Surging Crop Growth, Above Average Rainfall and High Temperatures

Tracy Pell

Jun 08, 2018

It’s only June 8 but crop growth has really taken off already. Corn and soybeans have gone from being planted later than normal to a GDD of 568 ahead of normal accumulation.

Most areas in the Corn Belt have also experienced normal to above normal rainfall. The rain, when combined with above normal temperatures, has shown a surge in crop growth in the past 10 days. Let's look at what's happening inside plants based on their growth stage and our management practices to date. 

What’s happening inside corn plants?

There is a lot going on inside the corn plants at this time. Corn in many places is now at about V4 to V5 (4-5 leaf) stage of growth and 12 to 16 inches in tall. The growing point of the corn is at the soil surface.

Here's a dissected corn plant showing a growing point and small tassel at the tip of the growing point. 

Corn tillers, or suckers, may begin to appear soon, if they haven't already. Tillers generally have little or no impact on yield and are usually variety related. Each corn plant has developed a tassel that can be seen with careful dissection of the plant. The ear is being formed with rows around, or girth, being determined by V6. The number of kernels per row will be established by V12.

What’s happening inside soybean plants?

Most soybeans, like those pictured below, are at V2 to V3 (first or second trifoliate) and 4 to 6 inches tall. Each soybean plant has at least two nodes from which more branches and trifoliates will grow. Expect to see an additional trifoliate to emerge every three to four days under the current environmental conditions.

Look for nodules when examining soybean roots. The nodules contain rhizobia, or nitrogen-fixing bacteria that help supply the plant with nitrogen required to produce desired soybean yields. A yield goal of 70 bushel per acre soybeans, requires 250 pounds of nitrogen. If not supplied by the rhizobia bacteria, the soybeans will need a supplemental commercial source of nitrogen fertilizer.

How fast crops are growing is important for what we apply to them

From what we’ve seen and farmers are telling us, both pre-emerge and post-emerge herbicides have worked extremely well in corn and soybean fields so far in 2018. In some cases, too good.

What I mean by that is that while very few weed escapes have been reported, several reports of herbicide injury to the crop have been seen. What do they look like?

It appears that as plants were growing at a faster rate than normal, the plants absorbed above average amounts of the herbicides that were applied. These corn and soybean plants were likely unable to metabolize the applied herbicides at the usual pace, so plant injury occurred and we can see those symptoms.

In corn, most damage consists of whorls with a yellow flash and some buggy whipping. Many different herbicide modes of action exhibited these symptoms.

Below is Balance® Flexx damage to corn. 

Below, here, is Halex® GT post-applied damage to corn. 

Some soybean stands were reduced by PPO (Group 14) herbicides splashed onto the hypocotyl at emergence. Yellowing of soybean leaves is evident from several herbicide mode of actions applied.

Below is issulfentrazonedamage to the hypocotyl in emerging soybeans. 

Below you can seemetolachlorpost-applied damage to soybeans. 

In a majority of both corn and soybean injury fields, we can expect them to grow out of this injury stage soon with little or no impact on final yield.

Balance Flexx is a registered trademark of Bayer  
Halex GTⓇ  is a registered trademark of a Syngenta Group Company 
Tracy Pell

Jun 08, 2018