Yellow leaf spot is also known by the name of leaf septoria. It comes from two fungal pathogens, Septoria cannabis, and S. neocannabina, which specifically affect marijuana plants. There is an unusually high risk for your marijuana plants to become afflicted with yellow leaf spot when the weather is particularly warm and rainy, as well as for plants that do not have adequate amounts of nitrogen.
Identifying yellow leaf spot
The first place you will likely detect this disease is on the bottom-most leaves of your marijuana plants. Despite its name, yellow leaf spot does not only include yellow spotting of the leaves; white, gray, and brown are also included in the spectrum of symptoms for the affliction. You will at first notice circular lesions on the bottom leaves of your plants, and then the colorful spotting begins. That spot on the leaf will turn into a bump and continue to expand outward until it affects the entire leaf.
The spot will increase in size and eventually dry out, therefore drilling a hole in the leaf and negatively affecting the leaf and stem both. Every leaf affected by yellow leaf spot will eventually dry up and drop off the plant, signaling its total death. The plant itself shouldn’t be too devastated by yellow leaf spot, but the yield will decrease significantly if the problem causing yellow leaf spot isn’t fixed as soon as possible. More about yellow leaf spot in my free grow bible.
Dealing with yellow leaf spot
Whenever you notice the leaves dropping off of your plant, be sure to take action against letting them sit there on the ground. Doing so could encourage spore-borne diseases to live there and then make their devastating appearance once the climate is right. One of these diseases is the yellow leaf spot, which spreads through the wind, water, and the touching of people or animals. Once the weather is nice enough, ‘waiting,’ yellow leaf spot spores will begin to attack your precious marijuana plants.
Besides picking up leaves as quickly as possible, rotating the location of your marijuana garden each growing season will help drastically with lowering the risk of yellow leaf spot. If rotation is not a viable option for you, then you may want to simply get all of the plant matter completely away from the site where you planted last (and plan to plant again). Take special precautions to ensure that any residual plant matter isn’t stuck in the soil -- or simply remove some of the soil altogether.
Before planting your marijuana plants in your grow location, prepare it with a sterilized compost to start things off well. Alternatively you can try using blood meal, fish meal, or soybean meal to add to the pre-existing soil, making it sterile and healthy. As far as tools go, make sure you properly clean and sterilize them after each use.
Fungicide is another effective way to prevent yellow leaf spot -- do this before introducing your seedlings to the grow area. These can easily be homemade or store-bought, so it depends on your personal preferences. Good bacteria (Bacillus Pumilis, for example) will allow your plants to thrive and should fend off some risky invaders, such as yellow leaf spot. For people without compost (and the beneficial bacteria that come with it), ingredients such as cinnamon, coriander, neem, sesame, and clove can come in handy. Properly mix these with essential oils and spray onto the area. Compost tea, baking soda, and trichoderma are other useful options for preventing yellow leaf spot.
Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible.