Why Does My Cannabis Have Yellow Spots?

Dealing with Leaf Septoria

Leaf Septoria….It starts with one or two tiny yellow spots on the bottom leaves, and before you know it, it’s climbing up your 15-foot giant. Most growers see yellow and immediately start dumping nitrogen on the plant, thinking she’s hungry. But if those spots have a dark border and look like a bullseye, you aren’t dealing with a hunger strike—you’re dealing with Leaf Septoria.

In my fifty years, I’ve seen this fungus thrive in humid, crowded gardens where the air gets stagnant. If you don’t catch it early, it’ll strip your plant’s “solar panels” right when she needs them most for flowering.

Stopping the Spread: The Ghost’s Fungal Defense…The Ghost

Septoria is a soil-borne fungus that “splashes” up onto the lower leaves during a heavy rain. Once it’s on the plant, it hitches a ride on the humidity to move upward. This fungus like alot of fungus’s, molds, and mildews are air born and around much of the time. They are just waiting for the right conditions to grow. The best defense is to not allow the right conditions….generally cool, wet, and stagnant air.

The Ghost’s Tactical Defense:

• The “Lollipop” Trim: This is your best defense. Clear out the bottom 20% of the plant’s branches and leaves. You want a “dead zone” between the soil and the foliage so the fungus can’t jump.
• The Mulch Barrier: Remember that “Black Gold” leaf mold we talked about? Covering the bare dirt around your plant with a thick layer of straw or dry forest “duff” prevents the rain from splashing fungal spores from the soil onto your leaves. You can also top with perlite, which also reflects light back up to your plants and helps repel fungus gnats.
• Airflow is Life: Indoor, outdoor, wherever your plants are make sure you’ve cleared enough space for the wind to go through. Stagnant air is a fungal playground.
• The Clean-Up: If you see spotted leaves, pull them off and get rid of them. Don’t just drop them at the base of the plant, or you’re just feeding the fire.

Don’t let a few spots ruin a season. Keep the bottom clean, keep the air moving, and let your plants breathe.