That's very possible. Or root aphids once had something to do with it and are now out of the picture but it's too late.
Another possibility, yes.
I've tried to become more aware of this possibility and using Physan 20 on cutting tools whenever possible, but mistakes are sometimes made. Fungus gnats are also very difficult to completely eradicate. They may turn one carrier mother into many. Is it possible to kill a virus within living plant tissue? My current understanding is it is not.
There's one big problem with Physan 20 (also sold as Consan 20, and other names): it is not virucidal. More precisely, it has never proven to kill viruses that afflict plants; there was one paper from the 1950s, published casually, concerning the use of
quaternary ammonium compounds in the control of... bean yellow mosaic virus in cucumbers, I think it was. Quats are very good at attacking enveloped viruses (which includes most animal viruses), but
tobacco mosaic virus is non-enveloped. Anyway- that paper was never followed up with a peer-reviewed journal. The evidence that quats work on plant viruses (most specifically, tobamoviruses like TbMV) is zero, to the best of my knowledge.
Now, these products are great detergents, and they will reduce the concentration of virus particles, same as any sort of washing or decontamination. But blades are excellent vectors for transmission of viruses. The primary chemical disinfectant used for years was trisodium phosphate (TSP), which has largely been replaced by "fake" TSP at the hardware store. Normally a saturated solution of TSP + soaking for a few minutes (scrub with a toothbrush to remove any sap) was considered enough to reduce transmission of viruses to a very low level. Heat was considered better; a propane torch works nicely, but it also removes the temper from the blade- so cheap blades were used: razor blades. But razor blades have an aluminum backing; get it too hot, and the aluminum will drip, usually on your feet. Not a good idea. Plus, for $7, you could buy a box of 100 single-edge razor blades; it hardly seemed a wise move to re-use them when they were so inexpensive. Put used blades into a coffee can, and (when full) add plaster of Paris (so nobody gets hurt) and chuck in the trash.
As noted, once virused, plants cannot be un-virused- not without some tricky lab techniques involving tissue culture, meristem work, and anti-viral compounds coupled with temperature treatments. (Temperature won't do a darned thing for TbMV as it is too damned stable, even at temperatures well over that to kill the live plant material, but some viruses denature at temperatures higher than 40C and can be eradicated with some tricks in tissue culture.) They may not even make good parent plants, as pollen and seeds are known to carry some types of virus in some crops. I doubt anything is known of this as it relates to cannabis.
Great point. I could go through the issues I've seen and explain much of it as a virus present that shows symptoms only as a result of stress. Stress can cause all kinds of things, but sometimes plants can be incredibly resilient and sometimes can fall into a downward spiral of ill health.
Indeed, I'd love to draw conclusions, but that would be more broscience. Can anyone recommend a lab doing testing for a wide array of possible viral infection of plant tissue? It would be great to have some real data backing up these guesses.
If you know what you're looking for, the Agdia strips are excellent. However, they will only search for the viruses you are looking for. Although we know some viruses probably (or certainly) infect cannabis, there may be others out there that are more cryptic, or are entirely asymptomatic. Plus, the test strips are pricey, particularly if one looks for multiple viruses- and as the page I link to above notes (from the
Hartowicz et al. (1971) paper) there could be over a dozen viruses affecting cannabis.
Plant Viruses Online suggests the Cannabidaceae has demonstrated susceptibility to a handful of viruses; however, these are all in hops. Perhaps understandably, not many plant virus papers have been published on cannabis itself. Moreover, perhaps cannabis shares little with Humulus in terms of viruses.
This page suggests there are a handful of viruses that afflict hemp, and notes that of 22 viruses found in other plants, "over half" were able to infect hemp. There's hemp streak virus (HSV), hemp mosaic virus (HMV), alfalfa mosaic virus, cucumber mosaic virus, and arabis mosaic virus. Aphids, whiteflies, and thrips are known vectors for at least some of these diseases.
There's a much older, less specific technique, that involves the use of index plants. This is the technique that I employ, but inasmuch as transfer of the material across state lines is illegal, my services remain local.
I would caution growers of the following:
- Use of tobacco concurrent with culture of cannabis.
- Growers who cannot answer "how do you know?" when they present a plant that they inform you a plant is clearly virused.
- Any measure other than new blades used to make cuts between different plants.
- "Communal" culture in which the plant parts are immersed or in contact with liquids that bathe multiple plants from different sources (i.e., not all clones taken from the same parent plant).
- Vectors such as whitefly, etc. in collections of plants that are from different sources.
- Reuse of pots. Clay pots can be baked at some insane temperature, while plastic pots need to be discarded if the occupant proves to be virused. Without knowing whether the previous plant was virused, it is best to wash/bleach/TSP pots prior to re-use. Similarly, potting medium may remain contaminated; this is particularly true with TbMV, which may remain infective for years, perhaps decades.
Someday perhaps we'll have indexed clones made available. That would be nice, and will almost certainly be a necessity from a pharmaceutical standpoint. Similarly, virus-resistant cultivars could be developed; however, as viruses seem to be more of a nuisance with cannabis, this is way down towards the bottom of the list for breeders, I'm certain.
