Beet Armyworm Control Guide for Scallions: 8 Methods at a Glance

Confronting the "Scallion Pest" crisis through IPM comprehensive management and AI smart alerts—helping farmers cut pesticide use by 20% while boosting yields by 24%.

2026-05-26 ( 2026-06-01 update )

｜ << BACK

Figure: Beet armyworm

The beet armyworm (Spodoptera exigua, commonly known as the scallion pest) is a total nightmare for scallion farmers across Taiwan, and it represents the most severe challenge faced by the Sanxing green onion industry in Yilan in recent years. Possessing astonishing reproductive capacity and drug resistance, its population numbers can grow exponentially, particularly in high-temperature and dry environments.

Beet Armyworm: The Arch-Enemy of Scallions

The threat posed by the beet armyworm to scallions is primarily concentrated during its larval (caterpillar) stage. Newly hatched, early-instar larvae burrow directly into the hollow stalks of the scallion plants, devouring the leaf mesophyll from the inside out.

Infestation Symptoms: Translucent white streaks or elongated patches will appear on the leaves. Eventually, this causes the scallion stalks to lose their nutrient support, turning entirely white and withering away.
Impact on Quality: Beyond devouring the crops, the larvae accumulate frass (insect excrement) inside the hollow stalks. This severely degrades the visual marketability, appearance, and edible texture of the scallions.

Figure: Scallion damage caused by the beet armyworm (Source: Hualien District Agricultural Research and Extension Station)

In recent years, the beet armyworm has become one of the primary drivers of economic losses for scallion farmers. For these growers, effectively controlling this pest has become the key to boosting competitiveness. By leveraging Integrated Pest Management (IPM) and smart agricultur, farmers can achieve early warnings before pest outbreaks occur, reduce labor and chemical pesticide costs, and subsequently increase yields—ultimately realizing the economic benefits of "high yield, premium quality, and low burden."

・・・

Beet Armyworm Control Methods

Method 1: Chemical Pesticides

Spraying chemical pesticides is the most direct and rapid method for combating the beet armyworm. When applying treatments, farmers should follow the principle of "pesticide rotation," alternating between chemicals with different modes of action to prolong the effective life of the pesticides. However, chemical control still has its limitations. If non-systemic pesticides are used, they only act on the surface of the crop, offering very limited control over larvae hidden inside the hollow scallion stalks.

Furthermore, over-reliance on chemical pesticides can lead to drug resistance. Long-term and excessive use risks harming the environment, as well as the health of farmers and consumers, which runs counter to the development of sustainable agriculture.

Method 2: Sex Pheromones

The sex pheromone control method can be implemented year-round. Scallion farmers need to hang approximately 3 traps per fen (approx. 0.1 hectares). Place the pheromone lures inside the traps and suspend them 30 to 50 centimeters above the top of the scallion canopy. This method captures male adult moths with absolute specificity, effectively disrupting reproduction and reducing pesticide use.

Figure: Controlling beet armyworms using sex pheromones (Source: Hualien District Agricultural Research and Extension Station)

Method 3: Microbial Control

Microbial control involves using biopesticides that take effect once ingested by the beet armyworm, leading to the pest's death. This method offers high safety, causes no environmental pollution, and poses no hazard to humans or other non-target organisms. The disadvantages are that its insecticidal effect is relatively slow, it has limited efficacy against mature larvae, and the agents are highly sensitive to ultraviolet (UV) light—making them best suited for application during late afternoons or on overcast days.

The two commonly used biopesticides mentioned are:

Nucleopolyhedrovirus (NPV): The most frequently used microbial control method, featuring a narrow and highly specific host range.
Bacillus thuringiensis (Bt): Ineffective against older, larger larvae; highly suitable for the 1st to 2nd larval instars.

Method 4: Manual Removal

Female moths frequently lay eggs on the surface of scallion leaves. While scouting fields, scallion farmers can manually crush and remove egg masses or pinch off the scallion stalks damaged by larvae. The removed stalks must be carried away and disposed of outside the field.

Because beet armyworm larvae hide inside the stalks and devour the inner leaf tissue, the affected stalks will wither due to nutrient deprivation. Therefore, when you notice a stalk becoming translucent or the tips of the scallions turning white, they must be removed immediately.

Method 5: Environmental Cooling

Beet armyworms reproduce and grow rapidly in hot environments. Farmers can deploy 50% black shading nets over the fields, which can lower the field temperature by an average of 2.5°C to 5°C. This creates an environment that suppresses the reproduction and growth of the beet armyworm while remaining highly favorable for scallion growth.

Figure: Shading with black nets (Source: Hualien District Agricultural Research and Extension Station)

Method 6: Nighttime Water Spraying

Adult beet armyworms mate and lay eggs at night. Therefore, spraying water at night can disrupt their mating behavior and reduce damage, while moderate watering also aids in scallion growth.

According to research by the Hualien District Agricultural Research and Extension Station of the Ministry of Agriculture, the three major guidelines for nighttime water spraying are as follows:

The Golden Window for Nighttime Spraying:
- The peak activity period for adult beet armyworms is between 19:00 and 01:00, during which they mate and lay eggs in the scallion fields. Nighttime spraying not only provides a cooling effect but also effectively disrupts adult mating.
Total Duration Limit:
- The total daily duration of nighttime spraying must not exceed 20 minutes to prevent the scallion leaves from lodging (falling over), becoming mushy, or triggering disease outbreaks. The watering needs to be done in intermittent batches, making it difficult to execute long-term for farmers who have not introduced smart monitoring and automated controls.
Suspension Mechanism:
- If it rains or when chemical pesticides are being applied, the water spraying must be suspended.

Method 7: Smart Agriculture — AgriWeather AI Early Warning System

In collaboration with the Hualien District Agricultural Research and Extension Station, "AgriWeather" has launched the "Scallion Beet Armyworm Early Warning and Response Control Technology." By performing AI analysis on data spanning the past 5 years and combining it with data from AgriWeather weather stations or nearby Central Weather Administration monitoring stations, the system can precisely provide an early warning 10 days before a beet armyworm outbreak occurs.

Working in tandem with AgriWeather's automated irrigation control system, the "intermittent batch spraying method" maintains proper moisture on the scallion stalks to disrupt the pests, while preventing the soil from becoming overly wet and causing bacterial soft rot. This drastically reduces the burden of field scouting for scallion farmers, eliminating the need to constantly rush out to the fields in the middle of the night.

AgriWeather Early Warning System Video: The Ultimate Weapon for Scallion Farming—Predicting Pest Outbreaks 10 Days in Advance, Delivering Even Greater Impact When Paired with Automated Sprinklers!

Figure: AgriWeather's beet armyworm early warning and nighttime automated sprinkler system

By logging into the AgriWeather web portal or mobile app, the system will remind scallion farmers when to set up sex pheromone traps, suggest which control pesticides to use, and pinpoint the optimal time for water spraying. Working in tandem with AgriWeather’s automated irrigation control system, farmers can easily configure the automated spraying zones and frequencies right from their smartphone app or web browser, allowing them to precisely seize the perfect timing for pest control.

Figure: AgriWeather's automated sprinkler irrigation system

👉 Free Trial: https://account.agriweather.com.tw/login
You can check out AgriWeather's tutorial video, "The Complete Guide to AI Early Warning System Operations." We will guide you through the process step-by-step, from registration and logging in to full system utilization.

Control Efficacy of the Beet Armyworm Predictive Model

According to statistics from the Sanxing Farmers' Association in 2025, after implementing this system:

Infestation Rate: Decreased by 10%
Pesticide Volume: Decreased by 20% (reducing application frequency by 3–5 times)
Average Yield: Increased by 24%

Preventing the beet armyworm is no longer just a traditional agricultural practice. Incorporating AI big data analysis from smart agriculture shifts management from a "dependence on chemical control" to a model focused on "ecological balance combined with precision control."

The initial setup costs for the AgriWeather early warning system and automated irrigation control system qualify for the pipeline irrigation subsidy program provided by the Irrigation Agency of the Ministry of Agriculture, offering a maximum subsidy of up to NT$500,000 per person per year.

Method 8: Green Light Illumination

Adult beet armyworms are highly sensitive to light and prefer to be active at night. The Fengshan Tropical Horticultural Experiment Branch of the Taiwan Agricultural Research Institute (TARI) utilizes light to disrupt their opportunities for mating and egg-laying. Experiments have shown that various light colors can be effective, but green light offers the added benefit of promoting scallion growth. Implementing this method adds approximately NT$500 per month in electricity costs per fen (approx. 0.1 hectares).

AgriWeather’s automated control system can fully integrate green light controls for beet armyworm management. This allows farmers to remotely turn the lights on or off directly through the mobile app, eliminating the need to make extra trips to the field.

Table: Beet armyworm control methods

To reduce the damage caused by the beet armyworm to scallions, in addition to utilizing the various methods mentioned above, "area-wide collective control" is the absolute key to success. Because adult moths possess the ability to fly and migrate, relying on a single farm for pest control often yields limited results. It requires the joint action and synchronized monitoring of neighboring scallion farmers to effectively suppress the pest population density from the source.

Furthermore, modern pest and disease management should strictly follow the principles of Integrated Pest Management (IPM):

Economic Injury Threshold: A minimal presence of pests and diseases on crops is permitted. Intervention measures are initiated only when the pest population reaches the "action threshold" that could lead to economic loss, thereby avoiding unnecessary waste of resources and costs.
Prioritizing Non-Chemical Methods: Preference should be given to eco-friendly techniques such as physical, biological, or environmental controls. If chemical agents are necessary, they should be selected based on having the minimal impact on ecology, human health, and the environment, thereby fulfilling the goals of agricultural sustainability and food safety.

・・・

Beet Armyworm Control FAQ (Frequently Asked Questions)

Q1: Is nighttime water spraying effective? Won't it cause the scallions to lodge (fall over) or experience root rot?
A1: It is highly effective. Nighttime water spraying primarily acts as a physical disruption to adult mating. To prevent root rot and lodging, the key lies in "intermittent batch spraying." Each spraying session should not exceed 5 minutes, and the total daily duration must be kept within 20 minutes. This method can be paired with AgriWeather’s automated irrigation system to ensure pests are controlled without triggering crop diseases.

Q2: Why is "area-wide collective control" emphasized?
A2: Adult beet armyworms possess exceptional flight capabilities. If control measures are restricted to a single farm, adult moths from neighboring fields will still fly in to lay eggs. By utilizing the professional data from the AgriWeather Early Warning System, farmers can synchronized their efforts—such as simultaneous water spraying, pesticide application, or hanging sex pheromone traps—before an outbreak occurs, suppressing the pest threat right from the source.

Q3: Are there subsidies available for AgriWeather's early warning system for beet armyworm control?
A3: Yes. AgriWeather focuses on smart agricultural solutions, providing precision irrigation and field early warnings through environmental sensors and automated sprinkler control systems. With the automated sprinkler system, farmers can configure settings via the platform to irrigate crops at the right time, with the right amount of water, and with high precision, thereby saving labor and time. To support this, the Irrigation Agency of the Ministry of Agriculture has been offering a maximum subsidy of up to NT$500,000 per person per year since 2024 (Year 113 of the Republic). The subsidized items include:
Irrigation Facilities: Perforated pipes, sprinklers, micro-sprinklers, and drip irrigation tubes.
Irrigation Regulation and Control Facilities:Power Equipment: Motors, engines, and water pumps.
Water Storage Facilities: Water storage tanks made of aluminum alloy, plastic, or stainless steel.
Control Facilities: Automated control systems, micro-climate regulation systems, liquid fertilizer injectors, filters, and other regulatory facilities compatible with irrigation systems.

Q4: How do I use the AgriWeather Early Warning System?
A4: You can refer to the instructional video produced by AgriWeather, "The Complete Guide to Operating the AI Early Warning System." We will guide you step-by-step through the entire process, from registration and logging in to daily operation.

"Smart agriculture empowers farmers and serves as an ultimate shield against climate change and pest outbreaks. With precision early warnings, we safeguard the authentic flavor of Sanxing scallions while nurturing the health of the earth."

・・・