Attack!

Many plants are attacked by a range of diseases, among which rusts are among the most noticeable. Frequently these rusts show up as crusts - often yellow or orange - or blisters.

Hollyhock rust affecting plant in garden. Hartwell, Northants.

24 June, 2018

Most gardeners are familiar with the Hollyhock Rust, Puccinea malvacearum, and the Snapdragon Rust, Puccinea antirrhini and, on groundsel, Coleosporium tussilaginis.

Groundsel showing, on the right, the rust Coleosporium tussilaginis.

Daventry town centre. 23 June, 2018

 
Two days ago I encountered another example, this one affecting hawthorn in a rather bizarre manner.
Gymnosporangium confusum is one of the many species which apparently requires an alternate host, in this case an introduced species of juniper, Juniperus sabina. This is a popular garden plant but for this to be involved seems a little unlikely. However, there is evidence that this rust may not need the alternating host.

As my photograph shows, the fungus forms a sort of gall and throws out a number of elongated tentacle-like structures - aecia - making the gall very distinctive.

Gymnosporangium confusum on hawthorn. Foxhill Farm, Badby, Northants.

21 June, 2018

Maps produced by the National Biological Network suggest that this species is largely confined to the west of Britain and this record is about as far east as it gets. Having said that, these rusts are not well recorded and the apparent absence of this species from eastern England may not reflect the true situation.


A second example from an adjacent bush

A related species is the European Pear Rust, Gymnosporangium sabinae, which has attacked our pears is the back garden. We grow 'Conference, and 'Concorde' but only the former has been infected. It looks like producing very few fruits this year.


The 'Conference' pear has had quite a severe attack of pear rust.

Stefen Hill, Daventry. 22 June, 2018

Our aquilegias are under attack of a different form, an insect rather than a fungus being the culprit. Their leaves have large discoloured blotches caused by the larvae of a fly, Phytomyza aquilegiae. It is unfortunately very common but, other than being rather unsightly, it seems to cause little damage.

Our aquilegias have been attacked by Phytomyza aquilegiae.

Stefen Hill, Daventry. 22 June, 2018

Is it my imagination or is this pest on the increase?