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Mycobiome of low maintenance iconic landscape plant boxwood under repeated treatments of contact and systemic fungicides

Summary

This study examined how different fungicide treatments affect the beneficial and harmful fungi living on boxwood plants. Researchers found that repeated applications of chlorothalonil-based fungicides reduced many beneficial fungi while having minimal effect on harmful pathogens, and that fungi became less sensitive to the same fungicide over time. The findings suggest that choosing the right fungicide and application method is important for maintaining plant health and preventing fungicide resistance.

Background

Boxwood is a low-maintenance landscape plant that has experienced rising health issues in recent years, requiring frequent fungicide applications at 2-3 week intervals. Fungicides can have unintended consequences on non-target fungal communities, disrupting the balance between beneficial and pathogenic microorganisms. Limited research exists on how repeated applications of different fungicide chemistries affect phyllosphere fungal communities.

Objective

This study aimed to determine how fungicide chemistry (contact vs. systemic) and repeated applications affect the epiphytic and endophytic fungal communities of boxwood. Three fungicides were tested: Daconil (chlorothalonil, contact), Banner Maxx (propiconazole, systemic), and Concert II (combination chemistry).

Results

Fungal community composition differed between shoot surface and internal tissue, dominated by Cladosporium (epiphytes) and Shiraia (endophytes). Daconil and Concert II suppressed significantly more epiphytic fungi than Banner Maxx. By August, many epiphytic genera showed reduced sensitivity to Daconil, indicating developing resistance after repeated applications.

Conclusion

This study provides the first mycobiome evidence supporting boxwood as a low-maintenance plant and demonstrates fungicide resistance development to multisite contact chemistry from repeated applications. Results suggest that single-site systemic fungicides should be preferred when chemical protection is necessary, and that product labels should include mycobiome impact information to guide informed agrochemical selection.
  • Published in:Scientific Reports,
  • Study Type:Experimental Study,
  • Source: PMC12358565, PMID: 40820086
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