Anthracnose, Blight, Canker and Damping-off

Anthracnose is somewhat common

Anthracnose Fungus

Common names: anthracnose, leaf blight, leaf shoot, brown blight

Specific diseases that cause anthracnose include:anthracnose (Colletotrichum coccodes = C. atramentarium Taubenhaus = C. dematium)

Threat to garden: low to medium

Identify: Leaves show first symptoms when they turn light green. Soon, sunken water-soaked spots that grow into irregular shapes develop grayish centers with dark borders. Stems develop white wounds that turn black. Little black and white dots soon develop in wounds. Stems may develop cankers. This disease is worst during cool, damp weather— especially in clay and bog soils—and when plants are stressed, especially in hydroponic systems. Anthracnose is not transmitted in seeds but can be found on seed surfaces.

Damage: Anthracnose slows growth and diminishes harvest. It is occasionally fatal.

Cause: Anthracnose is caused in cannabis by three species of Colletotrichum fungi. Colletotrichum atramentarium also causes anthracnose. Brown blight (anthracnose) is caused by Alternaria and Stemphylium. Fungi overwinter in plant debris or soil, and start to grow in the spring.

Prevention: Sanitation is the best prevention. Remove plant residues. When pruning, make clean cuts with sharp, sterile tools to keep wounds clean. Use new soil, and avoid underwatering or overwatering. Avoid planting in clay soils, or amend clay soils to improve drainage. Do not wet foliage and stems when watering.

Control: Trichoderma harzianum (Trichodex) controls anthracnose. Sulfur or copper powders or sprays applied weekly as soon as the disease is identified will keep spores from spreading, but they will not kill the disease. Look for contact fungicides that contain chlorothalonil. There are many systemic fungicides that kill anthracnose.

Blight

Blights Fungal disease

Common names: brown blight, southern blight, twig blight

Specific diseases that cause blight include: bacterial blight (Pseudomonas syringae pv. cannabina) Cylindrosporium blight (Cylindrosporium spp., C. cannabinum Ibrahimov) Leptosphaeria blight (Leptosphaeria cannabina, L. woroninii, L. acuta) brown blight (Alterneria alternata = A. tenuis) southern blight (Sclerotium olfsii), Sclerotium root and stem rot (Athelia rolfsii [teleomorph]) twig blight (Dendrophoma marconii, Botryosphaeria marconii [teleomorph])

Threat to garden: low to medium

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

Damage: kills leaves, slows growth, and kills plants Cause: unsanitary garden room conditions; infected soil, air or plant tissue is introduced into the garden

Prevention: 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 (Bacillus subtilis) against brown blight. Use Binab, Bio- Fungus, RootShield, Supresivit, Trichopel, (Trichoderma harzianum) or SoilGuard (Trichoderma southvirens).

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.

Control: Once blight takes over plant tissue, little can be done. Remove plants from the garden and sterilize the area to avoid contamination.

Canker

Canker Fungal disease

Common names: stem canker, hemp canker

Specific diseases that cause canker include:Cladosporium stem canker (Cladosporium cladosporioides, C. herbarum, Mycosphaerella tassiana [teleomorph])hemp canker (Sclerotinia sclerotiorum)Ophiobolus stem canker (Ophiobolus cannabinus, O. anguillidus) Phoma stem canker (Phoma herbarum, P. exigua) Phomopsis stem canker (Phomopsis cannabina, P. achilleae, Diaporthe arctii var. achilleae [teleomorph])

Threat to garden: low

Identify: The first water-soaked wounds appear on maturing stems and branches. They develop into dark cankers that continue to deepen, and fungus invades the plant. Finally, the black-hearted disease continues to grow on dead stems.

Damage: Hemp canker, mainly a fiber hemp disease, occasionally affects medicinal cannabis.

Cause: present in soil or unsterile, tainted soil

Prevention: Use fresh soil or growing medium for each crop. Keep garden and garden area clean. Remove all plant residues from soil surface. Compost by using a big pile and high temperatures.

Control: Best to prevent hemp canker. All chemical controls are systemic. Once disease takes over, it is often too late. Contans WG contains Coniothyrium minitans bacteria, a parasite to S. sclerotiorum.

Damping-Off

Fungus: kills seeds, seedlings, and clones

Common names: damping-off, stem rot, moldy germination, young plant disease

Damping-off hit seedling before it developed true leaves.

Specific diseases that cause damping-off include: (Botrytis cinerea, Botryotinia fuckeliana [teleomorph], Fusarium oxysporum, F. solani, Nectria haematococca [teleomorph], Macrophomina phaseolina, Pythium aphanidermatum, P. debaryanum auct., P. ultimum, Rhizoctonia solani, Thanatophorus cucumeris [teleomorph] = Pellicularia filamentosa).

Threat to garden: High threat to seedlings! See “Gray Mold (Botrytis cinerea, aka Bud Mold): Stems, Flower Buds.”

About: Damping-off is a catchall term; the disease has many causes.

Identify: There are two kinds of damping-off: one kills seeds when they germinate and before they break through the soil; the second type, post/ emergence damping-off, is the rotting or wilting of seedlings soon after they emerge from the soil. Succulent stems have become water-soaked and then necrotic and develop a sunken, zone at ground level. The little herbaceous plants fall over on the ground. Root decay follows.

Damage: Damping-off attacks rooting cuttings at the soil line if present in growing medium. As the fungi invade stem tissue, the stem loses girth at the soil line, weakens, and then discolors with a brown, watery soft rot. Finally, fluid circulation is cut, killing the seedling or cutting. Damping-off prevents newly sprouted seeds from emerging and attacks seedlings, causing them to rot at the soil line; it yellows foliage and rots older plants at the soil line.

Cause: Various fungal species, including Botrytis, Pythium, and Fusarium, are present in the air, growing medium, plant, or seed. This disease breeds in humid conditions and in poorly aerated, overwatered growing mediums. It attacks weak plants.

Prevention: Control soil moisture. Overwatering is the main precursor to damping-off. Careful daily scrutiny of soil will ensure that the proper amount of moisture is available to seeds or cuttings. Germinate seeds between clean, fresh, moistened paper towels and move seeds to soil once sprouted. Do not plant seeds too deeply; cover with soil one and a half times the width of the seed. Use fresh, sterile growing medium and clean pots to guard against harmful fungus in the soil. Start seeds and root cuttings in a fast-draining, sterile coarse sand, rockwool, Oasis, or Jiffy cubes, which are difficult to overwater. Set them on a grate or surface that readily drains. Do not place a humidity tent over sprouted seedlings—a tent can lead to excessive humidity and damping-off. Damping-off is inhibited by bright light; grow seedlings under the HID rather than fluorescent bulbs. Keep fertilization to a minimum during the first couple of weeks of growth.

Seeds: Coating the seed with protective dust is a form of insurance. Seed disinfection is used to kill organisms of anthracnose and other diseases carried on seed. Damping-off organisms are in the soil, not on the seed. The coating is intended to kill or inhibit fungi in the soil immediately surrounding the seed and so provide temporary protection during germination.

Cuttings: Cuttings are less susceptible to damping-off and love a humidity tent to promote rooting. Keep germination temperatures between 70ºF and 85ºF (21.1ºC–29.4ºC).

Control

Biological: Apply Polygangron (Pythium oligandrum) granules to soil and seed. Bak Pak or Intercept is applied to the soil and Deny or Dagger—forms of the bacterium Burkholderia cepacia—is put on the seeds. Epic, Kodiac, Quantum 4000, Rhizo-Plus, System 3, and Serenade also suppress many causes of damping-off

Chemical: Dust the seeds with Captan. Avoid benomyl fungicide soil drench because it kills beneficial organisms.