Fungicidal Drenches for Control of Postharvest Decay in d'Anjou
Blue and gray molds are the most common postharvest diseases of pears and apples. Gray mold, caused by Botrytis cinerea, is the most frequently encountered disease in untreated fruit stored in bins. Because B. cinerea frequently spreads from fruit to fruit (nests), losses from initial infection foci can be large. Furthermore, fruits with undetected nascent infections often are packed and can lead to situations in which boxes of fruit must be repacked before shipping.
Preliminary studies have shown that both primary and secondary gray mold infections can be prevented by treating fruit with a fungicide immediately after harvest and before it is put away in storage.
Fungicide drenches are not commonly used in pears because of fear that outbreaks of blue mold and Mucor rot may occur. Analyses of pear fungicide and ethoxyquin drench suspensions in the Mid-Columbia area disclosed the potential for large buildups of propagules of Penicillium species (Sanderson and Spotts, 1995). The following study was undertaken to determine if chemical and biological fungicide drenches could be used safely to control gray mold without incurring outbreaks of blue mold or Mucor rot.
Materials and Methods
Treatments were applied in a randomized complete block design to bins of commercially harvested d'Anjou pear fruit. Fruit bins were loaded onto straddle carriers (18 to 24 bins) as they were harvested from each of 10 grower lots and treatments were applied with a drive-through, recirculating, cascading drencher (2000 gal) for 1 minute. Each grower lot constituted a block and each straddle carrier load constituted a single replicate. Bins of fruit from each grower were drenched in the order in which they were received at the warehouse. A single tank was filled with each drench suspension and all replicates were treated with the same batch of suspension. A total of 400 to 600 bins of fruit were treated with each tank of drench suspension, at which point the pumps could not pick it up and the remaining suspension was discarded (about 500 gal). Most of the bins of fruit included in the experiment were treated within the first 250 to 300 bins which were drenched.
After treatment, all bins of fruit were placed in CA storage. After 5 months of storage, treated fruits were packed on a commercial packing line. All fruits with decay symptoms were removed at a presorting table and the type of decay (e.g., gray mold, blue mold, etc.) determined. Number of fruit per bin with each disease was calculated and log-e transformed data were analyzed with ANOVA (SYSTAT, SPSS, Chicago, IL 60611). Comparisons among treatment means were made with Tukey's HSD test.
Results and Discussion
In untreated fruit, the incidence of gray mold was higher than that of any other disease (Table 1). All drench treatments significantly reduced disease incidence over that seen in the untreated control. Interestingly, the incidence of disease observed in fruit treated with Biosave 110 + Mertect 340-F was higher than that observed in the fruit treated with Mertect alone.
In this trial, all decay caused by species of Penicillium were classed as blue mold. The majority of blue mold was caused by P. solitum rather than P. expansum, although both species were recovered from lesions on fruit. Blue mold incidence was low in all treatments, but generally was higher in those fruits that were drenched than in the undrenched control (Table 1). The least amount of blue mold affected fruits observed were in the Captan + Mertect treatment. Less decay was present in bins of fruit treated with Biosave 110 + Mertect than in those treated with Mertect alone. The addition of Aspire did not significantly affect the incidence of blue mold from that seen in the treatment with Mertect alone.
Mucor rot incidence in all treatments was low (Table 1) and the absence of Mucor probably should not be taken as an indication that the treatment lessened disease incidence as much as its presence indicates a lack of control. In that respect, Biosave 110 was ineffective in controlling Mucor rot.
The total amount of decay shown in Table 1 is the sum of gray and blue mold and Mucor rot incidence. The greatest reduction in decay was observed in the Captan + Mertect treatment. Decay incidence was not significantly different among other drench treatments.
Drenching with fungicides appears promising for controlling decay of pear fruits stored in bins. Most loss to decay in field run pears was from gray mold. Within the parameters of this study, all drenches reduced the number of fruits decayed from that in the untreated control. It must be reiterated, however, that most of the fruits assayed for decay were treated within the first 250 to 300 bins drenched. It is unlikely that the drenches had as high a density of pathogen spores as was present at the end of the drench run. However, all other treated fruits were packed commercially with no apparent adverse effects. This trial was conducted only once, and although its scale was relatively large, it must be repeated before recommendations based on these results can be made.
Sanderson, P. G., and Spotts, R. A. 1995. Postharvest decay of winter pear and apple fruit caused by species of Penicillium. Phytopathology 85:103-110.
Dr. Peter G. Sanderson(1) and Ken Miller(2)
(1)Washington Tree Fruit Research Commission
1719 Springwater Street, Wenatchee, WA 98801
(2)Blue Star Growers, Inc.,
P.O. Box I, Cashmere, WA 98815
13th Annual Postharvest Conference