STRESS ECONOMICS SERIES | AGRONOMIC PERSPECTIVE
Why understanding critical crop stages matters to yield potential and the value already invested in every acre
By Dave Dyson, lead agronomist, Locus Agriculture
August 7, 2026
Crop stress has an agronomic effect long before its financial impact becomes visible at harvest. Heat, moisture extremes, herbicide applications, nutrient limitations and soil constraints can interrupt development during critical growth stages and reduce a crop’s ability to turn investments in seed, fertility and crop protection into yield. Locus Agriculture refers to this cumulative financial impact as “Stress Economics.” From an agronomic perspective, managing it begins with understanding when each crop is most vulnerable and when a well-timed foliar application can provide the greatest value.
Stress affects crops differently
Everyone has heard of stress and the ill effects it has on people’s lives, but stress can be detrimental to a cropping system as well. Some crops, like soybeans, can handle a little stress during the vegetative stages, but corn, on the other hand, can’t take a day of stress without dropping potential yield. Each crop has a “sweet” spot during its growth cycle, that if a foliar application was applied, the plant will almost always increase yields.
Corn: count collars, not inches
Corn goes through numerous stressful periods during first 6 weeks after emerging from the soil. One might ask, how will I know when the stress periods occur in the corn plant? This can be determined by knowing the biology of a corn plant and taking some educated guesses. Once a corn plant emerges from the soil, it will generally gain one leaf stage per week. Sometimes the internodes will expand faster or slower than normal, depending on the growing conditions. One should never gauge how “old” a corn plant is by the height for this reason. Always count the collars, or V stages, of the corn, as shown in figure 1. This is extremely important because by V6, the corn plant will have determined the maximum rows of kernels around the cob.
[FIGURE 1: Corn leaf collars, or V stages, provide a more reliable staging reference than plant height.]
Soybeans: R3, when pods are on the line
Soybeans, on the other hand, have their “sweet” spot during the R3 growth stage, shown in figure 2. R3 is described as a pod at least ¼ inch long at one of the upper most nodes on the main stem. During the R3 growth stage, the soybean plant is undergoing a tremendous amount of stress. This stage helps set the foundation for establishing pods that will not be aborted. This is a prime time for yield-enhancing products to be applied.
[FIGURE 2: R3 growth stage in soybean is described by a pod being at least ¼ inch long at one of the four most upper nodes on the main stem.]
Wheat: The flag leaf window
During the last vegetative stage of a wheat plant, the flag leaf emerges. This single leaf is responsible for 75% of the yield potential of the plant. The flag leaf acts like a solar panel, collecting and converting sunlight to energy the plant can use to produce seed. We at Locus AG have seen a positive yield response to a Bombigro® application during this time. Because Bombigro is compatible with most crop protection and fertilizer products, growers can piggyback Bombigro with a fungicide or insecticide application.
Cotton, potatoes and peanuts: bloom stage
In cotton, potatoes, and peanuts, the “sweet” spot for a foliar application of Bombigro is during the bloom stage of the plant’s growth cycle. When Bombigro is applied during the bloom stage with these crops, we see, on average, more than a 10% increase in yield.
Trial work helps measure the response
You may be asking yourself how Locus AG knows we are mitigating stress in different crops after an application of Bombigro. The answer comes from trial work and collecting data. The University of Arizona grows large amounts of cotton in the Maricopa, AZ area, but one thing can be detrimental to the yield, heat stress. When the temperatures reach 120 F or higher, heat stress is not possible; it is certain. Dr. Debankur Sanyal at the Maricopa Agricultural Center tested stress in cotton plants by measuring how much viable pollen the plants produced. All of the Locus treatments produced more viable pollen by mitigating stress, as shown in figure 3. This reduction in stress directly mirrored the increase in yield shown in figure 4.
| [FIGURE 3: Figure 3. Cotton pollen viability ratings from the 2025 University of Arizona trial.]
| [FIGURE 4: Cotton lint yield from the 2025 University of Arizona trial, reported in pounds per acre.]
|
Adding stress mitigation to the crop program
Stress in all forms is a part of life that we all have to deal with and work through. Adding a stress mitigator to your spray program can add an extra layer of protection against a potential yield robber.
Understanding these critical growth stages is the agronomic side of Stress Economics. When growers help crops continue developing through periods of elevated stress, they are also working to protect the value of the inputs already committed to each acre.
Contact your trusted Locus Agriculture advisor for more details about rates and timing for your Bombigro® application.