Growing one’s own cannabis is an empowering feeling… until it goes horribly awry. Learning about proper nutrient balance, lighting, and watering can prevent many issues, but sometimes problems are more than grower error. Here are six signs that your plants are sick, and may need to be put down.

1. White powder on leaves

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If leaves look dusted in spots with white powder, be warned. Powdery mildew is a fungal infection that first appears as small bumps on fan leaves, and quickly evolves to a white powdery appearance.

This fungus not only makes plants sick but can affect people who ingest or smoke it as well. Plus, it makes the bud taste quite bad, so avoid it at all costs. The most common sources of PM are overwatering, crowding, open ventilation and cross-contamination from other sources.

The best way to deal with powdery mildew is prevention. But once it happens, turn off fans and trim small sections into a disposable container or isolate majorly affected plants, taking care not to shake loose any spores in doing so.

If you want to try to save infected plants, spray with a diluted mix of apple cider vinegar or baking soda and distilled water. Wipe away the mildew with paper towels, changing frequently.

2. Gray fuzz in the buds

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This fungal disease can ruin an entire crop in a very short period of time! Bud rot, or Botrytis, spores attack plants through any wound or trim site. It turns affected stems soft and brown, wilting anything attached, and moves quickly to the dense, moist buds.

Leaves will turn brown, wilt, and a gray mass of fuzz can be seen inside affected buds. Once this villain has struck a crop, the best thing to do is isolate and destroy the infected plants.

3. Circular lesions

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No one wants lesions! But yellow circular spots on lower leaves that turn brown and bumpy as leaves die off is due to Leaf Septoria. This disease not only affects the crop it surfaces on but can remain in the soil long afterward, affecting future crops.

An increase in nitrogen helps to fend off leaf septoria. Catching and removing any leaves affected early on can save a crop, as long as proper care is taken not to spread the disease to the rest of the plant.

4. Dark spots and curling

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Many different problems cause plants to droop, or even lose leaves. But Fusarium is easy to spot due to two factors. First, small dark spots appear on lower leaves, which soon become yellowish brown and turn upwards.

Second, when the leaves die, the remain attached to the plant in a distinctive wilted fashion. As the disease spreads through the plant, stems will swell and burst open, causing even more problems.

Fusarium fungus can also attack roots but is easy to see in hydroponic setups early on. Roots turn reddish instead of a healthy white, and the redness will begin to travel up the stems.

5. Browning of the stem

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A fungus similar to Fusarium, it turns lower leaves grayish and can also turn the bases of stem nodes brown as well. Leaves will yellow between veins before turning gray.

6. Root rot

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Obviously easier to catch in hydroponic setups, Pythium fungus travels through water or water in the soil to turn healthy white roots brown and slimy. A rotten smell soon emerges, and the outer sheath of the roots will slide off.

Above the soil, symptoms mirror general nutrient deficiencies which are in fact because of the root rot. The overall plant will show spots, yellowing, and telltale weakening of stems. When caught early enough, lowering root temperatures and increasing oxygen will help plants to recover.

7. Unusually shaped yellowing

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Most plant issues present in specific shapes, such as circular spots or discoloration spreading in an even fashion from one area of the leaf to the rest. If, however, the yellowing appears to have a random appearance across veins, tips, and the broad areas of the leaf, TMV or Tobacco Mosaic Virus is the likely candidate.

As its name indicates, this virus is mainly found in tobacco, but also affects lettuce and many weeds. It can even survive the commercial drying and packaging process to live in cigarette tobacco. The virus can stay dormant for a very long time and will travel inside the plant to affect it and any clones or seeds it may produce.

Early detection is difficult, as the rod-like structures that bind to plants are microscopic. Young leaves will show yellow and green patches and discolored wavy lines. Lower temperatures are this viruses friend, so warmer grows will be less affected. Plants may survive this disease, but due to leaf damage, yields can be drastically reduced.

Sickness prevention for your plants

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The best way to treat these diseases is to prevent them from happening in the first place. Fungus, bacteria, and other diseases most often occur due to cross-contamination.

  • Ensure the grow environment, tools, and clothing worn inside the grow are as sterile as possible.
  • Avoid excess humidity, standing water, and wet leaves, all of which encourage molds and bacteria.
  • For cannabis strains that grow thick and dense, trim and thin them to allow better air flow.
  • Remove all trimmings and dead plant material from the grow immediately.
  • Use soil that is sterile or treated with beneficial microbes. For compost, ensure that it is completely decomposed with no foul odor.

Bugs, wind, and humans can all carry these diseases into a grow. Unlike nutrient deficiencies or burn, once a plant has a serious disease, it is generally better to cull the herd than fight the problem.