By: Mike Toohill, AgVenture WSC

Bloomington, IL

June moisture was quite variable around the major U.S. corn growing areas. In looking at the observed month to date precipitation map below, my eyes are first drawn towards the hot pink plus areas that had over 10” of flooding rain.

Next, I look for the drier areas that are green on the map (2” or less). The green has shrunk with recent rains. The later planting dates (about 70% of the Illinois corn crop was planted Mother’s Day weekend or later for example) are allowing for increased recovery time prior to pollination in areas with recent rains. As far as mean June temperatures, it was much hotter than normal in most of Illinois, Missouri, and Iowa.

June weather impacts on kernel number/ear: Potential kernel number per ear has two main "components".

Rows around is determined from V-4 to V-6ish and is primarily a function of genetics but stress during determination (compaction, cold and wet or hot and dry) sometimes results in -2 compared to genetic average. Very good corn growing conditions during determination can result in +2. Based on overall neutral early growing conditions, I suspect most hybrids will be close to genetic average as far as rows around.

Potential ear length is usually determined by V-12 to V-15. With the very dry Junes in the I states in 2022 and 2023 I thought we would see more reduction in potential ear length, but that wasn’t the case. It seems like the vast majority of the highest yielding genetics maintain length despite hot and dry June conditions and I expect this to be the case again in 2024.

June weather impacts on kernel size/weight: This is mainly a function of July and August reproductive stage conditions, but I do think that soil saturation and nitrogen loss in the flooded areas will lead to smaller and lighter kernels (if they don’t abort).

Late June (for the pollinating corn) and potential July weather impacts on kernel

number/ear: In the wetter areas, I expect that nitrogen deficiency will reduce the number of supported kernels. Dry soils in combination with multiple 75 degree plus nights is the most common reducer of tip and side kernels. Corn diseases such as Anthracnose, GLS, Tar Spot, Southern Rust etc. can also abort kernels in July and August (worse with warm, cloudy, wet and humid conditions).Kernel abortion can occur through early dent.