3/30/2023 - By Dr. Jeff Atkinson

Each year, conversations kick up around fertility and preemergence herbicide programs. Sparging preemergence herbicides on a fertilizer carrier is an efficient way to complete two agronomically important tasks at once. However, pesticide sparging is not as simple as putting herbicide and fertilizer together in a mixer.

Is "Sparging" a new term to you? Find out what sparging is here.

Here are 5 tips to maximize the effectiveness of fertilizer as a preemergence herbicide delivery system:

Apply Sparged Fertilizer at an Appropriate Spread Rate

An argument for spraying preemergence herbicides is the superior coverage spray applications provide. While this may be true in a technical sense, applying preemergence herbicides using an appropriate amount of granular carrier per area is proven to provide equal weed control to spray applications. On a small scale, each fertilizer granule sparged with a preemergence herbicide can be thought of as having a ‘zone of influence.’

If a blend is applied at too low a rate, these zones will not overlap, allowing for weed seed germination and establishment in the voids (Figure 1). Alternatively, when a granular blend is applied at an adequate rate, the zones overlap and provide full coverage of the treated area (Figure 2).

Figure 1. Sparged fertilizer granules applied at a low spread rate will not have overlapping 'zones of influence,' resulting in poor weed control.

Figure 2. Sparged fertilizer granules applied at an adequate spread rate will overlap 'zones of influence', resulting in excellent weed control.

Select the Appropriate Active Ingredient for Sparging

All active ingredients sparged on fertilizer by Harrell’s are effective; however, they are not all effective for all purposes. Understanding which active ingredient to apply for which weeds and at what time is as important as applying any herbicide at all. When selecting which active ingredient to sparge on fertilizer the target weed species, the timing of the year, desired longevity, and mode of action rotation should all be considered. If you need any assistance with this or a diagnosis, your Harrell’s Rep is here for you.

Utilize a Quality Sparging Substrate

Better blends result from quality raw materials. In a perfect world, all raw materials would be spherical, and consistent in size, and consistent in density. However (and unfortunately), we don’t live in a perfect world. The reality is that some materials are round (urea), some materials are angular (muriate of potash), some materials have a range of sizing variability (filler), and others are very consistent (POLYON® fertilizer). When formulating a sparged blend, selecting materials that are similar in size, consistency, and density will result in better distribution uniformity of the active ingredient during application.

Align Fertility with Herbicide Longevity to Maximize Sparged Fertilizer

Turf 101 teaches that a dense turf stand is the best defense against weeds. The fact is many weed seeds require light to germinate. A dense turf canopy prevents light from infiltrating the soil surface, thus preventing weed seed germination. Applying a long-term nitrogen product to promote turf density, that aligns with the longevity of a preemergence herbicide application, is a multi-pronged approach to weed management. The predictability and consistency of POLYON® fertilizer allow for the matching of active ingredients to feeding longevity to create a holistic weed management program.

The example in Figure 3 assumes a longevity of 12 weeks for a preemergence herbicide applied on May 1^st. As can be seen in the product longevity section, this matches perfectly with fertility longevity. In this scenario, a second preemergence and fertility application will be required to provide full-season weed control and turf-feeding coverage.

Figure 3. POLYON® fertilizer programs can be formulated to match feeding longevity with preemergence herbicide efficacy.

Select Products Manufactured with Superior Formulation Techniques

Quality of formulation can make or break a sparged fertilizer blend and experience and technique are as important as the active ingredient that is being sparged. Several of Harrell’s sparge ingredients are applied using a ‘Hot Melt’ process which applies a liquified solution that freezes on the fertilizer substrate during cooling.

The result is a product with consistent coverage and reduced dust compared to alternative sparging techniques. This is especially important for herbicides such as oxadiazon (Ronstar (Restricted Use Pesticide)) which can be phytotoxic if applied using a dusty formulation.

Creating quality sparged fertilizer blends is as much of an art as it is a science, especially in a custom blending scenario. Harrell’s reps are equipped with the knowledge and experience to create quality blends that result in excellent weed control and fertility for any agronomic situation. If you have any other questions on sparging or are interested in some of our blends, reach out to your local Harrell’s rep.