There are 3 main keys in stopping the spread of poisonous plants.
Poisonous Pollen Storm Guide
(1) Cut down as many trees as you can
The reason why poisonous plants spread so quickly is because they can spread to nearby plants. If you have a number of patch of trees, they will all become the infected areas and thus begin to grow faster you can stop them. Basically, if you have more than 100 plants being infected, your run is pretty much over.
As soon as the game started, order at least 5 workers to actively cut all the trees. It is always worthwhile to spend extra time in preventing large spread of the poisonous tree in the first place, than having fancy techs which ultimately will not help you survive any pollen storm.
(2) Build essential buildings
You might think that it is crucial to build decontamination station, but in fact it is not the case. What decontamination station do is they burn down infected plants, but their active range is limited to a small area. Some might suggest to build 3, 4 or even 8 stations to cover the entire map, but it is a huge waste of resource of building so many decontamination stations, which you might be susceptible to other weaknesses, such as growing for too slow, missing variety in foods, lacking the resources to feed Onbu, and so on.
What I believe is the best solution, is to simply have 2 worker station, priority in harvest, and cut down all the infected tree before the spread during the pollen storm. Worker stations are cheap to build, and they essentially take the same time and effort in clearing all those infected plants, and unlike decontamination station, they have unlimited range. Do take note that you must mark all the infected plant at highest priority so the worker will cut all the unhealthy ones first.
Anyway, decontamination is a defensive building in nature (to protect your farm and main section of the map), so to effectively clear all the infected plants, you will need workers cutting all the infected plants down.
Have some village doctors by the way, you will need them to support the worker fighting infection.
It is also important to build hornblower. I’ve seen some suggest to not build it at all because it mess up with the Onbu’s… schedule? I find it questionable because all you need to do is build a feeding trebuchet and you basically solve all the problems with “messed up schedule”, which is something you need to build anyway as often time you will only find 1 or 2 feeding ground throughout the run.
To use hornblower properly, you need to help Onbu avoid pollen storm before crossroad. While many time you will have a pollen storm on either path, sometime it can save your run if one of the paths is actually clean. If you happen to stumble upon one of the pollen storm, watch the sleepiness meter. If it is less than 40%, right before Onbu approaches the pollen storm, order it to run. If it is between 40% and 60%, let Onbu walk into the pollen for a little while and then order it to run halfway across the storm. If it is more than 60%, you can’t risk it to command Onbu to run because running will greatly increase the sleepiness, which mostly will cause Onbu to sleep inside a pollen storm once Onbu is too tired, which is going to be fatal in most cases.
What, Onbu ignores your order? Cure him, feed him, and pet him, you animal.
(3) Make use of the pause
Some players might not know, but you can pause to give you sometime for planning. Especially when you are inside a pollen storm, it is important to pause every few seconds and check which plants have been infected, and order the worker to cut them down at highest priority. Not only it allow you to make decision as soon as possible, it also reduce the chance of overlooking, which causing butterfly effect and eventually costing you the run.
Also, during pause, while you’re check for infected plants, if you found any station (especially berry picker one) are at close proximity to the infected area, disable the building and convert them into worker (or making them unemployed) to assist in cutting down the trees. Remember, every second counts, so make use of the pause function.