PD&D: pests, diseases and disorders

As part of my coursework for the certificate, I had to write a Pest and Disease project. I researched 15 of the most common pests (vertebrates and invertebrates that feed, inhabit or otherwise live off plants, damaging or killing them) and diseases (caused by microorganisms such as fungi, viruses and bacteria), ones that I had the opportunity to see in person at Wisley.

We were not required to study disorders, which usually go together with the other two categories in the acronym "PD&D"; disorders are physiological conditions that cause the plant to behave abnormally, for whatever reason except pest and diseases (i.e. nutrient deficiencies, drought, heat, physical damage etc.) - they are very difficult to identify, as this excellent guide from Michigan State University explains.

One such disorders I encountered at Wisley was on 'Conference' pears. In some years more than others (maybe due to some nutrient deficiency and possibly facilitated by dry weather), some pears develop corky lesions on their skin, which may on occasion be mistaken for fungal disease scab (Venturia pirina) but have been identified as a likely disorder. 'Conference' pears are particularly prone to them: I had it on my tree at home and receveid a good few questions from visitors that spotted it in the Fruit Garden. Dealing with it means simply removing the worst affected fruitlets so they do not take up the plant's energy; most fruit grows out of it to be happy pears anyway.

Disorder, unspecified (badly affected fruitlets, left; mildly affected, right)

Pear scab (Venturia pirina) damage

But back to my project, on pests and diseaseses... knowledge is for sharing, so here it goes:

MPA - Pests and Diseases Project

The table of contents:

Fruit

Apple (Malus domestica) and pear (Pyrus communis)
Brown rot of apple and pears (Monilinia fructigena, M. laxa)
Apple and pear canker (Neonectria galligena) 
Apple powdery mildew (Podosphaera leucotricha)
Rosy apple aphid (Dysaphis plantaginea)
Codling moth (Cydia pomonella)
Apple and pear scab (Venturia inaequalis, V. pirina)

Blackcurrant (Ribes nigrum)
Big bud mite (Cecidophyopsis ribis)

Gooseberries (Ribes uva-crispa)
Gooseberry sawfly (Nematus ribesii)

Grapes (Vitis spp)
Grey mould (Botrytis cinerea)

Raspberry (Rubus idaeus)
Raspberry beetle (Byturus tomentosus)
Cane blight (Leptosphaeria coniothyrium)

Vegetables 

Cabbage (Brassica oleracea)
Cabbage root fly (Delia radicum)
Mealy cabbage aphid (Brevicoryne brassicae)

Leek (Allium porrum)
Leek rust (Puccinia allii)

Pea (Pisum sativum)
Wood pigeons (Columba palumbus)