Summertime and early fall is when Pythium usually appears. "Pythium" is a generic name for several different root and stem rot fungal species – Pythium, Verticillium, Phytophthora, and Fusarium. For example, "damping-off" in seeds, seedlings and clones is caused by Pythium.

Damage from Pythium includes infection, reduced yields, and ultimately crop failure. Pythium can spread like wildfire in water-based hydroponic systems. Recirculating hydroponic systems provide ideal conditions to rapidly spread Pythium throughout the garden.

In hydroponics Pythium flourishes in anaerobic, oxygen-poor, warm (24-33C), and poorly circulated nutrient solutions. Poor draining heavy clay soils also promote Pythium.

Pythium is spread by un-sterilized tools, tainted water and rotting roots from past crops. It can also be introduced into the grow room by infected plants.

The key to preventing Pythium is keeping plenty of oxygen available to roots. Water temperature dictates the amount of dissolved oxygen in the nutrient solution.

The amount of dissolved oxygen in a nutrient solution depends on the water temperature. Cold water can 'hold' more dissolved oxygen. A fully aerated solution at:

Amount of dissolved oxygen water can hold at different temperatures

10C is 13 ppm

20C is 9 – 10 ppm

30C is 7 ppm

Roots require twice as much oxygen for each 10-degree C. increase in root system temperature. But the oxygen carrying capacity of the nutrient solution will drop by more than 25 percent! There will not be enough dissolved oxygen to supply the root's oxygen needs. This leads to sustained oxygen starvation. Slow growth, nutrient deficiencies, root die-back and low yields result. This stress also makes plants susceptible to disease and pest attacks.

Fotos of healthy and sick roots

Symptoms

Yellow, limp, wilting leaves, often with nutrient deficiencies

The pH slowly becomes more acidic

Root tips brown – could also be from over-fertilization

Low water consumption

Darker roots, not bright white – Note: organic fertilizers also discolor roots

Roots turn brown and slimy and could smell bad. Often plants look healthy.

Root collar swells and becomes reddish and later darkens.

Outer portion of the root is easy to pull off, exposing a thin strand of hair-like tissue.

Damaged roots will not grow back. Slightly infected roots may turn white again if treated promptly. Dead roots are a breeding ground for Pythium.

Prevention

Keep plants healthy, vigorous and stress-free to prevent Pythium. Pythium is virtually impossible to eradicate from an infected system. It is best to clean and sterilize everything with bleach and start over with new clean plants.

Maintain a clean system with healthy plants

Do not over-fill reservoir use a device to meter out or shut off water when filling.

Use tank additives to keep tank clean and healthy

Change and sterilize reservoir weekly.

Keeping nutrient temperatures between 19 and 22 degrees C.

Constant aeration. Use venturis, air stones, and daily h2o2 usage to increase dissolved oxygen. Allow nutrients to fall back into the reservoir to create aeration.

Keep ph below 6.2.

Soil

Reduce chances of root rot by using good sterilized soil. Add amendments to improve drainage and aeration.

Avoid over watering. Saturated soil promotes anaerobic conditions.

Inspect roots for browning. Stressed plants are attacked first, so it is important to inspect crop and remove unhealthy plants.

Keep ph stable, between 5.5 and 6.0

Keep reservoir / root zone temps low: 15 and 21 degrees C. Submerged pumps will increase water temperature

Treating Pythium

Remove and destroy roots and surrounding soil near infected plants. Provide good drainage and avoid overcrowding plants.

1. Dip roots in Hydrogen Peroxide

Remove each plant from hydroponic system and cut off diseased roots. Dip in H2O2 for a minute or longer.

2. Sterilize equipment with 5 percent bleach solution

3. Apply anti-pythium additives, Vitamin B1, and fresh nutrients to a sterilized reservoir strength, at cooler temps. Reduce light levels until roots start to grow.

Biological additives provide vitamins, hormones and nutrients to the plant to encourage beneficial bacteria to colonize the root system, out-reproducing root disease organisms, and may "feed" on decayed roots. Additives should be added during every tank change, except for H2o2.

Garden Calendar

Outdoors

You can still plant seeds and clones outdoors. Plant seeds indoors and transplant for best results.

Prepare soil before transplanting by adding amendments. Use water-absorbent polymer crystals to hold water in remote gorilla gardens.

Harden-off seedlings and clones. Move transplants outdoors for an hour the first day and increase the time by an hour every day. In 7-10 days, transplants will be acclimated.

Transplant seedlings and clones outdoors. Remove lower leaves on leggy plants and bury up to first set of leaves.

Slugs, snails, caterpillars, rabbits, mice and deer are the main pests now. Set out bait for mollusks and caterpillars. Discourage rodents and deer with repellents.

Mulch plants weekly to conserve and attract water.

Water plants regularly. A healthy female clone in a 30-liter container can easily use 5 liters of water a day.

Fertilize if necessary with a complete mix with more N than P and K. Be careful to not over-fertilize. Apply a soluble fertilizer if able to water plants weekly.

Prune and bend plants to avoid detection. Prune top of plants to control growth.

Protect roots from cooking in pots by shading pots.

Indoors

Keep humidity at less than 60 percent in the grow room to avoid problems. High humidity promotes mold and pest attacks. Keep oscillating and extraction fans on 24 hours a day if necessary.

Temperatures below 30 degrees will keep your garden growing strong and healthy.

Water plants daily if necessary. Water usage goes up to more than a liter a day for strong healthy plants. But, be careful not to over-water.

Lower fertilizer dosage if leaves show signs of tip burn or are excessively green.

Flush plants with a mild nutrient solution at least once a month.

Take clones so they are ready to transplant the day you harvest.

Look at leaf undersides closely for spider mites and eggs. Spray mites with pyrethrum or neem as needed.

Harvest. Replace harvested plants with clones the same day of harvest.

Clean and disinfect room before moving in clones.

Remove odors from flowering plants with ozone or charcoal filter.