No. 12/June 12, 1998
Corn Begins Rapid Growth
The cool temperatures this past weekend caused some frost injury symptoms to appear, though there was much less injury in Illinois than in Indiana. In fields where temperatures may have dropped into the high 30s overnight, we are likely to have seen some bleaching and discoloration the next day, especially if the next day had bright sunshine. Temperatures in the low 40s and lower result in "chilling injury" to corn and grain sorghum, which leads to somedestruction of photosynthetic capacity. This loss is temporary, as the plant rebuilds its photosynthetic apparatus within 2 or 3 warm days. The effect on the crop should not be noticeable. Growth slowed greatly during the cool temperatures, however, such that the crop barely added a leaf during the past week. Corn planted in late April at Urbana is at V8 (8 leaf collars visible). It takes about 65 growing-degree days (GDD) to add a leaf stage during vegetative growth, and a day with a low of 50 or less and a high of only 60 provides only 5 GDD, while a high of 70 provides only 10 GDD. Thus a week to add a leaf is not surprising. As warm temperatures return, we should see rapid resumption of growth.
One development that has caused some concern this spring has been "rootless" corn, sometimes associated with "high crown syndrome." Some of this resulted from some rather unusual herbicide effects, but the high crown--nodal roots developing at or near the soil surface--has also been seen in fields without herbicide injury. We're not sure what causes this, but it is usually associated with very rapid emergence from warm soils. Thus we often see it with late planting, which was widespread this year, or with very warm soils at planting, which were also common. In extreme cases, plants may fall over before the nodal roots can develop; and, if the mesocotyl breaks before the plant has nodal roots in the soil, the plant dies.
There isn't much we can do about this problem, though cultivation can help, especially in fields that were tilled and so have some loose soil to move in to the base of the plants. Where rain has fallen to soften the soil, these plants may have developed nodal roots rather quickly, and unless we go a considerable period without rain, they may produce good yields. If cultivation is used, be careful not to cultivate too deeply near the row. Nodal roots grow downward at about a 45-degree diagonal, so they can easily be injured near the plant. In the row middles, deeper cultivation can be done and, in this year with compacted soils, may provide some useful aeration for the roots.
Emerson Nafziger (email@example.com), Crop Sciences, (217)333-4424