The Foliars Mystery – or No Mystery at All

Dan Davidson, Agronomist PhD, CPAg, CCA

How and when do you decide to apply foliars when there are so many choices?

Applying foliars on soybeans is becoming a popular practice that began a decade ago when we started to learn that applying fungicide at R3 improved plant health and soybean yield. However, it really can be traced back earlier, back in the first part of this century after the arrival of soybean aphids. Growers had to scout and spray an insecticide if they counted 200 aphids on a leaf (threshold for spraying). While soybean aphids have receded into our memory (natural predators now seem to keep the population under control), applying fungicides is now almost routine.

But foliars aren’t limited to fungicides and insecticides today. Growers are adding in nutrients, plant growth regulars, biostimulants, carbon products, about anything you can think of that is currently on the market.

Kris Ehlers, agronomist with Ehler Brothers Co. in Thomasboro, Ill., said, “Keeping that plant’s growth regulated and foliage nourished will help keep it on track for optimal yield potential.” Keeping soybeans nourished is the reason many growers apply foliars.

Soybean staging: Knowing stage development is important in making post application decisions – at the right time. Changes in planting date, rainfall and temperature alter development speed and soybean height with or without affecting flowering. Most applications are recommended for application at R or reproductive stages.

Timing: Most foliar plant protection applications are timed at R3. This is beginning pod stage, when you want to protect the foliage as pods form and field. An application at R3 will generally protect the plant through R4, R5 and into R6. Late R stage applications are never economically justified.

However, when it comes to nutrients and biostimulants, these can be applied earlier. At V2-V3 stages. applications are made to influence node number and eventual branching and growth, and usually limited to stimulants. At V5-V6 growers are making herbicide applications and can add in a PGR, biostimulant or nutrient package. At R1 soybeans are flowering and R3 producing pods, and since the plant tends to abort 60%-70% of them, remediating environmental stress will increase their survival. R3 and up to R4.5 is the more conventional application time to apply a combination of plant protection, nutrients and stimulants to both stimulate the plant and keep foliage and pods well nourished.

How many passes a season is for you and your pocketbook to decide. Some growers and yield chasers are making five passes across the field, keeping plants healthy and well-nourished. They begin at early vegetative and end out at R4-R4.5, running across the field every 2-3 weeks with a different cocktail of products. However, you can accomplish some of these goals by making the more conventional 2-pass at herbicide application and R3.

Stimulants: Today there are many biologicals on the market. Plant Impact markets Fortalis, a plant enhancement product that is applied at R1-R3 with a fungicide, insecticide or alone to improve pod set and yield. Other commercial products include biological stimulants, synthetic plant growth regulators and carbon (humic/fulvic acid) products. These products can be applied as a foliar and most are compatible with each and crop protection products. Manufacturers generally recommend these foliar products be applied along at standard times with plant protection products or they can be applied independently as well.

Nutrients: Because such small amounts of nutrients enter plant leaves, significant amounts of N, P and K shouldn’t be considered for a foliar feeding program, since the clear majority has to be taken up through roots. However, small amounts can be effectively applied. Micronutrients can be applied as a foliar since they are required in such small quantities, and leaf application and uptake is sufficient.

Foliar applications can increase metabolism, improve plant health, and signal the plant that it can support more flowers and pods. Instead of 60% to 70% of flowers and pods aborting, that loss may be reduced to 50% or 55%. Dr. Fred Below at the University of Illinois has shown that keeping one more pod per plant translates to two more bushels per acre. Striving to keep the plant healthy and metabolically active is a worthy goal.

Foliar nutrient mixes can include one or all the following, but for micros, zinc, manganese and boron are the most important:

  • Nitrogen (N) – Essential component of proteins and necessary for chlorophyll
  • Potassium (K) – Essential for N metabolism, promotes root growth, and stalk strength
  • Zinc – Catalyst for plant growth, chlorophyll production and essential for seed maturity
  • Manganese – Part of enzymes involved in respiration, protein synthesis, and herbicide metabolism
  • Boron – Producer of starch, promotes maturity, seed development and is involved in N and carbohydrate metabolism
  • Iron – Promotes the formation of chlorophyll
  • Copper – A part of the photosynthesis enzyme and important during the reproductive stages
  • Molybdenum – Essential for N fixation


Applying foliars is a good strategy that gives soybeans that little extra nudge to push yields to the next level.

Dan Davidson is a PhD agronomist, part-time farmer and soybean expert from Nebraska who consults with soybean checkoff and industry on crop production, marketing, and product development projects.


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