The fall time means waking up to cool, damp mornings and while this might be a nice break from the sweltering summer nights but can be a make or break time for outdoor growers. This time of the year while buds are putting on bulk, but the cool damp conditions are also the perfect conditions for Botrytis to establish itself and then quickly spread and ruin a crop. While it's way more common in outdoor growing it isn't unheard of in a controlled environment, and so it should be on the radar of indoor growers as well.
Botrytis is one of the easiest infections to diagnose. Like any type of infection, the key is to diagnose early in order to minimize the impact. In which case, be on the lookout for upper leaves turning yellow and then take a closer look. Early on the mould can be white in colour and then turns quickly into the grey colour which is unmistakable.
*Did you know?*
While Botrytis is a scourge to most crops, under some circumstances it can be welcome by winemakers. Noble rot is when a bunch of grapes is infected but instead of consuming them the fungus dehydrates them which elevates the sugar content. This results in a sweet desert wine similar to ice wine.
Like any fungal or insect pathogen, it's more effective and easier to try to prevent the infection than it it to try and fight it off once it has been established.
- Prune back any dead or dying leaves, stems, fruits, flowers ext. and dispose of the material well away from where the plants are being grown. Botrytis will colonize this material first and spread from there onto healthy plants.
- Do not compost infected material as it could survive and cause infections to future crops.
- Do whatever possible to control humidity. This won't be an option for many crops growing outdoors, but if the option is there take it. The next best thing is to gently knock off any dew that formed during the night, especially from areas of the plants that are dense and have poor air flow.
- Avoid any type of foliar feeding during the cool humid part of the season unless absolutely necessary. If it has to be done, then apply just before the hottest part of the day so that the water will evaporate as quickly as possible.
- If possible space out the plants. This will allow for better air circulation and the distance will slow down infection rates between plants.
- Inoculate the plants with biological control agents such as Bacillus subtilis, or Trichoderma. These microbes compete with the pathogen for space and will produce chemicals which inhibit it.
- If the risk of an infection is high then the drastic step of using a chemical fungicide should be considered. These are only approved for certain crops so be sure to thoroughly investigate the specific product before using it. Here again, fungicides work best before the pathogen has been established. Also keep in mind that many strains have developed genetic resistance to certain fungicides.
Sometimes whether through neglecting precautions or simply because the odds are stacked in favor of the pathogen an infection will start, what then?
- Quarantine or ideally, destroy infected plants. Trim back and dispose of infected parts.
- Treat the remainder of the crop with a fungicide.
- If possible move plants to a drier environment.
Like any kind of fungal or insect pathogen, it is much easier to prevent an infection than it is to try and fight off one that has been established. The time and money spent might seem like a waste, but is well spent compared to letting Botrytis take over your crop.