The Key Times

Managing crops through the reproductive stages

By Paul Hermans

It’s the cold, crazy days of winter and I am writing this article about harvest time. Why would I do that?

Anyone will tell you that the reproductive stages of crops are the most important – assuming, of course, you had all your ducks in line from planting through the vegetative stages of growth. (Which I covered in the January magazine.)

Think of growing any crop like a horse race. You want to get out of the gate quickly, you want to ensure you do not fall as you get closer to the finish line, and finishing as fast as you can for those last few feet means the world of difference.

Imagine you are now rolling into July through September 2023 … coming around that final curve with the checkered flag in sight.

Building on last month’s article, we will explore key times for both corn and soybeans, and offer tips to help manage these crops though the reproductive stages.

combine harvesting corn
    Paul Hermans photo

To start, the main goal for both crops during these reproductive stages (R Stages) is to make seed for the “next generation to continue on.” Both crops will sacrifice extra seed production to ensure viable seed. The trick to making more seed (yield) is to reduce stress during these R Stages.

Soybeans flowering

Soybeans are a unique crop. Their flowering period spans 30-plus days. The soybean plant produces more flowers than it can ultimately sustain. This is primarily a mechanism to adjust to stresses later. Under normal conditions a plant will abort one-third to one-half of the soybean flowers produced.

They move quickly through certain stages. Ensuring they are happy at all stages helps. The goal is to set a large pod load, fill a large pod load, and harvest a large pod load.

The enclosed charts give you a rough idea on how beans move through each phase.

chart showing soybean growth stages and yield loss from frost

Planting date is by far the biggest influencer on pod development. Getting a crop to six trifoliates or more before flowering is critical to achieving higher yields.

We all have experienced the “ugly June” bean development phase and wonder how this crop will ever yield.

In my trading area, early fall frost issues with soybeans are not our limiting factor. Rather, moisture availability in the months of July and August is the concern.

Insect pressure from soybean aphids or spider mites, or diseases like white mold, are important to control to maintain flower numbers and final seed set.

For white mold control, most preventative fungicides have a 10-to-14-day window of protection. In severe cases of mold history, a two-pass system is recommended for protection. Planting rate, rotations, tillage type, high fertility and planting date play a key role. Hence my thoughts on the early part of the race.

Rainfall makes or breaks soybeans. August will be the “yield revealer” on that. Seed size can change as much as plus or minus 20 per cent.

In essence, having marbles in the field, compared to BB-size seeds. How we can reduce plant stress to make higher-yielding marbles is key!

Fungicide trials in Eastern Ontario have shown a five- to six-bushel response 75 per cent of the time. Lower responses in drier, less-moisture yield environments.

However, higher yield loss will be seen when the disease triangle rears its ugly head.

In 2022, growers told me the fields that received an insecticide for aphids would yield five to 10 bushels more. A key custom combine operator mentioned his worst fields lined up exactly how he chronologically sprayed his soybeans for aphids.

Ensure a solid foundation for higher yields is present. Macronutrients, especially potassium, are needed in high amounts in reproductive stages.

The addition of micronutrien

ts, like sulfur, on finer textured soils with lower organic matter have shown yield benefits.

Hence the need to scout, scout, scout and manage, manage, manage.

Growing corn

Unlike soybeans, corn has a more “determinate reproductive” stage. From flowering on it takes corn about 50 to 60 days to reach maturity.

Early in the reproductive stages corn development can be sped up or slowed down based on ambient air temperatures.

The warmer it is, the faster corn will reach its reproductive stage. Ensuring a lengthy reproductive stage that misses a fall killing frost is key.

Since early in my career, I have never forgotten the statement that “for every day you miss in the spring you must make up two good days for growth in the fall.” We’re not worried as much about the first planted corn – but the last. Mainly due to the killing effects of the white combine ... frost.

In general, corn likes air temperatures around 28 C to 30 C and soybeans in that 23 C to 24 C range.

Corn’s most critical period revolves around the two weeks before and after flowering (tassel) time.

The enclosed chart reflects various growth stages of a corn plant and potential yield loss per day, given continued moisture stress.

chart showing relation between corn silage yield and moisture

Water demand goes up dramatically per day. Yield loss (or gain) changes dramatically as well. Since water is limiting in any crop, setting initial planting rates that support the water-holding potential of the field in question is important.

Understanding yield environment, yield goals at a field or sub-field level, and utilizing variable-rate seeding helps to ensure the correct ratio of plant to soil/water resources.

Switching gears, think of solar panel farms that harvest the sun to make electricity.

Growing crops is no different.

Heading into reproduction stages in corn, the trick is to keep all the “solar panels” – the leaves – as healthy as possible to maximize the sunlight.

Diseases like northern leaf blight and grey leaf spot can affect corn in Eastern Canada.

Added to this, a new disease called tar spot is another heavy hitter from a yield-loss standpoint. Scouting the corn crop prior to tasseling and determining disease pressure will assist greatly in determining a fungicide use.

So, what can you do as a grower to control periods of stress?

First, improve water-holding capacity. By improving soil health and organic matter, you can improve water-holding capacity.

Keep diseases at bay from tassel through the next 30 days. Like soybeans, a strong fertility foundation goes a long way in reaching final yield goals. Phosphorous plays a key role early on, and potassium is vital for standability and assisting with overcoming drought stress.

chart relating corn evapotranspiration and yield loss

Ensure nitrogen is not limited. Late-season hybrids that pack in their grain-fill later require ideal conditions for higher yields. If you run into nitrogen loss, research data has shown that rescue treatments up until the blister stage can help with yield-loss reduction and improve yield.

A lot of what happens in reproductive stages filters back to vegetative stages.

Picking the right product for the right acre, ensuring good stress emergence scores, optimal planting depth and more are akin to getting out of the starting gate at a horse race.

The toughest part of the horse race is getting around the final turn to the finish line.

Having the steam to get across the finish line wins the race. Think about what you can do production-wise to make sure your horse has all the energy to get past the wire.

All the best with your 2023 crop as we strive to reduce stress and get our horses to the finish line. BF

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