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Back to the basics of seed selection

By Staff | Nov 2, 2018

Mike Witt, Iowa State University Extension and Outreach field agronomist for west central Iowa, looks over a seed guide with Alexis Hooper, of Grand Junction. Hooper is attending women in agronomy sessions to help gain the knowledge she needs to run her family’s farm.



JEFFERSON – A women in agronomy class held last week at the Greene County Iowa State University Extension and Outreach office in Jefferson focused on 2019 corn and soybean seed selection.

Mike Witt, ISU Extension field agronomist for west central Iowa, led the discussion about the priorities of seed selection and how to decipher a seed guide.

Know who you are buying from

Witt said one of the first steps in the seed buying decision-making process is to know exactly who you are buying seed from.

“One of the things I find fascinating is seed brands and how brands have evolved and changed over the years,” he said. “Brand names don’t tell the ownership of the seed. Not even close and 2018 had the biggest changes to date.”

Although independent seed companies can still flourish, most seed comes from larger companies. Oftentimes, Witt said, producers think they are purchasing their seed from those independent companies, when it is just buying the brand – a brand owned by large companies.

This past year brought the retirement of several brands of seed that producers found themselves comfortable with purchasing. Witt said companies took a step back and decided to cut back with brands and condense them down.

“That has ruffled some feathers with farmers. They like to buy certain bags and it’s a force of habit,” he said. “Brands get a little complicated, but they come and they go. There are still choices out there.”

What are you planting?

Another first in the seed decision making process is to determine what type of crop are you planting.

Witt said land use in Iowa is primarily corn and soybeans. Deciding what crop to put on what acres is crucial.

“When deciding what to plant, there are benefits to considering a corn/soybean rotation,” he said.

Some of those benefits include the potential of improved soil organic matter, greater soil structure, pathogen pest control by breaking the cycle of the pest-host relationships, and soil nutrients – different crops either add or subtract nutrients from the soil and they require different rates of nutrients and weed management.

“Those are all benefits of a corn and soybean rotation,” said Witt.

Why would a producer choose to not use a corn and soybean rotation?

“The main reason could be the profitability potential,” he said. “That’s one of the main reasons why some people rotate and some people don’t.”


Once selecting which crop you are wanting to plant, Witt said to consider your priorities.

“What is the most important to you?” he asked. “Yield, maturity, agronomics, herbicides, insects.”

The No. 1 factor that everyone considers in corn and soybeans seed selection is yield.

“If you don’t get good yields on the products you put in the ground, then you’re not going to really want to plant them,” he said.

There are two kinds of yields to consider: an economic yield versus a maximum yield.

“There’s a big difference if you’re trying to be the top of the co-op and get the most yield or if you’re trying to drive the nicest truck to the co-op,” he said. “There is two different methodologies to do that and a lot of time they don’t align because the cost factors it takes to get to that top yield are not necessarily the ones that are going to make you the most money. You have to decide what value you place on those yields.”

The No. 2 priority for seed selection, Witt said, should be maturity.

“Corn and soybeans have different maturity but are all calculated the same way; by growing degree units,” he said. “Growth rate is not based on the number of days on the calendar, but based on heat units and the temperature and moisture that’s available out there.”

Priority No. 3 is agronomic traits.

“Agronomics is the key component of yield potential,” he said. “If you have bad agronomics, a.k.a., the structure of the plant, how it grows. If those are bad, then you won’t have a good yield.”

Agronomics, including a disease rating susceptibility, plant populations, product type and fit are all usually scored in seed guides.

Witt said the fourth priority is traits.

“Traits are available for multiple herbicides and insects,” he said. “You have to ask these questions: what weeds do you have? What have you done in the past? What insects do you have and what have you done in the past? All of those are important for resistance management.”

Seed guides

“We are going to understand our seed guide, because seed guides can be insanely complicated,” he said.

Witt said to keep in mind that every single seed guide you look at is in a different format.

“All seed guides contain way more information than you need,” he said. “You can get lost in these guides and that’s why you need to make a priority for yourself,” he said. “What things actually matter to me when I am making these decisions.”

Ratings of each hybrid or variety are company subjective and are research-based. Witt said to keep in mind that each company will most likely have a different rating scale.

“For some companies, a one is outstanding and a nine is poor. Other times nine is excellent and one is poor,” he said. “Every seed guide has a key to help decipher their ratings for each product, but it is always hard to find. Look for the fine print to help navigate those.”

Seed guide words vary but the terms should be easily deciphered.

“Some will say stalks, some will say stalk quality, some will say stalk strength, stalk standability,” Witt said. “But all of those, in essence, is the exact same thing because they are saying it in a different way because they put their own adjective on it.”

The first section of a seed guide for corn will show the CRM (comparative relative maturity) or RM (relative maturity). This shows the time it will take corn to reach black layer or physiological maturity.

A seed guide will also list characteristics of the seed, such as emergence, seed vigor, ear flex and more.

“Emergence is the ability of the seed genetics to withstand cold water stress and establish uniform stand,” said Witt. “We’re only talking about the plant coming up out of the ground. That is it. From under the ground in the seed portion to when it pops up out of the ground.”

For emergence, Witt added corn requires 100 to 120 GDUs.

“It’s those cold days in the spring, when you only get five days a week that had 10 GDUs total, that corn is just going to sit there because it needs 100,” he said. “However, if you get the warm conditions and you get 20 heat units a day, corn can be up in five to six days. That’s why if you plant stuff in early April, it might sit in the ground for awhile. That is where this emergence matters.”

Seed vigor, Witt explained, is the growth rate of the seedlings once emerged. This characteristic is not in every seed guide.

“Not all traits are always listed,” he said.

Other traits to consider when making your seed decisions for corn are plant height, ear height and other physical traits such as stalk and root quality, ear flex and a staygreen trait.

“The staygreen trait is the plant’s ability to maintain transpiration or photosynthesis longer into the season,” he said. “A.K.A., it’s green.”

There are some potential benefits of a staygreen trait when it comes to standability.

“If your plants are greener, healthier longer, whether that is putting on more grain or not, it will let them stand longer in the season,” he said. “They will eventually die, but if they don’t start to die until mid-October, that’s probably better if you want them to stand longer than if they started dying the beginning of September.”

A rating of soil types can be another part of a seed guide, Witt said.

“Certain hybrid genetics have a greater ability to handle different soil types,” he said. “Certain hybrids do well on good ground. Other ones are the soil hybrids you can grow on anything. You can grow them in a sand box. It doesn’t matter what you grow them on.”

“That’s where you decide what hybrid do you want. Yield potential or ability to grow in all sorts of soil conditions. Look at what you have. How do you adjust for that range?”

Disease characteristics

Choosing a corn hybrid or soybean variety with a disease resistance, Witt said, is one of the easiest ways to protect yourself from that disease.

“The plant is already inherently protecting itself from those diseases,” he said. “There are fungicides you can add after to help with some of those disease, but making sure you have that built in is something to think about.”

There are diseases in both corn and soybeans, but according to Witt, the best way to control a major disease in soybeans is to plant resistant varieties.

“Disease control is the biggest thing in your soybeans,” he said. “It’s really about controlling the diseases. That’s the big thing you want to do. That’s why you have a lot of disease ratings when it comes to the characteristics. You won’t see a lot of physical ones, but more disease ratings.”

Transgenic traits

Both corn and soybeans feature transgenic traits to help with weed and insect management.

To keep things simple, Witt advised to not worry about learning the science.

“You need to know what is it going to protect me against and how do I know what I am getting,” he said.

For corn, when it comes to understanding Bt traits, a single Bt trait hybrid is made to develop one pest either above or below ground.

Then there are hybrids that are available with more options. Those are called stacked and pyramid traits.

“A stacked trait is two or more traits attacking multiple pests, one or more, above and one or more below the ground,” he said. “That’s a stacked because you have the ones up above doing different thing than the ones down below.”

“A pyramid contains two or more traits targeting the same pests,” Witt added. “You can have two different ones. Two of these traits above ground and nothing below, that’s a pyramid because they are the same. They’re just attacking the same style of thing above ground. Stack requires above and below. Pyramid is either up or down.”

Smart stack hybrids will offer a combination of both a stack and a pyramid.

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