Choke fungus - Epichloe typhina

These strange white sheaths around the stems of grasses are the spore-producing tissue of the fungus known as choke Epichloe typhina. It's present inside the grass all year-round, living as microscopic hyphae within the spaces between cell and benefitting from sugars produced by the host's photosynthesis, but is only visible to the naked eye in summer, when it produces its spores externally around the stem. The white fungal sheath will turn orange-brown when the spores are ripe and ready to be shed, when they are often carried away by small flies.

 The fungal infection tends to prevent the grass culms from flowering, promoting multiple shoot formation instead, but in return the fungus increases its host's drought resistance and produces toxic alkaloids that deter grazing animals, so the relationship between fungus and grass is symbiotic and not simply parasitic.

I found these specimens growing beside a footpath at Wolsingham, Weardale this week.

Cherry-plum, infected with pocket plum disease

I had been hoping for a good cherry-plum harvest this summer - the fruits make excellent jam - but the hedgerow trees that I had my eye on are infected with pocket plum disease, caused by the fungus Taphrina pruni. In the first picture you can see one uninfected developing fruit, green, and then the rest are red, swollen and deformed so that they are flattened, resembling pockets. Soon spores will erupt from their surface.

In previous years I've seen infections on sloes and on bird cherry. This is the first year I've seen a severe infection on cherry-plum.

 

Rusty groundsel

 To many gardeners it's a weed; to botanists it's a wild flower; to ecologists it's a ruderal - a primary coloniser of disturbed ground. Call it what you will, groundsel Senecio vulgaris is a remarkable plant. It flowers all-year-round, produces seeds by self-pollination without the aid of pollinators and can thrive in an extraordinary range of habitats. 

Tenacious two-inch-tall plants can grow in a crack in the pavement and produce a single flower. Bushy, lush plants growing in a nutrient-rich farmyard can produce hundreds of flowers and thousands of seeds, which are carried away on the wind but are also eaten by finches, though the seeds can also pass unharmed through a bird's gut and germinate successfully. The seeds also have a covering of microscopically small hairs that extend when wet and help the seed to stick to animals' feet. 

The generation time of a groundsel plant is often around three months, so in a single year,  in favourable conditions, a single seedling can give rise to a million descendants. 

A wild flower for all seasons, then, and a plant on a world tour, taken to North America and Australia by European migrants long ago.

 

The name groundsel comes from the Old English word grundeswilage, meaning ground swallower. I always imagined that the generic name, Senecio, derived from the Latin senex, meaning 'old man' referred to the greyish-white whiskery plumes of its airborne seeds, but the real explanation can be traced back to botanist William Turner in 1538, who wrote that 'when the wynde bloweth it away, then it appeareth like a bald headded man, therefore it is called Senecio' ..... and in the photo below you can see what he meant.

Groundsel has an Achilles heel, a rust fungus called Puccinia lagenophorae, which has an interesting history. It is an Australian fungus, that infected groundsel there and was imported into the UK on groundsel that accidentally made the return journey to the UK, most likely with imported horticultural plants, and was first noted here in 1961. It has since spread throughout Britain and somehow crossed the Atlantic, first being observed on groundsel plants there in 2001.

Groundsel rust, being an efficient parasite, doesn't kill its host outright but does weaken it and render it susceptible to other fungal pathogens, like mildews.

The spore cups of Puccinia lagenophorae are quite beautiful when you look at them like this, magnified under a low-power microscope, appearing like tiny sunbursts with sunbeams formed from radiating chains of spores. 

Pocket plum disease

 This summer there have been some spectacular local outbreaks of pocket plum disease, affecting sloes on blackthorn on the Durham coast near Hawthorn dene  and bird cherry fruits in Weardale. It's caused by the fungus Taphrina pruni, which induces the fruits to swell, become spongy and fill with watery fluid. In bird cherry (bottom picture) the normally spherical, shiny black fruits become banana-shaped. No seeds are formed inside these deformed fruits, instead there is an empty 'pocket'.