Corn and soybean fields are making progress in Iowa as the calendar flips over and enters June. It's not uncommon to see V4 corn and even some V1 soybeans in fields. In most cases the corn has recovered from the frost or hail that hit in May, but there has been some acres that needed replanting due to large stand losses. The unofficial estimate is less than 1% of the acres. There are some other issues that have popped up this spring. Poor emerging corn and soybeans that were planted the last week of April or first week of May have been reported in some areas. Herbicide-related issues such as poor application timing and planting. "I've even had a case where the soybeans got planted a little too deep," says Mark Licht, ISU Extension field agronomist in west-central Iowa. "There is the occasional moisture stressed corn plants where the roots are developing poorly. So, yes, in west-central Iowa a little rain could be usefull. Central Iowa has got some rains and doesn't look too bad right now."
Assess poorly emerged fields, decide if you need to replant
Some farmers are busy assessing some poor emerging fields to determine if replanting is necessary. Replanting corn the first week of June results in about 90% yield potential, says Licht. A corn stand of 20,000 to 24,000 would result in the same yield potential. So, replanting of corn at this late date would only be economical if the stand is something less than that. Replanting of soybeans is another story. ISU agronomists say a final stand of 100,000 plants per acre would result in optimal yields. Data collected by retired ISU soybean agronomist Keith Whigham suggests that a stand of 75,000 is good enough to avoid replanting. Use the ISU Corn Replanting Guide and Soybean Replant Decisions if you need more information. Postemergence herbicide applications are being applied to cornfields. In some cases, fields are greening up more from the weeds than the corn. Lambsquarter, waterhemp and velvetleaf are the culprits that are often evident. ISU Extension weed control specialist Bob Hartzler has an ICM news article, Timing Restrictions for Postemergence Herbicides in Corn highlighting some of the timing restrictions for spraying corn. When you are counting leaves to stage the corn for spraying, don't forget that the frost damaged corn really has two leaves more than it shows (or however many leaves you lost with the frost). "This could come into play if post applications end up getting delayed," says Licht.
Check uniformity of bean stand, compare treated vs. untreated seed
As of last week 50% of Iowa soybeans were planted, and temperatures in the next two weeks are forecast to be normal to slightly above normal, ideal for getting in the fields and finishing planting. "We need to think about the impact that cold rainy weather may have had on the first beans planted," says David Wright, director of production research for the Iowa Soybean Association. "The cool wet conditions have made this an excellent spring to evaluate the use of seed treatment as a management tool. Now is a great time to check areas where you've planted seed treated with fungicides to check for uniformity of stand, compared to areas planted with untreated seed." Cold temperatures slowed soybean emergence, and repeated rainfalls created saturated soil conditions. Those, coupled with the late, wet harvest which compacted the soil in some areas last fall, may have created a situation for higher incidence of seedling diseases which could thin stands.
Will Sudden Death Syndrome be worse than usual this year?
Sudden Death Syndrome may also be more likely this year, says Wright. "When fields are at the two- to three-leaf stage, you could see yellowing of leaves that could be early signs of SDS," he adds. "Plants generally appear to grow out of it, but then the SDS re-emerges after flowering." He adds, "You will probably see those bean fields where emergence was slow due to cool temperatures will have the greatest advantage from fungicide seed treatments. Areas where nontreated seed was used will likely have greater stand loss due to seedling diseases. But be aware that a uniform soybean stand doesn't necessarily translate to getting a higher yield."