The use of nitrogen fertilisation for suppressing Mycosphaerella in Eucalyptus dunnii

Abstract

Mycosphaerella leaf disease (MLD) is a pathogen of eucalypt plantations causing leaf spots and defoliation, and affecting growth. In this study, two different dosages of nitrogen fertilisation together with a control treatment currently used for two clones being affected by MLD (C18 and C25) of Eucalyptus dunnii were tested. We measured root collar diameter (D) and height (H), and assessed disease severity in the apical, middle and basal portions of the crown at planting, three months after planting and five months after planting, and determined the Area Under Disease Curve Progress at the end of the study, for the following fertilisation treatments: reduced dosage 22.0 kg ha⁻¹ of NH₄NO₃; control dosage 44.0 kg ha⁻¹ of NH₄NO₃; and increased dosage 66.0 kg ha⁻¹ of NH₄NO₃. We added 133.4 kg ha⁻¹ of P₂O₅ and 28.0 kg ha⁻¹ of KCl to each treatment. MLD severity was higher in the basal portion of the crown. Only for C18 did the control dosage and the increased dosage promote growth in root collar diameter and reduce MLD severity, respectively. For C25 there were no differences for the variables across the fertilisation treatments. For C18 correlation analysis indicated that increased nitrogen dosage reduced MLD severity (r = 0.83; p < 0.01). In conclusion, improved nitrogen fertilisation proved to be effective to reduce severity, but differences were observed between clones and fertilisation.

Keywords:

• forest management
• leaf spots
• Mycosphaerella spp
• silviculture
• Teratosphaeria spp