Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue Office: 712-792-2364
Carroll, IA 51401 Cell: 712-249-6025
Email: vagts@iastate.edu Fax: 712-792-2366

Crop Development
Once again I’ve changed the format of displaying the accumulated GDD’s for corn (Figure 1). As before, Figure 1 has accumulated GDD’s on the Y-axis and Date of Planting on the X-axis. The line with the "Squares" tracks GDD’s for the southern area of my eight county region and the line with the "Diamonds" tracks GDD’s for the northern area. The top line (-) shows estimated accumulated GDD’s in seven days (June 11). For example, corn planted on April 20 (currently V6 to V7) should be at the V8 leaf stage on June 11.

As mentioned in earlier newsletters, the growing point (in the V6 corn) is above ground. The ear is developing in the growing point of the corn at V4 (corn planted from April 30 – May 5). As the earliest planted corn reaches V8 (predicted to be on June 11 for April 20 planted corn), the tassel will begin to be formed.

Soybeans: Soybean emergence continues to be slow with the cool, moist soils. Seedling disease from an array of pathogens is a possibility under the current stressful conditions. If a field is under attack from seedling disease, identification of the actual pathogen is generally not important. If replanting is necessary, consider a seed treatment only if the forecasted environmental conditions continue to be stressful and/or if the seed quality is marginal.

Assessing soybean stand loss (John Holmes, ISU Extension Crops Specialist)
The key things to remember when evaluating soybean stands is that research has shown (1) that roughly half a stand will produce yields equal to a full stand if weeds are controlled, and (2) that it’s critical to evaluate plants for bruising (hail) and/or seedling disease. When soybeans are planted in the first week of June they normally produce 90 - 95% of typical yields -- depending on the fall weather. Soybeans will develop from axillary buds located at each node in the plant if the top has been cut off. Watch for regrowth from the buds when evaluating the stand. Acceptable stands are 4 - 4.5 beans/foot of row in 30-inch rows, 3-4 beans/foot of row in 15-inch rows, and 80,000-100,000 plants per acre in drilled fields. Losses from 18 inch gaps or less are insignificant. When gaps range from 2-3 feet, yields are reduced by about 5%.

From ISU Extension Publication Pm-1851, June, 2000

If soybeans are going to be re-planted, use the same maturity as was planted originally. The only exception would be for very full season varieties. If a very full season maturity group was used originally, you may want to consider shifting to a slightly earlier maturity group. Don’t make dramatic shifts to an earlier variety --- it will cost you yield especially in a late fall.

Additional considerations:

• Planting or drilling directly into the existing stand without destroying the previous stand has given mixed results through the years -- more often bad than good.
• Late planted soybeans will be shorter than when they are planted in May, drilling helps establish the canopy quicker thus shading weeds & utilizing sunlight more efficiently.

Pest Management
Several fields across the area have had problems with herbicide carryover (last year’s applications) and/or herbicide injury from this year’s applications. Much of the injury that I’ve seen has been a result of the adverse environmental conditions that the area has experience the last couple of weeks. We need to continue to use caution when applying POST herbicides to corn (or soybeans) and wait (if possible) until the crop plant is not under stress.

As fields become weedy due to delayed herbicide applications, they become likely places for many insect pests to develop, particularly Armyworm. When the weeds are sprayed and die, the feeding larvae move to the crop plants and may inflict much damage. Therefore, when making herbicide applications to excessively weedy fields, be on the lookout for insect pests following the application