Three Tips for Effectively Troubleshooting Cannabis Plant Problems
April 8, 2021 
Skilled cannabis growers know that sometimes you need to go beyond the obvious to uncover the real cause of a crop problem. Not every issue has a straightforward solution, and sometimes it takes a little creative thinking to help identify the true culprit.
The next time you’re faced with a troubling crop issue, consider these three tips for getting to the root of the problem.
Use Your Senses
The best growers rely on more than just their sense of sight when diagnosing plant problems. Yes, seeing is believing, and visual clues are often the best indicators of why a plant is experiencing problems. But utilizing a few other senses can help provide critical insight into what is really going on with a crop.
A grower’s sense of touch can help determine if environmental factors are to blame for mysterious crop issues. Is the air stagnant or overly humid? Is the cultivation area too cold? High humidity, low humidity, and temperature extremes can encourage nutrient imbalances that result in poor plant health. If you’re sweating bullets at 10:00 a.m. in the greenhouse, how do you think your plants feel?
Other times, it helps to follow your nose. Smelling the substrate can help confirm suspicions of root rot. If the substrate smells rancid, it’s a sure sign that the crop has been chronically overwatered. Substrates that are not allowed to dry out between irrigations can result in anaerobic decomposition that will cause the roots to die.
A grower’s sense of smell can also help forecast potential problems that don’t yet exist. Although cannabis growers are prohibited from using chemical pest control products to fight spider mites and powdery mildew, unscrupulous growers still use them. The active ingredients in these products have a distinct smell, and their presence could indicate that a crop will likely fail a pesticide test, rendering it unsaleable in a regulated market.
As an ornamental flower grower, I sprayed Avid for spider mite control and Eagle 20 to combat systemic fungal infections. The smell of these products is immediately recognizable when they have been recently applied. A grower’s olfactory intelligence can help determine if the application of a prohibited product may have compromised a crop.
Don’t Take the Easy Route of Blaming Nutrient Deficiencies
Many crop problems masquerade as nutrient deficiencies, and novice growers can easily be tricked. A common tactic is to search online for photographs of crop issues similar to what the grower is experiencing. Once the suspected deficiency is identified, the grower bumps up the nutrient in question. But if the plant is not actually nutrient deficient, adding more fertilizer could aggravate the issue.
I once fixed a suspected nutrient problem without changing the fertilizer at all. The grower spent a lot of time online investigating possible nutrient problems and was constantly adjusting the fertilizer recipe. While troubleshooting, I observed the grower irrigate these large plants first thing in the morning. By mid-afternoon, they were bone-dry and left to bake under the grow lights until 7:00 pm. By the following morning, the crop was wilted.
I recommended that the grower apply a touch-up of clear water in the afternoon to hold the crop over until the following day’s full irrigation, and it worked. Symptoms that were suspected to be nutrient deficiencies were actually leaf damage caused by chronic underwatering.
Even if a crop is determined to be nutrient deficient, adding more fertilizer may not be the right move. It’s possible that sufficient nutrients are in the substrate, but the plant is unable to take them up. For example, root rot will prevent any nutrient from making its way into the plant, while high humidity will prevent less mobile nutrients like calcium from reaching the growing tips. A high or low pH will prevent many nutrients from being consumed at all.
Adding fertilizer is easy, but don’t be fooled by the easy path. The best growers dig deep to verify that suspected nutrient deficiencies are, in fact, just that.
Science Is Your Friend
Guessing helps, but science is irrefutable. Growers use intuition and work experience to help narrow down possible causes, but they use scientific tests and data reports to confirm their suspicions.
Testing media, nutrient solution, leachate, plant sap, and leaf analysis can help determine if the plant is receiving the correct nutrients and in the right quantities. These tests can also help show if they are evenly distributed throughout the plant. In the case of abnormal plant growth, labs can test for pathogens like hop latent viroid, and growers can quickly test in-house for infections of tobacco mosaic virus using Immunostrip test kits.
Sensors help verify that the optimal conditions for plant growth are being maintained at all times. For example, are you stumped as to why your indoor crop suffers from botrytis or powdery mildew? Are you confident that you are maintaining the proper humidity levels in the grow room?
Don’t guess; use sensors to be sure. A simple temperature and humidity gauge connected to a data logger will verify if there are peaks or dips in humidity over a 24-hour period. Many plant-damaging fungal spores don’t require standing water to germinate; they only need brief periods of high humidity. Sensors that read the room when you’re not there can provide valuable insight through the reports that they generate.
Guessing helps to form a hunch, but science confirms your suspicions.
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