R3103 June ’19

Q1

a)      Describe the symptoms of ash dieback (Hymenoscyphus fraxineus).          4 marks

b)     State how ash dieback disease spreads.                                                              2 marks

c)      State FOUR biosecurity measures to prevent the spread of ash dieback.   4 marks

This question relates to the following part of the syllabus:

Outcome 2. Review the control of pests, diseases and weeds in horticulture.

2.4 Describe how biosecurity measures, are intended to prevent the distribution of pests, diseases and weeds.

To include prevention of the spread through trade and plant movement: Phytosanitary legislation Plant passports (e.g. plants & plant products which must be accompanied by a plant passport at all stages down to final retailer) Codes of practice Notifiable pests and diseases (e.g. Phytophthora ramorum, Colorado Beetle and Ash Dieback). Describe THREE biosecurity issues; case studies to include: Japanese Knotweed Colorado Beetle Ash Dieback

This part of the syllabus includes ash dieback as a case study, which is quite a wide term.

Part a) asks for a description of the symptoms and the examiners’ comments state that some answers didn’t have enough detail or were too vague. It wasn’t sufficient to just state ‘dieback’.  It is always difficult with a question on a disease that has part of the description in its name; but always make sure you add something extra to this.

The examiners’ comments suggest suitable points as:

Affected trees show extensive dieback of shoots, twigs and branches and trees often have prolific epicormic shoots.

Black blotches on the leaf base and midrib. The veins and stalks of leaves can be pale in colour, turning brown.

The tips of shoots become black and shrivelled and may carry blackened, dead leaves that may look a bit like frost damage. These leaves usually remain wilted on the tree during the growing season and do not drop early.

It was pointed out that answers that gave detail on diamond shaped lesions were correct, but the subsequent oozing from these cankers may be due to secondary infections and not Ash dieback.

For part b) the examiners’ comments state that it was correct to state that Ash dieback is spread by wind borne fungal spores, but incorrect to say it is spread by rain splash. Further points could have been spreading by spores from fruiting bodies of the fungus in leaf litter; through the movement of diseased trees, timber and logs and seed borne.

The examiners comments point out that specific biosecurity measures were needed for part c) rather than just general ones.  However, if you can’t think of four measures specific to a particular disease, it is always worth including general points rather than leaving a question unanswered.

Correct points included reporting to the Forestry Commission via Tree Alert; the ban on import movement and sale of ash trees since 2012 in the UK and removing and burning the whole tree and others in the vicinity.