Beware of Red Onion Failure Caused by Pests

Why Can Leaf Damage Lead to Suboptimal Bulb Yields?

Shallot leaves are not merely the green parts standing above the soil surface. Leaves are the main organs where plants capture light and carry out photosynthesis. The products of this process are then used to maintain growth, form new tissue, and, at later stages, support bulb formation and enlargement. Therefore, leaf damage should be viewed as damage to the plant’s energy source, not merely as a change in appearance.

The impact is strongly influenced by the timing of the attack. If leaves are damaged when the plants are still young, canopy growth may be delayed. If the damage continues when the plants enter the bulb formation stage, the plants must divide their resources between maintaining the remaining tissue and filling the bulbs. Under severe attack conditions, the final result may include uneven bulb size, delayed growth, or productivity that falls below expectations.

However, SGI Friends also need to avoid drawing excessive conclusions. One damaged leaf does not automatically mean that the crop will fail. What needs to be observed is the pattern of damage, the extent of the attack, its development from day to day, the age of the crop, and the overall condition of the field. Therefore, regular monitoring is much more useful than waiting until the damage becomes obvious. The main purpose of monitoring is to determine whether the disturbance is still limited or is continuing to develop so that action can be taken at the right time.

Two Leaf Threats That Should Not Be Treated as the Same

In this article series, two pests will receive particular attention: the leaf miner and the beet armyworm. Both can damage leaves, but they cause damage in different ways. Understanding these initial differences is important because the control strategies in the upcoming POPT articles will be arranged according to the target pest, the stage of infestation, and the condition of the crop.

Leaf Miners Can Attack Even When the Crop Is Still Young

The leaf miner Liriomyza chinensis is one of the important pests of shallots. A publication by the Agricultural Research and Development Agency explains that this pest can damage newly emerging shallot leaves as well as older plants. Its life cycle is approximately three weeks, and a single female has been reported to lay around 50 to 300 eggs. This helps explain why mining trails that initially appear limited can increase when monitoring is delayed.

The same publication reported that leaf miner attacks have caused concern among farmers and, under severe conditions, may be associated with crop failure. This information does not mean that every attack will end in total crop loss, but it is sufficient reason not to consider mining trails on leaves as ordinary damage.

To learn more about the stages of infestation, field symptoms, and specific control strategies, read the follow-up article: The Danger of Leaf Miner Attacks on Red Onion

Beet Armyworm, a Small Pest with Potentially Major Impact

The beet armyworm Spodoptera exigua is also known as one of the major pests of shallots. The larvae can enter and damage leaf tissue, causing the leaves to appear whitish and transparent. A publication by the Vegetable Crops Research Institute noted that previous studies reported yield losses caused by beet armyworm ranging from 45 to 57 percent. The extent of the losses depends greatly on pest population, crop age, environmental conditions, and the accuracy of control measures. Therefore, these figures should be understood as an illustration of potential risk rather than a figure that will necessarily occur in every field.

What is more important for SGI Friends is how to recognize the early signs. Do not wait until extensive leaf damage occurs. In several locations, collecting egg clusters and larvae while the plants are still young has become part of mechanical control. This approach shows that simple actions carried out early can help prevent pest populations from developing uncontrollably.

Do Not Wait Until the Leaves Are Damaged Before Recognizing the Crop’s Enemies

Shallots have a relatively short cultivation period. Therefore, every growth stage matters. Leaf damage at a young age can interfere with canopy formation, while damage that continues during bulb formation can reduce the plant’s ability to supply energy for crop yield. This is the relationship farmers need to understand: pest threats are not only about whether insects are present or absent, but also about when the damage occurs and how quickly it develops.

The purpose of this article is to build awareness before farmers enter the control stage. SGI Friends do not need to immediately conclude that all leaf damage is caused by caterpillars or leaf miners. What is more important is developing the habit of inspecting crops, recognizing symptom patterns, and understanding growth stages. Once the target pest has been identified, control strategies can then be discussed more specifically through the POPT articles.

A discussion of vulnerable stages, egg clusters, larvae, control thresholds, and POPT strategies will be presented in the follow-up article: The Danger of Caterpillar Attacks on Red Onion

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