Winter is fungi’s favorite season around here! The December rains and January fog brought out an unusual number of mushrooms and fungi of all sorts. At least more than I’ve seen in the past three years. (None though, that I would eat!)
2010 was also the first year that downy mildew and other similar plant diseases have been a problem for me.
Here is a leaf with some sort of infection. I’m still not sure exactly what the infection is, and it’s probably not important, though I am curious:
Usually mildews and bacterials diseases spread from plant to plant by splashes of water (such as rain), wind, dirt, and insects. Once a leaf is infected, this particular disease spreads through the veins. You can see on the above leaf how the brown coloring is spreading along the veins. If you break off that infected leaf, you’ll see that the veins are carrying the infection down to the main plant stem. It has gone “systemic”:
Here is a leaf where the infection is just starting:
The leaf’s central veins still look clear; they have not yet spread the infection to the rest of the plant:
I haven’t found much information yet about controlling mildews on a small organic level. Ideally I won’t plant susceptible crops in this garden area for a few years (crop rotation!), but I still need to get the current plants through spring.
Here are a few things that help control mildews, fungi, and bacterial diseases:
1) taking infected leaves off plants at first sign of infection.
2) Not crowding plants. There should be sufficient room between plants for air circulation and light penetration. The air and sun dry off the plants, making disease less likely to spread. Luckily, the goats are happy to eat the slightly diseased plants I pull out:
3) Milk! Spraying plants with watered down milk (10-20% milk mixed into water) can help control mildews. I haven’t tried this yet but want to! Apparently the milk changes the surface pH of the leaves enough to discourage mildew growth. It works better as a preventative and for new infections than on already established infections though.
4) Compost Tea. Some people say the microorganisms in compost tea help the plant combat diseases. I don’t have an proof of my own to offer on this, but some people swear by it.
In other words, there are many experiments to do! But not today! It’s pouring outside!