Has my Garrya been hit by blackspot?
QMy Garrya elliptica, which is planted through weed-blocking membrane, started healthy but then developed what appeared to be blackspot. I thought I had beaten it with systemic fungicide but it has come back. The plant has lots of catkins; what should I do?
Dave Gibson, via email
AI think it’s unlikely that fungal leafspot is the problem at this time of year, but if it occurs in summer try removing affected leaves and improving airflow around your plant. Fungicides are not often effective against leaf spots.
There are several reasons why your Garrya may be looking sickly. It may be the time of year as it will be preparing to shed old leaves to make way for new ones. The older leaves may contain less nutrients and therefore be more susceptible to blackspot, making the problem look worse than it is.
This plant also suffers from cold, especially if a freeze follows a mild spell of weather. This can cause cold scorch, which is, again, unsightly but the plant will grow through it.
However, the spots of damage could also be a result of stress, either from summer drought or waterlogging. Removing the worst-affected leaves could help reduce the spread of the problem and I would rake up fallen leaves as they may be a source of any infection.
You may need to improve growing conditions, so check under the membrane and make sure that the roots are getting enough moisture, and that the soil is free-draining enough in order to prevent waterlogging. I would also feed the plant with general-purpose fertiliser in spring.