14/3/2013 - 09/05/2013 - Pests and Diseases Unit No 27208

My class on Pest and Diseases was conducted by Lisa Burton and mainly emphasis on Pest.

Pests and their Parts

Insects - have six legs, three body parts (head, thorax and abdomen) and a pair of antennae (feelers) and the adults are often winged. However, young stages - like caterpillars, grubs and maggots - may not resemble adults. Some insects pests are chompers, biting chunks out of leaves and fruits, often suckers, feeding on plant sap.

Mites - are related to spiders and have eight legs and one body part, without antennae or wings. They have an external skeleton or body skin that they need to shed and replace several times as they grow. All pest mites are very tiny, with the largest being barely 0.8mm long, some are as little as 0.2mm long. Mites feed by scraping and sucking plant sap from leaves.

Nematodes - are also sometimes known as "eelworms". They are very tiny, slender worms, a few of which live inside plants and cause them damage. Typically they are 0.2 - 0.8mm long. Larger nematodes can only just be seen with a hand lens.

Molluscs - are slugs and snails with a soft fleshly body that does not have an external skeleton. Snails have a shell, but slugs don't. Slugs and snails do not have legs but have four tentacles or feelers. Molluscs rap plant leaves, causing ragged holes.

Evidence of the pest or pathogen may be seen in two ways:-

1] Symptoms -
    The damage or growth response a plant makes in response to the presence of a pest or pathogen.

2] Signs -
    Those tell-tale structures of a pest or pathogen that are sometimes (but not always) visible on
     plants.

Various pests may cause problems when propagating, but as they attack a wide range of host plants they need only be considered in a general way so that the gardener can recognise them and treat them appropriately.

When infested propagating material, or a plant, is placed in a propagating environment, the increased levels of temperature and humidity often cause a population explosion. 

It is important, therefore to propagate, whenever possible, from material that appears to be free of pests. it is safer and often easier, to control pests on stock plants before taking cuttings rather than to treat the cutting later before they have established themselves as plants. This is not always possible however, and routine pest control measures should always be taken in the propagating area to combat invasions of pests from infested plants elsewhere in the greenhouse garden.

Aphids @ Sap Sucking Insects

Insects, such as greenfly and blackly, are invariably  present, in small populations on almost all plants during the growing season, and i is important to control them not only because they can debilitate plant material very quickly with rapid population build up but also because they may carry virus diseases.

Some aphids are easy to identify because they are found on just one host plant, or a few closely related plants. Others have a characteristic colours or markings. Some growers are taken by surprise when aphids infestations suddenly appear - often as if by magic. The reason for their surprise is that the tiny aphids that have  been establishing the population for several months have goon unseen. Many such aphids survive during the cooler winter months, hidden without plant buds. it is only at the onset of longer days and warmer spring weather that they multiply rapidly and move out onto lush spring growth - to the dismay of many gardeners.

Occasionally aphids or greenfly are found on cuttings and more rarely on newly germinated seedlings. When they are found on cuttings it is usually because some were already present on the material when the cutting are made.

Typically, aphids may cause : stunned shoots, distorted and curled leaves, wilting, honeydew and sooty mould.

Leaf roller @ Chewing Insects

Are the young larva stages of butterflies and moth and are one of the most common plant pest. Many of the caterpillars attacking plants in New Zealand has come from overseas. Caterpillars can cause damage to plants and to avoid this is essential to detect their presence early.

Mature green looper caterpillars are larger and stouter towards the rear end. Their bright green colour makes them quite hard to detect on plants, particularly when they are small and tucked under leaves.

Green looper - usually 35 - 40 mm long are stouter towards the rear end. Their bright green colour make them quite hard to detect on plants, particularly when they are small and tucked under leaves out of sight. They feed on a wide range of herbaceous plants and several weeds.

Leaf roller  caterpillars rolls and tie up leaves to make a shelter. They damaged plants by feeding on leaves and in orchards they also feed on the out side of fruits by damaging the surface. The larvae of each species are not easily distinguished and are one most serious and common horticultural pests.

Thrips @ Rasping Insects

Usually are tiny 2 -3 mm long insects. Adults are usually black and the nymphs cream. They infest and damage the the foliage and flowers of many ornamental plants, vegetables and fruit crops. Thrips may also infest bulbs and corms in storage.

The presence of brown / black sticky spots of excrement on the underside of leaves is a characteristics feature. The rasping-sucking mouthparts cause flecks and a silvery appearance to the surface of flowers, leaves and fruits.

White butterfly @ Chewing Insects

The most notorious and common pest attacks brassica vegetables (such as cabbage and cauliflowers). The dull green caterpillars grow to 30mm in length. They eat holes in leaves and plants may reduced to a collection of leaf skeletons. The white butterfly adults flit over the leaves on warm days from early summer to autumn.

Codling Moth @ Chewing Insects

Apples are damaged when the young codling moth caterpillars burrow through the skin and into the fruits. The larvae family reach the core where they consume the seed and much of the core itself. Mature larvae leave fruit and move down the tree in search of suitable protected spot beneath loose bark flakes, or in brk crevices, where they build a cocoon, become dormant. Pears, stone fruits and walnuts may also be attacked.

Gras Grub Beetles @ Chewing Insects

It is also called brown beetle. mature grass grub beetle are creamy white and 10-20mm long. They feed on the plant roots in the soil and curl up if you disturb them. Pasture, turf, container plants and field grown plants in nursery lines are frequently attacked. They feed on the foliage and may occasionally  strip the leaves of cherry and plum trees but they feed on the leaves of many other plants.

Whitefly  @ Sap sucking Insects

They are several whitefly pests, and greenhouse whitefly is the common and damaging. All whitefly are tiny insects that have scale-like young stages, commonly referred to as nymph through more accurately they are larvae, a pupal resting stage, Whitefly can be difficult to distinguish, particularly where different species share a preference for the same host plant.

Scale @ Sap sucking Insects

Most are tiny insects 2 - 3mm long that have hard coverings and they are often dome and mussel shaped. Scales are commonly brown, black, grey or white. Scale insects fix themselves to leaves and stems and suck sap. Infested leaves turn yellow and often are covered with copious quantities of sooty mould. Some scales live beneath bark and so are not easily seen.

Apparently at teh end of this session whe gave a test and Assesment to meet the competency of the topic.