Hemp (Cannabis sativa)-Gray Mold (Botrytis Bud Blight and Stem Canker)
Hemp plant with gray mold symptoms on flower buds. Note the dead tissues that have turned brown.
Photo by Cynthia M. Ocamb, 2020.
Hemp plant with gray mold symptoms on the terminal flower (cola). The affected tissues have turned brown.
Photo by Cynthia M. Ocamb, 2020.
Hemp plant with gray mold symptoms on a flower. The affected tissues have turned brown and the fungus is sporulating on the tissues as denoted by the fuzzy brownish-gray mass.
Photo by Cynthia M. Ocamb, 2020.
By N. K. Osterbauer and C. M. Ocamb
Cause The fungus, Botrytis cinerea (teleomorph: Botryotinia fuckeliana ), is an opportunistic pathogen that easily invades weak, damaged, or senescing tissue. This fungus is very common in the Pacific Northwest and occurs worldwide in greenhouses. Cannabis can be killed within one week. Spores (conidia) are produced throughout the growing season under a wide range of temperatures and humidity; and stem infections are a durable inoculum source, producing conidia throughout bloom. Cool temperatures (68°F is optimal but the fungus can grow between 50°F and 80°F), high humidity, and free water on plant surfaces favor the disease, as do close plant spacing and irrigation practices that keep plants wet for a longer time. Durable sclerotia overwinter in soil.
Symptoms The pathogen causes brown, water-soaked spots on buds or chlorotic areas on stems. Buds eventually rot producing a gray-brown mass of spores; infections start within buds. Botrytis cankers develop to the point of limb breakage or stem splitting, especially if plant canopies are dense and heavy. Small, black sclerotia can develop within stem tissues. Like the buds, cankers produce gray-brown masses of spores. Seedlings can also be killed.
- Limit irrigation during and after bloom. Irrigate in the morning so plants do not stay wet more than 12 hours.
- In greenhouses, maintain the relative humidity below 50%, temperatures warm, and high light intensity. Filtering out UV light may prevent epidemics since sporulation requires UV light.
- Avoid over-fertilization with nitrogen.
- Canopy management is the best preventive method.
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 3- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
- Regalia (Group P5) at 1 to 4 quarts/A on 7- to 10-day intervals. Does not benefit from the addition of an adjuvant. Studies by OSU show efficacy of this formulation for gray mold control. Preharvest interval is 0 days. 4-hr reentry. O
References Bates, T.A., M. Dietrich, and C.M. Ocamb. 2021. Evaluation of biofungicides for gray mold on hemp in Oregon, 2020. Plant Disease Management Reports: Report No. 15:V048.
Punja, Z.K., Collyer, D., Scott, C., Lung, S., Holmes, J., and Sutton, D. 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Front. Plant Sci. 10:1120. DOI:10.3389/fpls.2019.01120
Ward-Gauthier, N., Beale, J., Amsden, B., and Dixon, E. 2015. Greenhouse hemp in Kentucky exhibits many common diseases. American Phytopathological Society Annual Meeting, Poster 502-P.
How to Spot Bad Cannabis Seeds [Comprehensive Guide]
You may not realize it, but the quality of your cannabis crop is, in part, determined before you have even begun. Seed quality is an enormous part of growing, so it’s vital to source marijuana seeds from a reputable company.
Sometimes, you can end up with ‘bad’ cannabis seeds that will cause problems later down the line. In some cases, these seeds just won’t germinate. Although this won’t ruin your entire crop, it is a waste of time and money, which can be frustrating.
Today, we will help you work out whether your cannabis seeds are good or bad. Hopefully, this guide will help you to determine which seeds are worthy of your time and which ones are duds.
What Makes a Cannabis Seed ‘Bad’?
A ‘bad seed’ is any cannabis seed that will cause problems. In some instances, this means a dud seed that never sprouts, wasting your valuable time and a few resources. While dud seeds aren’t damaging, they are irritating.
Another type of bad seeds is male cannabis plants. There’s a 50/50 chance with regular seeds as to whether any given seed is male or female. The problem is that male plants will pollinate the females once they reach maturity, destroying the valuable THC content of female plants.
Having male cannabis plants in your garden is basically a recipe for disaster, so you want to avoid it at all costs. By the way, here’s how to figure out if your plants are male or female.
One way around this is to purchase feminized marijuana seeds. In theory, all seeds in a feminized bunch will be female – unless you buy from a disreputable grower. Unfortunately, there’s no way to tell whether a plant is male or female simply based on the seeds.
This guide will only cover how to tell the difference between a potent seed and a dud seed.
The complete guide…
How to Test Cannabis Seeds
There are several easy methods for testing cannabis seeds. Most of them can be performed before germination, saving you some time and resources. Let’s find out how to check your seeds.
Method #1: The Sight Test
Cannabis seeds are surprisingly beautiful. They have a mottled brown appearance with patches of light and dark, and sometimes gorgeous tiger stripes. The seeds are also quite shiny if you view them close enough.
Sometimes, you can tell if a seed is good or bad just by looking at it. Here’s how to spot a healthy seed:
- Coloration: A dark coloration with black or gray patches is a sign of a healthy seed. Conversely, white or green seeds are unlikely to germinate because they are not mature. Pale seeds are also more likely to be old and ineffective.
- Waxy coating: Healthy seeds have a waxy, shiny coating. If it doesn’t, then the seed is likely a dud
- Cracks: Cannabis seeds should not be cracked. If your seed has cracks in it, it’s probably best to discard it.
- Shape: The rounder and fatter the seed, the more likely it is to sprout into a healthy plant. Some growers are concerned about large seeds with thick shells but don’t worry. The shell will break down with water.
- Mildew: Grab a magnifying glass and view the seeds close up. A white, dusty powder is a sign of powdered mildew, which means the seeds have a fungus and should not be planted.
In some instances, you can crack the seed open and see inside if you can’t tell anything from the outer shell. An oily inside with a musty smell means that the seed has gone bad. Similarly, black inside the seed means that it’s fermenting. Again, it won’t germinate in this instance.
Method #2: The Touch Test
The feel of cannabis seeds is another good indicator. Hold the seed between your thumb and forefinger and give it a light squeeze. Don’t apply too much pressure – just enough to test its integrity.
If the seed cracks under slight pressure, then it’s unusable. It’s likely to be past its sell-by date.
Strong seeds, however, have a better chance of germinating and growing into a healthy plant.
Method #3: The Water Test
Are you still unsure about your cannabis seeds? You can always do a floating test to see if they’re healthy. By the way, this method works for numerous plant seeds and not just cannabis.
Disclaimer: Don’t perform this test unless you’re ready to germinate the plants right away. The water could damage the seed and ruin a perfectly healthy plant if you dry it out afterward.
For this test, you will need a cup, glass, or bowl of warm water. It should be quite warm, but not hot. It also works best with spring water or distilled water.
Add your seeds to the water, and then wait for 1-2 hours. Those that float on the surface are bad seeds that are unlikely to grow, whereas the seeds that sink are probably healthy.
This method is a great way to check your seeds because it’s low effort. You can also test multiple seeds at once, and it’s really cheap and easy to do.
After you’ve done this test, you need to germinate the healthy seeds. At this point, they will have absorbed water, which can damage the seed if you don’t germinate it at this point. Incidentally, germination is the final test for your seeds.
Method #4: The Germination Test
If all else fails, it’s time to germinate. You might have no idea whether your seeds are healthy but attempting to grow them is an easy final test that will separate good seeds from duds.
There are multiple ways to germinate, including planting the seed directly in soil and seeing if it sprouts. This is a pretty ‘old-school’ method, but sometimes, it works.
More commonly, growers use the paper towel method. Dampen a paper towel, ensuring it isn’t soaking wet. Place this on a kitchen plate and put the seeds on top, then put another plate upside-down on top. A moist, dark, warm environment allows the seeds to sprout. Check on the seeds once a day; after germinating, you should see a white taproot emerge.
At this point, you can transplant the seed into its pot. Use a pair of tweezers and handle each seed carefully, being careful not to touch the taproot. The taproot is fragile and may break if you’re not delicate; furthermore, touching it with your hands may contaminate it.
After germination, you’re good to go. Remember to check back as the plants mature to make sure you haven’t got any male cannabis plants.
Waste not, want not!…
How to Buy Good Cannabis Seeds Every Time
It’s recommended to buy feminized cannabis seeds to eliminate the possibility of males ruining your crop. Even so, some subpar retailers will advertise feminized seeds, only to sell regular cannabis seeds.
It’s vital to buy from a reputable seller that you trust. If this is your first time, read reviews on the seed banks to find out what other customers thought. If lots of buyers were disappointed by low-quality seeds, avoid that company!
Unfortunately, you might still get some bad seeds sometimes. Plants are living beings and can be a bit unpredictable – even the seller might not be aware that some of their seeds are duds. With any luck, the majority of seeds you buy will be healthy and good to go.
The sign of a bad seller is that their seeds are consistently old, dead, and covered in powdery mildew. That said, don’t be too harsh on a seed bank if a couple of their seeds don’t work from time to time when they’re generally reliable.
Final Thoughts on Good and Bad Cannabis Seeds
Telling good and bad cannabis seeds apart is not an exact science. Sadly, you don’t know what’s inside the seed beyond its appearance, so you won’t know what the plant is truly like until you start growing it.
Cultivating marijuana is a bit of a learning curve, so don’t worry if you mess up your crop from time to time. It will only get easier with time.
Hopefully, you can now tell apart some seeds, at least, giving you more opportunities to create a successful grow.