New soybean pest discovered in Argentina

Date:03-26-2020

A team of researchers from INTA Rafaela, Santa Fe, confirmed the presence of the soybean stem fly (Melanagromyza sojae), first reported by the Argentine National System of Surveillance and Pest Monitoring (Sinavimo) in soybean crops in Argentina.

The soybean stem fly is an insect native to Asia. Currently, it is present in Russia, Australia, Spain, Brazil and Paraguay. The insect can reduce both the size of plants and number of pods, affecting crop yield. In Argentina, this species was first reported in 2019 in chickpea crops in northern Córdoba.

Researchers from INTA Rafaela-Santa Fe warned of the presence of this species in soybean crops in central Santa Fe. "It was detected in various samplings carried out since January in the INTA Rafaela experimental field, during tests on various batches in the area," said Marcia Trossero (Entomology Specialist at INTA).

According to Sebastián Zuil (Crop Specialist at INTA Rafaela-Santa Fe), there is currently no local information on the management of this species, stating, "Although we detected stem fly larvae by drilling the lower part of the stem near the root, these plants still did not show visible symptoms or a reduction in height or damage to their floral structure compared to healthy plants."

"We will continue to investigate the effects of this insect on the performance of late-planted soybean plants. The results will be available towards the end of the campaign," he added.

In terms of management considerations, Jorge Frana (INTA Entomology Specialist) pointed out that strategies, such as rotation of crops with grasses, early planting and the incorporation of cultivars of long maturity groups, are a good complement and could help minimize the impact of insect pests. "It is important to reduce unnecessary controls during the early stages, so beneficial insects can act as natural factors of mortality," Frana stressed.

Therefore, Zuil recommended the permanent monitoring of soybean batches to determine the presence and distribution of the pest species. "It is important to carry out random sampling of plants and make a longitudinal cut to stems and branches to assess the presence of the pest," he said.

When in doubt, INTA specialists called on farmers to send samples to the Entomology Laboratory of the Rafaela Agricultural Experiment Station or the Rural Extension Agency closest to their town.

“Plants with symptoms must be placed in a polyethylene bag with the date of collection, name of collector, variety, phenological state, date of sowing, cultural work, predecessor cultivation, geo-referenced location of the lot, and any additional information considered important,” Trossero said.

Due to a lack of local information on managing this species and the apparent absence of external symptoms in affected plants, no chemical control practice is recommended on soybean batches. "It is important to remember that, in integrated pest management, non-action is the best action in the face of ignorance," said the specialists.

The original Spanish version of this piece is from Clarín Rural.