Pests and diseases in the garden

It helps to know what you are dealing with, because each of the three takes a different measure. A pest is an animal that feeds on the plant: an aphid, a caterpillar, a mite, a slug. A disease is a fungus, a bacterium or a virus that gets into the plant and multiplies inside it. A disorder is neither. Nothing is attacking the plant, the conditions are wrong, as with blossom end rot and moss in the lawn.

Diseases nearly always spread with water. Spores germinate on a wet leaf, rain and watering over the leaves carry them to the next plant, and tools you do not disinfect do the rest. So the measures that help most against disease need no spray at all: enough space between plants, watering at the roots rather than over the leaves, a resistant variety, pruning in dry weather and tools disinfected between cuts. In autumn clear the fallen leaves and dead stems, and keep infected plants off the compost, because that is where the disease overwinters. Powdery mildew is the exception, since it spreads in heat and humid air, even when the leaf is dry. Once there are spots on a leaf, nothing will save that leaf. On 21 of the 24 diseases here the source names no product at all.

With pests, timing matters most. A net over the bed has to be there from sowing or planting, because it stops butterflies and flies laying their eggs. By the time you are picking caterpillars off, the damage is usually done. A few aphids on a shoot tip are no reason to act, since ladybirds, lacewings, parasitic wasps and birds eat them if you leave them room in the garden. On 19 of the 25 pests there is no product. A net, hand picking, a trap, a jet of water or simply acting in time is enough.

A product makes sense on 9 problems out of 51. Not one of them is a synthetic insecticide: potassium soap against aphids and spider mites, mineral oil against powdery mildew, Bacillus thuringiensis against caterpillars and fungus gnats, iron phosphate against slugs, copper as a preventive against downy mildew and late blight. Natural does not mean harmless. Potassium soap can scorch a leaf and copper does not help on a leaf that is already affected, so every problem here says when a product works and when it is already too late for one.

Pests 25

Aphids 56 plants Box tree caterpillar 1 plant Cabbage caterpillars 10 plants Cabbage root fly 9 plants Carrot fly 3 plants Codling moth 2 plants Colorado potato beetle 5 plants European corn borer 8 plants Flea beetles 18 plants Fungus gnats 7 plants Gladiolus thrips 4 plants Gooseberry sawfly 2 plants Leaf miners 3 plants Lily beetle 1 plant Mealybugs 15 plants Narcissus bulb fly 2 plants Raspberry beetle 1 plant Rodents and birds at the bulbs 4 plants Rosemary beetle 4 plants Sage and ligurian leafhopper 8 plants Scale insects 14 plants Slugs and snails 30 plants Spider mites 15 plants Spotted wing drosophila 8 plants Vine weevil 13 plants

Diseases 24

American gooseberry mildew 2 plants Apple scab 1 plant Bacterial canker of stone fruit 5 plants Box blight 1 plant Brown rot (monilia) 7 plants Clematis wilt 1 plant Clubroot 10 plants Fire blight 3 plants Grape downy mildew 1 plant Honey fungus 31 plants Iris leaf spot 1 plant Iris soft rot 1 plant Late blight 2 plants Mint rust 2 plants Peach leaf curl 2 plants Pear rust 2 plants Pear scab 1 plant Peony botrytis 1 plant Powdery mildew 36 plants Quince leaf blight 1 plant Rose black spot 2 plants Silver leaf 7 plants Tulip fire 1 plant White rot of alliums 4 plants

Disorders 2

Blossom end rot 5 plants Moss in the lawn 1 plant
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