'Aphids' is a generic term for over 500 species (in the UK) of sap-sucking insects which secrete honeydew. The moulds that often grow on this are unsightly, but generally harmless. However, the aphids do weaken plants and distort growth and leaves. More seriously, aphids transmit many viruses and the physical wounds they cause encourage further infections.
- Distorted growth & leaves
- Discarded white exoskeletons on tops of leaves
- Sooty and/or sticky patches on leaves
- Presence of ants which may protect the aphids in return for the honeydew they produce
These small (6-8mm long) beetles are either black with six yellow spots (common asparagus beetle) or orange with black spots (spotted asparagus beetle). The adults eat emerging spears during the spring, lay eggs and then the larvae eat the stems and foliage.
- Holes and yellow or brown discolouration in emerging asparagus tips
- Whole spear may die if damage severe
Also known as Gall mite, this microscopic (1/4 mm long) white mite lays its eggs in buds from June until spring. Many thousands of mites can infest each bud. As they suck sap from the developing leaves, they cause the bud to change shape and swell, sometimes forming galls. By the spring, the buds may be dry and leaves fail to emerge.
From April until July, the mites emerge from infected buds and then spread to surrounding buds and plants, often transported by passing insects, by wind or even rainsplash. The blackcurrant's relatives, gooseberries and redcurrants are also affected but without the chatacteistic big buds.
Yields may be reduced but far more important than it's direct effects is the fact that the mite transmits reversion virus.
- Enlarged buds from late summer:
- spherical appearance unlike the normal pointed appearance of buds
- up to twice the size of normal buds by autumn
- most visible when leaves have fallen in the autumn
- Buds may turn into galls
- In spring buds fail to open or leaves are stunted
Pigeons and other birds can quickly strip the tender parts of crops, demolish berries and pull up sets. Severe attacks can leave you with no crop but, before you make your allotment a bird-free zone, don't forget that birds are a vital part of integrated pest control.
- Brassicas and peas stripped leaving little but the tough stems and veins
- Bush fruit such as currants and tree fruit, especially cherries, either removed completely or left half-eaten.
- Onion sets pulled from the soil and left scattered about
A serious disease which affects first the top leaves, with brown blotches in late summer, in warm, wet weather. More often than not, the fungus then spreads down the stems killing the foliage.
- Brown spots which begin on upper leaves
- Brown patches on tubers, firm at first but quickly turning to a soft, wet rot
A sunken, dark patch at the end of fruit where the petals were indicates calcium deficiency. This causes cells to swell and burst. As a lack of calcium in soil or compost is rarely a problem, it is almost always due to inadequate distribution of that calcium around the plant by water - either because of insufficient water at the roots or too little transpiration (loss of water through the leaves).
- A dark (yellow, green, brown or black), often sunken, patch at the end of the fruit where the flower was
- Tends to affect the earliest trusses and larger fruited varieties more seriously
Plants are said to 'bolt' when they start flowering before you have had a chance to harvest the roots or leaves that you are growing the plant for. This concentrates the plant's resources on the flower and often leads to toughness or bitterness.
- Vary from crop to crop but, generally, one or more fast-growing spikes of growth appear which show signs of flower formation
This innocuous-looking fly lays its eggs on the soil surface near brassica roots. When they hatch, the 6-8mm long maggots begin eating the roots. The maggots go through a brown pupal stage before emerging as adults, mating, and infecting new plants. There are typically three generations every year, with the pupae of the third generation overwintering in the soil, emerging in the spring to begin on a new crop.
- Leaves may have a bluish tinge
- Damage to the roots means that plants tend to wilt in dry weather and can be pulled up easily
- Growth will be reduced and seedlings and young plants may die
- Brassicas grown for their roots may be totally unusable
- The white maggots are often clearly visible when the roots are examined
This fungal disease can be a serious problem in raspberries, hybrid berries and blackberries. Spots first appear in May and June then travel up the plant. The purple spots grow like fairy rings, leaving dead cells in a depression as they expand. Infections which overwinter on last years' canes will infect the following year's new growth unless checked.
- Purple spots on lower parts of stems
- Spots grow and spread upwards, leaving silvery-white depressions with purple margins - typically elliptical on stems and circular on leaves.
- Leaves and fruit may be distorted and leaves may die back
- In severe cases, plant may die
Despite giving plants a ragged appearance and, in severe cases, causing some die-back of leaves and deformation of fruit, this is rarely a serious disease. This is just as well as the bugs are often long gone by the time the damage is noticed, and they are quick-moving, dropping to the ground when disturbed - this makes control difficult. Adults are green and about 6mm long, with wings which make a distinctive diamond pattern when folded. The nymphs are wingless and paler in colour. Eggs hatch in April (2nd generation in early/midsummer). The nymphs feed on woody plants for a few weeks before moving on to surrounding herbaceous plants, pupating, emerging and laying more eggs on woody plants - it is as eggs that they overwinter. Like aphids, they suck the sap from the growing parts - shoot tips, buds, young leaves and flowers - of the plant. Unlike aphids, however, they inject a toxin which kills surrounding cells, leaving brown edges. As the leaves grow, these holes expand and tear.
- Small holes in young, growing parts of the plant, particularly young leaves
- As leaves expend, brown-edged holes which may tear
- Flowers and fruit may be deformed
This small black fly, which only flies low to the ground, lays its eggs around the roots of any of this family of crops, generally from mid-April until the end of May and from mid-July until the end of August, although there may be three generations in some areas.
The maggots emerge about a week later and begin feeding on the roots, smaller ones at first, before moving into the main tap root. They tunnel through the root which turns brown where soil enters the tunnels, either emerging as adults immediately or overwintering.
- In some cases, the leaves take on a reddish tint and growth may be stunted
- Roots are ringed with brown tunnels, often containing the white or cream maggots which are around 1cm long
- The damage caused may allow secondary infections to cause further damage
- Damage is generally most serious in carrots
Caterpillars can very quickly cause considerable damage to crops, particularly brassicas. They are the larval stage of butterflies and moths - on brassicas, normally the large white (Pieris brassicae) , the the small white (Pieris rapae) or the cabbage moth (Mamestra brassicae).
SymptomsAside from the caterpillars themselves which reach 3-4cm in length and can be very numerous:
- Yellow eggs on the undersides of leaves
- Holes in leaves
- Dark droppings at the base of leaves where they collect
Small (5mm long) white maggots 'mine' tunnels through the leaves, leaving brown blotches and blisters. Up to three generations each year mean an attack can come at any time from late spring onwards. These can cause stunted growth and bitterness.
- Long silvery trails along leaves
- Stunted growth
As the name suggests, this fungus (and, less commonly, its relative Botrytis cinerea) causes small red/brown spots on leaves and streaks on stems. The disease progresses rapidly in damp conditions, when the spots enlarge and spores are released, spreading the infection to other plants. In serious cases, the spots merge and darken, and may cause stems to collapse and even kill the plant.
- Red/brown brown spots, sometimes with a white/grey centre as they expand, on all parts of the plant
- Shrivelled and dropped leaves and flowers
- In severe cases, collapsed stems
A serious disease which infects the roots, causing swelling and distortion as it creates a gall from which spores are eventually released. This fungus-like organism, related to powdery scab in potatoes, leads to poor growth and even death.
- Poor growth
- Foliage wilts in dry weather, recovering when wet
- Foliage discoloured - purple tinge
- Roots swollen and distorted
- Distinctive light green/yellow and dark green mosaic pattern on leaves
- Leaves may curl downwards
- Fruit become misshapen, knobbly and pale, even white
- Growth is stunted and the plant may eventually die
These are the caterpillars, 20-50mm long, of two species of noctuid moth - Agrotis ypsilon (greasy cutworm) and Agrotis segetum (turnip moth) which attack the stems of seedlings and young plants at ground level at night.
Females lay the eggs on all parts of the plant. A fortnight later, the caterpillars emerge, feeding on the leaves for a fortnight before moving into the surface layer of the soil. They feed here for a month or two before pupating in the soil to emerge as moths a fortnight later.
They are more common in dry, light soil and can be seen in the soil around the plants at night and can be recognised by the way they bend into a crescent ('C') shape when disturbed.
- Sudden wilting through partial damage or even complete severing of the stem at soil level.
- Discoloured, often yellow (but also brown, purple or pale green) patches on the surface of leaves. Infections on other parts of plants are less common but pea pods are sometimes affected
- Corresponding grey (lettuce), white (brassicas) or purple (legumes) mouldy/furry patch on the underside.
- Weak or stunted growth
- Leaf die-back or fall
- Small, round(ish) holes appear in the middle and at the edges of leaves. They may not go all the way through the leaf and are generally smaller than those caused by slugs
- Brown edges or whole brown leaves appearing overnight
- Darker, almost translucent patches on pumpkins, courgettes and squash
A serious pest of gooseberries and its relatives, red and white currants, which can strip all of a bush's leaves down to the veins in a matter of days in serious cases. While this won't necessarily kill the plant, it will seriously affect yields and encourages disease.
The adult emerges in April and lays its eggs, often along the veins on the underside of the lower leaves in the centre of the plant - just where it is hardest to spot them. The eggs hatch and the larvae, which eventually reach 2cm long, emerge. They look very much like caterpillars - pale green with black spots and a shiny black head - but have more back 'legs' than butterly and moth caterpillars. They feed first low down, at the centre of the plant, before spreading outwards and upwards. Within a month they will have grown to full size. They then drop to the soil and form a cocoon from where the next generation emerges - there may be three or four of these a year.
- Very pale green, 1mm long eggs laid on the undersides of leaves near the bottom of the plant
- Tiny holes in leaves near where the eggs have hatched
- Larger holes further up and towards the ouside of the plant follow
- In severe cases, complete defoliation
- Generally start with a brown rot followed by the grey fluffy mould which gives it its common name
- Lettuce commonly show a reddish-brown colour and the leaves may break away from the roots
- Tomatoes may show spots on the surface
- Light yellow/brown patches on leaves
- Yellowing/twisted leaves
- Yellow, orange, red or purple areas between leaf veins affect lower/older leaves first
- These leaves may then turn brown and die
- Reduced photosynthesis leads to stunted growth and lower yields
- Seeds appear to have failed to germinate
- They sometimes leave a small hole from their burrowing
- On pea pods and sweetcorn cobs, look for tell-tale ragged teeth marks
- Yellow wilting foliage (outer leaves first)
- Young plants may die
- Growth of older plants is stunted and bulbs may rot
- The maggots, or at least their tunnels, are easy to see of an affected bulb is lifted
- Rough orange-brown patches on roots and spots on the leaves and/or just black or purplish rot
- U-shaped notches around the edges of young leaves
- The pinhead-sized, flat eggs are difficult to spot
- First sign of infection is usually when the pod is opened. A damaged pea or two, a caterpillar or two and caterpillar poo (frass) are a sure sign of pea moth
- The crop grows poorly
- Leaves turn yellow or brown from the bottom up, and die down early.
- In severe cases, the crop may fail altogether.
- Almost any part can be affected with a white powdery coating which may spread
- Upper surfaces of leaves are often particularly affected.
- In gooseberries (American Gooseberry Mildew, Sphaerotheca mors-uvae), the fruit are covered with a brown furry coating, which becomes a bit like felt with age. However, the fruit beneath are still edible if it is scraped off.
- Brown, dry, shrivelled 'drupelets', particularly near the stalk
- Secondary fungal infections such as grey mould
- At harvest time, the grub may be visible, either in the fruit, or trying to escape from fruit in the bowl!
- Mottling and yellowing of leaves with silvering and silky webbing when advanced.
- Badly affected leaves may fall.
- Rusty (yellow, brown or orange) spots and blotches on leaves
- In severe infections, leaves can shrivel and die
This is a bacterial disease that favours high pH (>5.2) and dry conditions. It overwinters in the soil or in tubers which were missed at harvest, infecting new tubers as they grow. The plant reacts with a corky scab which eventually bursts then regrows, leading to the characteristic raised and layered appearance of the scabs produced. Common scab is usually less serious than powdery scab, the damage being largely cosmetic - tubers are still completely edible - although in severe cases, where the skin cracks, it can affect storage.
- Raised rough corky brown patches on tubers
- Initially, small purple/brown marks
- These develop into irregular depressions with raised edges. These pustules contain the powdery/dusty spores which go on to infect other tubers
- Initially, wet, slimy patches appear on particularly near the base of the stem
- Plants may suddenly wilt and collapse
- Lower leaves turn brown and soggy
- Cotton wool like growth on any aerial part of the plant
- Affected parts may develop a bleached and/or shredded appearance
- Seedlings which have been munched down to the ground or just had their tops chewed off
- Irregular, rounded holes in leaves, roots and tubers
- Shiny remnants of a slimy trail
- Slowly spreading patches of crop which yellow, wilt and may die
- Soil clings to the surface of root crops when lifted - they develop a leathery skin texture
- Only when you lift the root might you see the fine violet/purple mat of threads which gives this disease its name
- Roots may also develop a brownish rot as secondary infections enter the wounds created by the fungus
- Yellow, wilting foliage which then dies
- White mould is usually visible on the base of the plants but it can spread to cover the whole bulb
- The mould is sometimes dotted with the poppy seed-sized black sclerotia
- Scales on the undersides of leaves
- Clouds of white flies which fly up when disturbed
- Sooty moulds on the top sides of leaves
- In young plants, damage to the roots means plants can't get enough water so leaves will wilt, and, in severe cases, the plant may die
- Potatoes are riddled with narrow tunnels which fill with soil. These then let in diseases and other pests like millipedes.