Foliar spots started on this leaf after it became se verely nitrogen-deficient

It appears as whitish-yellow spots on top of leaves creating pale patches. Grayish mycelium spawn is on leaf undersides, opposite the pale patches. Downy mildew can spread very quickly, causing a lack of vigor and slow growth; leaves yellow, die back, and drop. The disease is In the plant system and grows outward. It is often fatal, spreads quickly, and can wipeout a crap. Avoid promoting this disease by not crowding plants. Keep temperatures above 76°F (26°C) and the humidity below 50 percent.

Control: Cleanliness! Use sterile growing medium. Remove and destroy affected plants, not just foliage.

Biological: Apply Serenade"! (Bacillus subtilis). Bordeaux mixture is also somewhat effective.


Identify: Blight is a general term that describes many plant diseases which are caused by fungus, most often a lew weeks before harvest. Signs of blight include dark, blotchy spots on foliage, slow growth, sudden yellowing, wilting, and plant death. Most blights spread quickly through large areas of plants,

Control: Cleanliness! Use fresh, sterile growing medium. Avoid excess nitrogen fertilization. Avoid blights by keeping plants healthy with the proper nutrient balance and good drainage to prevent nutrient buildup.

Biological: Use Serenade'ii1 (Bacillus subtilis) against Brown Blight, Use Binabiff, Bio-Fungus^, Root Shield dit, Supresivltw, Trichopelw, (Trichodcrma harzianum) or SoilGuard 8) (Trichoderma wrens). Use a Bordeaux mixture to stop fungal blights. Stopping blights in advanced stages is difficult; the best solution is to remove diseased plants and destroy them.

Foliar Spots and Fungi

Identify: Leaf and stem fungi, Including leaf spot, attack foliage. Brown, gray, black, or yellow to white spots or blotches develop on leaves and stems. Leaves and stems discolor and develop spots that impair plant fluid flow and other life processes. Spots expand over leaves causing them to yellow and drop. Growth is slowed, harvest prolonged, and in severe cases, death results, Leaf spot is the symptomatic name given to many diseases. These diseases may be caused by bacteria, fungus, and nematodes. Spots or lesions caused by fungi often develop different colors as fruiting bodies grow. Leaf spots are often caused by cold water that was sprayed on plants under a hot HID. Temperature stress causes the spots that often develop into a disease.

Control: Cleanliness! Use fresh, sterile growing medium with each crop. Move HIDs away from the garden canopy about 30 minutes belore spraying so plants won't be too hot, Do not spray within four hours of turning the lights off as excess moisture sits on the foliage and fosters fungal growth. Do not wet foliage when watering, avoid overwatering., and lower grow room humidity to 50 percent or less. Check the humidity both day and night. Employ dry heat to raise the nighttime temperature to 5-10°F (3-6°C) below the daytime levels, and keep humidity more constant. Allow adequate spacing between plants to provide air circulation. Remove damaged foliage. Avoid excessive nitrogen application.

Biological: Bordeaux mixture may help keep leaf spots in check, but it is often phytottixic when applied regularly indoors.

Sprays: Bordeaux mixture.

Fusarium Wilt

Identify: Fusarium wilt is most common in warm grow rooms and greenhouses. Recirculating nutrient solutions above 75°F (24°C) creates perfect conditions for fusarium. The water and nutrient solution carries this disease with it when contaminated. Fusarium starts as small spots on older, lower leaves. Interveinal leaf chlorosis appears swiftly. Leaf tips may curl before wilting and suddenly drying to a crisp, Portions of the plant or the entire plant will wilt. The entire process happens so fast that yellow, dead leaves dangle from branches. This disease starts in the plant's xylem, the base of the fluid transport system. Plants wilt when fungi plug the fluid How in plant tissue. Cut one of the main stems in two, and look for the telltale reddish-brown color.

Control: Cleanliness! Use fresh, clean growing medium. Avoid nitrogen over-fertilization.

Preventive action is necessary. Keep nutrient solution below 75°F (24°C). Hydrogen peroxide infusions will also arrest fusarium. Always remove infested plants and destroy.

Biological: Mycostopm (Streptomyces griseoviridis), or Denyw, or Daggerm (Burkhoiderici cepacia) and Trichoderma.

Sprays: Treat seeds with chemical fungicides to eradicate the seed-borne infection. Chemical fungicides are not effective on foliage.

Green Algae identify: Slimy green algae need nutrients, light, and a moist surface on which to grow. These algae are found growing on moist rock-wool and other growing mediums exposed to light. They cause little damage but attract fungus gnats and other critters that damage roots. Once roots have lesions and abrasions, diseases enter easily.

Control: Cover the moist rockwool and growing mediums to exclude light. Run an algaecide in the nutrient solution or water with an algaecide.

Powdery Mildew

Identify: First indication of infection is small spots on the tops of leaves. At this point the dis-

Powdery Mildew

Identify: First indication of infection is small spots on the tops of leaves. At this point the dis-

Fusarium wiit causes the center of the stem to turn reddish-brown in color.

Fusarium wiit causes the center of the stem to turn reddish-brown in color.

case has been inside the plant a week or more. Spots progress to a fine, pale, gray-white powdery coating on growing shoots, leaves, and stems. Powdery mildew is not always limited lo the upper surface ol foliage. Growlh slows, leaves yellow, and plants die as the disease advances. Occasionally lalal indoors, this disease is at its worst when roots dry out and foliage is moist. Plants are infected for weeks belore they show the first symptoms.

Control: Cleanliness! Prevent this mildew by avoiding cool, damp, humid, dim grow room conditions, as well as fluctuating temperatures and humidity. Low light levels and stale air affect this disease. Increase air circulation and ventilation, and make sure light intensity is high. Space containers far enough apart so air freely (lows between plants. Allow foliage to dry before turning off lights. Remove and destroy foliage more than 50 percent infected. Avoid excess nitrogen. Copper and sulfur-lime sprays are a good prophylactic.

Biological Control: Apply Serenade»' (Bacillus subtilis) or spray with a saturation mix of baking soda and water.

Sprays: Bordeaux mixture may keep this mold in check. A saturation of baking soda spray dries to a fine powder on the leaf; the baking soda changes the surface pH of the leaf to 7, and powdery mildew cannot grow.

Root Rot

Identify: Root rot fungi cause roots to turn from a healthy white to light brown. As the rot progresses, roots turn darker and darker brown. Leaf chlorosis is followed by wilting of the older leaves on the entire plant, and its growth slows. When severe, rot progresses up to the base of the plant stock, turning it dark. Root rot is most common when rools are deprived ol oxygen and stand in un-aeratcd water. Soil pests that cut, suck, and chew roots create openings for rotting diseases to enter. Inspect roots with a 10X magnifying glass for signs of pest damage.

Control: Cleanliness! Use fresh, sterile growing medium. Make sure calcium levels are adequate, and do not overfertilize with nitrogen. Keep pH above 6.5 in soil and about 6.0 in hydroponic mediums to lower disease occurrence. Control any insects, fungi, bacteria, etc., that eat roots.

Biological: Binab-i«, Bio-Fungus'»; RootShield i<<, Supresivitw, Trichopol'"1

Rotten roots have been soaking in stagnant nutrient solution. Foliage is very slow to grow when roots are rotten!

(Trichoderma harzianum), or SoilGuard'»' (Trichoderma wrens). Sprays: Sprays are not eflectivc.

Pythium Wilt/Rot

Identify: (See Dcimping-off above.)

Sooty Mold

Identify: Black sooty mold is a surface fungus that grows on sticky honeydew excreted by aphids, mealybugs, scale, whiteflies, etc. Sooty mold is only a problem on indoor plants when honeydew is present. Sooty moid restricts plant development, slows growth, and diminishes harvest.

Control: Remove insects that excrete honeydew, Once honeydew is controlled, mold dies. Wash away honeydew and mold with a biodegradable soapy solution. Rinse away soapy water a few hours after applying.

VerticiIlium Wilt

Identify: Lower leaves develop chlorolic yellowing on margins and between veins before turning dingy brown. Plants wilt during the day and recoup when the light goes off. Wilt soon over-


Identify: Viruses are still a mystery. They act like living organisms in some instances and nonliving chemicals in other cases. They must enter plants via wounds. Once a virus takes over plant cells, it is able to multiply. Viruses are spread by insects, mites, plants, animals, and human vectors. Aphids and whiteflies are the worst. Infected lools also transport viruses from one plant to another. Typical symptoms ol viral infection are: sickly growth, leaf and stem spots, yellowing, and low yields. Viral diseases move into the plant's fluid distribution system and destroy it, which olten cause leaf spots and mottling. A virus can completely lake over a plant in a few days. Once a plant gets a virus, there's little you can do.

Control: Cleanliness! Always use fresh, sterile growing medium. Disinfect toots before cutting foliage on different plants. Destroy all jragr planls infeclcd with virus. "^frair*

Biological: None. jf^

arc effective against viruses.

Right: Verticillium wilt is less common than fusarium wilt, but the symptoms are similar. Cut a stem and look for discolored xylem.

comes parts of the plant or the entire plant. Cut the stem in two and look for (he telltale brownish xylem tissue. The fungus blocks the flow of plant fluids, causing wilting.

Control: Cleanliness! Use fresh, sterile soil, Good drainage. Use amonical nitrogen as a source of nitrogen, Do not overfcrtilize.

Biological: BioFungus k> (Trichoderma species), Rhizo-Plus«ii (Bacillus subtilis).

Sprays: No chemical spray is effective,



This simple troubleshooting chart will solve 90 percent of the grow problems encountered when growing cannabis. This chart started with an article in High Times magazine and borrowed from the "Problem Identification Keys" presented in Hemp Diseases and Pests: Management and Biological Control, by J. M. McPartland, R. C. Clarke, D. P. Watson.. Please see that book for much, much more information. One word of cau-tion-this troubleshooting chart assumes the grow room is clean.

Clones are relatively easy to root. Success rate depends on the proper combination of heat, humidity, light, rooting hormone, and growing


medium aeration/moisture. The more precise the combination, the faster and stronger roots grow.

The vegetative growth stage is when problems begin to show. Often, these problems continue through flowering. Remedy problems before they progress. If allowed to persist through flowering, yield will be substantially diminished.

Flowering is the last stage in life and only six to ten weeks long. Problems must be solved within the first two weeks (at the absolute latest, three weeks) of flowering, or yields decrease in relation to the severity of the problems.

Note: Keep growing area super clean to help prevent problems. If you notice insects or fungus on foliage, remove them and check them against color photos and drawings in this book and the troubleshooting chart below,

Troubleshooting Chart

Growth Stage


Quick Fix

Seeds and Seedlings

Seeds do not germinate

Damping off Bad seed

Buy new seed, start over Get your money back!

Root maggots

Drench soil with neem or horticultural oil

Seed germinates, seedling has signs of pests eating/sucking foliage

Spider mites (stippled leaves) Aphids (exude honeydew)

Spray neem oii pyrethrum Spray pyrethrum, insecticidal soap, or nicotine sulfate

Seedling stem at base has dark or sickly growth, suddenly falls over, or suddenly wilts

Damping off

Damping off or a wilt disease Too much or too little moisture

Drench soil with metalaxyl or buy new seeds

Uncommon in clones Correct accordingly

Seedling leaves have yellow, gray, black, and/or dark green (fungus-like) spots

Blight or anthracnose

Remove growing plants and growing medium

Continued on next page:


Wilt and die

Wilt and die Won't root

Vegetative stage

Leggy, weak plants

Lack of moisture Medium too wet

Medium too dry or too wet

Inconsistent rooting hormone

Lack of light

Add humidity dome, mist 4-6 times daily

Drain medium, do not water, no standing water in tray

See "Wilt and die" see above

Change to liquid or gel rooting hormone

Add lamp, change reflector, move lamp closer to plants

Leggy, weak plants

Lack of ventilation, Soil too wet Soil too dry Toxic nutrient buildup

Add vent fan Irrigate less Irrigate more Leach grow medium* change nutrient solution

Stunted, stubby plants

Insect damage Rotten roots Toxic nutrient buildup

Spray pyrethrum** Irrigate less Leach grow medium*

Burred leaf tips Purple stems & burned leaf spots

Toxic nutrient buildup-Could be one of many different nutrients

Leach medium* weekly Lower nutrient dose & leach medium* weekly

Leaf spots, margins burned, discolored leaves, pale leaves

Nutrient toxicity

Leach medium*, change nutrient solution, change fertilizer, refer to specific nutrient problems

Small, whitish spots on leaves

Spider mite damage

Spray pyrethrum**, neem

Insect damage-chewed leaves, Whiteflies, aphids, scale, Spray pyrethrum** or insects/eggs visible on plants- caterpillars, larva, etc, neem oil check under leaves with 20X loop.

Fungus or mold on foliage or soil High humidity (above 60%) Add vent fan

High temperature (above 80°F) Add vent Ian

Spray soil with 5% bleach solution and wash olf next day. Spray foliage with 10% baking soda solution

Continue reading here: Chapter Fourteenpests Diseases

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