Spotting the Early Signs of Root Rot, Mold, or Bug Invasions on Cannabis Plants

Growing cannabis at home is incredibly rewarding - but even the most careful growers can find themselves facing silent threats beneath the soil, between the leaves, or hidden behind buds. Root rot, mold, and pest infestations don’t always scream their arrival - they creep in quietly and take hold before you know it. Here's how to spot them before they destroy your grow.

Root Rot: Trouble Starts Below the Surface

What It Is:

Root rot is a fungal or bacterial condition that kills off the roots, usually caused by poor drainage, stagnant water, or overwatering. It’s more common in hydroponic systems and containers without proper airflow or runoff.

Early Warning Signs:

• Slowed Growth: The plant seems “stuck” in veg or suddenly stops stretching in flower.
• Drooping Despite Moist Soil: Leaves hang like they're thirsty, but the soil is wet.
• Mushy, Brown Roots (If Visible): In hydro or during transplant, roots look slimy and smell rotten.
• Yellowing Lower Leaves: Begins at the base and spreads upward, mimicking nutrient deficiency.

What to Do:

Improve drainage, reduce watering, add beneficial microbes or enzymes like Hydroguard, and consider transplanting to fresh soil if the damage is severe. In hydro, flush and sterilize the system ASAP.

Mold: The Hidden Harvest Killer

What It Is:

Mold - especially bud rot (Botrytis) and powdery mildew - thrives in humid, stagnant conditions. It’s a nightmare for home growers because it often strikes late in flower when you’re least willing to intervene.

Early Warning Signs:

• White Dusty Spots on Leaves: Looks like flour or ash - usually powdery mildew.
• Grayish or Brown Bud Centers: Buds that seem dry on the outside but are mushy in the middle.
• Sweet, Sickly Smell: Bud rot often smells like fermentation or wet hay.
• Leaf Curling Around Bud Sites: This can trap moisture and give mold a place to spread.

What to Do:

Increase airflow with fans, drop humidity below 50%, and remove infected material immediately (don’t compost it). A foliar spray like Actinovate or a mild baking soda solution can slow down early mildew.

Bug Invasions: Pests That Sneak Up on You

What They Are:

Aphids, spider mites, thrips, fungus gnats - these pests don’t just eat leaves, they can transmit diseases and devastate entire plants if left unchecked.

Early Warning Signs:

• Tiny Bite Marks or Stippling: Looks like pinholes or silvery patches on leaves.
• Specks That Move: Check the undersides of leaves with a magnifier - those “dots” might be mites.
• Sticky Residue or Webbing: Aphids secrete honeydew; spider mites leave webs in crevices.
• Flying Gnats Near Soil: Fungus gnats hover around wet medium and lay larvae in it.

What to Do:

Introduce beneficial insects (ladybugs, predatory mites), use organic sprays like neem oil (early veg only), or apply BTi (Bacillus thuringiensis israelensis) to kill fungus gnat larvae. Always spot-test sprays first and apply during lights-off.

Prevent It Before It Starts

• Inspect daily – especially under leaves and around base of stems.
• Keep air moving – oscillating fans reduce mold risk and deter bugs.
• Control humidity – 40–60% is ideal depending on stage of growth.
• Sterilize your tools – pruners, scissors, and trellis gear can carry pathogens.
• Don’t ignore your gut – if a plant “looks off,” investigate immediately.

You don’t have to be a plant whisperer to detect the early signs of trouble - just an observant grower. Catching root rot, mold, or bug invasions early means fewer losses and better yields. A few minutes of inspection every day can save you weeks of frustration and preserve your harvest.

Homegrow Helpline provides practical, no-fluff advice for everyday cannabis cultivators - whether you’re growing in a closet, a tent, or your backyard.