An indoor grower must make quick and precise decisions when evaluating the plants. A delayed or incorrect decision will not only fail to correct the problem, but may make it worse. This is why education and experience play such vital roles in indoor horticulture.

The symptoms of many plant ailments mimic each other. Without education or experience, or both, it is likely that a problem may be misdiagnosed.

Root diseases in an indoor garden are commonly misidentified as other problems. Because of this, many growers who experience a root disease never know what they actually had. Proper identification of a root disease could be the determining factor in salvaging a reasonable yield from a damaged crop.

Pythium

Pythium, a.k.a. root rot, is the most common root disease to plague the indoor horticulturist.

This damaging, parasitic root fungus is capable of quickly spreading and destroying otherwise healthy crops. This is a very common ailment for growers who tend to overwater their plants.

Pythium thrives in anaerobic conditions and dies off in well oxygenated conditions.

Planting containers that stay saturated eventually become stagnant. This stagnant environment, which is depleted of much of its dissolved oxygen content, is perfect for pythium.

The first signs of pythium can mimic a nitrogen deficiency, with the lower leaves turning yellow. Eventually these leaves may also acquire brown spots, a symptom that mimics other nutrient deficiencies.

The entire plant will eventually appear wilted and, in extreme cases, the plant will die. Upon inspection of the roots, the grower can quickly identify pythium. Brown, slimy roots are a dead giveaway that pythium lurks in your grow room.

Treatment/Prevention

If caught early enough, it is possible to recover from a pythium attack. There are many oxygen-boosting additives available in hydroponic stores.

Diluted hydrogen peroxide is a way growers can increase the dissolved oxygen content. A hydroponic grower must be sure to maintain a consistent temperature of 65-70ºF in the reservoir.

When the temperature of water rises, the dissolved oxygen content decreases. Pythium is notorious for showing up in hydroponic systems when the water temperature reaches above 75ºF.

Hydroponic gardeners can also add an ultraviolet (UV-C) filter to their reservoirs to kill live spores.

Rhizoctonia

Rhizoctonia, a.k.a. damping-off, is also a very common pathogenic fungus found in indoor gardens.

The early signs of this fungus may appear as dark sections on a leaf’s edge or surface and mimic nutrient deficiencies or insect damage.

As this nasty fungus progresses in the plant’s tissue, brown spots will appear on the stem. These spots are a telltale sign of rhizoctonia.

Eventually, a brown, mushy mess is all that will remain at the base of the plant. Rhizoctonia commonly affects seedlings and clones and is one of the biggest contributing factors to unsuccessful propagation.

Treatment/Prevention

Use only sterilized or pasteurized media for your seedlings and cuttings. Studies show that soils rich in calcium or soil amended with wood ashes (which adds calcium) are less likely to allow rhizoctonia to develop.

The best possible way to avoid rhizoctonia is to ensure that your media is rich in beneficial microorganisms. Many strains of beneficial organisms will actually eat rhizoctonia until it is vanquished from the medium. Rich compost teas or quality microorganism additives are a grower’s best defense against rhizoctonia.

Other Diseases

In Part 2, we will discuss phytophthora, fusarium wilt, and vertcillium wilt. These three root diseases are less common than pythium and rhizoctonia for the indoor horticulturist, but are equally as detrimental.

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