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Resources for Growing Quality Medical Marijuana

Plant Troubleshooting Guide: Advanced Section

By St0ney:

1. Ventilation
2. Compost Tea
3. Composting
4. Help from kelp
5. Homemade Emulsion
6. How to SoG
7. Humate Benefits
8. Organic Gardening
9. Soil Primer
10. Why incandescent lights suck
11. Worm Bins
12. Growers Glossary
13. Hydrogen Peroxide
14. CO2
15. Plant Troubleshooting Guide
16. Lighting
17. Non-Organic Soil Test for Organic Gardening
18. PH & Magnesium Deficiency

 

Welcome to our plant troubleshooting guide. We have put together this guide to help answer some of the repetitive questions we get on a daily basis.

 

Most Common Problems

The most common problems are: over watering & over fertilizing, followed closely by an incorrect pH & root bound.

****Before ANY corrective steps are taken these factors MUST be ruled out.****

Nutrient Deficiencies - Nutrient deficiencies in modern gardens are really rare. What most people see as a ‘Nutrient Deficiency’ is, 9 times out of 10, a pH problem. A pH that is too high or too low ‘locks out’ your plants ability to uptake nutrients. Since the plant can not uptake those nutrients they appear to be deficient. When in fact, there are plenty of nutrients in the solution/soil but, due to pH Lock-out, they are unavailable to the plant. Adding supplements or more nutrients (which is what most do) will only compound this problem by throwing the pH off even more and further raising the nutrient/soil PPM. The best thing to do if you suspect ANY form of nutrient deficiency is to check and adjust the pH as necessary. The proper pH ranges for both hydroponics & soil is shown in the chart below. Pay particular attention to the ranges that certain nutrients are available and when they are locked out.

Solution - Adjust the pH to the correct range for your type of grow.
Hydroponics = 6.1 to 5.5
&
Dirt = 6.8 to 6.3

Over Watering - Signs of over watering include: Leaf wilting/drooping and Chlorosis (Leaf Yellowing). Also, smelly soggy soil is another indication in soil gardens.

Solution - Increase the temperature and airflow to evaporate some of the excess water. Also, you can add some h2o2 when watering to help the roots still receive O2. And just don’t water as much. You should only water when your soil/medium is dry. If you have smelly soggy soil the best thing to do is transplant it into fresh dry soil.

Over Fertilizing - Signs of over fertilization include: dead/burnt leaf tips/margins and leaves curling under.

Solution - Check and adjust the pH level as necessary. Flush and decrease the fertilizer/nutrient level.

pH Problems - pH problems can manifest it self in many different ways. Anywhere from: nutrient deficiencies to over fertilization and leaf burn. The key to telling which you have is, knowing your pH.

Solution - Check and adjust the pH level as necessary.

Root Bound -Root bound is where the roots of your plant outgrow the container they are potted in. Plants that are root bound exhibit stunted growth, stretching, smaller and slower bud production, easier to burn with nutrient solution, needs watering too often, and wilting. A root bound plant will always start yellowing with the bottom leaves and work its way up the plant until all the fan leaves are gone.

Solution - See root bound below in the Root Problems section.

Heat Stress - Signs of heat stress can look a lot like nutrient burn, except it occurs only on the top of the plant closest to the lamps. A yellowing of the upper leaves is usually a bleaching from being too close to HID lights.

Solution - A good test to see if your lights are too close is to put your hand between the light and the plant. If your hand gets too hot for comfort, the light is too close and needs to be moved up higher.

 

Leaf Problems

Yellowing (Chlorosis) - Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots (see Root Bound below), high alkalinity, and nutrient deficiencies. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH. **Note- Always check the pH before increasing nutrient level. In the last few weeks of flowering a yellowing of the leaves is completely normal as the plant uses up all stored nutrients.

Yellowing - Lower/Middle Leaves - Yellowing of the lower leaves/older growth is a sign of a possible Nitrogen (N) deficiency. Nitrogen is a transferable element (this means the plant can move it around as needed). If a plant is not receiving enough Nitrogen from the roots then it will rob Nitrogen from the older growth. Plants that are Nitrogen deficient will exhibit a lack of vigor and grow slowly resulting in a weak and stunted plant that is significantly reduced in quality and yield. In a Hydroponic system, usually the pH is too high and has locked out the available Nitrogen. In soil a yellowing of the lower leaves could also be an indication of a root bound plant (see Root Bound below).

Solution - First, check the pH, and adjust if necessary. The correct pH for marijuana is 6.3 - 6.8 in soil and 5.5 - 6.1 in a hydroponic system. Second, make sure you are giving the correct amount/type of fertilizer/nutrients. For the vegetative stage of growth marijuana needs a fertilizer/nutrient with a high Nitrogen (N) content like 2-1-1 (or 20-10-10).

Yellowing - Upper (New Growth) - Yellowing of the upper (new growth) of the plants could be a sign of a Sulphur (S) deficiency. Sulphur deficiency is pretty rare but usually start off as a yellowing of the entire ‘younger’ leaf including the veins. Other signs of sulfur deficiency are: Elongated roots, woody stems, and Leaf tips curling downward. **Note- Most yellowing of the upper leaves is a bleaching from being too close to the lights.

Solution - Check and adjust the pH level as necessary. Check your fertilizer/nutrient levels and make sure you are giving the correct amount/type for you particular stage of growth. Also a good test to see if your lights are too close is to put your hand between the light and the plant. If your hand gets too hot for comfort, the light is too close and needs to be moved up higher.

Leaf Curling Up - Leaf curling up can be a sign of a Magnesium (Mg) deficiency caused by too low of a pH level. Magnesium deficiency will show as a yellowing (which may turn brown and crispy) and interveinal (in between the veins) yellowing beginning in the older leaves. Interveinal chlorosis (yellowing) will start at the leaf tip and progressing inward between the veins. It could also be a sign of excess heat and humidity in the grow room.

Solution - Check and adjust the pH level as necessary. When the pH is not at the proper level marijuana will lose its ability to absorb some of the essential elements required for healthy growth. If you’re growing in soil Magnesium will begin to be locked out at a pH of 6.5 and lower, in hydro it starts at 5.8 and below. If the pH is correct, then add 1 teaspoon of Epsom salts per each gallon to your water. Or, to foliar feed them, add a ½ teaspoon per quart to a spray bottle. **Note- If your tap water is over 200 ppm Magnesium will be locked out due to the calcium in the water. Magnesium can get locked out by too much Calcium (Ca), Chlorine (Cl) or Ammonium Nitrogen (NH4+). If this is your problem we suggest using bottled or RO (reverse osmosis) water.

Leaf Curling Down - When the leaves curl under and burn at the tips and margins it’s usually a sign that the nutrient level is too high.

Solution - Check and adjust the pH level as necessary. Flush and decrease the nutrient level.

Droopy Leaves - Leaves that are drooping are most likely caused by over watering/under watering or lack of light.

Solution - First off, for soil, Place you finger into your soil a few inches and see if it's dry or wet. If over watering is your problem, increase the temperature and airflow to evaporate some of the excess water also you can add some h2o2 when watering to help the roots still receive O2. **Warning!- Chronic over watering can lead to soggy roots and stagnant, icky soil. if you slide the plant out of the pot to check the soil and it stinks or is soggy then transplant into fresh dry soil. For a hydroponic system, check to see if your medium is dry or wet before you water (or your pump comes on). If your medium is still pretty wet, then you are over watering and need to water less often. If your medium is very dry before watering, under watering is your problem, just water more frequently. And lastly, If lack of light is the problem, Add more light.

 

Root Problems

Root Bound - Root bound is where the roots of your plant outgrow the container they are potted in. Plants that are root bound exhibit stunted growth, stretching, smaller and slower bud production, easier to burn with nutrient solution, needs watering too often, and wilting. A root bound plant will always start yellowing with the bottom leaves and work its way up the plant until all the fan leaves are gone.

Solution - To fix this problem you need to transplant your plant into a bigger pot. The 'rule of thumb' with soil is 1 gallon of soil for every foot of growth except for clones which can use a smaller size. So a 2' tall plant is going to need AT LEAST a 2 gallon container. First thing you need to do is gently remove your plant from it’s smaller container. While it’s out, inspect its roots, if the roots run in a tight circle around the outside of the root ball, you caught it just in time. Very carefully use your fingers to dig into the outside 1/2" of these circular roots, loosen them up and pull them gently (yes, I said gently ) outward. If the roots are extremely tight, you can VERY carefully slice a thin layer (less then a ½") off the outside of the entire root-ball. Once you have tended to the roots It’s time to replant it. Set the now un-bound root-ball into its new larger pot.**Note- Do not pack down this new soil, you want the soil to be settled (with no air pockets) but loose enough to allow the roots to easily penetrate it.

Stunted Roots - Stunted roots (slow or no new root growth) is could be caused by a calcium deficiency, aluminum toxicity, copper toxicity, pH acidity, or soil toxicity.

Solution - As always check and adjust the pH level as necessary. If soil toxicity, of any kind, is your problem then you need to flush it real good.

Stem Problems

Stem Breakage - Everyone from time to time has had this problem or will. This is when your stem is broken. Stem breaks can come from a number of things: training, dropping something on it, animals, weather. No matter how it happened the most important thing is to not panic.

Solution - Fixing this is not really a problem. Splint it with something and tape it in place. Marijuana has a great ability to come back even after a stem break. Give her a week or so to recover before she will start to grow again. And be more careful next time!

Insect Problems

First off, our grow guide has a great section on insects and animals that should be read. ( Deer, Rodents and Insects) Here is a recipe taken from there for an organic insect repellant.
Quote:

Ingredients:
3 hot green peppers (canned or fresh)
2 or 3 cloves garlic
3/4 tsp liquid soap
3 cups water

Puree the peppers and garlic cloves in a blender. Pour into a spray bottle and add the liquid soap and water. Let stand 24 hours. Strain out pulp and spray onto infested plants, making sure to coat both tops and bottoms of leaves.

 

The best way to keep insects out of your garden is to be Pro-active and always on the look out for trouble. At the first signs of an infestation you must move quickly or quality and yield will be greatly affected. Since we are growing a consumable crop, getting rid of any insects prior to flowering is an absolute must. It’s VERY important to enter flowering without any bugs! We cannot stress this strongly enough, it’s about removing all bugs from any plants in the vegetative stage so the problem isn’t carried into flowering. We all want the yield/potency to be the most it can be and it can only do this without any bugs attacking its systems.

Aphids - Aphids are soft-bodied insects that use their piercing sucking mouthparts to feed on plant sap. They usually occur in colonies on the undersides of tender terminal growth. Heavily-infested leaves can wilt or turn yellow because of excessive sap removal. Aphids produce large amounts of a sugary liquid waste called "honeydew". The honeydew that drops from these insects can spot the windows and finish of cars parked under infested trees. A fungus called sooty mold can grow on honeydew deposits that accumulate on leaves and branches, turning them black. The appearance of sooty mold on plants may be the first time that an aphid infestation is noticed. The drops can attract other insects such as ants, that will feed on the sticky deposits. Infestations generally result from small numbers of winged aphids that fly to the plant and find it to be a suitable host. They deposit several wingless young on the tenderest tissue before moving on to find a new plant. The immature aphids, or nymphs, that are left behind feed on plant sap and increase gradually in size. They mature in 7 to 10 days and then are ready to produce live young. Usually, all of them are females and each is capable of producing 40 to 60 offspring. The process is repeated several times, resulting in a tremendous population explosions. Less than a dozen aphid "colonizers" can produce hundreds to thousands of aphids on a plant in a few weeks. Aphid numbers can build until conditions are so crowded, or the plant is so stressed, that winged forms are produced. These winged forms fly off in search of new hosts and the process is repeated.

Solution - Early detection is the key to reducing aphid infestations. The flight of winged colonizers cannot be predicted, so weekly examination of plants will help to determine the need for control. Examine the bud area and undersides of the new leaves for clusters or colonies of small aphids. The presence of these colonies indicates that the aphids are established on the plants and their numbers will begin to increase rapidly. Fatty acid salts or insecticidal soaps are very good against aphids. They apparently work to disrupt insect cell membranes. They require direct contact with the insects and leave no residual effect. Nervous system insecticides, such as malathion, Dursban (chlorpyrifos), and Orthene (acephate), are labeled for use on many shade trees and ornamental plants for aphid control. As with soaps, coverage is very important and a follow-up application may be necessary. Sevin (carbaryl) is not effective against many aphids so it is generally not a good choice for control unless recommended specifically. In fact, applications of Sevin may reduce the number of beneficial insects, such as lady beetles, and increase the potential for aphid outbreaks. Beneficial insects, such as lady beetles and lacewings may eat large numbers of aphids but the reproductive capability of aphids is so great that the impact of the natural enemies may not be enough keep these insects at or below acceptable levels. We have this great organic recipe in our Grow Guide: To keep aphids and other pests off your plants just finely choped onion and 2 medium cloves of garlic. Put ingredients into a blender with 2 cups of water and blend on high. Strain out pulp. Pour liquid into spray bottle. Spray a fine mist on plants, making sure to coat both tops and bottoms of leaves.

 

Spider Mites - Spider mites are not insects but are more closely related to spiders. These arachnids have four pairs of legs, no antennae and a single, oval body region. Most spider mites have the ability to produce a fine silk webbing. Spider mites are very tiny, being less than 1/50 inch (0.4mm) long when adults. Spider mites have tiny mouthparts modified for piercing individual plant cells and removing the contents. This results in tiny yellow or white speckles. When many of these feeding spots occur near each other, the foliage takes on a yellow or bronzed cast. Once the foliage of a plant becomes bronzed, it often drops prematurely. Heavily infested plants may be discolored, stunted or even killed. Web producing spider mites may coat the foliage with the fine silk which collects dust and looks dirty. Spider mite species seem to be warm weather or cool weather active pests. The twospotted, European red, honeylocust, and oak spider mites do best in dry, hot summer weather. The spruce and southern red spider mites do best in cool spring and fall weather. All spider mites go through the same stages of development. Adult females usually lay eggs on their host plants. The eggs hatch in days to weeks into the first stage, called a larva. Larvae are round bodied and have only three pairs of legs. The larvae feed for a few days, seek a sheltered spot to rest and then molt into the first nymphal stage. The first nymph now has four pairs of legs. The first nymphs feed a few days, rest and molt into the second nymph. The second nymphs feed, rest and molt into the adult stage. The males are usually the size of the second nymph and have pointed abdomens. The females have rounded abdomens and are the largest mites present. Most spider mites spend the winter in the egg stage but the twospotted spider mite over winters as adult females resting in protected places.

    

Solution - Early detection of spider mites, before damage is noticed, is VERY important. The tiny spider mites can be detected only by a full and thorough leaf inspection (on both sides of the leaf). If you find Spider Mites you must act fast and hit them hard with either a bleach solution (1 tablespoon of bleach to 1 gallon of 95°F, pH balanced, water in a spray bottle.) or use a miticide with Abamectin or lindane in it. That seems to work best. There are insect predators that can help in providing some CONTROL but this does not mean 100% eradication and in a consumable crop that is what we are after. The predator mite can help to control them if chemical sprays are not your thing.

 

White Flies - White flies behave just like spider mites. The insect hides underneath the leaf, and sucks it's dinner from it. Which results in white spots on the top side of the leaf. White flies are easily spotted with the naked eye. If you shake the plant a little, they'll fly around. They look like little white moths, around 2 millimeters in size.

Solution - A sizeable infestation can be combated with your favorite insecticide. If you're not so anxious to use such strong methods, you can purchase assassinator wasps, the ichneumon fly (Encarsia formosa). This natural enemy doesn't sting people, but works well at eliminating white flies. Since it's only a small wasp (smaller than the white fly itself), it takes a while before all the white flies have disappeared. Additionally, you have to put new assassinator wasps out approximately every two weeks.

 

Thrips - Are small, fast-moving insects with wings. They rasp, or grate the marijuana leaves open, and suck the sap out. Thrips prefer flowering tops, and fresh, young leaves. Affected leaves have shiny, silvery spots. This is caused by the thrips sucking the chlorophyll out of the leaves. In spite of the fact that they're small, you can see them marching in columns on an infested plant.

Solution - Thrips can be fought with your favorite insecticide. Or predatory insects, the thrips' natural enemy is Amblyseius cucumeris.

 

Lice - Also see Aphids above. Lice are found inside as well as outside. And thrive during the summer months. Lice are the most interested in plants with questionable health.

Solution - There are two methods to kill lice, spraying with insecticide, and setting out assassinator wasps. The problem with most flying predatory insects is that they're attracted to the high-pressure gas lamps we all love to use, which sends most of them to a quick and fiery death.

 

Slugs/Snails - The common slug is too common a pest to even need much of an introduction. Slugs attack a wide range of plants, causing anything from slight damage to death.

Solution - Unfortunately, there is no foolproof method for eradicating slugs. All one can hope for is to reduce their numbers and protect plants when they're at a vulnerable stage. Toads, frogs, and beetles eat slugs and are worth encouraging in your garden. One of the best ways of dealing with slugs is to use physical barriers. Place plastic bottle cloches around plants, or sprinkle circles of lime, eggshells, or sawdust around plants. Slugs are attracted to saucers or plastic pots of milk or beer (they drown themselves in ecstasy). To be sure you're keeping your slimy slug population under control; collect them by hand at night or on damp days. Try collecting them under a tile or wet cardboard, and squash all eggs you find while digging. Placing a saucer of salt is another method that’s as old as the hills. Martha Stewart recommends coiling a piece of wire around the base of your plants to give slugs a shocking experience. Of course Martha probably doesn't have the same plants in her garden as we do, but we won't tell her if you don't.

 

Marijuana Diseases/Viruses

"Diseases of Cannabis are caused by organisms or abiotic sources. Organisms include fungi (first and foremost), nematodes, parasitic plants, bacteria, and viruses. Abiotic (non-living) causes include nutrient deficiencies, pollutants and genetic diseases. Different diseases prevail in different crops (e.g., drug cultivars versus fiber cultivars). Disease prevalence is also modulated by geography and climate. The claim that Cannabis has no diseases is not correct, Cannabis suffers over 100 diseases, but less than a dozen are serious. Serious diseases include gray mold, hemp canker, damping off, assorted leaf spots, blights, stem cankers, root rots, nematode diseases, broomrape, macro- and micronutrient deficiencies, and genetic diseases. Environmentally stressed plants become predisposed to diseases. Stress includes drought, insufficient light, untoward temperatures, or growing plants in monoculture."
(McPartland, J. M., 1996. A review of Cannabis diseases. Journal of the International Hemp Association 3(1): 19-23.)

That quote was taken from a great page on Cannabis diseases that everyone should read.

Grey Mold/Fungus (Botrytis) - Botrytis blight or gray mold is a fungus disease which infects a wide array of herbaceous annual and perennial plants. There are several species of the fungus Botrytis which can cause blights; the most common is Botrytis cinerea. Botrytis infections are favored by cool (60 degrees Fahrenheit or 15 degrees Celsius), rainy spring and summer weather. Gray mold can be particularly damaging when rainy, drizzly weather continues over several days. Look for masses of silver-gray spores on infected plant parts that are growing in humid areas. Tiny, black, shiny specks might also be seen embedded in diseased plant tissue. These are sclerotia of Botrytis: they allow the fungus to survive the winter. Botrytis blight can affect leaves, stems, crowns, flowers, flower buds, seeds, seedlings, bulbs, and just about any other part of a plant with the exception of the roots.

Solution - The best way to manage this disease is by inspection and sanitation. Remove infected flowers, leaves, or the entire plant if it's infected at the base, and take it away from your grow area before dispose if it. It is best not to do any sanitation when plants are wet since this could spread fungal spores during conditions which favor infection. Likewise avoid overhead watering, or misting plants especially if you have had trouble in the past. To promote rapid drying of plants space them to allow good air circulation. Sanitation alone is not sufficient to control this fungus. The fungus can produce 60,000 or more spores on a piece of plant tissue the size of your small finger nail. Even one spore can infect a plant and cause disease. So, avoid injuring plants in any way. Do not leave large stubs of stems when taking cuttings. Ventilate your grow space to prevent high humidity conditions. Even lowering the humidity slightly can have a significant effect on Botrytis. Outdoor planting should be planned to provide good air circulation patterns. This is the most important means of stopping this fungus. Added protection is available for many crops by applying a fungicide or combination of fungicides. However, Botrytis can develop resistance to certain chemicals. An ozone treatment is also an option, ozone is excellent for decimating spore counts in the grow room and a decent UV tube unit placed high in the room with a fan blowing through it can reduce dramatically the risk of botrytis.

 

Tobacco Mosaic virus - The tobacco mosaic virus can attack a wide range of plants, including tomato, pepper, eggplant, tobacco, spinach, petunia, marigold, and our beloved herb marijuana. On marijuana the virus infection causes light and dark green mottled areas on the leaves. The dark green areas tend to be somewhat thicker than the lighter portions of the leaf. The leaf mottling is seen more easily if the affected plant surface is partially shaded. Stunting of young plants is common and often is accompanied by a distortion and fern-like appearance of the leaves. Older leaves curl downward and may be slightly distorted. Certain strains of the virus can cause a mottling, streaking and necrosis of the buds. Infected plants are not killed, but they produce poor quality buds and low yields. Tobacco mosaic, is incited by a virus. The tobacco mosaic virus is very stable and can persist in contaminated soil, in infected plant debris, on or in the seed coat, and in manufactured tobacco products. The virus is transmitted readily from plant to plant by mechanical means. This may simply involve picking up the virus while working with infected plant material, then inoculating healthy plants by rubbing or brushing against them with contaminated tools, clothing, or hands. Aphids are not vectors of the virus, although certain chewing insects may transmit the pathogen.

Solution - Virus diseases cannot be controlled once the plant is infected. Therefore, every effort should be made to prevent introduction of virus diseases into the garden. Sanitation is the primary means of controlling virus diseases. Infected plants should be removed immediately to prevent spread of the pathogens. The use of tobacco products during cultural practices should be avoided to prevent inoculation of plants with the tobacco mosaic virus. Those people using tobacco or working with infected plant material should wash their hands thoroughly in soapy water before handling your plants.

 

Pythium Root Rot (Pythium spp.) - Pythium root rot can be caused by several different species of the fungus Pythium. These fungi are common in field soil, sand or sediment of surface water supplies, and dead roots of previous crops. Pythium has also been found in some commercially available soilless potting mixes. Pythium is easily introduced into pasteurized soil or soilless mixes by using dirty tools, dirty pots or flats, walking on or allowing pets to walk on the mixes and by dumping the mixes on benches or potting shed floors that have not been thoroughly cleaned. When introduced into pasteurized soil or soilless mixes, Pythium can cause severe root rot because it has few competitors to check its activity. This fungus poses a threat to crops grown hydroponic systems. If the reservoir is heavily contaminated with debris or soil harboring Pythium, the fungus can spread to a large number of plants quickly. If the fungus infests a cutting bed or if contaminated water is used in propagation, large losses usually occur. Almost all plants are susceptible to Pythium root rot. Root tips which are very important in taking up nutrients and water are attacked and killed. Pythium also can rot the base of unrooted cuttings. Symptoms of Pythium include: Stunted plants, root tips are brown and dead, Plants yellow and die, Plants wilt at mid-day and may recover at night, rot may proceed up the stem, brown tissue on the outer portion of the root easily pulls off leaving a bare strand of vascular tissue exposed, and the cells of roots contain many microscopic thick-walled spores.

Solution - Pythium root rot is difficult to control once it has begun. Every effort should be directed toward preventing the disease before it begins. Pasteurize soil and sand with heat (a microwave) or chemical fumigant treatments. If the water supply is suspected of being the primary source of Pythium, it may be necessary to treat the water before use. Slow sand filtration has been shown to be an effective, simple, and inexpensive method for removing Pythium from water. Cover the treated soil and store it or the soilless mix in an area that will not be contaminated through the introduction of non-treated soil. Likewise, cover ebb and flow system reservoirs. Disinfest all surfaces, tools, and equipment that will contact the potting mix. We have also found that Hydrogen Peroxide (H2O2) is great for controlling Pythium in both dirt and hydro.

 

Damping-off - Damping-off generally refers to sudden plant death in the seedling stage due to the attack of fungi. These fungi are soil borne and are stimulated to grow and infect the seed or seedling by nutrients released from a germinating seed. However, seedlings may be injured or killed by something other than fungi, for example, toxic materials in the soil, excess or deficient soil moisture, seed defects, temperature extremes, toxic gases in the air, etc. A correct diagnosis is the key to effective control measures. Damping-off disease of seedlings is widely distributed and is a problem on a worldwide basis. It occurs in most soils, temperate and tropical climates, and in greenhouses. The disease affects seeds and seedlings of various crops. The amount of damage the disease causes to seedlings depends on the fungus, soil moisture, and temperature. Normally, however, cool wet soils favor development of the disease. Seedlings in seedbeds often are completely destroyed by damping-off, or they die after transplanting. Frequently, germinating seeds are killed by damping-off fungi before they emerge from the ground, which accounts for poor stands in many crops. Older plants are seldom killed by damping-off fungi mainly because the development of secondary stem tissue forms a protective barrier and limits fungal penetration. However, portions of the roots and stems still can be attacked, resulting in poor growth and reduced yields. When seeds are planted in infested soils, damping-off fungi may attack them at any stage. The damping-off fungi may attack the seed prior to germination, or they may attack after the seed has germinated but before the seedling has emerged above the soil line. Infected seed becomes soft and mushy turning a brown to black color, and it eventually disintegrates. Seeds that have germinated and become infected develop water-soaked spots that enlarge and turn brown. The infected tissue collapses, resulting in death of the seedling. Penetration and death of seeds before they emerge is termed preemergence damping-off. Seedlings that have emerged are usually attacked at or below the soil line. The organism can easily penetrate the young soft stem tissue. The infected stem portion becomes discolored and begins to shrink. As this occurs, the supportive strength of the stem's invaded portion is lost, and the seedling topples over. The fungi continue to invade the remaining portion of the seedling, resulting in death. This phase of the disease is termed postemergence damping-off. Older established plants also can be attacked by damping-off fungi. Usually the new developing rootlets are infected, resulting in root rot. Infected plants show symptoms of wilting and poor growth.

Solution - Proper conditions for seed germination and seedling emergence also favor vigorous growth of fungi that cause damping-off. Seed and roots must be kept moist and warm until the roots have penetrated the soil and the seedlings have emerged. As the seedlings continue to grow, moisture at the soil surface can be decreased, and the damping-off fungi then will have less of an advantage. When watering, thoroughly saturate the soil and then apply no more water until soil approaches the point at which plants wilt. This procedure will keep surface soil dry for a maximum time. Pasteurization of Soils is the best way to protect yourself. Soil for growing transplants in flats can be steam pasteurized. If steam is used, the entire soil mass should be maintained at a temperature of 160 degrees F for 30 minutes. The home gardener obviously does not have facilities to steam soil; however, pasteurized, packaged soil mix is available from many garden centers. To prevent soil recontamination, all items such as tools, pots, and flats, etc., must be clean. The items can be cleaned in hot water (160 degrees F for 30 minutes) or in a chlorine bleach solution (1 part bleach to 9 parts water; soak for 30 minutes). It is important to use fresh chlorine bleach-water solutions.

 

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