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Background to avocado dieback:

Dieback is becoming an increasing problem for avocado producers in Spain. The disease is of fungal origin – symptoms first become visible at the ends of the branches with progressive death of the branches and finally cankers in the tree stem.

The disease has always existed in the Malaga and surrounding areas but in the last 3-4 years is now raising serious concerns in other avocado areas in Spain (Comunidad valenciana, Cadiz,etc..). In the past only a few tree branches were infected but now dieback can affects half of the tree and is now dramatically reducing commercial production. 

Avocado dieback is caused by a large family of fungi called Botryosphaeriaceae – all of them can cause the disease in different fruits, such as avocados, grapes or walnut, and they are airborne.

Dieback can be a serious problem in new plantings, as plants sometimes arrive from the nursery with latent infections in the graft. In older trees infections often enter through wounds or when the plant is under stress from harsh environmental conditions (such as caused by global climate change).

Being specialists in plant stress management, Ecoculture Iberica, based in Almeria, decided to look at controlling the disease symptoms by enhancing plant health using the products XStress and Dentamet.

Ecoculture product choices:

XStress is a foliar micro-nutrient fertiliser designed specifically for the control of abiotic and biotic plant stress. It acts by promoting the plant’s natural defences, activating natural metabolic pathways used against all types of stress. XStress naturally helps the infected plant to reduce damaging levels of ROS (reactive oxidative species) in the plant cell. 

By reducing the stress in the plant caused by environmental conditions the fungi finds a healthier plant that is much more difficult to infect.

Dentamet is a specially formulated liquid fertiliser containing copper and zinc complexed with citric acid hydrazide. Its systemic formulation is rapidly absorbed by the plant both by leaf and root.

Although Dentamet is not a fungicidal product, it makes the cellular environment in which the Botryosphaeriaceae develops inhospitable. This prevents any infection from spreading rapidly in the plant.

The combination of both XStress and Dentamet act synergistically, reducing initial infection and reducing fungal spread once infection has occurred. Both products can be used on organic as well as non-organic crops.

The joint application of both products has been shown to be effective in helping to combat the damage caused by the aerial fungus in avocado in local trials.

Avocado dieback trial results:

Between 2021 and 2022, two trials were carried out on farms located in the Malaga area on avocado plants. Plants were between 1 and 2 years old of the Hass variety.

All treated areas showed moderate to severe damage by the Botryosphaeriaceae fungus prior to start of the trial. 

A spray programme of XStress + Dentamet (1.5 litres + 2.0 litres in 1000 litres of water) was applied to the avocado foliage. 4 applications were made monthly in March, April, May and June.

Assessments were made in June, July and October and the mean result of both trials are presented. Untreated control is compared to the spray treatments.

Results: % incidence of fungus in tress

avocado dieback 1024x754

avocado dieback 1024×754

By comparison the plants treated with XStress + Dentamet showed a 36% decrease in disease levels over the same period.

Conclusions:

Avocado dieback is a serious and growing problem, that can infect stressed or damaged plants through aerial infection or remain latent in infected nursery plants until triggered by stress.

The combination of XStress plus Dentamet applied as a foliar spray programme has shown significant ability to reduce the incidence of the disease.

Although neither product is fungicidal, the ability of the XStress to reduce build up of stress related substances helps prevent initial infection and cell damage, while the nutrients in Dentamet helps prevent spread of the fungus within the plant once an infection occurs.

The synergistic effect of both products working together gives avocado growers a new approach to reducing the negative effects of Botryosphaeriaceae even in organic crops.

Copyright Ecoculture Iberica 2024

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