Fungicides can be applied by crop dusters

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Optimizing fungicide applications

Fungal infections cause most foliar diseases with a regional variation in the type of diseases present. However, not all fungal diseases affect yield. An infection that arrives late in the season will most likely not affect the crop yield, and an application of fungicide may not provide ROI. But many fungicide applications can give a positive ROI. If there is a lot of disease pressure on the crop due to fungal pathogens, a fungicide application is often the desired action to take. However, before deciding on the application, there are ways to minimize the chances of a severe fungal infection happening.

Optimizing for foliar diseases before the season

While crops are exposed to unpredictable weather events each growing season that can increase the chances of fungicidal infections, steps can be taken to minimize the chances that a foliar disease will reduce yield. The best way to start is knowing the history of the fields, what crop has been planted, and what type of infestations happened in the past. Crop rotation, if possible, can help minimize the overwintering of diseases. Selecting suitable varieties and hybrids can be an essential factor as well.

Fighting foliar diseases in-season

When the crop has been planted and starts to grow, diseases have the opportunity to develop. Scouting fields early and frequently or using digital data regularly can help detect areas in the field where growth is stunted. Inspecting those areas more closely can indicate the cause of the reduced growth. When a fungal disease is detected, a fungicide application can be the right tool to use.

fungicide application on a tomato field

What to consider when making a fungicide application?

When a fungal disease has been detected that can affect yield, and a fungicide application is justified, there are several things to consider minimizing fungicide resistance and achieve the desired results:

    • Select the right chemistry. For example, look at newer chemistries or products that combine multiple chemistries and modes of action.
    • Time the application properly, considering the weather, the time of day, and when it makes sense for the growth stage for the crop, including considering harvest timing.
    • Use the suitable adjuvants to make sure the fungicide reaches its target and stays on target long enough to do its work.

Details regarding recommended adjuvants can be found on the label of the fungicide. Following these steps can make fungicide application a valuable tool to ensure or even increase yield.

Supporting fungicide efficacy

Fungicide efficacy by itself is affected by:
    • Photo decomposition – UV light of the sun will break down the fungicide.
    • Wash-off from rain.
    • Plant growth adding unprotected leaf surface.
    • Deposition on to the affected plants.

If a fungicide cannot work properly or long enough, all these factors increase the chances of fungicide resistance.

Spreader - stickers Adjuvants

Adjuvants that protect fungicide efficacy fall into the Spreader Sticker category. These Spreader Stickers typically combine a surfactant with an adhesive. The surfactant functionality ensures that the fungicide spreads sufficiently over the leaf surface, while the sticker functionality keeps the fungicide on the plant even through rainfall. The spreader sticker will form a thin layer on the leaf that dries. This keeps the active ingredient in place and can protect the efficacy against decomposition. Some of the best sticker raw materials are pinene terpenes, as they are more flexible and continue to provide protection when the plant grows, safegard against UV decomposition, and provide protection against rain wash off.

A spreader sticker adjuvant will spread the fungicide over the leaf and keep it in place long enough to achieve maximum efficacy.
The difference between using a surfactant (NIS) -only adjuvant or one that has sticker spreader functionality can make the difference for an effective fungicde application.


Another adjuvant functionality, deposition, is vital to making sure the fungicide makes it to the target. It is critical to use a deposition agent that does not harm the crop and causes an adverse effect in season. There are NPE-free deposition agents that do not cause arrested ear development and offer more flexibility in the time of use during the season. And care needs to be taken that the adjuvant does not burn the leaves. Information about whether the adjuvant is appropriate for in-season use can be found on the label.

A quick summary

A fungicide application might be the desired action to take when there is disease pressure early or mid-season to optimize yield. To maximize results, the following needs to be taken into consideration:

    • Knowing the history of the fields
    • Early detection
    • Selecting the right fungicide chemistry
    •  Application timing
    • Adding the proper adjuvants

As for any application made, it is essential to follow the fungicide and adjuvant labels.

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