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Spiroplasma bacteriosis keeps Argentine corn in suspense

Since its detection in the 90s, when it was considered a secondary pest, today, Spiroplasma surpasses other relevant pests and diseases of this crop.


Effects of Spiroplasma bacteriosis on Argentine corn.

In this campaign, Spiroplasma is being the main phytosanitary threat to corn production in the country, while its vector, the leafhopper, rose to fame as a key pest of the crop. This insect (Dalbulus maidis) is one of the fundamental gears of a complex pathosystem that, among other viruses and bacteria, includes Spiroplasma kunkelli, which causes stunting of corn.

Past and present of Spiroplasma: advance from north to south

This disease was first seen in Argentina in the 90s, in the Northwest of the country, and then spread to the northeast of Argentina until reaching the center of the country. At that time it was considered a secondary disease, until in the 2006/2007 campaigns and then in 2018/2019 and 2019/2020 it gained relevance, especially in the center of the Chaco, causing significant losses in corn.

Faced with this problem, the Pest Management Network (REM) of the Argentine Association of Direct Sowing Producers (Aapresid), in its mission to promote actions to address the issue, began to survey the disease and its vector in more than 29 million hectares throughout the country.

The REM maps of the 2021/2022 campaign showed the pest restricted mainly to late corn in the northeast and northwest of Argentina (Chaco, Sgo del Estero, Tucumán and Salta) and some departments in northern Santa Fe. The survey also showed that treatments were necessary in 32% of the plots in the northeast and 11% in the northwest, even exceeding 50% in specific departments of Chaco and Salta.

The thick 22/23 arrived, and the results of the surveys set off alarms: Dalbulus maidis and Spiroplasma appeared as the most important pests in late corn according to Aapresid producers in northeastern Argentina (36% and 23%, respectively). The pressure of this duo was such that it surpassed other relevant pests of the crop, such as Spodoptera, Helicoverpa or Dichelops, and frequent diseases such as stem and root rot and blight.

In the current campaign, preliminary reports show a worrying advance in its distribution throughout the Argentine productive area.

Future of Spiroplasma: Córdoba and Santa Fe in the eye of the storm

A 2019 study already warned of the great adaptation of the leafhopper in practically all of Brazil and northern Argentina. The same publication also predicted a shift towards the north of Córdoba and Santa Fe by the year 2050, under a global warming scenario.

The researchers referred to the fact that the future scenario of higher temperatures could increase the incidence of the disease in these areas. What no one expected is that this direct impact of climate change on the distribution and severity of pests was going to arrive sooner than was assumed.

In search of solutions

To face this challenge, the REM works together with different actors and thematic corn networks - NEA Corn Network, Aapresid Late Corn Network and the Southern Corn Network. In this way they seek to closely monitor the evolution of both the vector and the disease in different strategic sites.

Beyond individual practices such as avoiding the presence of corn guachas in the plots, according to the Network, it is crucial to collaborate regionally to coordinate joint decisions. For example, concentrate planting by region (avoiding staggering), eliminate loose corn from the plots, collect minute-by-minute data on each plot and carry out surveys and controls at the regional level.

Faced with a future with many uncertainties, they emphasize the importance of collaboration between producers, companies, science and the State, as well as the need to improve the genetic supply of corn. “The dissemination of information, networking and the adoption of proactive measures are the key to finding effective and sustainable solutions,” they maintain from the REM.

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