Notebook 9: Rust. End of October

California's North Coast is fertile ground for the cultivation of many varieties of fruits, berries, and flowering plants, but it was actually during a discussion of a somewhat seedier crop that I really began to understand what might be happening to my blackberries. It seems that Humboldt's cannabis growers (and there are a great many cannabis growers in Humboldt County) have long struggled to protect their plants from a number of destructive fungi endemic to the region. One of the blights my acquaintance described bore a distinct resemblance to the red-orange rust I had already observed on the leaves of a great many blackberry plants in the region, including those that squatted in the airport field.

Rusts are fungi that belong to the order Pucciniales. They are defined by a complex, multiphase life cycle that I can't even begin to explain here (nor would my explanation be worth much). There are thousands of species of rust that have specialized in infecting everything from coffee to chrysanthemums. According to the Pacific Northwest Plant Disease Management Handbook (http://pnwhandbooks.org/plantdisease/blackberry-rubus-spp-blackberry-rust), The last decade has apparently seen something of an epidemic of Blackberry Rust (phragmidium violaceum) in the Pacific Northwest, so that seems to be the likely suspect, but the stuff growing on the airport blackberries could easily be a completely different fungus than those plaguing cultivated blackberries and almost certainly differs significantly from those that affect the cannabis plant. However, my conversation with the grower still yielded some valuable insights.

The first is that all rusts are pure parasites. They derive all their nutrients from their host plant and don't really offer it much of anything in return. They are diseases pure and simple. In addition, most rusts are also systemic parasites. They begin by infecting leaves, but with each phase of their life cycle they burrow their way deeper into the plant, affecting buds, flowers, and then the stem itself. If left alone long enough, an outbreak of blackberry rust will ultimately affect the whole plant in a way that even systemic fungicides have difficulty addressing. After a certain point, it is virtually impossible to destroy the fungus without also destroying the plant.

Until I learned this, I had assumed that the rust I saw on the field's blackberries was simply affecting the leaves – a minor nuisance, perhaps, but nothing life threatening, but now I am coming to realize that there has been a major epidemic under my nose this entire time. The fertile blackberry brambles across the street do show signs of the rust (I am now reasonably certain they are Himalayan blackberries, a common vector for blackberry rust), but I suspect they were well established enough at the time of the infection that they will soldier on all right for the time being. I am a lot less sanguine about the prospects of the smaller, younger plants in the airport field. Before I really looked at it, I had imagined that the rust was merely common in the airport field, but now I see it is ubiquitous. Every single berry plant I looked at showed signs of infection and many, upon closer examination, seemed quite sickly indeed.

Blackberry rust stunts growth in young plants causing leaves to take on a shriveled and sickly appearance. It can also prevent stalks from growing into proper brambles and keep buds, flowers, and berries from growing at all. As the infection rages on sapping nutrients from the plants, it becomes much less likely that they will ever develop as they should and successful reproduction becomes increasingly unlikely. When I first observed the little plants in the field with their low, slender stalks, malformed leaves, and complete absence of flowers, buds, or berries, I imagined they were just children. Now I realize they are children who will never grow up.