Mississippi has been blessed with excellent growing conditions thus far this season, but it is a little early to assume the 2004 corn crop is already made. Although this corn crop was planted early and has had relatively few problems, there could be some management decisions growers will need to make before the crop is in the bin.

Despite plentiful rainfall in June in most areas, we may need to finish out the corn crop with supplemental irrigation, if we experience normal July rainfall. A common irrigation error is terminating irrigation before physiological maturity (black layer) occurs. Although this crop is slightly earlier than normal, most corn likely will not reach physiological maturity until mid- to late July — depending upon the latitude and planting date.

Premature irrigation termination will accelerate maturity, prohibiting kernels from reaching their full potential size and weight.

Although kernels appear somewhat mature and corn water use begins declining, the dent stage is too early to terminate irrigation. Potential kernel weight is only about 75 percent complete at the dent stage. Thus, termination of irrigation at the dent stage can reduce grain yields as much as 15 to 20 percent when hot, dry conditions persist.

Corn producers can monitor kernel maturity for scheduling irrigation by observing the progression of the milk-line between dent stage and black layer. The milk-line is the borderline between the bright, clear yellow color of the hard seed coat outside the hard starch layer and the milky, dull yellow color of the soft seed coat adjacent the dough layer.

To observe the milk line, break a corn ear in half and observe the cross-section of the top half of the ear (the flat side of kernels opposite the embryo). It generally takes about 20 days for the milk line to progress from the kernel tip, down to the base.

Growers can use this guideline to estimate the approximate maturity date. For instance, if the milk-line is half-way down the kernels, it will take about another 10 days to reach physiological maturity. Thus, the field needs supplemental irrigation water to provide moisture for 10 more days.

Harvest timing may also be more important this season. The large amount of soybeans expected to come out of fields during August will likely compete for combine and elevator capacity.

Although unharvested corn endured tremendous rains during the 2001 and 2002 harvest seasons quite well, the potential for harvest loss caused by lodging is considerable, particularly if high winds accompany late-summer storms.

Furthermore, if high populations of southwestern corn borers develop this season, they may promote substantial corn harvest losses, if corn harvest is delayed.

Southwestern corn borers can cut stalks down by tunneling within and chewing a groove internally around the rind of the stalk a few inches above ground level. This “girdling” action predisposes stalks to nearly certain lodging under moderate wind.

Those stalks and the connected ears are nearly impossible for a combine to pick up.

The girdling damage normally begins appearing about 20 days after egg laying. Thus, since the third generation southwestern corn borer moth flight normally occurs in early August, producers should try to finish harvesting non-Bt corn fields by late August.


Erick Larson is a grain crops specialist with Mississippi State University. e-mail: elarson@pss.msstate.edu