Rhyssomatus subtilis arrives in Córdoba and worries soybean producers

Rhyssomatus subtilis first appeared in the northern province of Córdoba, Argentina. Until the 2023/24 harvest, the insect was restricted to the Northwest Argentine region (NOA). Its presence, still localized, worries experts, who warn of the importance of immediate prevention to halt its spread. This information comes from the Argentine Association of Direct Sieve Producers (Aapresid).

Roberto Peralta, an integrated pest management specialist, confirmed the presence of the insect in fields near the Malvinas Argentinas region, between Córdoba Capital and Monte Cristo. According to him, it is likely R. subtilis was already present previously, but its damage went unnoticed.

The spread to Córdoba was likely due to the movement of agricultural machinery from infested areas in the NOA. Therefore, the main recommendation is to thoroughly clean equipment to prevent the insect from settling in new regions.

Severe crop damage

Rhyssomatus subtilis is known for the severe damage it causes throughout the soybean cycle. In the early stages (up to V3), adults feed on the cotyledons and shoots, causing seedling death or impaired plant development. In later stages, damage to the terminal shoots reduces productivity, resulting in smaller plants with fewer pods.

During the reproductive phase, the impact is even more severe. Females lay eggs inside the pods during the R5 and R6 stages, the most sensitive stages of the crop. The larvae remain inside the pods for up to 45 days, feeding on the grains and causing significant yield losses. Furthermore, damage to the pods allows the entry of pathogens and moisture, affecting the final quality of the grains.

In situations of high infestation, losses of over 60% can occur and, in extreme cases, practically all plants may show symptoms.

Difficulty in management and control

R. subtilis exhibits cryptic behavior, being more active at night, hiding during the day in plant debris or nearby plants. These characteristics make traditional chemical control difficult.

Experts recommend weekly monitoring, especially at the edges of plots, to detect the pest's presence early. For this, the vertical cloth method and direct observation of the shoots are recommended. It's important to remember that this method captures approximately 60% of the insects present, due to their evasive behavior.

Chemical management can be effective if applied correctly. Initially, seed treatment with insecticides such as thiamethoxam and imidacloprid is recommended, protecting the plants for up to 25 days after sowing. Subsequently, nighttime foliar applications with pyrethroids, neonicotinoids, or isoxazolines are required.

Crop rotation as prevention

One of the main preventive strategies is crop rotation with grasses, such as corn or sorghum, which interrupt the pest's cycle. Monoculture soybeans, on the other hand, favor the insect's proliferation.

Although it does not yet represent a regional problem, the appearance of Rhyssomatus subtilis in Córdoba is a warning. According to Peralta, if there is no immediate preventive action, the plague could become more widespread.