When to spray fungicide on almonds — a drone operator's view

If you're growing almonds in the San Joaquin Valley, fungicide timing is the part of the spray program you can't cheat on. Miss the window for hull rot or Alternaria and you're looking at yield loss, hull staining, and — worst case — dead wood on your scaffolds the following year.

This is a quick operator's view of the three passes that matter most, and how we plan them around drone flights.

Pink bud to full bloom — brown rot and jacket rot

Brown rot blossom blight (Monilinia laxa) and jacket rot are the season's first big threats. The window is narrow: pink bud through petal fall, typically mid-February to early March in the valley, depending on the year's heat units and cultivar.

What we watch for:

• Sustained periods of leaf wetness (>12 hours)
• Overnight lows in the 45–55°F range
• Cultivar timing — Nonpareil is earlier than hard-shells like Fritz and Monterey

Drone advantage here is getting into wet blocks a ground rig can't. If it rained Sunday night and the forecast is clear Monday morning, we can fly at dawn without rutting the orchard floor.

Two weeks post-petal fall — shot hole and scab

Shot hole (Wilsonomyces carpophilus) and scab (Fusicladium carpophilum) both ride in on those early spring rains. The standard program is a protectant fungicide applied 1–2 weeks after petal fall, often tank-mixed with a boron nutrient spray.

What makes this pass tricky:

1. It's right when bees are still active on cover crop and adjacent plantings — every application needs to respect the label's pollinator language
2. Windows are short — 2-hour morning flights between inversions
3. Coverage into the canopy matters more than raw volume

The T50's dual centrifugal atomizers give us a 16–400 µm droplet range. For this pass we dial into the finer end — better leaf-surface coverage, better canopy penetration, less runoff into the inter-row.

May through July — hull rot, Alternaria, anthracnose

This is where most of the yield protection happens. The target diseases:

• Hull rot — Rhizopus stolonifer and Monilinia fructicola
• Alternaria leaf spot — usually worst in Monterey, Sonora, and Carmel
• Anthracnose — Colletotrichum acutatum, increasing risk on hullsplit

UC guidance is typically two applications: the first at hullsplit (roughly mid-June to early July depending on variety), a second 10–14 days later if conditions stay humid. Some operators add an early May protectant on high-pressure blocks.

Drone is an especially good fit for this window because:

• It's hot. Ground crews in 100°F + a Tyvek suit aren't running long shifts
• Canopy is closed. Ground rig booms can't reach the tops of mature trees; we fly directly over them
• The block doesn't need to dry out first — no wheel marks to wait for

What the paperwork looks like

Every application we make is logged. You get:

• A coverage map showing the flight lines over your block, with sprayed/unsprayed zones colored
• A copy of the Pesticide Use Report (PUR) we file with the county ag commissioner
• Flight telemetry on request — wind speed, spray flow rate, altitude, ground speed

This matters because the grower's obligation to keep accurate application records under Title 3 CCR § 6624 doesn't disappear just because the applicator is flying instead of driving.

Planning your program

If you're sketching out the season, here's the cheat sheet we use for almonds in a typical Madera/Merced/Fresno county year:

| Stage | Timing | Primary targets | |---|---|---| | Pink bud → petal fall | Mid-Feb → early Mar | Brown rot, jacket rot | | 1–2 wk post-petal fall | Mid-Mar → late Mar | Shot hole, scab | | Early May (optional) | First week of May | Early Alternaria pressure | | Hullsplit | Mid-Jun → early Jul | Hull rot, hullsplit anthracnose | | Hullsplit + 10–14 d | Late Jun → mid-Jul | Residual hull rot, Alternaria |

Your actual program should come from your PCA with current UC IPM guidelines — this is just the rhythm we see most of our almond blocks running.

Ready to get a block on the schedule? Request a quote. Send variety, acres, and your target week — we'll reply the same day.