Print PageCoffee rust, caused by the fungus Hemileia vastatrix, is an important pest of Coffea arabica. Multiple factors affect coffee rust prevalence, including precipitation, shade, and coffee variety susceptibility. Producers manage this disease with fungicides, but also by varying the level of shade, pruning infected leaves and planting resistant varieties. There is interest in using the biotrophic fungus Lecanicillium lecanii as an inundative biological control for H.vastatrix, but poor survival of sprayed L.lecanii spores in the field has hampered effectiveness. Vandermeer et al. (2009) reported that coffee rust prevalence is negatively correlated with distance from L. lecanii-infected Coccus viridis – hemipteran mutualists of the ant Azteca instabilis. This data suggests the ant-hemipteran mutualism could act as a natural source of L. lecanii spores in coffee agroecosystems.
We studied the relative effect of the ant-hemipteran-L.lecanii complex on H.vastatrix prevalence compared to shade, coffee variety and precipitation in a shade-grown organic coffee farm. We used monthly survey data on the prevalence of both coffee rust and L.lecanii-infected C.viridis. We also collected data on coffee variety, per cent shade and daily precipitation to compare to the response of H.vastatrix prevalence.
Results/Conclusions
Prevalence of H. vastatrix lesions increased with distance from the ant-hemipteran-L. lecanii complex in both sites (linear regression, Site A: R2 = 0.315, P < 0.001; Site B: R2 = 0.011, P = 0.017). Linear regression models suggest that per cent shade has a stronger effect on rust prevalence in some months relative to others, but there is not a clear seasonal effect. In contrast, coffee rust prevalence is significantly negatively correlated with mean monthly precipitation. Of the five varieties of coffee bushes in the farm: Typica, Bourbon, Catuai, Caturra and Catimor, Catimor is the most resistant to coffee rust fungus and had the least amount of infected leaves. We analyzed the effect of neighbouring varieties (within 2 meters) on coffee rust prevalence in individual coffee bushes and found that rust prevalence per coffee bush increased with the number of neighbouring Catuai individuals in 2009, but there was no effect of the Catuai variety in 2010. In contrast, rust prevalence per coffee bush decreased with the number of neighbouring Catimor individuals in 2010. In conclusion, the data suggest that L. lecanii, shade, precipitation and coffee variety all significantly coffee rust prevalence.
