The developing U.S. corn crop has experienced considerable stress in recent weeks, as excessive rainfall in late spring gave way to sudden dryness and increasingly hot conditions in early June. A sudden transition from very wet to very dry weather in early summer creates a challenging environment for corn, as the early wetness promotes shallow root systems that can prove to be inadequate in rapidly drying soils.

The figure below shows that rainfall was nearly zero in key central Midwestern growing districts during the two weeks ending June 12. The sudden onset of dry weather coincided with rapidly developing heat in the Upper Midwest, as temperatures reached 90°F in Minneapolis on June 2 and 96°F on June 10; the month of June so far has been the warmest since 1956 in Minneapolis. The second figure below illustrates the wide extent of above-normal growing degree days for June 1-18.



As hot and dry weather intensified in early June, the CropProphet corn yield models reacted by showing steady decreases in expected yield in many areas, and the U.S. yield forecast dropped to about 165 bushels per acre (see figure below). Corn prospects are now quite poor in the eastern Corn Belt, and this is where the satellite indications of crop vitality are considerably worse than normal (see figure below). Overall there has been a notable worsening of satellite indications in recent weeks, as 86% of the top corn growing counties now show below-average NDVI, compared to only 50% at the end of May. However, some of this deterioration may reflect regional delays in corn development this year owing to widespread replanting, and so the satellite appearance of the crop may improve as replanted fields mature.



The sudden emergence of dry weather at the end of May raised concerns that drought may take hold of the central U.S. this summer, but that possibility now appears less likely as a result of significant rainfall in the past several days combined with a relatively wet forecast for coming days and weeks. Rainfall totals of 1-3 inches have occurred quite widely in the past week, and the CropProphet U.S. yield forecast has already recovered slightly. In particular, significant improvements occurred in parts of the eastern Corn Belt in the latest daily update (see figure below), and this trend would be expected to continue if wetter weather persists, as seems fairly likely.

The next update to the corn commentary will occur on July 5.