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At a Glance: 5 Application Tips
GDD monitoring: Bean leaf beetle adult pressure begins at 1,212 GDD — scout ahead of this threshold.
Scouting cadence: Walk fields every 7 days to catch economic thresholds before damage compounds.
Preventive vs. curative: Apply Group 11 fungicides before infection; Group 3 fungicides can stop early disease cycles after infection starts.
Timing: Soybeans hit peak fungicide ROI at R3 stage; corn at VT/R1.
Tank mix: Combining insecticide + fungicide in one pass reduces application cost and closes insect-created entry points for disease.
As you start to think about using fungicide and insecticide applications this year to combat disease and pests, you’ll want to consider the best ways to get the most out of your spray applications.
Here are five key tips to keep in mind when applying insecticides and fungicides:
Insect development can be tied to growing degree days (GDD), which are a measurement of heat accumulation over time. This is helpful in years where days are hotter than previous years and result in an acceleration of insect pressure and more opportunities for pests to affect yield potential by causing damage to roots and foliage.
Growing degree days vary by pest and region, but a few benchmarks to track in common Midwest crops (based on university extension thresholds):
Bean leaf beetles (1st gen adults): ~1,212 GDD
Corn rootworm (adult emergence): ~684–767 GDD (base 50°F)
Soybean aphid (peak pressure): Watch from R1 onward; threshold is 250 aphids per plant
European corn borer (1st gen flight): ~50% egg hatch at ~370 GDD (base 50°F)
(Source: Iowa State University Extension, University of Wisconsin Extension)
Tracking GDD against these thresholds lets you get ahead of pressure rather than reacting after damage starts. Upload your planting data to your free FBN account to see growing degree unit accumulation by field.
See growing degree units by uploading your planting data and unlocking this feature on your free FBN® account.
Typical crop scouting of walking fields every seven days can help to identify patterns of increased pest or disease pressure. Knowing the economic threshold of specific pests can build confidence in determining when the time is right to make an insecticide application.
Fungicides can be segmented into two camps: curative or preventive.
Preventive activity happens when the fungicide is present in the leaf tissue but before initial infection occurs. Applications with a Group 11 fungicide, such as GCS Azoxy 2SC, can help create a protective barrier before plant diseases are present.
A curative fungicide stops the early growth of the fungal pathogen after infection, the first step of the disease cycle, has occurred. Most curative fungicides are also preventive if applied prior to infection. Despite their name, curative fungicides will NOT cure a plant of the disease; they are not effective against advanced disease cycles. A Group 3 fungicide such as Willowood Propicon 3.6EC is considered to be a curative fungicide.
GCS Azoxy 2SC and Willowood Propicon 3.6EC can be tank mixed together to provide a one tank mix solution that's both preventive and curative.
The window for maximum fungicide ROI is narrow and crop-specific. Applying too early wastes product; applying too late means disease has already begun limiting yield.
Soybeans: Target the R3 stage (beginning pod) for fungicide applications. This is when the crop is most vulnerable to yield-robbing diseases like white mold, frogeye leaf spot, and sudden death syndrome, and when the economic return on a well-timed application is highest.
Corn: Target VT to R1 (tasseling to silking) for fungicide applications. This window protects ear leaf and upper canopy tissue through the critical grain-fill period. Gray leaf spot, northern corn leaf blight, and tar spot are the primary targets.
If insect pressure is present at the time of your fungicide application, this is also the moment to add an insecticide to your tank. Insect feeding creates physical entry points for fungal pathogens — treating both in the same pass reduces total applications and prevents disease amplification from insect damage.
GCS Azoxy 2SC and Willowood Propicon 3.6EC tank-mixed together give you both preventive and curative coverage in a single pass. Add Willowood Lambda-Cy 1EC* if insect pressure warrants it.
Make the most of your fungicide and insecticide applications by using adjuvants and crop nutrition products.
Adjuvants are not optional extras — they directly affect whether your insecticide or fungicide performs as labeled. There are two primary types relevant to this type of application:
Spreader-stickers reduce surface tension so the spray droplet spreads across the leaf surface rather than beading off. This is critical for contact insecticides, which have to coat the pest or plant surface to be effective.
Penetrants (also called activator adjuvants) improve absorption of systemic fungicides into leaf tissue, which is exactly how products like Group 3 and Group 11 fungicides work — they need to get inside the plant to move through the vascular system.
Nourish Vitals™ can be added to your fungicide application to support plant uptake and aid in recovery from stress. Use the FBN Adjuvant Product Guide to match the right adjuvant to your specific tank mix — not all adjuvants are compatible with all products.
FBN's crop protection portfolio includes the fungicides, insecticides, and adjuvants you need for a complete application program — with transparent pricing, seamless online ordering, and 3-day direct-to-farm shipping.
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What is the difference between a preventive and curative fungicide?
A preventive fungicide is applied before infection occurs and creates a protective barrier in the leaf tissue. A curative fungicide is applied after infection has begun and stops the early growth of the fungal pathogen. Most curative fungicides also work preventively if applied before disease is present. Importantly, curative fungicides will not reverse advanced disease — they are only effective in early infection stages.
When should you apply fungicide to soybeans?
The R3 stage (beginning pod) is the optimal timing for soybean fungicide applications. This is when yield-robbing diseases like white mold, frogeye leaf spot, and SDS are most likely to cause economic damage, and when the plant's canopy is full enough that disease can spread rapidly without intervention.
When should you apply fungicide to corn?
Target VT to R1 (tasseling to silking) for corn fungicide applications. This protects the upper canopy and ear leaf through the critical grain-fill period. Tar spot, gray leaf spot, and northern corn leaf blight are the primary targets.
Should you tank mix insecticide and fungicide?
Yes, in most cases — if insect pressure exists at the time of your fungicide application, combining both in a single pass reduces application cost and equipment passes. Insect feeding creates physical entry wounds that fungal pathogens can exploit, so treating both simultaneously addresses the disease pathway, not just the symptom.
What are growing degree days (GDD) and why do they matter for pest management?
Growing degree days are a measure of heat accumulation over time, calculated from daily high and low temperatures. Many insects develop on a predictable GDD schedule, so tracking accumulation tells you when to expect first-generation adult emergence and peak pressure — allowing you to time scouting and applications proactively rather than reacting to visible damage.
Do adjuvants really make a difference in spray performance?
Yes. Spreader-sticker adjuvants improve contact insecticide coverage by reducing droplet beading on waxy leaf surfaces. Penetrant adjuvants improve systemic fungicide absorption into plant tissue. Using the wrong adjuvant — or none at all — can meaningfully reduce the efficacy of an otherwise well-timed application.
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