June 8, 2007

This week's CropWatch includes two stories on assessing early-season hail damage on corn and the effect of stand loss on corn yields. One article is by Kraig Roozeboom, Crop Production and Cropping Systems Specialist at Kansas State University, and reprinted with his permission. The other is by UNL Extension Crops Specialist Bob Klein.

The producer is often confronted with whether to replant or plant another crop after hail, flood or other events which damage the crop and/or reduce crop stand. Some fields suffered so much damage from this spring's heavy rains that some tillage or other operation will be needed to fill in the washouts before replanting. Where soil erosion is minor, sweep tillage may be used while still maintaining much of the crop residue. In many situations enough soil will need to be moved that all crop residue will be destroyed, leaving the soil more susceptible to wind and water erosion.

The producer also must consider such factors as weed management, diseases and insects and how the crop will be affected. If the crop is herbicide tolerant, this helps in being able to manage weeds with reduced crop competition as a result of reduced plant populations, skips, delayed crop canopy, etc. Insect problems can increase especially in non Bt hybrids by delaying plant growth. Also, disease problems usually increase because of damage to the plants.

Table 1. Agronomic performance of short season corn hybrids planted mid- to late-June and harvested December 10, 1992 at North Platte, NE. (Nordquist)
		Yield, bu/ac		% Moisture		% Broken		wt/bu
		Date planted
Hybrid	Days*	6/16	6/23	6/16	6/23	6/16	6/23	6/16	6/23
1	85	100	71	12.9	15.7	2	12	54.0	50.0
2	87	130	104	13.6	16.5	0	0	55.5	53.0
3	94	119	91	15.4	18.0	5	6	54.0	52.0
4	99	133	92	16.1	24.3	2	0	48.7	44.5
5	100	155	120	19.7	27.5	8	0	46.5	46.5
6	105	134	101	18.1	22.4	5	7	50.0	46.5
*Comparative Relative Maturity Days

If the damage to the corn crop was enough to consider replanting or planting to another crop, be aware of potential problems. If the damaged crop was Roundup Ready corn, make sure that the previous crop is destroyed or volunteer corn could become a major problem. If the corn crop was conventional and Roundup Ready corn or Roundup Ready soybeans are planted, it would be easy to control the conventional corn.

If Roundup Ready soybeans are planted after Roundup Ready corn and the corn before it was damaged at when the corn was taller than 18 inches, treatments such as Fusion or Select may not adequately control the regrowth.

Both soybeans and grain sorghum can be planted later than corn without giving up as much yield. Some growers will be able to use Lumax for weed control in grain sorghum this year. Check label.

Before replanting or selecting another crop always check for replant options and rotation restrictions for any herbicide that may have been used on the field.

What is the yield potential for late planted corn? In 1992 Paul Nordquist conducted research at North Platte (see Table 1).

Bob Klein
Extension Crops Specialist
West Central REC, North Platte