Use Caution if Considering Planting Corn or Soybean

Apr 12, 2022

By Mark Licht

Soil temperature is one of the most important factors to guide planting decisions. The rule of thumb is to wait until the upper 4 inches reach at least 50 degrees, with a warming temperature trend in the forecast. One way to track soil temperatures across Iowa is by using the soil temperatures map compiled by the Iowa Environmental Mesonet at Iowa State University. Updated daily in the spring, this map provides current measured and estimated soil temperatures for each county in Iowa.

The outlook for the next two weeks indicates a strong likelihood of well below average temperatures that will keep soils well below the optimum. Within this timeframe, there is a moderate chance of “much below average temperatures” from April 14^th through the 19^th. Planting into these cold soils will place seeds into very cold conditions for an extended period of time. Soils are unlikely to be excessively wet after the cold period and should be in better condition to plant.

Fields warm up and dry out differently based on factors such as soil texture, soil organic matter, soil moisture and surface residue coverage. Just because your neighbor may be preparing for or planting, does not mean all fields are ready to be planted. Daily fluctuations are common, especially in early spring. Historically, the optimum planting window for Iowa corn has been April 11 to May 18, with a shorter window in the northern part of the state compared to the south.

Last year, there was a cold spell with frost damage the over Memorial Day weekend. That is pretty uncommon to have frost injury that late into may. The average last spring freeze date (30^oF) varies across Iowa from late March in southern Iowa to late May in northern Iowa. Determine your frost risk using the Freeze Date Tool developed by the Midwestern Regional Climate Center and the Midwest Climate Hub.

We want to make sure that we have a soil temperature that is warm enough for the seed to germinate and also for the shoot to emerge, without having to worry about heavy frosts or low emergence rates. Planting early ensures you will not be planting late, but it does not mean that you will not experience damage or have to replant. Planting into cooler soil conditions extends the time from planting to emergence. This puts the seed at greater risk of seed mortality, loss of seedling vigor, and seedling disease infection.

Pay attention to the forecast and hold off on corn and soybean planting until there is a rising trend for several days. This 50^oF and rising soil temperature trends gives the best chances for excellent stand establishment and seedling vigor.

risk of seed mortality

Source : iastate.edu

Video: Turning Plant Defense Into a Management Strategy

Turning Plant Defense Into a Management Strategy

Understanding how a plant responds to stress is one thing.

Using that knowledge to make better management decisions is another.

Systemic acquired resistance, or SAR, is the plant's more direct defense response. When stress or infection occurs, the plant begins signaling throughout its system and preparing defensive compounds.

But if we know that response exists, can we help prepare the plant before the stress arrives?

The answer starts with understanding what triggers the response and what the plant needs to carry it out.

The Trigger and the Fuel

Salicylic acid plays an important role in triggering the SAR pathway.

Think of it as turning the truck on.

The engine may be running, but it still needs fuel to do the work.

In this case, manganese plays an important role in supporting the enzyme systems involved in the plant's defensive response.

This makes manganese status an important part of the conversation. Whether a producer is using tissue testing, sap analysis, or simply scouting for visible deficiency symptoms, the goal is to make sure the plant has adequate manganese available.

Manganese is required in relatively small amounts, but that does not make its role small.

If the plant receives a signal to defend itself but lacks the nutrition needed to support that response, it may struggle to carry out the process efficiently.

The trigger matters.

The fuel matters too.

Prepare Before the Stress Arrives

The best time to think about stress management is before the plant is overwhelmed.

Once a crop is already struggling, management can quickly turn into a game of catch-up.

This is similar to nitrogen management. Once a plant becomes severely deficient, correcting the problem does not necessarily erase the time and yield potential already lost.

Plant defense can work the same way.

Low-rate, targeted approaches designed to support the SAR pathway may fit best ahead of an expected stress event rather than after significant damage has already occurred.

That requires producers to think about predictable stress.

We may not know exactly what the weather will do tomorrow, but we generally know summer heat is coming. We know certain field conditions increase disease pressure. We know a herbicide application can temporarily stress a crop as the plant processes the chemistry.

Even a properly timed and labeled herbicide application can create a temporary response in the plant.

That does not mean the herbicide is bad.

Weeds can create significantly more yield loss than the temporary stress caused by controlling them.

The question is not whether we should eliminate every stressor.

The question is whether we can better prepare the plant to manage necessary and predictable stress.

Not All Stress Is Bad

Stress is a normal part of plant growth.

A perfectly stress-free environment does not exist in the field.

In fact, some stress is necessary for normal plant development. A plant responds to wind, temperature, moisture, sunlight, and countless other environmental signals throughout the season.

The environment is stress.

The plant's job is to manage it.

Problems begin when the stress load becomes greater than the plant's ability to respond.

Extreme heat, drought, high salt concentrations, disease pressure, and even certain management practices can add to that load.

This is where understanding SAR becomes useful.

Instead of waiting until the plant is visibly struggling, producers can begin identifying periods when stress is likely and make management decisions around those windows.

ISR Starts With the Soil

While SAR is a more direct defense response, induced systemic resistance, or ISR, brings the conversation back to soil health.

The longevity of a farm is closely connected to the health of its soil.

Carbon plays a major role because it supports biological life within the soil. Bacteria, fungi, and other organisms interact with plant roots and influence how the plant grows, accesses nutrients, and prepares for stress.

This is why soil health cannot be reduced to one product or one application.

It is a system.

Keeping living plants in the field longer can support biological activity. Cover crops may fit some operations. Better water management can improve soil conditions.