Yellow Corn
Those farmers that are fortunate to not have flooded
fields at this point may begin to notice areas of their fields with a mixture of green and yellow corn. The yellow and often smaller corn is most likely the result of a combination of three factors: limited root growth, lack of nutrient availability and the soil environment. Poor root development began with the prolong period of cold/wet weather after planting. There just weren’t enough heat units to promote active root or shoot growth. Some fields were even planted a bit on the "moist" side. This has lead to side-wall compaction in some cases. Restricted roots cannot take up or grow in the direction of available nutrients. Water-logged soils can also deplete the root zone of much needed oxygen further weakening the plant. If you’re not convinced, dig up a healthy, green plant nearby and compare root systems. The healthy plant’s roots have a balanced symmetry of nodal and secondary roots – far larger than their yellow companions.
Yellow plants may also be lacking important nutrients. With the cold/wet conditions we’ve experienced this past spring, planters with a plugged starter fertilizer unit have been very noticeable across certain fields. The use of starter or pop-up fertilizers in cold springs often helps give the young plants some extra vigor to withstand those stresses. This is why it is often recommended to use a starter fertilizer containing nitrogen in no-till systems. Also, with the abundant rainfall nitrogen can be lost through either denitrification (ponding/saturated soils) or leaching (sandy soils). Side dressing with nitrogen this year will no doubt help "bring back the green" in many fields across the region. Just the opening of the soil with the applicator knives can quickly improve the look of a struggling field of corn. On very light, sandy knobs where the CEC of the soil is low to begin with, heavy rain can leach the magnesium out of the root zone. Improved growing conditions, i.e. better root growth, and a shot of nitrogen will help green-up these knobs.
Weeds Marching Onward
The weeds haven’t slowed down with the rainy weather! In fact, many corn fields are now very woolly with weeds that weren’t even noticeable a few days ago. Again, heavy rainfall may have quickened the dissipation of the soil-applied herbicides. Roundup should be very effective on these actively-growing weeds, but we’ll start losing yield as four-inch or larger weeds begin competing with the crop. Grasses are particularly troublesome as they compete for the soil nitrogen. Bottom line – spray as soon as field conditions permit it. Walking fields today I was alarmed as to how brittle the corn plants were. Recent warm/hot weather has jump-started this crop and lengthened the internodes making them susceptible to snapping off. Be careful using growth regulator herbicides, i.e. 2,4-D, dicamba, during this rapid growth. Also, note the "age" or growth stage of the plant. For example, a V6 plant is much smaller than normal this year due to its slow start. This will have an affect on applying some post herbicides. Check the label for crop stage restrictions.
Have a safe planting season
Dan Childs, Agronomist
