Pest 1 - Black Scale (Order : Hemiptera)

Black Scale infestation observed on umbrella plant during clean up of nursery greenhouse for preparation of upcoming propagation practical. 

Host Plants : 

Black Scale affects a wide range of plants, mostly woody.

Fruit crops include citrus, but also apricots, passionfruit, olive, vines. Ornamentals include house plants.

Distribution on Plant : 

Twigs and stems preferred, although any part of plant may be infested. 

Damage : 

Black scales are sap suckers and can target various parts of the plant. The young scales secrete honeydew with resultant growth of sooty mould fungus. Plants develop a black look and photosynthesis is affected, causing general weakening, stunting if untreated, sometimes defoliation. Fruit covered with black sooty mould. 

Appearance of Pest : 

Adult females are larger than males, are dark brown to black in colour,  hemispherical or "bun-shaped" and measure 3mm x 2mm, with a raised "H" formation on the back, although I did not notice this at the time. Before laying eggs, females are softer, grey and mottled - the "rubber" stage.  Male scales are narrower, flat and often not seen.                                                                       Nymphs are light brown and 0.5mm long. 

Life Cycle : 

2,000 eggs can be laid at a time beneath the adult female looking like little heaps of sand. Body of female shrinks and falls off after eggs hatch. Juveniles remain beneath the parent scale for a couple of days before actively settling on the leaves. After about a month, young scale moults and migrates to stem, where it remains. Another month, the scale develops the "H" backing, female deposits eggs shortly after and eggs hatch in 2-3 weeks, usually around early summer and also in autumn. 

Spread is by crawling from plant to plant, by insects (eg. ants), birds, wind or from clothing. They prefer humid conditions, moderate temperatures. 

Control methods

 cultural : severely infested portions can be pruned out.

 biological :  introduction of parasitizing wasps (target adult scale insects), or predatory insects like variety of ladybirds, green lacewing larvae, scale-eating caterpillars. 

 chemical : spray when eggs are hatching with white oil (2oml per litre of water). Rub scales carefully off with hand or 10ml of white oil + 2ml of maldison per litre of water. 

In this example, the plant was pruned back quite heavily as it can tolerate this. Less affected areas could have been washed with soapy water as another method of control. 

Reference : Kerruish  F-157

 

Disease 1 - Spotted Tomato Wilt Virus

Disease - Spotted Tomato Wilt Virus

Spotted Tomato Wilt Virus identified in my vegie patch yesterday, affecting tomato heirloom variety "Principe Borghese."

First noticed shriveled, blackened leaves. On closer inspection of younger leaves, noticed brown, rust coloured spots, quite discreet and areas of larger yellow discolouration. Young fruit had started to drop off and some appeared shriveled. Only one plant out of six was affected and symptoms had come on quite rapidly. 

Host : 

wide host range, including ornamentals (eg. dahlia, nasturtium, petunia and zinnia), vegetables (eg. lettuce, celery, members of solanaceae family - tomato, eggplant, potato, capsicum), weeds (particularly solanaceous weeds eg. nightshade). 

symptoms :

start 14 - 21 days after infection. Disease recognizable by abnormalities on leaves. In tomatoes, small areas of bronzing in the terminal growth and upper surface of young leaves to eventually affect whole leaf, whilst in older leaves quite distinct bronze spots or rings between veins. Spots eventually extend and join up. Affected areas blacken and shrivel "as if they have been scorched by flames."  Leaf stalks and stems may develop brownish-black streaks, young fruit shrivel and fall. 

spread : 

by onion thrips, rarely by seed, not by contact between plants, not by pollen.

control : 

cultural methods - early planting increases severity, do not grow tomatoes next to flower crops or weeds which act as alternative hosts for onion thrips (eg. nightshade), plant excess plants to allow for losses. Most tomato varieties are susceptible, no cure for infected plants so they must be removed and destroyed as soon as possible. Remove weeds that act as host for onion thrips. 

chemical - onion thrips can be sprayed with dimethoate in cases of commercial crop or widespread infestations. 

In this example, I removed the affected plant and disposed of it in the rubbish bin - I didn't think my compost was reliably hot enough to destroy the virus. From what I have read, pesticides to control onion thrips have a very limited use in the home garden, although in commercial crops pesticides are best used to spray seed or cutting beds. 

references :  Judy McMaugh pg 189, 286

                      Kerruish E-13