Old but Gold: Captan Is a Valuable Tool for Managing Anthracnose and Botrytis Fruit Rots and Improving Strawberry Yields Based on a Meta-Analysis.

Botrytis fruit rot (BFR) and anthracnose fruit rot (AFR) are diseases of concern to strawberry growers. Both diseases are managed mainly by fungicide applications from the nursery (plant production) to the end of the growing season (fruit production). In Florida, captan is the main broad-spectrum fungicide used to control BFR and AFR. It has been tested in many trials over the years in various programs in alternation with single-site fungicides or weekly applications. Due to its broad-spectrum activity, captan is a pivotal tool in fungicide resistance management, because resistance to several fungicides has been reported in populations causing BFR and AFR. Our objective was to determine the effectiveness and profitability of applications of captan for controlling BFR and AFR based on a univariate meta-analysis considering data from 25 field trials conducted from 2005 to 2021 in Florida. Captan applications significantly improved marketable yields and reduced BFR and AFR incidence during late- and total-season periods. Marketable yields were significantly improved even when the effect on disease control was not significant. Our results indicate 100% probability that weekly captan applications would return the investment during low, medium, and high strawberry pricing regimes, although the magnitude of the return will depend on strawberry market prices. However, the probabilities of reducing BFR, AFR, and culls were lower. Results from our meta-analysis demonstrate the value of captan as an important tool for strawberry growers. Captan applications, in addition to effectively controlling BFR and AFR and improving marketable yields, will result in investment returns at any strawberry price level.

Efficacy of Single- and Multi-Site Fungicides Against Neopestalotiopsis spp. of Strawberry.

Recently, the Florida strawberry industry faced unprecedented outbreaks of an emerging disease caused by the fungus Neopestalotipsis spp. Currently, there are no fungicides labeled to control this disease in the United States and the efficacy of single- and multisite fungicides is unknown. Therefore, this study aimed to determine the in vitro sensitivity of Neopestalotiopsis spp. isolates to fungicides with different modes of action and to evaluate the efficacy of these products on detached fruit and in the field. In preliminary in vitro tests, 30 commercially available fungicides were screened using discriminatory doses. The effective concentration that inhibited mycelial growth by 50% was determined for the most effective single-site fungicides. Four field experiments were conducted during the 2019-20, 2020-21, and 2021-22 seasons to determine product efficacy in managing the disease. The single-site fungicides fludioxonil, fluazinam, and sterol demethylation inhibitors, and the multisite fungicides captan, thiram, and chlorothalonil were the most effective in inhibiting pathogen growth and suppressing disease development. Conversely, products in Fungicide Resistance Action Committee (FRAC) groups 1 (methyl benzimidazole carbamate) and 7 (succinate-dehydrogenase inhibitors), except for benzovindiflupyr, were not effective against Neopestalotiopsis spp. Resistance to fungicides from FRAC group 11 (e.g., azoxystrobin) was confirmed by the presence of the G143A mutation in the cytochrome b gene together with inoculation tests and field trials. Our results provide information to support or discourage the registration of fungicides to manage Neopestalotiopsis fruit rot and leaf spot in strawberry production.

Validation of a Decision Support System for Blueberry Anthracnose and Fungicide Sensitivity of Colletotrichum gloeosporioides Isolates.

Blueberry is an increasingly important crop in Florida. Anthracnose fruit rot (AFR), caused mostly by Colletotrichum gloeosporioides, is favored by long wetness periods and temperatures from 15 to 27°C. Currently, the model in the Strawberry Advisory System (StAS) guides fungicide applications targeting strawberry AFR. Given the similarity between blueberry and strawberry AFR, we hypothesized that the model used in StAS could be used in a decision support system (DSS) built for blueberry AFR. There is no information on inhibition posed by fungicides on C. gloeosporioides isolates from blueberry. Our objectives were to demonstrate that the model used in the StAS could be used for blueberry AFR management in Florida and to assess the sensitivity of isolates to fungicides. Four trials were undertaken in blueberry fields in Florida during two seasons to compare the effectiveness of fungicide applications according to the model with that of the growers' standard calendar. Sensitivity of blueberry C. gloeosporioides isolates to azoxystrobin, benzovindiflupyr, penthiopyrad, pydiflumetofen, boscalid, thiophanate-methyl, fluazinam, and fludioxonil was evaluated. AFR incidence and yield were compared between treatments. Following recommendations from the model resulted in disease control as effective as the standard program and in some cases with fewer applications. All isolates were sensitive to benzovindiflupyr, penthiopyrad, fluazinam, and fludioxonil. Low frequency of in vitro inhibition of isolates by azoxystrobin, pydiflumetofen, boscalid, and thiophanate-methyl should raise concern about fungicide resistance. Our results indicate that the model used in StAS could be used in a DSS to help Florida growers to manage AFR in blueberry.

Sensitivity of Colletotrichum acutatum Isolates from Citrus to Carbendazim, Difenoconazole, Tebuconazole, and Trifloxystrobin.

Postbloom fruit drop (PFD) of citrus is caused by the Colletotrichum acutatum and C. gloeosporioides species complexes. The disease is important when frequent rainfall occurs during the flowering period of citrus trees. In Brazil, until 2012, PFD was mainly controlled by preventive applications of the methyl-benzimidazole carbamate (MBC) carbendazim and demethylation-inhibitor (DMI) fungicides such as difenoconazole. Since then, mixtures containing the DMI tebuconazole and the quinone-outside inhibitor (QoI) trifloxystrobin have been commonly used. Fungicides are often applied preventively, sometimes even when conditions are not conducive for PFD development. Excessive fungicide applications may favor the selection of resistant populations of Colletotrichum spp. In this study, we assessed the fungicide sensitivity of C. acutatum isolates collected during the two distinct periods of PFD management in Brazil: before and after the trifloxystrobin and tebuconazole mixture became widely employed. The sensitivity of 254 C. acutatum isolates to carbendazim and difenoconazole and of 164 isolates to tebuconazole and trifloxystrobin was assessed. Mycelial growth inhibition of these isolates was evaluated for all the fungicides using either serial dilution of fungicide rates or the spiral gradient dilution method. In addition, inhibition of conidial germination was also assessed for trifloxystrobin. Analysis of partial ß-tub, cytb, and cyp51b gene sequences did not reveal any mutations related to resistance to MBCs, QoIs, and DMIs, respectively. In mycelial growth assays, mean EC50 values were 0.14, 0.11, and 0.21 µg/ml for difenoconazole, tebuconazole, and trifloxystrobin, respectively. The conidial germination inhibition by trifloxystrobin was similar among the tested isolates, and the mean EC50 value was 0.002 µg/ml. All isolates had similar mean mycelial growth inhibition for carbendazim, regardless of the fungicide concentrations. Therefore, based on similar EC50 values and molecular analyses, no shift in the sensitivity of isolates has been observed to the fungicides commonly used in different citrus-producing areas in Brazil.

A Threshold-Based Decision-Support System for Fungicide Applications Provides Cost-Effective Control of Citrus Postbloom Fruit Drop.

Postbloom fruit drop (PFD) of citrus, caused by Colletotrichum acutatum sensu lato and C. gloeosporioides sensu lato, is an important disease in the humid tropics of the American continent. PFD mainly affects flowers, on which typical symptoms are characterized by orange-brown lesions with presence of acervuli. The disease has a sporadic occurrence, but preventative fungicide sprays are applied every season. The objective of this study was to evaluate the effectiveness of a fungicide spray strategy for PFD based on a predictive model of C. acutatum conidium germination linked to weather conditions. Fungicide sprays were performed when the model predicted pre-established thresholds of 10, 15, 20, and 25% of germinated spores (T10, T15, T20, and T25, respectively). Five experiments were conducted in two different seasons in the state of São Paulo, Brazil. PFD control efficacy of the threshold-based treatments was compared with a nontreated control and to a calendar-based spray system. Additionally, an economic analysis was performed to assess the gross income revenues of the fungicide spraying strategies. Disease control in plots treated at T10, T15, and T20 was as effective as the calendar-based strategy. The number of fungicide applications was reduced by 33 to 71% when sprays were applied at T15 and T20, and gross income increased or was comparable to that of the other treatments. Therefore, using a conidium germination model with a threshold of 15 or 20% is recommended as a spraying strategy for PFD management in Brazil.