Our objectives were to 1) characterize the fungi colonizing used wooden pallets; 2) assess the ability of fungi to grow on wood surfaces and cause disease on carrots under cold storage conditions; and 3) evaluate the efficacy of selected disinfectants as pallet sanitizers.

From 40 pallets previously used for carrot storage, 455 isolates were recovered that were classified into ten fungal groups: Alternaria spp., Aspergillus spp., Botrytis cinerea, Fusarium spp., Mucor spp., Penicillium spp., Rhizoctonia carotae, Rhizopus stolonifer, Sclerotinia sclerotiorum, and Trichoderma spp. Occurrence of fungal groups was highly variable among investigated carrot farms; however, the most prevalent were isolates of Penicillium spp., Rhizopus spp., and Trichoderma spp.

Most (26 or 28) tested fungi caused various degrees of rot symptoms on carrot roots after four weeks in cold storage. Fungi that caused the largest lesions were the isolate of S. sclerotiorum (29.7 mm), R. carotae (28.9 mm), and Botrytis cinerea (25.1 mm). Similarly, fungi that developed most extensively on wood surfaces after four weeks in cold storage were isolates of B. cinerea (62.8 mm), S. sclerotiorum (58.9 mm), Fusarium sp. (39.2 mm), and R. carotae (36.2 mm). Except for Alternaria spp. and Aspergillus spp., all other fungi growing on wood caused disease on whole carrots after three weeks of contact in cold storage. All tested fungi, however, caused disease on carrot slices, suggesting that the presence of wounds on carrot can increase the disease-causing potential of these isolates that otherwise would not pose any risk.

Bleach at 10 percent concentration provided complete control of all tested fungi. However, only S. sclerotiorum was significantly affected by the tested disinfectants (P=0.003). Chemprocide and Virkon also controlled completely S. sclerotiorum on wood surfaces. Although not significantly different, Virkon was superior in suppressing Fusarium sp.

Several fungal pathogens can survive on the surface of used wood pallets, and can be active under cold conditions. S. sclerotiorum, R. carotae, and B. cinerea cause the most common and most destructive diseases on stored carrots worldwide. In these tests, these fungi were best adapted to develop and cause disease in cold storage, and represented 12 percent of all recovered isolates. Isolates of Aspergillus spp., Mucor spp., Rhizopus spp., and Trichoderma spp., represented 43 percent of recovered fungi, and were unimportant in causing disease on stored carrots, as their growth was restricted in cold storage. The remaining 45 percent included isolates of Alternaria spp., Fusarium spp., and Penicillium spp. that caused little or no disease on carrots, but showed potential to develop on wood surfaces under cold conditions. The presence of diverse fungal colonies on the pallet surface may increase disease levels as a result of secondary infection, presence of wounded roots, and poor storage conditions.

Reusing infested wooden pallets could affect long-term carrot storage, and their sanitation should be considered as a component of integrated management of storage diseases of carrots. However, pallets from different farms were not equally infested by pathogenic fungi. This suggests that decisions made on a case-by-case basis, considering the degree of pallet infestation and the farm’s history of crop losses due to storage diseases, may be a cost-effective approach.

Bleach is a potent sanitizer that provides superior control of a wide range of pathogenic organisms on several surfaces, but it is highly persistent and hazardous for the environment. In this study, Virkon and Chemprocide had, overall, the highest incidence of complete, or relatively superior, control of most tested fungal isolates on wood surfaces, following bleach. Therefore, these disinfectants may be considered as potential alternatives to bleach for safe sanitizing operations in the future.