Grow Basics
Go Back

Plant Pathogens & Diseases

The Next Big Hurdle
By Zac Ricciardi

Plant pathogens and diseases are nothing new to most growers, but they can catch even the most experienced off-guard.

A plant disease is defined as “anything that prevents a plant from performing at its maximum potential”.

This is a very broad definition that covers both abiotic (nonliving) and biotic (living) issues. Growers have been dealing with pathogens and diseases as long as they have been growing plants. And while there are a plethora of issues growers continue to face, thankfully, there are ways to ensure successful harvests and overcome unexpected issues as they arise.


Collectively, fungi cause more problems than any other type of plant antagonist organism.

Fungi lack the ability to make their own food, cannot photosynthesize, and may or may not utilize spores to spread. Dormant spores can lay in wait for long periods until the conditions are conducive to growth. They can overwinter in media and plant debris, as well as being present in a water column. They are by definition parasites.

Like all pathogens, fungi are extremely dangerous because more often than not you don’t know you have a problem until you have a problem.

Some of the fungal issues we will face as growers are: anthracnose, alternaria, botrytis, downy and powdery mildew, fusarium, rusts, rhizoctonia, verticillium, sclerotinia, and sclerotium.

Symptoms of a fungal infection are: wilted leaves, chlorosis followed by necrosis, leaf spotting, diminished vigor, altered dry-backs, distorted growth, and ultimately plant death. The good thing is that fungal infections can be cured and eliminated if an outbreak occurs. Proper sanitation and IPM practices can ensure that fungal contamination is addressed before it ever becomes a problem.


Bacteria are simple single-celled organisms that replicate through a process called binary fission (one cell divides itself into two).

Bacteria typically find their way into a plant through a wound or through a natural opening like stomata, but can also be spread through insect pressure. They grow in the spaces in between cells. Once the bacteria is present in the plant’s vascular system the infection spreads and will lead to symptoms that may include wilt, necrosis, soft rot, and tumors/cankers.

Like fungi spores, bacteria can also lay dormant until the conditions are favorable for their growth, as is the case with crown gall.

Some bacterial issues growers will encounter are: erwinia, pseudomonas, xanthomonas, and agrobacterium.

Symptoms of a bacterial issue are: wilting of the leaves, chlorosis followed by necrosis, rot and swelling of the vascular tissue.

The biggest determinants of bacterial growth are temperature and moisture levels.

The good news is bacterial issues can be eliminated with the implementation of correct procedures. Just like in the case of fungal contamination, proper sanitation and a solid IPM rotation can prevent the spread of bacteria by ensuring everything is as clean and disinfected as possible.


Just like people, plants are also susceptible to viruses.

Viruses are parasites by definition as they need a host to replicate and spread; they grow inside the cells of the host. The scary thing about viruses is their small size: the typical diameter of a spherical plant virus is only 30nm. For example, the tobacco mosaic virus (TMV) protein is 300x18nm in size.

Viruses have many modes of transmission and can be passed from plant to plant by insects, through plant material, nematodes, and mechanical spread.

Unfortunately, unlike the previous two pathogens, viruses cannot be cured; once a plant is infected it is always going to be infected (exception: tissue culture has the ability to preserve clean genetics without retaining viral pathogens). The best a grower can do to address a viral issue is to mitigate the symptoms of the virus and try to get the plants to harvest without contaminating the rest of the facility.

Given a virus’s ability to spread, it is the single largest threat to growers today because of the potential to lose an entire operation.

Proper sanitation and periodic tissue testing is the best way to avoid contamination from viruses, and field test kits are readily available. Again, there’s no going back and you can’t spray your way out of the situation.

Preventative actions are the only way to stop this issue from decimating your harvests. Being proactive in this situation will ensure you’re not losing crops due to negligence or oversight.

The most common viruses you will see in cannabis are: tobacco mosaic virus, hop latent virus, and curly top virus.

Symptoms of a viral issue are: distorted and diminished growth, loss of vigor, loss of essential oils, chlorosis, variegation, and plant death.

While pathogens and diseases can be scary, they aren’t the end of the world, or your crop.

We as cultivators have many options at our disposal to remedy most situations that arise.

The worst possible scenario for anyone is an unchecked viral outbreak that could be devastating to any operation.

Periodic tissue testing is advised for ALL growers now that field kits are available and you’re able to get real-time data. Making sure that tools are cleaned and that sanitation is paramount will lessen the chances of anything negative occurring in the environment.

Being proactive with products like OxiPhos, ZeroTol 2.0, and SaniDate 5.0 can ensure you keep your crop and environment as clean as possible so that the potential for outbreaks is minimized exponentially.

Starting from seed is also a great way to keep contaminants out of the environment. Seeds avoid bringing in potentially contaminated tissue and minimize your potential exposure to said pathogens.

A wise grower once said, “An ounce of prevention is a pound of cure.”

Let’s match.
Search for the strain that suits you.
You’ll know it when you see it.
Flowering Time (Days)
Life Cycle (Days)
Cannabinoid Profile (TAC)
Terpene Profile
Height / Vigor
Internode Length
Ideal Environment
Grow Level