Interaction of vascular streak dieback disease of cocoa with soil nutrient status in Indonesia

Abstract

Vascular Streak Dieback (VSD) is a disease of cocoa trees, caused by Oncobasidium theobromae. The disease has become one of the major causes of economic losses to cocoa productivity in commercial plantations in Indonesia. A severe infection causes the death of young seedlings and canopy loss in older trees. The maintenance of soil fertility by fertiliser management is one of the recommendations for integrated VSD disease management. The aim of this study was to evaluate the impact of fertiliser application in the plantation environment, and to observe if nutrient management can potentially control VSD disease.Historical environment data showed that the cocoa plantation of Treblasala Estate, London Sumatra Indonesia experienced a soil pH decline associated with the annual urea application as a source of nitrogen. Soil P status is also relatively high when compared with the suggested critical level for growing cocoa. However, triple superphosphate fertiliser as source of P is applied annually and has resulted in high residual P levels.Soil and leaf nutrient sampling from selected plantings and genotypes has revealed higher soil pH and soil nutrient levels when compared with historical soil data. Soil phosphorus levels are very high and this might have reduced the uptake of some nutrients, since the levels of these nutrients in cocoa leaves were found to be lower than the critical levels.Magnesium, calcium, copper, zinc and manganese were the nutrients whose levels were found to be below the suggested optimum ranges. These nutrients were also low in the genotype that is susceptible to VSD disease. Calcium and manganese levels of diseased leaves were also lower than healthy leaves, indicating a probable relationship with VSD disease.To investigate whether high phosphorus supply reduces the micronutrient status, nutrient studies were carried out using young cocoa seedlings in Gatton, Australia under glasshouse conditions, and under the natural environment in Indonesia. The studies revealed that nutrient imbalances may occur in response to high P fertiliser application, although a reduction in leaf micronutrient status was not observed. The results suggest that P application is not beneficial to the soils on the Treblasala Estate.

Traits of farming practice affecting vascular streak dieback disease on cacao in Central Sulawesi

“…Weather extremes, such as extended droughts, heavy rains, or dramatic temperature swings, may harm trees and increase their susceptibility to VSD diseases [15]. Inadequate pest and disease control, improper pruning methods, or excessive fertilizer or pesticide use are just a few examples of poor agricultural practices that can damage trees and hasten the emergence of VSD [3,16].…”