Managing Root Rot

Chile is the fifth largest exporter of walnuts in the world, with approximately 30,000 hectares of walnut orchards distributed across nine growing regions. Despite being a traditional Chilean crop, the increased worldwide demand is pushing new planting into areas with less than ideal conditions, such as areas with more humidity and heavier soils.

Chile is the fifth largest exporter of walnuts in the world, with approximately 30,000 hectares of walnut orchards distributed across nine growing regions. Despite being a traditional Chilean crop, the increased worldwide demand is pushing new planting into areas with less than ideal conditions, such as areas with more humidity and heavier soils.

This expansion has left Chilean growers facing a new enemy: root and crown rot disease, a fungal infection caused by Phytophthora (PT). PT represents the largest cause of death of walnut trees in Chile.

Damage on an afflicted tree is indicative of a PT infection.

Dynamic Wings, an agronomic service provider in Chile, recently worked with a walnut orchard located in the Metropolitan region, just southwest of Santiago. They captured high-resolution images and data using a MicaSense RedEdge multispectral sensor.

Comparison of leaves of healthy trees (left) and trees afflicted with PT (right).

After mapping the area, they viewed the analysis outputs with MicaSense Atlas. The Chlorophyll Map layer was particularly useful here. This layer indicates the level of chlorophyll content in the leaves of the trees, which is generally a direct indication of the health and stress level of the crop. In this case, the Chlorophyll Map highlighted significant variability in the field, primarily attributed to excessive salt content in the soil in specific areas of the orchard. Also, a stand of trees near the southeast corner of the field exhibited particularly low health. Scouting this area confirmed the presence of not only high salinity soils but also disease marks consistent with PT infection.

Chlorophyll Map of the walnut orchard shows a group of low health trees at the southeast corner of the field. Scouting confirmed that PT, combined with soils that had excess salinity, was the likely cause.

Correlating the information from the Chlorophyll Map with the data from the Digital Surface Model (DSM) layer in Atlas provided further clues towards finding the cause of this problem. The DSM layer, generated from the images taken by the RedEdge sensor, shows the elevation of soil and trees. The southeast corner of the orchard is at a lower elevation than the rest of the field. As a result, water is likely to accumulate here and saturate the soil, leading to more susceptibility for PT infection.

DSM map shows the changes in the elevation of the orchard, indicating that the afflicted area is likely to accumulate water due to the sloping terrain.

As it turns out, an irrigation canal runs near the affected area. This fact, combined with the sloping terrain, made this area have a propensity for fungal disease.

Color image (left) and photo (right) of the irrigation canal in the southeast corner of the orchard. Accumulation of water and moisture is likely to have caused the PT problems in this area.

Aided with the results of this analysis, Dynamic Wings was able to make several recommendations for the grower, including lining the irrigation canal with plastic to prevent water from leaching into the soil, and performing more detailed soil tests. Using the information from RedEdge and Atlas provided Dynamic Wings with the information to make these recommendations with more confidence and more efficiently.

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Read about how chlorophyll mapping helped a farmer identify potassium deficiency in table grapes. If you have a case study that you would like to showcase, please send us an email here.

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