Early pest detection is the key to predictable yields

Powdery Mildew is the most destructive fungal pathogen for Cannabis. It is an obligate biotroph that can vascularize into the plant tissue and remain invisible to a grower. Under ideal conditions, powdery mildews have a 4-7 day past innoculation (dpi) window where it remains invisible as it builds a network internal to the plant (work performed in arabidopsis).  Research performed in a close cousin to cannabis, (Humulus lupulus  or hops) has demonstrated incubation periods up to 49 days with P.macularis. The powdery mildew vascularized network in cannabis is detectable with a youPCR DNA based test prior to conidiospore generation. Later stage powdery mildew infection and conidiospore generation results in rapid spreading of the fungus to other plants. This tends to emerge and sporulate 2 weeks into flowering thus destroying very mature crop with severe economic consequences. It is believed to travel in clones and it is not known if it travels in cannabis seeds, however evidence of P.macularis transmission in Hops seeds has been reported. Detection of this pest prior to sporulation can help eradicate powdery mildew before it infests a grow. DNA based tools could facilitate early detection and rapid removal of infected plant materials or screening of incoming clones.

MacPartland et al. reported L.taurica and P.macularis as the organisms responsible for powdery mildew on cannabis. Multiple unsuccessful attempts to amplify DNA sequences from these organisms on cannabis derived powdery mildew led us to whole genome shotgun sequence the New England sourced organism. This sequence assembly presented a novel organism not found in NCBI. Utilizing these novel sequences we designed a colorimetric DNA amplification assay that can detect Powdery Mildew from a leaf punch prep on a $650 USB driven PCR device. 

This assay was then brought to several field tests in New England. Four different isolated collections of Powdery Mildew from New York, Connecticut, Rhode Island and Massachusetts were tested.



Expanded study on Powdery Mildew from CT, MA, RI and NY

These results demonstrate positive detection results for the DNA target in 4 different states. We also hyper sampled negative samples to ensure the leaf punches were not under sampling the infected or uninfected plants.

Microscopic views of the original plant with Powdery Mildew


Sampling frequency required to detect dormant powdery mildew

Do other parts of the plant with no visual signs of Powdery Mildew have genetic evidence of its vascularization?

Sample 1pict1590pict1591

Positive for Powdery Mildew


Sample 2


Negative for PM

Sample 3


Positive for PM

Sample 4

pict1600pict1601Positive for PM


3/4 Hole punches from microscopically clean leafs from a plant that was visually positive with powdery mildew triggered a positive results.



These results confirm previous reports of powdery mildew being heavily vascularized even if not visible by eye. This presents an opportunity to use genetic tests on Clones of a Powdery Mildew tested Mother plant. While the test costs may be $15, a few tests on a mother can significantly reduce the likelihood that the 100 clones derived from that mother contain PM. While a single clone can cost $15, one may not need to test every clone from a mother. A single cheap clone can destroy a whole grow. Periodic genetic screening of grow rooms or mother plants can help eradicate this pest from your facility.


WeBling et al. Stained for Powdery Mildew. One can see the mycelium network of PM inside the leaf even if powdery mildew is not visible to the human eye. DPI = Days Post Inoculation. HPI = Hours Past Inoculation.

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