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US Corn Plant-Health at 20-Year Low, Gro Index Shows

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Gro’s vegetative health index for the US corn crop is at one of the lowest levels in more than 20 years, largely a result of a cold and wet start to the planting season. With forecasts now calling for hot and dry conditions across much of the Corn Belt, concerns are mounting that volatile weather patterns at the beginning of the season — should they persist — could present a risk to US crop yields.  

The vegetative health index, known as NDVI, is a satellite-derived measure of plant greenness that can often detect changes in crop conditions more quickly than the naked eye. Gro’s Climate Risk Navigator for Agriculture is able to chart NDVI values weighted specifically for acres planted to corn, as can be viewed here

NDVI, which typically peaks in early August for US corn, is one of several environmental variables used in Gro’s machine learning-based US Corn Yield Forecast Model. The model, which is currently pointing to a year-over-year yield decline, updates on a daily basis and generates forecasts for each county and state as well as a national yield forecast.

The US corn crop is at one of its lowest levels in more than 20 years on Gro’s vegetative health index, as shown by the red line on this chart from Gro’s Climate Risk Navigator for Agriculture.

Cold and wet weather sharply delayed corn planting early in the season to the slowest pace in nine years. Now, most of the Corn Belt is expecting above-normal temperatures and below-normal precipitation for the next two weeks, conditions that will initially be favorable for crop development. 

However, if the same hot and dry weather continues into July and August then crop yields may be negatively impacted. Gro’s Climate Risk Navigator shows NOAA GFS forecasts highlighted specifically for corn-growing areas. 

Acres planted to US corn were already slated to drop by 4% year over year to the lowest level since 2019, as farmers turn to less fertilizer-intensive crops such as soybeans. Any further declines in corn production will tighten the US corn balance sheet at a time when every bushel counts because of squeezed global supplies and higher prices brought on by the Russia-Ukraine war. 

Corn yields in past years have managed to recover from low, early NDVI values, a Gro analysis shows. NDVI values were similarly low at this time of year in 2013 and 2017, for example, but by the end of the season, final national yields had increased to 6.8% and 11%, respectively, above their trailing 5-year average levels. In 2019, however, the corn crop wasn’t able to recover after early poor conditions and yields ended up 3.4% below average. 

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