Pests, Weeds & Disease
From the moment we started to cultivate land thousands of years ago to produce food for our family and community, we have had to contend with weeds, insects and diseases who were also looking for a good source of food. Not all these predators are bad and in fact a good mix of wildlife (called biodiversity) is essential to maintain a natural balance in the ecosystem. The modern farmer encourages biodiversity in his fields by adding beetle banks, wild flowers and hedgerows around his crops to keep a good mix of wildlife.
However, infestations of pests and diseases can occur which cannot be kept in balance by local insects and birds and if left unchecked can seriously damage or destroy a growing crop. Below are a few examples of the many pathogens that effect European crops.
Pests
CODLING MOTH
Affects: Apples, pears, walnuts and other fruit trees
The larva of the codling moth is found in apples and is commonly recognised as the apple worm or maggot. Originating from Europe, it is now found almost worldwide. It also attacks pears, walnuts, and other tree fruits.
The codling moth lay eggs on fruit or leaves and the black-headed yellow larvae attack the fruit immediately upon hatching. Each larva burrows into the fruit, eats for around three weeks, then leaves the fruit to overwinter and pupate elsewhere.
APHIDS
Affects: Potatoes, cereals, sugar beets and citrus plants.
Aphids, also known as plant lice (and in Britain as greenflies) are small plant-eating insects. Aphids are among the most destructive insect pests on cultivated plants in temperate regions. As they feed, aphids often transmit plant viruses to the plants. These viruses can sometimes kill the plants.
WHITEFLY
Whiteflies typically feed on the underside of plant leaves. Their ability to transmit or spread viruses has had the widest impact on global food production. While several species of whitefly cause crop losses through direct feeding, a group of whiteflies also transmit plant diseases.
A major problem is the fact that the whiteflies and the viruses they carry can infect many different host plants, including agricultural crops and weeds.
Whiteflies feed on the plant and the damage is quickly increased as they congregate in large numbers, quickly overwhelming plants. Damage is further exacerbated as whitesflies, like aphids, excrete honeydew as a waste product, which promotes mold growth and may seriously impede the ability of farms to process cotton harvests.
GREENFLY
See section on aphids.
THRIPS
Affects: Onions, carrots, melons, cucumbers, peas, beans, roses, gladiolus, irises
Many thrips feed on developing flowers or vegetables which causes discoloration, deformities of the crop. Flower-feeding thrips may be responsible for pollination while feeding, but they can cause considerable damage during feeding. Thrips eat plants and parts of plants, such as pollen, flowers, leaves, fruits, twigs, or buds.
Further information* and more.
LEAFHOPPERS
Affects: Potatoes, beet, apple, grasses, broad-leafed woody and herbaceous plant
Leafhoppers are also known as hoppers. They are found all over the world. They have piercing sucking mouthparts, they feed on plant sap and can transmit plant-infecting viruses and bacteria.
A Leafhoppers' diet commonly consists of plant sap from a wide and diverse range of plants.
THE EUROPEAN CORN BORER
Affects: Maize
The European Corn Borer is a pest of grain, particularly maize. The insect is native to Europe originally infesting varieties of millet including broom corn. European corn borer caterpillars damage the ears of corn, as well as the stalks, chewing tunnels which cause the plants to fall over.
Oak Processionary
Oak Processionary The Oak Processionary is a moth whose caterpillars affect forests in Europe and can cause serious treats to human health. The backs of caterpillars are covered by hairs with toxin that can cause skin irritation and strong allergies. Oak processionary moths are mainly distributed in central and southern Europe but their rang e is expending northward where they have no natural predators.
Weeds
BLACKGRASS
Blackgrass is one of the most damaging weeds of winter cereals in the UK. Its distribution is closely linked to that of winter cereals. Although individual plants are not particularly competitive, it frequently occurs at densities in excess of 500 plants/m², causing severe loss of yields. Traditionally, it has been a weed of autumn sown crops, but in recent years has started to occur more frequently in those sown in spring.
WILD OATS
Wild oats (Avena fatua) is one of the most aggressive arable weeds. Worldwide it remains one of the most 'successful' weeds and continues to be very common in arable fields. Historically it is one of the weed species that has been encouraged by the increasing dominance of autumn sown cereal cropping.
BLACK BINDWEED
Black bindweed can form very large clumps in open crops such as potatoes but is less aggressive in spring cereals. Their germination 'window' and only occurs in spring-sown crops
CLEAVERS
Cleavers (Galium aparine) is one of the most aggressive arable weeds in autumn sown crops. In spring sown crops it is less of an immediate concern, but the effective management of cleavers is a very important consideration for creating sustainable arable rotations. Control of cleavers in break crops can be particularly difficult or expensive.
COMMON CHICKWEED
Common chickweed (Stellaria media) is the commonest broad-leaved arable weed. Seeds have little periodicity in emergence and so infestations can establish in almost any month of the year, provided temperatures are not too low and there is adequate moisture. Seeds can be produced for long periods of time. In autumn sown cereals, flowers can be present in late winter and the plants will still be flowering in the following June.
MATRICARIA
Matricaria is part of the sunflower family (Asteraceae). Most are very common in the temperate regions of Europe, Asia, and America, as well as in northern and southern Africa, and some are naturalised in Australia.
These are hardy, pleasantly aromatic annuals. Their many-branched stems are prostrate to erect, glabrous, and very leafy. Their bipinnate leaves have numerous linear, narrowly lobed leaflets.
The flowers are radially symmetrical. The greenish-yellow capitula are semi-spherical. The white ray florets can be present (M. recutita) or lacking (M. discoidea). The disc florets are 4- to 5-dentate. The receptacle is 2-3 times as high as wide. The pappus may be crown-shaped and short, or lacking.
Disease
SEPTORIA
Affects: Wheat, barley
Septoria is a fungus that causes numerous leaf spot diseases on field crops such as wheat, forages and many vegetables. It is responsible for significant yield losses. Septoria leaf blotch is a fungal disease that affects wheat and occasionally other grasses including barley.
Septoria apiicola is the cause of late blight of celery. The symptoms include chlorotic spots that turn brown and necrotic. This fungus can survive on seeds.
WHEAT LEAF RUST
Affects: Wheat, rye
Wheat leaf rust, also known as brown rust, is a serious fungal disease affecting wheat and rye caused by the rust fungus. It is the most prevalent of all the wheat rust diseases, occurring in nearly all areas where wheat is grown. It has caused serious epidemics in North America, Mexico and South America.
It is most destructive on winter wheat, probably because this allows the fungal disease to overwinter. Infections can lead to a 1-20% yield loss because infected leaves die earlier and all the nutrients are directed to the growing fungi. Infection can also cause grain to shrivel.
Small brown pustules develop on the leaf blades in a random scatter distribution. They may group into patches in serious cases. Infectious spores are transmitted via the soil. Onset of the disease is slow but accelerated in temperatures above 15°C, making it a disease of the mature cereal plant in summer, usually too late to cause significant damage in temperate areas. Losses of between 5 and 20% are normal but may reach 50% in severe cases.
MILDEW
Mildew refers to certain kinds of mould or fungus. In Old English, it meant honeydew (a substance secreted by aphids on leaves, formerly thought to distil from the air like dew), and later came to mean mildew in the modern senses.
POWDERY MILDEW
Affects: Grapes, hops, wheat, barley, artichokes, onions and roses
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi. It is one of the easier diseases to spot, as its symptoms are quite distinctive: infected plants display white powder-like spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any part of the plant that shows above the ground. As the disease progresses, the spots get larger and thicker as massive numbers of spores form, and the mildew spreads up and down the length of the plant. Powdery mildew caused an epidemic in France 1854 which led to a 75% decline in wine production.
DOWNY MILDEW
Affects: Grapes, hops, cabbage, cauliflower, turnip, Chinese cabbage, rapeseed, common radish, horseradish, tobacco, melons, gourds, cucumbers, squashes, luffas, melons and watermelons
Downy mildews are caused by fungus-like organisms. It first appeared in France 1878, uncontrolled outbreaks reduced French wine production by 50% in 1910 and 1915. Sulphur did not control downy mildew. Bordeaux Mixture: Copper sulphate crystals are cooked with lime in water. The mixture killed the downy mildew fungus.
Hop Downy Mildew is specific to hops. the fungus thrives in moist climates. Infected young hop bines become stunted with thickened clusters of pale curled leaves. These spikes have a silvery upper surface, while the undersides of leaves become blackened with spores. These dwarfed spikes are called "basal spikes". 'Lateral' or 'terminal' spikes occur further up the bine. An entire hop crop could be devastated in only a few days.
BLIGHT
Affects: Tomatoes, potatoes
Blight refers to a specific symptom affecting plants caused by bacterium, fungus, or a virus. It causes a browning of plant tissues which kills the leaves, branches, twigs, or the flowers. On leaf tissue, symptoms of blight are the initial appearance of lesions which rapidly engulf surrounding tissue. However, leaf spot may, in advanced stages, expand to kill entire areas of leaf tissue and thus exhibit blight symptoms.
Blight was the cause of the Irish Potato Famine which killed 1.5 million people and forced another 1.5 million to emigrate between 1845-1850. In 1845 the blight wiped out the potato crop nationwide, totally about 900,000 acres altogether.
It was also the major culprit in the 1846 Highland potato famines.
LATE BLIGHT or POTATO BLIGHT
Affects: Potatoes, tomatoes, chilli, peppers, tobacco, aubergines, and petunia.
Late blight causes the potato disease known as late blight or potato blight and is brought on by water mould. The disease can also infect tomatoes and some other members of the Solanaceae which include paprika, chilli pepper, potato, tobacco, aubergine and petunia.
Further information* and more.
EARLY BLIGHT
Affects: Potatoes, tomatoes
Early blight is a fungus, producing a disease in tomato and potato plants. It produces small, darkened lesions on the plants, that spread into growing black spots of dead tissue, often killing most of the plant. Seeds infected with the disease may even damp off (disease which kills seeds and seedlings) during germination.
Early blight is caused by a fungus which survives in infected leaf or stem tissues on or in the soil. This fungus is universally present in fields where these crops have been grown.
DAMPING OFF
Affects: seeds and seedlings
Damping off is the term used for a number of different fungus-caused ailments which can kill seeds or seedlings before or after they germinate.
APPLE SCAB
Affects: Apples
Apple scab is a disease of apple trees caused by a fungus. The disease manifests as dull black or grey-brown lesions on the surface of tree leaves, buds or fruits. Lesions may also appear less frequently on the woody tissues of the tree. Fruits and the undersides of leaves are especially susceptible. The disease rarely kills the plant, but can significantly reduce fruit yields and fruit quality. Affected fruits are less marketable due to the presence of the black fungal lesions.
* Wikipedia source. As Wikipedia is a collaborative encyclopedia we can not always vouch for the content, although Wikipedia's editorial process should ensure that it is verified by experts. However, at this time, it is the best basic online resource for this term. We will update with more sources once these become available.
