Emerson Nafziger, the well-known agronomy professor at the University of Illinois, has an interesting article on the impacts of the cool weather and late start to corn and soybeans in Illinois in the U of I Integrated Pest Management “the Bulletin”. He starts out by saying,
Late planting and weather that continues to be cooler than normal into August has many wondering if the corn and soybean crops will reach maturity and harvest moisture within a reasonable time this fall. Crop conditions remain good for both crops, but crop development, including pod formation and filling in soybean and grain fill in corn, remains well behind normal. Corn is 10 days to 2 weeks behind normal, and soybeans are 2 to 3 weeks behind normal. The number of days behind will “stretch” as the weather cools, so late crops get even later. Ten days behind in mid-August will be become 15 or 20 days behind in mid-September, even if temperatures are normal. (read more) …
Currently, the average temperature for the first 12 days of August in Illinois was 1.7 degrees below average. The temperatures over the next five days are expected to be about 6 degrees below average, according to the NWS. The 6-10 and 8-14 day forecasts look a little better with near-average temperatures in northern and central Illinois. However, cooler-than-average temperatures are expected to continue in southern Illinois.
The new NWS monthly and season outlooks for September and the next 12 months will be coming out on Thursday.
Here are the early, late, and average frost and freeze dates for Illinois.
Illinois State Climatologist 