Leaf spot caused by Stemphylium sp. is one of the most limiting diseases in onions, especially under moderate humidity and mild temperatures. Its development leads to leaf necrosis, a reduction in photosynthetic area, and consequently, direct losses in yield and commercial quality.

In intensive production systems, disease pressure can increase rapidly, forcing technicians to seek effective strategies that combine phytosanitary control and sustainability.

With this objective, a trial was carried out to evaluate the effectiveness of biological control with BOTRYBEL, based on Bacillus amyloliquefaciens, under real onion cultivation conditions.

The study was carried out in Llano de Brujas (Murcia) in the cultivation of the Spinning Star variety onion, under open field conditions and clay loam soil.

During the trial period, conditions favorable for the development of the disease were recorded:

• Average temperature: 10 °C
• Average relative humidity: 66%
• Accumulated rainfall: 24 mm

A realistic disease pressure scenario where foliar protection is critical.

Trial design and data

The trial evaluated the incidence of Stemphylium sp. on leaves by comparing:

• Treatment with BOTRYBEL
• Untreated control

Main protocol parameters:

Application

• Method: foliar spraying
• Broth: 500 L/ha

Treatment program

• 3 applications
• 14-day interval
• Dosage: 12 ml/L per application

Phenological stage

• Applications from BBCH 41 to BBCH 45, during the vegetative development of the crop.

Evaluation criteria

• Parameter: Incidence

• Unit: Number of affected leaves

This approach allows for accurate measurement of the real impact of the treatment on disease progression in the field.

The solution: BOTRYBEL

BOTRYBEL is a biofungicide formulated with Bacillus amyloliquefaciens, a microorganism with a recognized ability to inhibit the development of foliar pathogens through multiple biological mechanisms.

Among them are:

• Production of antifungal metabolites
• Competition for space and nutrients
• Protective effect on plant tissue

This biological approach allows for reducing pathogen pressure while maintaining crop functionality, easily integrating into sustainable management programs.

Trial results

The results showed a significant control of Stemphylium incidence compared to the untreated control.

Efficacy of biological control:

75.29% reduction in incidence

This level of effectiveness confirms BOTRYBEL SC’s ability to limit disease development and protect the active leaf area, a key factor in crops such as onions where photosynthesis determines bulb filling.

Under real field conditions, the three-application program achieved:

• Significantly reduce the presence of affected leaves
• Maintain a larger functional leaf area
• To contain the progression of the pathogen during the crop cycle