Pest Control
Anderson Pre Emergent Application: Timing With Spring Fertilizer
The Agronomics of Anderson Pre Emergent and Soil Nutrition
Applying a pre-emergent herbicide and a spring fertilizer simultaneously is a common practice to save time, but it requires a precise understanding of soil chemistry. When integrating an Anderson pre emergent into your spring soil nutrition plan, you are dealing with two distinct chemical behaviors: the creation of a hydrophobic barrier in the top inch of soil, and the dissolution of water-soluble nutrients (Nitrogen, Phosphorus, Potassium) into the root zone.
Andersons Professional Grade pre-emergents, particularly those utilizing prodiamine or dithiopyr, rely on soil organic matter (SOM) binding to maintain their efficacy. According to research documented by University of Minnesota Extension, pre-emergent molecules adsorb tightly to organic carbon. If your spring nutrition plan includes heavy compost top-dressing or liquid humic acid applications, you are actively increasing the SOM in the topsoil. High organic matter (above 5%) requires a higher application rate of the pre-emergent to ensure enough active ingredient remains unbound to form a continuous chemical barrier against crabgrass and poa annua germination.
DG Pro Technology vs. Standard Granular Carriers
Andersons utilizes Dispersible Granule (DG Pro) technology in many of their premium lines. Unlike standard prilled fertilizers that melt slowly, DG Pro granules break down into thousands of micro-particles upon contact with moisture. This is critical for soil nutrition because it prevents nutrient stratification. When paired with a pre-emergent, the micro-particles ensure the herbicide is distributed evenly across the soil surface, eliminating the "striping" effect common with standard granular carriers where weeds sprout between spreader passes.
Timing Your Application: The Soil Temperature Matrix
Timing an Anderson pre emergent application is dictated by soil temperature, not calendar dates or air temperature. Crabgrass germinates when the soil temperature at a 2-inch depth reaches 50°F to 55°F for three consecutive days. To track this accurately, turf managers rely on regional data hubs like the Iowa State Mesonet soil temperature network.
⚠️ Critical Timing Warning: Applying your Anderson pre emergent too early (when soil is below 45°F) risks the herbicide degrading via photodegradation and microbial breakdown before the primary weed flush occurs. Applying it too late (after soil hits 60°F) allows the first flush of crabgrass to germinate and bypass the chemical barrier entirely.
Spring Application and Nutrient Ratio Table
When selecting an Anderson combination product (pre-emergent + fertilizer) or tank-mixing a liquid pre-emergent with a granular fertilizer, the N-P-K ratio must match the turf's spring metabolic needs. Cool-season grasses require different spring nutrition than warm-season grasses.
| Turfgrass Type | Target Soil Temp (2-inch) | Recommended N-P-K Ratio | Anderson Pre Emergent Active Ingredient | Nitrogen Release Type |
|---|---|---|---|---|
| Cool-Season (Fescue, Kentucky Bluegrass) | 50°F - 53°F | 20-0-10 or 24-0-11 | Prodiamine (0.48% or 0.58%) | 50%+ Slow-Release (Methylene Urea) |
| Warm-Season (Bermuda, Zoysia) | 55°F - 58°F | 15-0-15 or 16-4-8 | Dithiopyr or Prodiamine | Fast-Release (Urea) for green-up |
| Transition Zone (Mixed Stands) | 53°F - 55°F | 22-0-8 | Prodiamine + Isoxaben | 70% Slow-Release (PCU) |
The Watering-In Protocol: Activating Herbicide Without Leaching Nutrients
The most common failure point in combining weed control and soil nutrition is the irrigation phase. Both the Anderson pre emergent and the spring fertilizer require water to activate, but their hydraulic requirements conflict if managed poorly.
Prodiamine requires approximately 0.25 to 0.5 inches of water to move off the granule and bind to the soil particles in the top 1 inch of the profile. However, soluble nitrogen (especially urea-based fertilizers) can leach past the root zone if subjected to heavy, prolonged irrigation immediately after application.
The Two-Cycle Irrigation Strategy
To satisfy both the herbicide barrier and the fertilizer uptake, use a split-cycle irrigation method:
- Cycle 1 (Immediate Activation): Apply 0.25 inches of water within 24 hours of application. This is enough to dissolve the DG Pro granule, release the prodiamine into the topsoil, and begin dissolving the fertilizer salts.
- Wait Period: Allow the soil to dry slightly for 24 to 48 hours. This drying period encourages the turf roots to pull the dissolved nitrogen upward via capillary action.
- Cycle 2 (Deep Soak): Apply another 0.25 to 0.5 inches of water 3 days post-application. This drives the remaining nutrients deeper into the 4-to-6-inch root zone without washing the pre-emergent barrier past the germination zone.
The Core Aeration Conflict
Spring soil nutrition plans often include core aeration to alleviate compaction and improve oxygen flow to the roots. However, core aeration physically destroys the pre-emergent barrier. According to turfgrass management guidelines from NC State TurfFiles, pulling soil cores disrupts the continuous chemical layer required to halt weed germination.
Rule of Thumb: Never apply an Anderson pre emergent within 14 days before or after core aeration. If your soil requires spring aeration, perform the aeration first, apply your spring fertilizer to take advantage of the open soil channels, and delay your pre-emergent application until the soil cores have broken down and been mowed back into the canopy.
Frequently Asked Questions
Can I apply Anderson pre emergent to newly seeded lawns?
No. Prodiamine and dithiopyr do not distinguish between weed seeds and turfgrass seeds. They will inhibit the root development of newly germinating fescue or bluegrass. You must wait until the new lawn has been mowed at least three times (usually 60 to 90 days post-seeding) before applying any pre-emergent. For newly seeded lawns, rely on post-emergent selective herbicides like quinclorac for weed control, and focus your spring nutrition on high-phosphorus starter fertilizers.
Does the Anderson pre emergent affect soil microbe health?
Prodiamine has a relatively low toxicity to soil-dwelling microorganisms compared to older chemistries like benefin. It binds tightly to soil carbon and is largely unavailable to soil microbes, meaning it does not significantly disrupt the nitrogen cycle or mycorrhizal fungi networks. Your soil nutrition program, particularly the use of organic amendments like kelp or humic acids, will continue to function normally beneath the chemical barrier.
What is the maximum annual application rate for Anderson prodiamine?
The maximum annual application rate for prodiamine depends on your turf species to avoid root stunting. For Kentucky Bluegrass and Tall Fescue, the maximum is generally 2.3 lbs of active ingredient per acre per year. For Bermuda and Zoysia, it can be pushed to 3.0 lbs per acre. Always check the specific Anderson product label for the exact granular weight required to hit these active ingredient thresholds, and split the applications between early spring and late summer for season-long control.
