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Full Research Article

The Integrated Effect of Insect Net Covers and Pgpr on Pest Infestation, Disease Development and Productivity of Shallots

R
Retno Wijayanti1,*
B
Birgitta Tessa Crossyta2
S
Supriyadi1
R
Retna Bandriyati Arniputri2
N
Nadia Azzahro2
1Departement of Plant Protection, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia.
2Departement of Agotechnology, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia.

ABSTRACT

Background: Shallots were widely utilized by the community with increasing demand but were threatened by pests such as Spodoptera exigua and diseases that spread throughout the year. One possible solution was the use of insect net and the application of plant growth promoting rhizobacteria (PGPR) to reduce S. exigua infestation and disease incidence while enhancing the growth and yield of shallots. The purpose of this study was to determine the effect of applying net covers and PGPR on S. exigua infestations, disease incidence and shallot production.

Methods: The research was conducted in the fields of Ceper, Gemawang, Ngadirojo, Wonogiri, Indonesia, from May-August 2023. The research was carried out using one field with four treatments: beds with the application of PGPR, beds with insect net protection and PGPR, beds with insect net protection only and beds without insect net protection and PGPR (control). Observations were conducted weekly, with 30 samples randomly taken from each bed. The observed variables included, S. exigua population, S. exigua damage intensity, disease incidence, number of leaves, number of tubers and tuber wet weight.

Result: The results showed that insect net covers modified microclimate conditions by reducing air temperature and light intensity while increasing humidity compared to beds without insect net covers. There was no population or infestation of S. exigua (0%) when using insect net covers. The use of PGPR influenced the increased growth of shallots, with the highest average yield recorded in the PGPR treatment (fresh bulb weight: 119.623 g).

INTRODUCTION

Shallot (Allium ascalonicum L.) is one of the most important vegetable crops in Indonesia, widely used by the community as a natural seasoning for cooking and as a traditional medicine (Moldovan et al., 2022; Ruksiriwanich et al., 2022). In addition, shallots are a source of income for farmers in several regions. In line with the development of the market and the shallot processing industry, consumer demand has increased. Consumer demand can be met by increasing the production and quality of shallots. Shallot production in Indonesia in 2021 reached 2.01 million tons, but 20 of the 24 provinces experienced a shallot deficit of more than 50 per cent (BPS, 2022).

The productivity of shallots needs to be increased, but this increase is threatened by pests that attack plants such as Spodoptera exigua (Pangestu et al., 2021). Sudden attacks in large numbers can cause damage of up to 81.90% (Soumia et al., 2020). To date, efforts to manage S. exigua still rely heavily on intensive use of insecticides, which risks the loss of natural enemies and pest resistance. The use of insect netting can be one of the environmentally friendly pest control measures. (Alvarez et al., 2025). This physical technique works by creating a barrier that prevents insect pests from reaching plants, thereby directly reducing infestation levels and the need for insecticide applications. However, the successful implementation of mesh insect nets to optimally increase productivity often requires an integrated approach, as this method does not directly address the threat of soil-borne pathogens or increase plant vigor.

The use of Plant Growth Promoting Rhizobacteria (PGPR) is known to stimulate plant growth and root physiology and reduce disease or damage caused by insects. PGPR promotes plant growth both directly and indirectly, regulates plant growth and plays a role in the soil nutrient cycle and biological control (Zhang et al., 2024). The direct effect of PGPR is based on its ability to provide and mobilize nutrient uptake in the soil. Meanwhile, its indirect effect is PGPR’s ability to suppress or produce metabolites, such as antibiotics and siderophores. PGPR is known to be effective in reducing the incidence and severity of disease (Wiyono et al., 2023). The effect of PGPR on plant nutrition can influence how well plants absorb nutrients or how quickly they grow (Etesami and Adl, 2020). PGPR can increase the production of secondary metabolites in plants. Plants inoculated with PGPR have been reported to increase the synthesis of secondary metabolites that enhance plant survival and competitiveness (Fasusi et al., 2023).

Research related to the use of insect netting and the application of PGPR (Plant Growth Promoting Rhizobacteria) in the management of S. exigua and disease incidence as well as the growth and yield of shallots has not been widely conducted. Therefore, further research is needed to determine its effect on the control of S. exigua, disease incidence and the growth and yield of shallots.

MATERIALS AND METHODS

Study area
 
The research was conducted in Ceper Hamlet, Gemawang Village, Ngadirojo Subdistrict, Wonogiri Regency, Central Java, with coordinates 7°52'38.3"S 111°01'58.5"E from May to August 2023.
 
Material
 
The materials used in this study included Philippine onion seeds, insect netting and commercial liquid PGPR containing Rhizobium and Bacillus bacteria with a cell density of ~108 CFU/mL. The equipment used in this study included a lux meter, a hygrometer, a thermometer and a digital scale.
 
Experimental design
 
The study was designed using one plot with four treatments, namely beds with PGPR application, beds with insect net and PGPR application, beds with insect net application and beds without insect net and PGPR application (control). Each bed was 14 m long, 1.2 m wide, 45 cm high and spaced 30 cm apart. In the insect net application treatment, covering was done immediately after planting shallots. The insect net was installed with a height of 50 cm, length of 19 m and width of 3 m. Observations were made every week and 30 samples were taken randomly from each bed for each treatment.
 
Procedures
 
The research involved preparing the land, planting shallots, installing insect netting, maintaining the shallots and harvesting. Land preparation included sanitizing the land, loosening the soil, making beds and applying basic fertilizer NPK 16:16:16 200 kg/ha. The planting of shallots begins with watering the beds until they are wet, followed by making planting holes measuring 20 cm × 20 cm. The netting is installed by stretching it over the beds. The maintenance of shallots consists of fertilization, irrigation and weed control. The plants and bulbs are pulled out at harvest time and the yield is then weighed. Observations and data collection are carried out every week by observing variables such as, S. exigua population, S. exigua damage intensity, disease incidence, number of leaves, number of bulbs and wet bulb weight.
 
Data analysis
 
The data were analyzed using the pest attack intensity formula, disease incidence formula and T-test.

RESULTS AND DISCUSSION

Pest investation
 
The S. exigua pests found in this study were all in the larval stage (Fig 2). Based on Fig 1, during cultivation, it was found that the use of insect nets could inhibit caterpillar infestation. This proves that insect netting covers can inhibit or reduce pest infestation. (Johnson et al., 2020; Wang et al., 2025). The use of insect net installed on each shallot bed acts as a physical barrier to insect pests. The insect nets are installed to form a tunnel that envelops the beds, thereby limiting the population of insect pests outside the insect nets, such as limiting the number of S. exigua imagoes that will lay eggs on shallot plants. The population of S. exigua is also influenced by environmental factors, such as air temperature, air humidity and light intensity (Maharjan et al., 2022; Zhang et al., 2025). The air temperature in the insect net, namely the insect net and the insect net + PGPR, was lower than the air temperature in the treatment without insect nets, namely the control and the PGPR. Meanwhile, the population of S. exigua caterpillars was found to be high in the treatments without insect netting, namely the control treatment and the PGPR treatment. Optimal conditions for development range from 25-30°C, at which egg hatching and larval survival are maximized; an increase in temperature will reduce these rates (Dash et al., 2024). The use of insect netting lowers the microclimate temperature around the plants, creating conditions that are physiologically less favorable for the development and reproduction of pests (Böckmann, 2022). At the same time, the insect net functions as a physical barrier that limits insect access to plants. Air humidity in the insect net, namely the insect net treatment and the insect net + PGPR treatment, was higher than the air temperature in the treatment without an insect net, namely the control treatment and the PGPR treatment. Meanwhile, the population of S. exigua caterpillars was found in the treatments without insect netting, namely the control treatment and the PGPR treatment. S. exigua can generally live at a humidity of 70-75%, where the temperature is not too high. In the use of insect nets with high humidity, S. exigua was not found. The use of insect nets plays a greater role as a barrier than as a modification of the microclimate in controlling S. exigua pest attacks (Jaba et al., 2020).

Fig 1: Average population of S. exigua and damage intensity.


Fig 2: S. exigua larvae and symptoms of S. exigua infestation.



The highest damage intensity was found in the control treatment, with an average of 9%, while the lowest damage intensity was found in the insect net treatment and the insect net + PGPR treatment, which was 0%. Meanwhile, in the PGPR treatment, the average damage intensity was 8% (Fig 1). The use of insect net gauze can inhibit the egg-laying of S. exigua adult, so that no eggs or larvae were found in this treatment and therefore no damage intensity was recorded. These results are in line with the results of research on shallots by Pangestu et al. (2021) which shows that the average intensity of damage caused by S. exigua between the control treatment and the cover treatment shows a significant difference. Damage caused by S. exigua on shallots is characterized by transparent spots on the leaves due to the consumption of the inner leaf tissue, while the outer epidermal layer is left intact (Fig 2). The extent of plant damage caused by pests can be influenced by the population of the pest. The higher the population of plant pests, the greater the damage they cause. (Bakry and Abdel-Baky, 2023).
 
Incidence of disease
 
Based on observations, two diseases were found to occur: trotol (wilt) disease, caused by the fungus Alternaria porri and moler (blight) disease, caused by the fungus Fusarium oxysporum. The appearance of trotol (wilt) disease was characterized by the presence of white or gray curved spots on the leaves and wilted leaves (Fig 3). In addition, the affected leaves will bend. According to Kim et al., (2022), symptoms caused by the Alternaria porri fungus species appear as sunken lesions that are often elliptical in shape with yellow to pale brown borders. As the disease progresses, the lesions enlarge and produce purplish-brown necrotic lesions on the leaves, which eventually wilt, delaying bulb formation and maturation (Dar et al., 2020). Meanwhile, moler (blight) disease is characterized by twisted or curved leaves, yellowing leaves and wilting plants (Fig 3). These symptoms were consistent with those described above Elvira et al. (2023). These were symptoms visible on plant leaves, including longer pseudostem growth, so that the leaves do not grow upright but grow twisted or curled. This disease, was caused by infection with the fungus F. oxysporum, will eventually cause the plant to be uprooted due to disruption of root growth. This disruption also affects water or nutrient absorption and ultimately causes plant death (Punja, 2021).

Fig 3: Trotol (wilt) and moler (blight) disease symptoms.



The most prevalent disease incident was trotol disease. The incidence of trotol (wilt) disease was more than 50% in all treatments. Meanwhile, the incidence of moler (blight) disease occurred in the control and PGPR treatments. The incidence of moler (blight) disease in the control treatment was 3.34% and in the PGPR treatment was 1.34% (Fig 4). The high incidence of trotol (wilt) disease in all treatments, including those using insect net, indicates that the F. oxysporum pathogen is able to adapt to high humidity conditions under insect net. Increased air humidity actually supports spore germination and infection on leaves, especially if there is persistent dew or leaf moisture (Attri et al., 2024) . However, it provides indirect benefits by stabilizing the microenvironment, making plants healthier and potentially more resilient even when infected with wilt. The presence of PGPR also plays a role in increasing the systemic resistance of plants (Mazuecos-Aguilera et al., 2025; Zhu et al., 2022), Although its effect on trotol (wilt) is not as strong as its effect on moler (blight), because trotol (wilt) is highly dependent on air humidity conditions that remain high regardless of any treatment.

Fig 4: Trotol (wilt) and moler (blight) incidence disesase.



The use of a insect net significantly reduced the ambient temperature compared to conditions without a insect net (Fig 5). This reduction in temperature may play a role in suppressing the development of F. oxysporum, the pathogen that causes moler (blight), which develops optimally at temperatures of 28-32°C (Sharma et al., 2024). Although the temperature under the insect net is still within that range, more stable and less extreme temperature fluctuations reduce thermal stress on plants, thereby increasing their natural resistance. On the other hand, higher humidity under the insect net does not exacerbate moler (blight), because Fusarium is primarily influenced by soil moisture and drainage, not just air humidity. The insect net also prevents excessive direct rainfall and minimizes soil splashes containing pathogenic inoculum onto plant parts, thereby reducing the risk of infection through the roots (Bahri, 2024).

Fig 5: Correlation between temperature and incidence of moler (blight) and trotol (wilt) diseases.


 
Number of leaves
 
Leaves play a major role in plant growth because they cause differences in plant biomass production due to differences in the ability of leaves to photosynthesize (Yue et al., 2019). Based on Fig 6, the use of PGPR can increase the number of shallot leaves compared to other treatments, even when infected with wilt and blight. The microclimate conditions for PGPR use are similar to those for the control, but PGPR plays a role in inducing systemic resistance, fertilizer supplier and produce hormones such as auxin and cytokinin (Dutta et al., 2022). Through the production of growth hormones such as auxin, PGPR affects cell proliferation and new tissue formation, which can produce more leaves. In addition, without shade, plants receive full light intensity that supports maximum photosynthesis rates, producing abundant assimilates for vegetative growth even though some are diverted for resistance responses. Meanwhile, the treatment using insect net resulted in a lower number of leaves compared to the PGPR treatment. Although the insect net treatment prevented plant infection, the reduction in light intensity due to the physical barrier of the insect net became the main limiting factor for photosynthesis (Formisano et al., 2020). The availability of assimilates for leaf formation also decreased. Stable high humidity also reduced the rate of plant transpiration, resulting in less efficient nutrient transport from the roots to the canopy. In the combination treatment of insect nets and PGPR, although PGPR continues to play a role in providing nutrients and hormones, its benefits cannot be optimally manifested because limited light and overly stable environmental conditions actually reduce the physiological drive of plants to grow vigorously (Li et al., 2024).

Fig 6: Number of shallot leaves.


 
Shallot yield
 
Based on Table 1, the results show that the average number of tubers and wet weight of tubers for each treatment differed. These results are related to the number of shallot leaves; the use of PGPR produced more leaves, resulting in more bulbs. Maximum bulb yield was observed in the treatment PGR 0.6% through foliar application (Kale et al., 2021). Additionally, PGPR produces growth hormones such as auxin and gibberellin, which stimulate cell division and the development of storage organs (bulbs) (Shaikh et al., 2022). Although plants in this treatment were exposed to high temperatures and the risk of disease infection, the root system strengthened by PGPR enabled the plants to optimize water and nutrient absorption, allowing more energy to be allocated to tuber formation. In addition, full light intensity without shade support maximized photosynthesis, producing abundant assimilates to be transported to the tubers. The use of insect net resulted in lower tuber yields compared to the use of PGPR due to light as a limiting factor (Singh et al., 2023). Reduced light decreases the rate of photosynthesis, thereby limiting the availability of assimilates for tuber filling. PGPR in this combination continues to contribute to nutrient supply, but its benefits are not fully manifested due to the limited energy from photosynthesis (Khoso et al., 2024; Su et al., 2024). The control treatment recorded the lowest results because the plants faced multiple stresses: high temperatures, low humidity, disease risk and no improvement in soil conditions through PGPR. The plants allocated more energy to survival than to tuber production, resulting in minimal tuber yield and weight (Chen et al., 2025).

Tabel 1: Number of bulbs and wet weight of shallot bulbs.

CONCLUSION

The use of insect nets can modify microclimate conditions. The air temperature in the insect net treatment was lower and the humidity was higher due to the shade. The use of insect nets affected the reduction of the S. exigua pest population, with the result that no S. exigua caterpillar population was found in the insect net and insect net + PGPR treatments. This resulted in low attack intensity (0%) in the treatment using insect net. The use of PGPR affected shallot production, with the highest number of leaves, number of bulbs and wet bulb weight (wet bulb weight: 119,623 g).

ACKNOWLEDGEMENT

This study was independently funded by the authors. The authors would like to thank the Institute for Research and Community Service (Lembaga Penelitian dan Pengabdian kepada Masyarakat) Universitas Sebelas Maret for the administrative support provided under research grand number 862/UN27.22/PT.01.03/2024.

Disclaimer
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of interest regarding the publication of this article.

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    Full Research Article

    The Integrated Effect of Insect Net Covers and Pgpr on Pest Infestation, Disease Development and Productivity of Shallots

    R
    Retno Wijayanti1,*
    B
    Birgitta Tessa Crossyta2
    S
    Supriyadi1
    R
    Retna Bandriyati Arniputri2
    N
    Nadia Azzahro2
    1Departement of Plant Protection, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia.
    2Departement of Agotechnology, Faculty of Agriculture, Universitas Sebelas Maret, Indonesia.

    ABSTRACT

    Background: Shallots were widely utilized by the community with increasing demand but were threatened by pests such as Spodoptera exigua and diseases that spread throughout the year. One possible solution was the use of insect net and the application of plant growth promoting rhizobacteria (PGPR) to reduce S. exigua infestation and disease incidence while enhancing the growth and yield of shallots. The purpose of this study was to determine the effect of applying net covers and PGPR on S. exigua infestations, disease incidence and shallot production.

    Methods: The research was conducted in the fields of Ceper, Gemawang, Ngadirojo, Wonogiri, Indonesia, from May-August 2023. The research was carried out using one field with four treatments: beds with the application of PGPR, beds with insect net protection and PGPR, beds with insect net protection only and beds without insect net protection and PGPR (control). Observations were conducted weekly, with 30 samples randomly taken from each bed. The observed variables included, S. exigua population, S. exigua damage intensity, disease incidence, number of leaves, number of tubers and tuber wet weight.

    Result: The results showed that insect net covers modified microclimate conditions by reducing air temperature and light intensity while increasing humidity compared to beds without insect net covers. There was no population or infestation of S. exigua (0%) when using insect net covers. The use of PGPR influenced the increased growth of shallots, with the highest average yield recorded in the PGPR treatment (fresh bulb weight: 119.623 g).

    INTRODUCTION

    Shallot (Allium ascalonicum L.) is one of the most important vegetable crops in Indonesia, widely used by the community as a natural seasoning for cooking and as a traditional medicine (Moldovan et al., 2022; Ruksiriwanich et al., 2022). In addition, shallots are a source of income for farmers in several regions. In line with the development of the market and the shallot processing industry, consumer demand has increased. Consumer demand can be met by increasing the production and quality of shallots. Shallot production in Indonesia in 2021 reached 2.01 million tons, but 20 of the 24 provinces experienced a shallot deficit of more than 50 per cent (BPS, 2022).

    The productivity of shallots needs to be increased, but this increase is threatened by pests that attack plants such as Spodoptera exigua (Pangestu et al., 2021). Sudden attacks in large numbers can cause damage of up to 81.90% (Soumia et al., 2020). To date, efforts to manage S. exigua still rely heavily on intensive use of insecticides, which risks the loss of natural enemies and pest resistance. The use of insect netting can be one of the environmentally friendly pest control measures. (Alvarez et al., 2025). This physical technique works by creating a barrier that prevents insect pests from reaching plants, thereby directly reducing infestation levels and the need for insecticide applications. However, the successful implementation of mesh insect nets to optimally increase productivity often requires an integrated approach, as this method does not directly address the threat of soil-borne pathogens or increase plant vigor.

    The use of Plant Growth Promoting Rhizobacteria (PGPR) is known to stimulate plant growth and root physiology and reduce disease or damage caused by insects. PGPR promotes plant growth both directly and indirectly, regulates plant growth and plays a role in the soil nutrient cycle and biological control (Zhang et al., 2024). The direct effect of PGPR is based on its ability to provide and mobilize nutrient uptake in the soil. Meanwhile, its indirect effect is PGPR’s ability to suppress or produce metabolites, such as antibiotics and siderophores. PGPR is known to be effective in reducing the incidence and severity of disease (Wiyono et al., 2023). The effect of PGPR on plant nutrition can influence how well plants absorb nutrients or how quickly they grow (Etesami and Adl, 2020). PGPR can increase the production of secondary metabolites in plants. Plants inoculated with PGPR have been reported to increase the synthesis of secondary metabolites that enhance plant survival and competitiveness (Fasusi et al., 2023).

    Research related to the use of insect netting and the application of PGPR (Plant Growth Promoting Rhizobacteria) in the management of S. exigua and disease incidence as well as the growth and yield of shallots has not been widely conducted. Therefore, further research is needed to determine its effect on the control of S. exigua, disease incidence and the growth and yield of shallots.

    MATERIALS AND METHODS

    Study area
     
    The research was conducted in Ceper Hamlet, Gemawang Village, Ngadirojo Subdistrict, Wonogiri Regency, Central Java, with coordinates 7°52'38.3"S 111°01'58.5"E from May to August 2023.
     
    Material
     
    The materials used in this study included Philippine onion seeds, insect netting and commercial liquid PGPR containing Rhizobium and Bacillus bacteria with a cell density of ~108 CFU/mL. The equipment used in this study included a lux meter, a hygrometer, a thermometer and a digital scale.
     
    Experimental design
     
    The study was designed using one plot with four treatments, namely beds with PGPR application, beds with insect net and PGPR application, beds with insect net application and beds without insect net and PGPR application (control). Each bed was 14 m long, 1.2 m wide, 45 cm high and spaced 30 cm apart. In the insect net application treatment, covering was done immediately after planting shallots. The insect net was installed with a height of 50 cm, length of 19 m and width of 3 m. Observations were made every week and 30 samples were taken randomly from each bed for each treatment.
     
    Procedures
     
    The research involved preparing the land, planting shallots, installing insect netting, maintaining the shallots and harvesting. Land preparation included sanitizing the land, loosening the soil, making beds and applying basic fertilizer NPK 16:16:16 200 kg/ha. The planting of shallots begins with watering the beds until they are wet, followed by making planting holes measuring 20 cm × 20 cm. The netting is installed by stretching it over the beds. The maintenance of shallots consists of fertilization, irrigation and weed control. The plants and bulbs are pulled out at harvest time and the yield is then weighed. Observations and data collection are carried out every week by observing variables such as, S. exigua population, S. exigua damage intensity, disease incidence, number of leaves, number of bulbs and wet bulb weight.
     
    Data analysis
     
    The data were analyzed using the pest attack intensity formula, disease incidence formula and T-test.

    RESULTS AND DISCUSSION

    Pest investation
     
    The S. exigua pests found in this study were all in the larval stage (Fig 2). Based on Fig 1, during cultivation, it was found that the use of insect nets could inhibit caterpillar infestation. This proves that insect netting covers can inhibit or reduce pest infestation. (Johnson et al., 2020; Wang et al., 2025). The use of insect net installed on each shallot bed acts as a physical barrier to insect pests. The insect nets are installed to form a tunnel that envelops the beds, thereby limiting the population of insect pests outside the insect nets, such as limiting the number of S. exigua imagoes that will lay eggs on shallot plants. The population of S. exigua is also influenced by environmental factors, such as air temperature, air humidity and light intensity (Maharjan et al., 2022; Zhang et al., 2025). The air temperature in the insect net, namely the insect net and the insect net + PGPR, was lower than the air temperature in the treatment without insect nets, namely the control and the PGPR. Meanwhile, the population of S. exigua caterpillars was found to be high in the treatments without insect netting, namely the control treatment and the PGPR treatment. Optimal conditions for development range from 25-30°C, at which egg hatching and larval survival are maximized; an increase in temperature will reduce these rates (Dash et al., 2024). The use of insect netting lowers the microclimate temperature around the plants, creating conditions that are physiologically less favorable for the development and reproduction of pests (Böckmann, 2022). At the same time, the insect net functions as a physical barrier that limits insect access to plants. Air humidity in the insect net, namely the insect net treatment and the insect net + PGPR treatment, was higher than the air temperature in the treatment without an insect net, namely the control treatment and the PGPR treatment. Meanwhile, the population of S. exigua caterpillars was found in the treatments without insect netting, namely the control treatment and the PGPR treatment. S. exigua can generally live at a humidity of 70-75%, where the temperature is not too high. In the use of insect nets with high humidity, S. exigua was not found. The use of insect nets plays a greater role as a barrier than as a modification of the microclimate in controlling S. exigua pest attacks (Jaba et al., 2020).

    Fig 1: Average population of S. exigua and damage intensity.


    Fig 2: S. exigua larvae and symptoms of S. exigua infestation.



    The highest damage intensity was found in the control treatment, with an average of 9%, while the lowest damage intensity was found in the insect net treatment and the insect net + PGPR treatment, which was 0%. Meanwhile, in the PGPR treatment, the average damage intensity was 8% (Fig 1). The use of insect net gauze can inhibit the egg-laying of S. exigua adult, so that no eggs or larvae were found in this treatment and therefore no damage intensity was recorded. These results are in line with the results of research on shallots by Pangestu et al. (2021) which shows that the average intensity of damage caused by S. exigua between the control treatment and the cover treatment shows a significant difference. Damage caused by S. exigua on shallots is characterized by transparent spots on the leaves due to the consumption of the inner leaf tissue, while the outer epidermal layer is left intact (Fig 2). The extent of plant damage caused by pests can be influenced by the population of the pest. The higher the population of plant pests, the greater the damage they cause. (Bakry and Abdel-Baky, 2023).
     
    Incidence of disease
     
    Based on observations, two diseases were found to occur: trotol (wilt) disease, caused by the fungus Alternaria porri and moler (blight) disease, caused by the fungus Fusarium oxysporum. The appearance of trotol (wilt) disease was characterized by the presence of white or gray curved spots on the leaves and wilted leaves (Fig 3). In addition, the affected leaves will bend. According to Kim et al., (2022), symptoms caused by the Alternaria porri fungus species appear as sunken lesions that are often elliptical in shape with yellow to pale brown borders. As the disease progresses, the lesions enlarge and produce purplish-brown necrotic lesions on the leaves, which eventually wilt, delaying bulb formation and maturation (Dar et al., 2020). Meanwhile, moler (blight) disease is characterized by twisted or curved leaves, yellowing leaves and wilting plants (Fig 3). These symptoms were consistent with those described above Elvira et al. (2023). These were symptoms visible on plant leaves, including longer pseudostem growth, so that the leaves do not grow upright but grow twisted or curled. This disease, was caused by infection with the fungus F. oxysporum, will eventually cause the plant to be uprooted due to disruption of root growth. This disruption also affects water or nutrient absorption and ultimately causes plant death (Punja, 2021).

    Fig 3: Trotol (wilt) and moler (blight) disease symptoms.



    The most prevalent disease incident was trotol disease. The incidence of trotol (wilt) disease was more than 50% in all treatments. Meanwhile, the incidence of moler (blight) disease occurred in the control and PGPR treatments. The incidence of moler (blight) disease in the control treatment was 3.34% and in the PGPR treatment was 1.34% (Fig 4). The high incidence of trotol (wilt) disease in all treatments, including those using insect net, indicates that the F. oxysporum pathogen is able to adapt to high humidity conditions under insect net. Increased air humidity actually supports spore germination and infection on leaves, especially if there is persistent dew or leaf moisture (Attri et al., 2024) . However, it provides indirect benefits by stabilizing the microenvironment, making plants healthier and potentially more resilient even when infected with wilt. The presence of PGPR also plays a role in increasing the systemic resistance of plants (Mazuecos-Aguilera et al., 2025; Zhu et al., 2022), Although its effect on trotol (wilt) is not as strong as its effect on moler (blight), because trotol (wilt) is highly dependent on air humidity conditions that remain high regardless of any treatment.

    Fig 4: Trotol (wilt) and moler (blight) incidence disesase.



    The use of a insect net significantly reduced the ambient temperature compared to conditions without a insect net (Fig 5). This reduction in temperature may play a role in suppressing the development of F. oxysporum, the pathogen that causes moler (blight), which develops optimally at temperatures of 28-32°C (Sharma et al., 2024). Although the temperature under the insect net is still within that range, more stable and less extreme temperature fluctuations reduce thermal stress on plants, thereby increasing their natural resistance. On the other hand, higher humidity under the insect net does not exacerbate moler (blight), because Fusarium is primarily influenced by soil moisture and drainage, not just air humidity. The insect net also prevents excessive direct rainfall and minimizes soil splashes containing pathogenic inoculum onto plant parts, thereby reducing the risk of infection through the roots (Bahri, 2024).

    Fig 5: Correlation between temperature and incidence of moler (blight) and trotol (wilt) diseases.


     
    Number of leaves
     
    Leaves play a major role in plant growth because they cause differences in plant biomass production due to differences in the ability of leaves to photosynthesize (Yue et al., 2019). Based on Fig 6, the use of PGPR can increase the number of shallot leaves compared to other treatments, even when infected with wilt and blight. The microclimate conditions for PGPR use are similar to those for the control, but PGPR plays a role in inducing systemic resistance, fertilizer supplier and produce hormones such as auxin and cytokinin (Dutta et al., 2022). Through the production of growth hormones such as auxin, PGPR affects cell proliferation and new tissue formation, which can produce more leaves. In addition, without shade, plants receive full light intensity that supports maximum photosynthesis rates, producing abundant assimilates for vegetative growth even though some are diverted for resistance responses. Meanwhile, the treatment using insect net resulted in a lower number of leaves compared to the PGPR treatment. Although the insect net treatment prevented plant infection, the reduction in light intensity due to the physical barrier of the insect net became the main limiting factor for photosynthesis (Formisano et al., 2020). The availability of assimilates for leaf formation also decreased. Stable high humidity also reduced the rate of plant transpiration, resulting in less efficient nutrient transport from the roots to the canopy. In the combination treatment of insect nets and PGPR, although PGPR continues to play a role in providing nutrients and hormones, its benefits cannot be optimally manifested because limited light and overly stable environmental conditions actually reduce the physiological drive of plants to grow vigorously (Li et al., 2024).

    Fig 6: Number of shallot leaves.


     
    Shallot yield
     
    Based on Table 1, the results show that the average number of tubers and wet weight of tubers for each treatment differed. These results are related to the number of shallot leaves; the use of PGPR produced more leaves, resulting in more bulbs. Maximum bulb yield was observed in the treatment PGR 0.6% through foliar application (Kale et al., 2021). Additionally, PGPR produces growth hormones such as auxin and gibberellin, which stimulate cell division and the development of storage organs (bulbs) (Shaikh et al., 2022). Although plants in this treatment were exposed to high temperatures and the risk of disease infection, the root system strengthened by PGPR enabled the plants to optimize water and nutrient absorption, allowing more energy to be allocated to tuber formation. In addition, full light intensity without shade support maximized photosynthesis, producing abundant assimilates to be transported to the tubers. The use of insect net resulted in lower tuber yields compared to the use of PGPR due to light as a limiting factor (Singh et al., 2023). Reduced light decreases the rate of photosynthesis, thereby limiting the availability of assimilates for tuber filling. PGPR in this combination continues to contribute to nutrient supply, but its benefits are not fully manifested due to the limited energy from photosynthesis (Khoso et al., 2024; Su et al., 2024). The control treatment recorded the lowest results because the plants faced multiple stresses: high temperatures, low humidity, disease risk and no improvement in soil conditions through PGPR. The plants allocated more energy to survival than to tuber production, resulting in minimal tuber yield and weight (Chen et al., 2025).

    Tabel 1: Number of bulbs and wet weight of shallot bulbs.

    CONCLUSION

    The use of insect nets can modify microclimate conditions. The air temperature in the insect net treatment was lower and the humidity was higher due to the shade. The use of insect nets affected the reduction of the S. exigua pest population, with the result that no S. exigua caterpillar population was found in the insect net and insect net + PGPR treatments. This resulted in low attack intensity (0%) in the treatment using insect net. The use of PGPR affected shallot production, with the highest number of leaves, number of bulbs and wet bulb weight (wet bulb weight: 119,623 g).

    ACKNOWLEDGEMENT

    This study was independently funded by the authors. The authors would like to thank the Institute for Research and Community Service (Lembaga Penelitian dan Pengabdian kepada Masyarakat) Universitas Sebelas Maret for the administrative support provided under research grand number 862/UN27.22/PT.01.03/2024.

    Disclaimer
     
    The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

    CONFLICT OF INTEREST

    The authors declare that there are no conflicts of interest regarding the publication of this article.

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