• Angular leaf spot

  lesions on the underside of the leaf. They enlarge to angular spots, often limited by the small veins. The distinctive feature is the way the lesions look [...] translucent. When conditions are humid, a viscous bacterial exudate forms on the underside of the leaf. This exudate changes to a white film when it dries. Lesions [...] visible on the upper side of the leaf as irregular spots which are first reddish brown and then become necrotic. The foliar symptoms are the most important

• Aphids

  aphids have two pairs of wings, one of which is much larger than the other. For a large part of the season an aphid population consists of viviparous females [...] more about What are aphids? Aphids form a single, very large group of insects: the super- family Aphidoidea, belonging to the order Hemiptera . The aphids [...] on the species, aphids can inflict various types of damage to a crop: Nymphs and adults extract nutrients from the plant and disturb the balance of growth

• Bacterial wilt, brown rot

  show signs of wilting during the day which may disappear in the early stages of infection. Under conditions favourable for the bacteria, the whole plant [...] s roots on the stem. The vascular stem tissue is coloured brown and when the stem is cut, bacterial slime oozes from the wound. This is the way to distinguish [...] wilting and yellowing of leaves and stunted plants. Inside, vascular browning is common with bacterial slime oozing from the cut. When the bacteria transfers

• Apple scab

  available. They infect the plant by direct penetration of the cuticula and then grow between the cuticula and the epidermis of the plant cells. This causes [...] through the cuticula. The asexual conidia are released and repeat the cycle of infection of new plant parts and spore production. In autumn, the fungus [...] have already fallen off the trees. In response to the infection, the plants produce cork as a defence against further growth of the fungus. In cultivars that

• Asian citrus psyllid

  southern states and Mexico however the state of Florida is the most affected area by the vectored disease. Damage symptoms The psyllid is a sucking insect that [...] mature. Worst damage is done when the insect is vector of the bacterium Candidatus Liberibacter asiaticus that cause the fatal citrus disease called citrus [...] and the disease is responsible for the destruction of several citrus industries in Asia and Africa. In North America, it has spread through most of the

• Charcoal rot

  Cutting the roots may show the same discolouration of the internal tissues of the main roots. In most crops, necrotic lesions on the roots are the first [...] by wilting, dropping of leaves and collapse of the entire plant. Life cycle and appearance of Charcoal rot The fungus survives in the soil and on crop residues [...] 24 hours the fungus infects the roots of the host by direct penetration via germ tubes. During the next two days, necrotic spots occur on the roots and

• Onion

  y produced species of the genus of Allium . The onion plant is usually a biennial or perennial plant. When cultivated however, the plant is mostly handled [...] About The onion ( Allium cepa L.) , also referred to as the bulb onion or common onion, is a vegetable. This particular species is the most extensively [...] and harvested at the end of its first production season. Onions are popular and therefore cultivated and used for cooking all around the world. Their flesh

• Early blight

  occur at the side of the stem. Life cycle and appearance of Early blight From the primary infection of leaves, Alternaria solani can spread to the flowers [...] particular when spores surviving in the soil are the main source of infection. Especially wheat and barley reduce the number of surviving conidia in the soil [...] humidity (RH) of over 90% or when the leaves are wet. Small differences in optimum temperature occur between species, but in general the risk of Alternaria

• Apple collar rot

  from the root to the foot, but direct infection of the foot also occurs. Exudates leaking from growing root tips promote germination and attract the zoospores [...] readily move through water. This explains why the disease spreads more rapidly when the water content of the soil or substrate is higher than normal or optimal [...] root system and black discolouration of the roots. On the foot, dark brown lesions with sharp borders occur. Above the graft and on leaves, dark brown, irregular

• Glasshouse potato aphid

  deformations in the growing tip of the plant. Precisely where the plant is pierced is unimportant. The piercing of the lower leaves in the crop can cause [...] sometimes tomato. Damage symptoms When the glasshouse potato aphid (Aulacorthum solani) pierces the leaves or the fruit of sweet pepper it secretes a toxic [...] leaves and curled leaf margins. The immediate effects of piercing by the aphids are visible in lower leaves in the form of yellow patches. Heavy yellowing