Forsythia Leaf Spots: Environmental Injury, Not Rust Disease

Newly planted dwarf forsythia in NM with rust-colored leaf spots after rainy month in drought—environmental injury, not rust fungus. Watering 3x/week may be excessive for clay soil.

Why Not Rust

• Rust = powdery orange pustules on leaf undersides, not flat spots
• Spots don't match rust morphology
• No infectious progression pattern

Likely Causes

• Water injury: Overhead watering + sun = lens effect burns
• Chemical contact: Herbicide drift, fertilizer on leaves
• Edema: Water blisters from cool/wet soil + warm days
• Nutrient deficiency: Yellowish leaves suggest nitrogen/iron need

Diagnostic Steps

1. Hand lens check: spores? insects? residue?
2. Review any foliar applications
3. Soil test for nutrients/pH
4. Close-up photo to nursery/extension

Water Management

Soil should be moist, not wet. Finger test: soil sticks to thumb/forefinger when squeezed = perfect. Clay holds water—3x/week likely excessive after rain. Reduce to 1x/week deep soak.