The Van Trump Report

What You Need to Know About the “Leafhopper” Plaguing Argentina’s Corn Fields

Argentina’s corn growers have been fighting a plague of “leafhopper” insects that have led to dramatic downgrades to production estimates. The country earlier this year was headed toward a record corn crop but the stunt disease spread by the insects has caused those forecasts to plunge. The question now is, how much more of the crop will be lost before farmers can get it out of the fields?

The corn leafhoppers spread a disease known as “corn stunt disease” caused by a Spiroplasma bacteria that is actually transmitted by leafhoppers in the field, according to Dr. Darcy Telenko, Associate Professor of Plant Pathology at Purdue University. Experts say the bug is endemic to Argentina and appears to have built numbers in the past three hot and dry La Niña years. Then, an extremely wet and humid April provided the ideal conditions for corn stunt disease to spread.

Corn stunt disease can decimate the maturing corn plant, resulting in weighty yield penalties and even complete crop failure in severe outbreaks. Characterised by the development of small ears with missing kernels and reduced kernel weights, the disease poses a considerable threat to crop yields. Compounding the challenge is the difficulty in visually identifying infected fields from a distance.

According to reports, this season’s favorable environmental conditions have led to the worst infestation in recent memory in the northern provinces and the worst ever for central Argentina. It has also spread to regions further south, such as Santa Fe and Cordoba, where it has not previously been a problem.

The Buenos Aires Grains Exchange just recently knocked back its estimate for Argentina’s 2023/24 corn harvest to 46.5 million metric tons (MMT), down from its February projection of 56.5 MMT and versus the USDA’s April estimate for 55 MMT. The exchange said that harvest in the core region was nearly complete but as of May 1, just over 22% of the late-planted crop in more southern corn areas had been harvested. It also noted continued reports of lower-than-expected yields and a significant increase in non-harvestable areas.

Additionally, due to stress, heavily affected corn has ended its growing cycle prematurely, which will lead to an earlier start to the harvest in these areas. The exchange estimated that for some areas, an average of some 17% of the planted area may not be harvestable. The full extent of the losses probably won’t be known until harvest is complete, which typically finishes up in July and August but this year, who knows.

Corn growers in Argentina are already concerned about the potential impact on 2024/25 production as well. Apparently, the leafhopper does not die off once the corn is harvested. Instead, it looks for host plants, such as wheat, oats, barley, rye, grasses and other pastures, in which it can survive and breed over the winter before attacking again when the next corn crop emerges. If it is a warm winter, survival rates and next season’s risk will subsequently be high, which could lead farmers to ditch corn in favor of other crops.

USDA’s Foreign Agriculture Services (FAS) post in Buenos Aires says the cut in area in MY 2024/25 is expected to be primarily in the central/northern region of Argentina where the disease hit worse. However, FAS is also projecting a minor cut in the most productive area, which  goes from south-central Cordoba and Santa Fe provinces down to Buenos Aires, where so far symptoms of the disease have been found in some areas but with somewhat minor negative impact on production. (Sources: Bolsa de Cereales, USDA, Reuters)

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