List of Pests and Diseases That Can Ruin Your Crops

Just as there is an infinite range of cultivated and natural plants, so too, is there a myriad of insects and minute life in the form of fungal and bacterial diseases, which depend on plants for their existence.

cabbage white butterfly

The cabbage white butterfly.

Left to their own devices, a balance is usually struck between the plants and their hosts, but there is a constant ebb and flow with the resurgence of a particular pest or disease overtaking the plants and vice-versa.

The need to keep all garden pesticides in a safe place cannot be emphasized too strongly and still more important. Use them according to the directions supplied with them.

The Main Diseases and Pests of Vegetables

Crop Pest/Diseases Description Control
Beans, broad Black fly (Aphis fabae and other aphids) Very prevalent and damaging by restricting growth. In gardens, pinch out tops.
Brassicas (broccoli, Brussels sprouts, cabbage, cauliflowers, radish, savoys, turnips) Clubroot (Plasmodiophora brassicae) Cabbage aphis (Brevicoryne brassica) Cabbage caterpillars Cabbage root fly (Erioischla Hylemyia brassicae) A slime mold or fungus invading and distorting the root tissue causing inability of the root to extract water and nutrients. Symptoms: wilting of plants, especially cabbage and cauliflower. Effects are typical of those caused by sucking pests-distortion and' dwarfing. Collectively known as cabbage butterflies, the eggs are laid from April onwards on the underside of the leaves. Causes wide destruction, especially to cabbage, cauliflowers and sprouts. Pests overwinter in the soil as pupae and flies appear round about, mid April (or later if the weather is cold). Heavy liming of growing area in spring to give a pH of about 7. Puddle the roots of plants prior to transplanting in a paste of calomel dust. Crop rotation and the avoidance of all brassicas in extreme cases are necessary. Spray early and persistently with varied chemicals to avoid build up of disease within the pest. Use derris and pyrethrum. Control measures are becoming less effective due to rapid buildup of resistant strains of root fly. Best chemicals for control are composed of pyrethrum. Control measures are becoming less effective due to rapid build-up of resistant strains of root fly. Best chemicals for control are available on the market.
Carrots Carrot fly (Psila rosae) The female fly lays its eggs in clusters or singly in cracks close to the carrot. Where thinning is carried out, the holes left are ideal repositories for the eggs. A range of chemicals are used, including both seed dressings (made from pyrethrum) dusted on to the seed before it is sown, and this is probably the best and safest method for the amateur.
Celery Carrot Fly (Psila rosae) see carrots Malathion (as for carrot fly) is likely to give a measure of control.
Leeks Rust (Puccinea porri) Orange spots on leaves causing death of leaves and stunting growth are typical symptoms. No really effective control, but reduced by copper, maneb or zineb
Onions Onion fly (Delia Hylemyia antigua) The adult fly, like the common house fly in appearance, lays its eggs in stem or leaves at ground level in May and early June, giving rise to small grubs in 3 days. Grubs eat into the base of the bulb. Control lies in seed dressing with approved insecticide. Note: Calomel dust can be used around the plants in the rows and can also be used for seed dressing.
Peas FuSarium foot rot (Fusarium solani) (F.pisi) Lower leaves begin to turn brown and if stems are examined at ground level, they will be seen to be brown and pinched in. Drazoxolon or thiram seed dressings help and many seedsmen carry this out at no extra cost. Rotation is also helpful.
Potatoes Blight (Phytophthora infestans) Virus diseases Potato root eelworm (Heterodera rostochiensis) (also known as Potato cyst eelworm) Slugs A serious disease, especially in wet summers, when foliage is prematurely destroyed reducing total yield. Potatoes can be affected by virus diseases, some transmitted or spread by aphids, others in the soil, and by pests such as eelworm. Virus disease presence in planting stock is one reason why the Certification Scheme for seed potatoes was implemented. Do not keep self-saved seed too long, it is better to buy new seed from a reliable source. A persistent pest because of the method which the larvae 'rest’, which is a cyst. In a severe attack, the foliage yellows and dies back. No other single pest causes so much harm in the vegetable garden as slugs, and this is true of the potato. Tubers are holed irrevocably and the whole crop can be ruined. Do not plant doubtful tubers. Crop rotation is the best answer. If eelworm levels are .low, plenty of organic matter and gross feeding can enable crops to be grown to a reasonable level despite their presence. Early lifting is best, especially in a wet season.
a hedgehog in my garden

The hedgehog is the gardener’s friend—he eats many pests!

Diseases and Pests of Fruit

Crop Pest/Diseases Description Control
Apple Apple mildew (Podosphaera leucotricha) Apple scab (Venturia inaequalis) Apple canker (Neclria galhgena) Aphid species (Rhopalosiphum insertum, Dysaphis Plantaginera Aphis pomi, Dysaphis devecta) Apple sawfly (Hoplocampa testudinea) Leaves, blossom trusses and new shoots can all be affected by white fluffy mold, which reduces and distorts growth. A very common trouble causing spotting of leaves, splits and scars on fruit rendering it useless. A vicious and serious disease attacking branches, causing scars and eventual die-back. All cause distortion of leaves and shoots and restrict growth. A nasty pest. Fruit is mined by caterpillars Systematic fungicide (thiophanate-methyl) or dinocap at pink bud stage (late April-early May). Prune out badly mildewed shoots before this. Follow up with further sprays at intervals of 7-14 days. The same spraying program as for mildew is effective using systemic fungicide at 10 day intervals. Avoid leaving large open pruning cuts. DNC sprays plus mercury at bud break stage. Spray with winter wash (tar oil or DNOC). If bad attack occurs in spring or summer, use dimethoate, malathion or derris. A wide range of chemical can be used, including systemic insecticides and BHC, usually about 7 days after petal fall.
Peach Plum Damson Red spider sps. (glasshouse red spider) (Tetranychus urticae) Silver leaf (Stereum purpureum) Foliage hard, parchment­like with yellow mottling on upper surface, becoming completely yellow. A bad disease which is always a risk when plums are grown. Leaves go silver hue (usually July/August)—one branch on side of a tree to begin with, followed by death of branch. Resistance may occur as in aphids and treatment should be varied. Many acarides are available including (on seedlings) sprays of dimethoate. Remove old crop immediately fruit finished to prevent hibernation of mites. Disease spread by spores. Prune only in summer June/July/August. Paint over cuts with tar oil was or paint. Remove and burn dead branches by July 15th.
Currants: Black White Red Reversion Blackcurrant gall mite (Big bud mite) (Cecidophyopsis ribis) A virus disease spread by bud mite and possibly other pests. At grape stage of flowering, color of flower seems darker, but more significant is reduction of veins on leaves, causing them to alter shape. No other pest of fruit is perhaps as well known as this. Tiny mites infest leaf scales preventing buds opening, which results in small blackened buds. No control, other than avoidance of cuttings from infected bushes. Lime sulfur applied at the grape stage is the best general recommendation.
Gooseberry American gooseberry mildew (Sphaerotheca mors-uvae) Gooseberry sawfly caterpillar (Pteronidea ribesii) White hairy growths on shoots, leaves, and fruit. Often considered the worst pest of the gooseberry. Green caterpillars spotted with black dots and black heads start to eat leaves in April/May. Spray at first open flower stage with benomyl or dinocap. Azinphos-methyl, fenitrothion, derris and malathion are recommended as soon as pests are seen.
Raspberry Raspberry moth ('Borer’) (Lampronia rubiella) Dead cane tip if examined at end of April or early May will be found to contain red grubs or brown chrysalis. As the base of bud is eaten away, canes die. Spray with tar oil and DNOC winter wash. In April, spray with carbaryl.
Strawberry Botrytis or grey mold (Botrytis cinerea) Total loss of fruit due to botrytis grey mold is very high, especially in moist areas or a wet season. Control measures should be taken before attack starts. Chemicals recommended are: benomyl, captan, and thiram. Directions given with the product must be followed.
a ladybird chilling out on a plant leave

Another friend, the ladybird, feeds on greenfly and aphids.

Pest and Diseases in the Greenhouse

Crop Pest/Diseases Description Control
Cucumber Grey mold (Botrytis cinerea) Stem and roots rots (Rhizoctonia sp, Pythium sp, Phytopthora sp) Red core (Phytophthora fragariae) Water-soaked lesions at nodes and at side shoots and leaf scars. Fruits rotted. Light brown (Rhizoctonia) or dark brown (Pythium/Phytophthora) lesions at stem bases of seedlings or young plants. Rotting of the shoots. A very serious problem in infected soils. Remove infected tissue. Reduce humidity. Sterilize soil in seed boxes and in beds. If Rhizoctonia occurs, apply quintozene dust to surface of bed and rake in. Long rotation the only answer.
Tomato Damping-off rot and foot rots (Rhizoctonia solani, Pythium spp. Phytophthora spp) Leaf mold (Cladosporium fulvum) Wilts (verticillium alboatrum, V. dahliae, Fusarium oxysporum F.lycopersici and F.redolens) Greenback Collapse of seedlings or young plants at soil level. Roots may be rotted. Yellow patches on upper surface of leaves with brown or purplish velvety fur of fungus on lower surface. Yellowing and/or wilting of leaves progressively up the plant. The shoulder of the fruit stays green. Ailsa Craig and its offspring are susceptible. Sterilize seed boxes, pots and compost. Ensure clean water supply. Drench soil surface with Cheshunt compound. Avoid conditions of high humidity (i.e. ventilate and give a little heat to create a buoyant atmosphere). Give reasonable space between plants. Hygiene and soil sterilization essential. Stem base drench (1 pint/plant) with benomyl after planting may reduce infection. Grow resistant varieties. Do not over-defoliate. Shade in extreme cases when very hot weather persists. Increase the application of potash.

Pest and Diseases of Trees

Diseases Symptoms Control (if any)
Chafer beetles (Cock chafer-Melonontha vulgaris) (Garden chafer Thyllopertha horticola) (Rose chafer-Cetonia aurata) Seen in swarms in spring and early summer and especially abundant in vicinity of woods and heaths where the ground tends to be of the lightest nature and dry. Attack a great variety of trees, shrubs and other hard- wooded plants. Larvae feed on the roots of grass and other plants. Very difficult to control and involves hand picking, the application of naphthalene, trapping with turf, and the protective spraying of foliage of trees and shrubs with various insecticides.
Cutworms (Many different species which are larvae of various moths) Attack a wide range of trees and shrubs, especially at young stage. Eat lower leaves and bite into roots. Poison bait is effective, also derris and BHC dusts. The destruction of weeds in borders and waste ground in vicinity of garden is also helpful.
Tree Root Rot fungus (Armillaria mellea) One of the most commonest and most destructive of fungi to trees. Fungus first develops on stumps and dead roots of old trees, then spreads to young trees. The mycelium travels quickly through the ground. Remove and burn all roots from the ground before planting young trees. Check mycelium by digging a trench 45cm/18in wide and 60-90cm/2-3ft deep to cut off infected area.

Diseases Which Attack Many Plants Out of Doors and Under Protection

Diseases Symptoms Control (if any)
Aphids or 'Greenfly’. Green, black and various colored winged and wingless pests, many of which are described under specific plants or crops. The leaf-curling aphid produces extreme curling of leaves. Green apple aphids distort shoots and stems. Tulip aphid causes distortion of foliage, etc. Often impossible to control effectively on large trees or shrubs. Malathion is useful but it is better to interchange insecticidal materials to avoid build up of resistance within the pest.
Birds Pull seedlings out and eat leaves. Eat grass seed. Netting on small scale. Bird scarers, or use of repellants.
Common black ant (Lasius niger) Spread pests such as mealy bugs and disturb seed after it has been sown. Carbon disulphide inserted into the nests is highly effective.
Damping off and root rots (Pythium spp, Rhizoctonia solani, Phytophthora spp, Thielaviopsis basicola) Grey mold (Botrytis cinerea) Seedlings and plants keel over and die at a fairly early age or staee of growth. Soft rotting of the tissues, which later become covered with smoky grey fur of fungal growth. Spots may occur on leaves and flowers which later rot. More common under glass than out of doors because of humid atmosphere. Remove diseased, moribund, or dead tissue and destroy. Avoid overcrowding. Under glass, give adequate ventilation and warmth to create a buoyant atmosphere. Spray or dust with captan or thiram. Spray with benomyl or use tecnazene smoke under glass. Dichlofluanid may also be used.
Leaf spots (Various species of fungi including Septoria, Cercospora, Phyllosticta etc) May coalesce to form larger areas of dead tissue. Remove and burn affected leaves. Protectant sprays with copper or dithiocarbamate fungicides may be helpful. Check for any phytotoxicity before using extensively.
Mice Stems and foliage, bulbs and tubers nibbled. Use traps and/or poison baits.
Stem and bulb eelworm (Ditylenchus dipsaci) Nearly all soft-leaved plants are susceptible. Eggs are laid in the tissues of the plant and develop into larvae which cause the leaves to become narrow and stunted. Extremely difficult to control. Various potent chemicals can be used but it is best to contact your garden center to check what is available.
Springtails (Collembola) Seedlings and young plants with pin holes or scraping of surface of foliage. Springtails (minute white or colorless wingless insects) present in large numbers when soil floated in bucket of water. Apply gamma-BHC dust to soil, or drench with gamma-BHC or malathion.
Whitefly (Trialeurodes vaporariorum) (Mainly under protective cultivation) Small adults with white wings, larvae stage scalelike. Adults fly away in clouds when foliage disturbed. Found in large numbers in young plants and growing point of old plants. Spray with malathion or diazinon. Biological control possible but not always practical.
Wireworms (Several species) (Most common are Athous haemorrhoidalis and Agriotes lineatus) Larvae of the click beetle. Attack roots, stems, bulbs, corms, tubers and rhizomes of a wide range of plants. Generally brown in color. They feed first on decaying root and vegetable matter but as they grow they attack many plants. Wireworms are universally present in newly broken grassland and a useful cleaning crop is the potato, which should be lifted early and the wireworm riddled tubers destroyed. Mustard as a green crop sown in July and dug in when about 7.5cm/3in high is also useful for control.

Roses

some black spots on this leaf

Black spots on rose leaves.

Diseases Symptoms Control (if any)
Black Spot Very much a problem now with the lack of sulfur in the atmosphere as the effect of the 'Clean Air Act’ has spread over the country. Leaves progressively develop black spots. As the fungus develops, leaves wither and drop. Worst in a wet summer Spray with mancozeb, zineb or dichlofluanid. Ground should be sprayed in spring with colloidal copper or a household disinfectant. Nurserymens’ catalogs usually list varieties resistant to black spot.
Stuart Jones
 

My name is Stuart Jones and I'm the guy responsible for most of the content on this website. I'm a horticulturist with over 25 years of experience in gardening and garden plants. To bring color throughout the year, I regularly grow a wide variety of plants, bulbs, flowers, shrubs and trees. Oh, and let’s not forget the fruits and vegetables to ensure the fridge is always stocked!

Click Here to Leave a Comment Below 0 comments

Leave a Reply: