must be considered in future resistance management practices for sustained gray mold control.

Resistance to Cyprodinil and Lack of Fludioxonil Resistance in Botrytis cinerea Isolates from Strawberry in North and South Carolina.

Chemical control of gray mold of strawberry caused by Botrytis cinerea is essential to prevent pre- and postharvest fruit decay. For more than 10 years, the anilinopyrimidine (AP) cyprodinil and the phenylpyrrole fludioxonil (Switch 62.5WG) have been available to commercial strawberry producers in the United States for gray mold control. Both active ingredients are site-specific inhibitors and, thus, prone to resistance development. In this study, 217 single-spore isolates of B. cinerea from 11 commercial strawberry fields in North and South Carolina were examined for sensitivity to both fungicides. Isolates that were sensitive (53%), moderately resistant (30%), or resistant (17%) to cyprodinil were identified based on germ tube inhibition at discriminatory doses of cyprodinil at 1 and 25 mg/liter at 10 of the 11 locations. None of the isolates was fludioxonil resistant. Phenotypes that were moderately resistant or resistant to cyprodinil were not associated with fitness penalties for mycelial growth rate, spore production, or osmotic sensitivity. Detached fruit assays demonstrated cross resistance between the two AP fungicides cyprodinil and pyrimethanil, and that isolates that were characterized in vitro as moderately resistant or resistant were equivalent in pathogenicity on fruit sprayed with pyrimethanil (currently the only AP registered in strawberry as a solo formulation). This suggests that the in vitro distinction of moderately resistant and resistant isolates is of little if any field relevance. The absence of cross-resistance with fludioxonil, iprodione, cycloheximide, and tolnaftate indicated that multidrug resistance in the form of multidrug resistance phenotypes was unlikely to be involved in conferring resistance to APs in our isolates. Implications for resistance management and disease control are discussed.

Severity of crown and root diseases of strawberry and associated fungal and oomycete pathogens in Western Australia

The decline/death of strawberry plants is considered to be a serious challenge to strawberry production in Western Australia (WA). Although crown and root diseases have been found to be important contributing factors, little is known on the extent of crown and root diseases or the associated fungal and oomycete pathogens. Surveys were undertaken in 2008 to determine the severity of crown and root diseases in commercial strawberry fields in WA, to determine the influence of cropping history, fumigation, soil nutrients and pH on severity of such diseases, and to identify the associated pathogens. Among the sites surveyed, there was a significant variation with the decline/death index (%DI) ranging from 2.9 to 39.7. The level of strawberry plant decline/death progressed significantly from August to October, with the %DI rising from 13.0 to 39.2; There was a significant difference in strawberry plant decline/death between fumigated and non-fumigated beds, with a %DI of 7.1 for fumigated and 45.2 for non-fumigated beds. However, it was evident that in situations where there were periods of 3 or more years involving crop rotations between successive strawberry crops that the level of plant decline/death was lower, even in the absence of fumigation. Both the severity of crown disease and root disease were positively correlated with that of strawberry plant decline/death. There was a significant negative correlation between soil pH and the decline/death of strawberry plants. The main pathogens associated with crown and root diseases of strawberry were Fusarium oxysporum, Rhizoctonia spp. (AG-A, AG-C, AG-I, AG-K and others), Cylindrocarpon destructans, Phoma exigua, Gnomonia fructicola, Phytophthora cactorum, Pythium ultimum and Macrophomina phaseolina. F. oxysporum was most frequently isolated from crowns, at a frequency of 41.2%. Rhizoctonia spp. and C. destructans were most frequently isolated from roots, at a frequency of 11.8% and 12.0%, respectively. This study demonstrates, for the first time, that strawberry production in WA is severely compromised by crown and root diseases, especially late in the production season, and impacts are clearly greater in non-fumigated field beds as well as those with relatively lower soil pH (4.5 ~ 6 in CaCl2). This study also demonstrates that F. oxysporum is the major pathogen associated with crown disease, and Rhizoctonia spp. are important pathogens associated with root disease of strawberry in WA.

Relative Contribution of Various Sources of Botrytis cinerea Inoculum in Strawberry Fields in Norway.

To identify the most important sources of inoculum of Botrytis cinerea (causal agent of gray mold) in commercial strawberry (Fragaria × ananassa) fields in Norway, soil and overwintered plant material were collected from planting beds and alleys at five locations in 2000 to 2002 (13 samples altogether). Plant material was sorted by category (e.g., leaves, stems, mulch, and weeds). After subsamples of each material were incubated for 5 days at 20°C at high humidity, conidiophores of B. cinerea growing from mycelia and sclerotia were counted. Overwintered plant debris within planting beds yielded more than 96% of total conidiophores counted, the remainder originating from plant debris collected from alleys or soil. Overwintered strawberry plant debris produced 98% of the conidiophores within planting beds and 80% of the conidiophores in the alleys, while the remaining was produced by weeds. Senescing and dead leaf laminae produced 45% of the conidiophores while stem residues (i.e., petioles, stolons, inflorescences, and unidentifiable stem parts) produced 50% and mummified fruit produced 5% within planting beds. The contribution of sclerotia, compared with mycelia, to conidiophore production varied greatly between fields and years. Overall, 47% of the total number of conidiophores produced in plant material within planting beds originated from sclerotia. More than 90% of the conidiophores from sclerotia were found in dead stem residues.