Crop Protection calculators

Spray only when the scouted pest density crosses the Economic Threshold (ETL) — the level set just below the Economic Injury Level (EIL), the point where the value of crop saved equals the cost of control. Below the ETL, the spray costs more than the damage it prevents, so monitor instead. Use the Economic Threshold and EIL calculators with your scouting count, crop value and control cost.

Measure the spray volume the machine actually puts out per hectare, then compare it to the label's target rate. Spray volume (L/ha) = (nozzle flow L/min × 600) ÷ (speed km/h × nozzle spacing m). The Sprayer Calibration and Knapsack Sprayer Calibration tools do this and tell you how far off target you are and the product per tank to correct it.

PHI (pre-harvest interval) is the minimum number of days between the last spray and harvest, set so residues fall below the MRL — harvesting early risks an illegal residue. REI (re-entry interval) is the minimum time before workers may re-enter the treated area without protective equipment, set for human safety. They are independent: a product can have a 7-day PHI and a 24-hour REI.

The pest density at which you must act to prevent the population reaching the Economic Injury Level (EIL). The EIL is where the cost of control equals the value of the yield it protects: EIL = control cost ÷ (crop value × yield loss per pest × control efficacy). The ETL sits a little below the EIL to give you time to spray before damage occurs.

Rotate the mode of action (MOA), not just the product name. Group insecticides by IRAC number, fungicides by FRAC code and herbicides by HRAC group, and avoid using the same group twice in a pest generation or season. Tank-mix or alternate with a different group, keep refuges of susceptible individuals, and combine chemistry with cultural and biological control. The IRAC, FRAC and HRAC rotation planners flag repeats and suggest a swap.

The window after sowing during which weeds must be kept out to protect yield — typically the first 15–45 days for most crops (about 20–40% of the season). Weeds emerging before or after this window cost little yield; weeds inside it can cut yield 20–50%. The Critical Weed-Free Period and Weed Critical Period & Herbicide Window tools give the dates and the yield protected by timely control.

Spray when Delta-T (the gap between dry-bulb and wet-bulb temperature) is between 2 and 8 °C, wind is a steady 3–15 km/h, and there is no temperature inversion. Below 2 km/h droplets hang and drift on inversions; above 15–20 km/h drift rises sharply. Hot, dry air (Delta-T over 10–12) evaporates fine droplets before they land. The Spray Weather Window and Spray Drift Buffer tools give a go/wait verdict.

Field crops typically use 100–300 L/ha; high-clearance and orchard sprays use more by canopy size (use the Tree-Row-Volume tool). Once you fix the volume, total water = volume/ha × area, tank loads = total water ÷ tank capacity, and product per tank = label rate × area ÷ tank loads. The Spray & Tank Mix calculator returns all four figures.

It depends on rainfastness — most products need 1–6 hours dry before rain, and systemic chemistry that has been absorbed is safer than a contact protectant on the surface. The Spray Rainfastness & Reapplication tool estimates wash-off % from the rainfall amount, the time since spraying and the product type, and gives a reapply / no-reapply verdict.

Droplet size (measured as VMD in microns) trades coverage for drift. Fine droplets (under 200 µm) give better coverage but drift easily; coarse droplets (over 400 µm) resist drift but cover less. Contact and fungicide work wants finer, more numerous droplets (use the Droplet Density and Water-Sensitive Paper tools to check ≥ 20–30 droplets/cm²); systemic herbicide tolerates coarse, low-drift droplets.

Confirm the products are compatible (do a jar test) and add them in the W-A-L-E-S sequence: Wettable powders/water-dispersible granules first, then Agitate, then Liquid flowables, then Emulsifiable concentrates, then Surfactants/adjuvants last — with the tank half-full of water and the agitator running throughout. The Tank-Mix Compatibility & Sequence tool gives the per-pair verdict and order.

Avoid spraying bee-toxic products during bloom and daytime foraging. Spray in the evening or at night when bees are not flying, choose products with a short residual (low RT25 hours), and respect the bloom and foraging window. The Pollinator Protection Spray Window tool combines product toxicity, residual hours and foraging time into a bee-safe window — or tells you to wait.