By Iowa Soybean Association
Responses collected by Allie Arp, ISA research communications specialist
Mother Nature may be wreaking havoc on planting intentions this spring — but she’s no match for Iowa Soybean Association (ISA) regional agronomists.
ISA’s Matt Hoffman, Brett McArtor and Anthony Martin fielded planting questions from soybean farmers on replant windows, herbicide options and how long soybeans can hold their breath.
I planned on applying a pre-emergent herbicide but couldn’t get in the field. What are my herbicide options?
While using a pre-emergent is an important component of a weed control program, you still have options when it comes to post-emergent herbicides. Which specific herbicide you choose should depend on what you have used in the past and the control you need. Start by scouting to see which weeds are present. Rotate modes of action and use multiple modes of action when possible. Apply in appropriate conditions, at the labeled rate and before the weeds get too big. If you have had resistance problems in the past, be prepared to get that iron out and mechanically remove weeds before they set seed. — Matt Hoffman, regional agronomist for northwest Iowa
What are the ideal soybean populations and planting depths?
Soil conditions, planting date and other factors play a large role with differences occurring even within Iowa. A final harvest population of approximately 100K plants per acre has shown to be the most profitable in Iowa, so planting populations should be higher to achieve that final stand. ISA research has found that planting after May 20 requires higher planting populations as compared to planting dates before May 20. Planting depths should generally be in the 1-1.75 inch range, but again, will depend on soil conditions at planting. Results will vary field to field, hence the importance of On-Farm Network replicated strip trials. Contact your regional agronomist next season to see what works best in your fields. — Matt Hoffman
What is the window to replant corn and beans?
Making the decision to replant a field of corn or soybean can be a tricky one. Two factors ultimately make the decision: remaining plant population and date. If you refer to Iowa State University’s (ISU) “Corn Production Guide Book” there is a handy chart that gives you an idea of yield potential by planting date and population. Unless the remaining corn stand is less than 10,000 plants/ac replanting corn after June 1 won’t gain you much in terms of yield.
Soybeans are a little trickier because they are more likely to branch out and make up for lost stand. Weed control ends up being a major factor when considering soybean replant. Once the decision is made to replant, depending on stand, replant up until July 1 can provide a yield benefit. However, replanting into an existing stand is not recommended. It might seem like a quick fix to thicken up the stand, but the replanted plants will act more as weeds rather than contribute to yield. — Brett McArtor, regional agronomist for southern Iowa
When does it make sense to switch maturities for both corn and beans?
For corn, hybrid maturity is an important consideration when replanting. This can influence grain moisture content at the end of the season. A hybrid maturity change is recommended when replant is occurring in late May through June.
For soybean, there is no need to change maturities unless replant is occurring beyond July 1. — Brett McArtor
What level of nitrogen loss am I looking at because of the rain?
There is not a single answer to this question so I’ll answer with a simple, “it depends.” This is a tough question to answer because it depends on what was applied, when it was applied, the location of the farm (rainfall totals, soil types) and other factors. With all of these factors, the answer for someone in southwest Iowa will be different than someone in northeast Iowa. If you are worried about nitrogen loss on your farm, I would recommend utilizing one of the nitrogen tools available online, such as ISA’s Risk of Late-Season Nitrogen Deficiency tool. While this tool won’t tell you exactly what your losses were, it can use rainfall totals and management information to help identify areas with a risk of being nitrogen-deficient at the end of the season. — Anthony Martin, regional agronomist for northeast Iowa
How long can soybeans survive under water?
Any sort of extended flooding on soybean is going to negatively affect germination to a varying degree. If you are looking for a specific number of hours or days, 24-48 hours underwater is going to be the interval where germination rates begin to drop and farmers might need to consider replanting areas of the field.
Side note, given the amount of rain and cooler temperatures that we’ve seen this spring, farmers will want to keep an eye on disease levels and consider adding a fungicide to their program — if they weren’t already planning to use one. — Anthony Martin
Have a question that isn’t answered here? Email your regional agronomist or contact firstname.lastname@example.org for additional information.