Control of Sciarid Fly and Aphids in Glasshouse

Chilli plants showing fungal damage secondary to sciarid fly infestation.


Sciarid Fly or fungal knat is a serious pest of glass house environments. Adults fly above ground in an erratic fashion, whilst the larval and pupal stages occur below ground. The damage to propagation material is done below the soil by the larvae (maggots). Adults indirectly spread disease through carrying fungal spores on their feet (eg. Pythium). Female adults deposit eggs from 2 days after emergence, live for about a week and can lay up to 200 eggs each. The maggots feed on root hairs or the inside of stem cuttings. The maggot damage creates sites for fungal infection as well as reducing water and nutrient uptake, further weakening the plant. Potato discs are a clever way of monitoring activity and effectiveness of control (discs of potato are placed peeled side down on top of the growing media - larvae feed on this and can be seen underneath or burrowed into discs). Adult flies can be monitored by yellow sticky traps. Conditions favouring sciarid fly include low light levels, high humidity, constantly moist media, media with high levels of organic matter.

Control Measure : to control for sciarid fly, a soil dwelling predatory mite, Hypoaspis, was introduced. These mites are packaged in a pasteurised peat and vermiculite mix for commercial use. They should be released as soon as possible and not stored at temperatures below 10 or above 25 degrees celsius. The material they are shipped in is sprinkled on soil around infected plants.

Aphids were also causing significant damage to chilli plants in the glasshouse.

An initial control measure was to use Eco-Oil, a registered organic insecticide, grown from canola oil and a blend of tea tree and eucalyptus oil.

It acts by coating and blocking spiracles and suffocating the pest. Protective membranes around pest eggs are also degraded and render them prone to dehydration. It is reported to also have a repellency action on the surface of the leaves, discouraging pests laying their eggs. Eco-Oil can be phytotoxic if overused, causing burning of foliage, particularly with warm weather or if plants are stressed from moisture loss. The oil can block pores on leaves, limiting transpiration. Application rates are 5mL per 1L of water and should be re-applied 3- 5 days later for aphid control.

other control measure : Many had already been parasatised by Aphidius wasps. Female wasps lay its eggs into the body of the aphid. Parasatised aphids are darker in colour compared to normal. Mature wasps cut an escape hole in the back of the aphid and emerge. More of these wasps were introduced to add to existing numbers. They are shipped as aphid mummies and the wasps emerge soon after arrival.

Lacewing larvae, Mallada signata, were also introduced to tackle the aphid problem. Adult lacewings live for about 3-4 weeks and lay up to 600 eggs. Each egg sits on the end of a slender stalk, elevated from the ground to prevent attack by ants. Larvae initially are 1mm but then grow to 8mm before they pupate. They have small spines on their backs upon which they impale their prey, in this case aphids. They camouflage themselves with these dead bodies to appear inconspicuous amongst their prey. They are seen usually by the visible eye as little bits of debris moving around. It is a native lacewing and is most active in warm climates. Adults feed on nectar and pollen, so presence of flowers after release will assist in keeping the lacewings within the target plants. They are shipped as eggs packed in with lucerne chaff along with a small quantity of sterilised moth eggs for food for emergent larvae.

Ref : www.bugsforbugs.com.au

www.goodbugs.org.au

Eco-Oil website

Some more pests and disease around the botanic gardens

1. Leaf miner

There are a number of different insects whose larvae feed inside the leaves. They can be referred to as "leafminers." Adults may be beetles, wasps, sawflies, moths or flies. They lay their eggs on or in the leaf. Each species always produces the same shape and size "mine." Some look like blisters, some as in this case, look like meandering lines. A wide range of plants are attacked. Control is by removing affected leaves promptly.

2. Case moths (order Lepidoptera)

The larvae of these moths make bag-like structures to protect themselves while they feed on foliage. Different species will have different ways of covering these cases - some have no coverings at all. Below is an example of a case moth larvae which has covered its case with pieces of twig and leaf. It is very well camouflaged. The case increases in size as the larva grows. When fully fed, pupation occurs inside the case. Female moths are wingless and lay eggs inside the case. The larvae that emerge will disperse and make their own cases.

A wide range of plants are affected by different species of case moth. Control is by hand removal of the cases.

3. Leaf Spot - Iris x germanica

Below is an example of this disease which is caused by a fungus which attacks plants in their dormancy. It first shows up as tiny brown spots, each with a watersoaked area around it. As these spots enlarge they turn grey and develop brown to red margins. The spots eventually coalesce to form large dead areas and the leaves are killed. Ongoing spread can weaken plants and hinder flower production.

Worse in warm, wet weather. Fungal spores are spread about by the wind and by water splash. Irises grown from rhizomes commonly have this disease. Irises grown from bulbs are less affected.

Control is by removing affected foliage and destroying. In severe infections, a copper oxychloride spray can be used. A suitable wetting agent can help the spray stick better to leaf surface. It may be necessary to repeat treatment every 10-14 days in ongoing humid, wet weather.

4. White rust - Capsella bursa-pastoris

This fungal disease affects plants in the Brassicaceae family. It is not related to the group of disease generally referred to as rusts. Usually it is characterised by small raised yellowish-green spots on upper surface of leaves with corresponding white soft-looking spore masses on the undersurface. These spores are carried to other plants by the wind or by insects. Badly affected leaves are misshapen. It is most serious in cool, moist conditions.

Control of weeds is important - Capsella bursa-pastoris (shepherd's purse), Coronopus didymus (bittercress), Raphanus raphanistrum (wild radish) are part of the Brassicaceae family. Crop hygiene is important - crop rotation and destroying diseased plant material. Spraying is not effective.

Ref : What Garden Pest or Disease is That? Judy McMaugh

Petal Blight in Rhododendron spp.

The buds and flower is the only part affected by this fungal disease. Humid conditions favour the spread of this fungus, which initially starts as small circular spots that quickly enlarge into irregular blotches.

Affected flowers dry out and turn brown and papery. They remain stuck to the plant for some weeks, unlike healthy flowers which would fall from the bush once faded. Grey mould can look similar and only affects petals.

The specific fungus particularly affects Kurume and Indica azaleas.

Control by collecting and destroying dead and diseased flowers, but spores can blow from plants considerable distance away. Spray with triadimefon as soon as buds show colour in humid weather if severe infection.

Reference : Judy McMaugh, pg 269

Iron Deficiency in Griselinia lucida

This example of iron deficiency was photographed in the RTBG.

When a plant is unable to take up enough iron, leaves become light green fading to pale yellow or even white. This happens gradually and the veins remain green, until the end of the process. Youngest leaves are affected first. In mild cases, the leaf size and new growth appear normal, but if severe, can reduce the size of the leaf and cause dieback. Fruit crop will be reduced.

Handreck suggests a quick and easy way of checking whether yellowing of leaves is due to iron deficiency : spray the plant with an iron chelate. Greening within a week indicates iron deficiency.

Problem often occurs as a result of soil pH being too high. An attempt to lower the pH can be made but this is a slow means of correcting the problem.

Handreck recommends treating the deficiency with the use of an "iron compost" which essentially involves adding iron sulphate to either compost, peatmoss or animal manure in the ratio of one cup (about 230g) to 10L, then digging holes around the rootzone and filling holes with this mix (see Gardening Down Under pg. 146).

Reference : Judy McMaugh pg. 254, Gardening Down Under, Handrek

Disease 6 - Leaf twist virus in grapefruit

Citrus trees are best grown in warm to hot climates, with mild winters. Some varieties of citrus, however, can be successfully grown in colder climates, including this grapefruit variety, "Wheeney." 

The above photo shows a viral infection, with symptoms of yellow mottling on leaves and puckering, although this could be also due to a combination of frost and wind damage. Viral infections in citrus are untreatable and like with all other viral infections, prevention by buying specimens propagated from virus-tested and/or more resistant material is the key. 

Ref : Judy McMaugh, pg. 73-4

Disease 5 - Daphne Virus

Daphnes grow best in cool areas and need soils rich in organic matter and slightly acidic. They prefer semi-shade and a cool, moist root run, so mulching is important. Daphne odora, the most common species, suffers from a number of viruses. These viruses are untreatable, but more resistant varieties have been released, termed "High health" plants. 

Symptoms of viral illness are shown in the specimens above, found in the Royal Botanic Gardens. They can include yellow blotches, irregular streaks, dead flecks, twisting or puckering. Flowers are often small, distorted and green. The whole plant may be stunted. 

Ref : Judy McMaugh, pg. 107

Pest 8 - Borers in Cercidiphyllum

Borers are a major problem for ornamental trees. There are a wide variety of borers. Once infested, there is little that can be done to control the insects in the wood. Keeping trees as healthy as possible is the best way to prevent borer damage. Trees that are old, drought stressed, or over watered, or otherwise unthrifty are most likely to be successfully attacked by borers. Borers always attack at joins of branches. The activity of borers encourages fungal disease, general weakening and eventual destruction of that part of the tree. 

Most of the borers encountered are beetles but some are caterpillars of clearwinged or other moths and others are primitive wasps. Pictured below is the frass (collection of excreta, thread, dead material), which acts as a protective, cushioning covering over the hole of the borer insect. The plant affected is a Cercidiphyllum japonicum (Katsura Tree), a deciduous tree found in the Japanese garden area of the Royal Botanic Gardens. 

An attempt can be made to treat borers by applying methylated spirits via a straw down the hole and sealing the entrance with putty. 

On a neighbouring Katsura tree, there is also a preying mantis egg case or ootheca. 

ref : University of Idaho website, pers. comm. Marcus Ragus

Disorder 3 - Frost damage to capsicum

Frost and, more specifically, alternate freezing and thawing can destroy plant cell walls, often killing tender plants, but hardier species can be affected as well. Bedding plants and tender vegetables, such as potatoes and tomatoes, show a range of symptoms in cold weather: leaf darkening or yellowing, leaf curling, scorch, tissue destruction and even plant death. Here is an example of damage to foliage of a variety of capsicum following an early morning frost in the production gardens at TAFE. Preventing frost damage involves choosing planting positions carefully to avoid 'frost pockets' (where cold air settles at the bottom of a slope), or a position in early morning sun. Other tips to prevent frost damage : 

- don't apply nitrogen-rich fertilisers late in the season as they stimulate soft, sappy growth which is especially vulnerable to cold damage

- Cover plants with a double layer of horticultural fleece or in a frame when frosts are forecast.

- Grow frost sensitive plants near walls that may radiate some heat at night. 

Ref: Judy McMaugh, pg. 20, Royal Horticultural Society Website

Disorder 2 - Phosphorus deficiency in brassica seedlings

Phosphorus is one of three major elements required by plants for healthy growth, flowering and fruiting. It remains relatively immobile in soil and resists leaching from heavy rain or watering. Australian soils are often, however, deficient in phosphorus. 

In soils with low pH, phosphorus is less soluble and therefore less available to plants. This limits growth. Cold weather can cause a temporary deficiency. Symptoms include poor growth and leaves that turn blue-green but not yellow (as in nitrogen deficiency).  Oldest leaves are affected first. Here, in the brassica seedlings at TAFE, the leaves are a red-purple colour. 

This phosphorus deficiency can be corrected by planting out these seedlings in a soil with plenty of organic matter. Decomposted animal manure, particularly poultry droppings is rich in phosphorus. 

ref: Wikipedia and Gardening Australia, Judy McMaugh pg.10

Pest 8 - Red-headed cock chafer

These are the larvae of scarab or cock-chafer beetles. They were removed from the soil they were dug out of and placed on asphalt for the sake of this photo. 

McMaugh refers to the larvae as white curl grubs. They are whitish with an orange-brown distinct head and long jointed legs. They usually rest curled into a semi-circle. Most larvae feed on plant roots, but some feed around the base of low-growing plants. Strawberry plants may have their roots eaten right to the crown. They can be a serious problem in potted plants. A wide range of plants are attacked. 

Control is achieved naturally through birds, fungal and viral diseases, predaceous insects like ground beetles. In potted ornamentals and in turf they can be controlled by fenamiphos granules (Lawn Beetle Killer) applied as directed. 

Beetles mate in summer and eggs are laid in soil usually where there is no thick grass cover. beetles form a tunnel to the surface and emerge at night to feed on leaves which they chew off at ground level. Feeding continues through summer, autumn and winter. In late spring, the larvae pupate and the next generation of adults emerge in summer. 

Ref : Judy McMaugh, pg. 139, 209

Pest 7 - Galls caused by insects on Allocasuarina

Various species of insects, especially coccoids (Hemiptera) form distinctive galls on Casuarinaceae; some of these may be mistaken for fruiting cones but they are actually modified vegetative branchlets. Coccid galls also affect eucalyptus species. They are a group of sap-sucking insects whose saliva stimulates plant cells to grow in such a way as to form a gall that looks somewhat like the fruit of the allocasuarina. Control is usually unnecessary, but removing young galls from the plant may reduce future infestations. 

Above is a photo of a psyllid gall on the same allocasuarina species in the Domain near the Botanic gardens.

Ref : Judy McMaugh, pg 148, Australian National Botanic gardens website.

Pest 6 - Echium leaf miner

There are a number of different insects whose larvae feed inside the leaves. These are referred to as "leafminers." Adults may be beetles, wasps, sawflies, moths or flies.

In the case of the Echium leaf miner, the pest is a caterpillar feeds underneath a blister-like, brown papery patch in between the veins on the undersurface of the leaf. The adult is a moth pictured below :  Photo: courtesy of Ken Bond, Dept of Zoology, Ecology & Plant Science,

University College, National University of Ireland, Cork, Ireland)

Echium leaf miner was officially introduced in the mid to late 1980s in South Australia to control the noxious weed Echium plantigeneum or Patterson's Curse. In the photos above it is affecting leaves of an ornamental species, Echium pininana, found in the Asian Woodlands section of the Royal Tasmanian Botanic Gardens. 

Ref :  Judy McMaugh pg. 179, University of Technology Sydney Website, pers. comm. Marcus Ragus

Bacterial Leaf Spot on Fuchsia

Bacterial Leaf Spot affects a range of hosts and is caused by a variety of bacterial organisms. Hosts include cucurbits, lilac, lettuce and pelargoniums. These photos show the ill-defined, black spots with irregular edges which can coalesce. Copper-based sprays may help. 

reference : McMaugh, pg. 224-225

Anthracnose on Rose

Anthracnose is a fungal disease which shows up on roses as black small, circular spots with distinct and clear-cut edges. As the spots enlarge, the centre dries out and becomes grey. The centre may eventually fall out to give a shot-hole appearance. The leaves may yellow, but not to the same extent as in black spot disease of roses. Defoliation is not as serious either. Spots can occur on stems and flowers rarely. Spores are spread by wind and is worse in cool, humid conditions. Rosa Multiflora,  used as rootstock is commonly affected. 

Control is by improving air circulation around the plants and ensuring they receive sun almost all day long. Chemical control includes copper oxychloride spray or zineb sprays which are used to also target black spot. 

Reference : McMaugh, pg. 219

Disease 3 - Rust on Rosa and Fuchsia

Above photo showing rust on the undersurface of fuchsia leaf from Botanic Gardens

Above is a close up of rust fruiting bodies through a hand lens. Fungus within the leaf produces stalks with spores on the end, with the continued growth of these stalks bursting the epidermis of the leaf in that area. The masses of spores are then blown about by the wind. 

Below are photos showing what rust looks like on both sides of rose leaf.

Rust is a collection of fungal diseases that refers to the orange-brown spore masses which are produced on affected plants. There are a large number of different fungal rust species which all lead to the presence of rust disease on susceptible plants. 

Host Range : ornamentals, fruit, vegetables, field crops and weeds. Generally a particular species of rust can attack only certain host species, but there are some special species of fungal rust that can attack different genera. 

Symptoms : Leaves, stems and fruit can be attacked. 

On leaves, the upper surface becomes speckled with small yellow patches which can coalesce. On the under surface there are corresponding orange-brown or rusty spots. In heavy infection there may be premature defoliation and serious weakening of plant. 

A few rusts stimulate plants cells to grow into gall-like structures (eg. acacia)

Disease Cycle : Rust can overwinter as thick walled spores on infected plants, on debris from infected plants, within the soil and on seed. Wind can blow the spores onto new hosts. Can also be spread from water splash from infected host plants. Generally speaking, most rusts favour high humidity, but vary in their preference for temperature. 

Control : 

cultural : avoid planting too thickly, avoid overhead irrigation in rusts that favour moist conditions, use resistant varieties (although this can cause emergence of new strains), do not vegetatively propagate from diseased plants or use seed from these plants, remove and burn diseased plants and prunings, control susceptible weed species.

chemical : copper or sulphur-based sprays (sulphur based can cause scorch on some plants in temperatures over 30 degrees celsius ). Most widely used fungicide is mancozeb. 

Reference : Kerruish, G-36

                     McMaugh, pg. 277

Disorder 1 - Fasciation in Dodonaea

This is an example of fasciation involving the flowering parts of this Dodonaea shrub found on the TAFE campus. 

Fasciation is a condition of plant growth in which the apical meristem (or growing tip - an area of undifferentiated plant cells found in buds and tips of roots, its main function to initiate growth in young plants at the tips of roots and shoots) becomes elongated perpendicular to the direction of growth. Normally, growth is focused around a singular point and produces cylindrical growth. In fasciated plants, the area of growth is flattened, fan shaped, ribbon-like or generally highly contorted. This can involve stem, root, fruit or flowerhead. 

Causes include a genetic mutation in the cells, bacterial infection, mite or insect attack, chemical or mechanical damage. Usually it is benign and can be left alone if tolerated. Pruning affected areas may or may not remove the condition in that area of the plant.

Reference : Wikipedia  

 

Tar Spot on Callistemon Pallidus

This noted on a group walk around TAFE campus

Tar Spot is a fungal disease which from the literature on line seems to particularly target Acer species. Here it is infecting Callistemon pallidus. Causes raised black spots on upper and lower leaf surface. Rarely affects the overall health of a tree, but can be widespread and aesthetically displeasing. In severe infections, can cause quite marked early leaf drop in deciduous trees like the maples. Often first starts in early summer as yellow spots which gradually gain black colour within their centres, with the black spots gradually enlarging. 

The fungus overwinters on leaves that are left on ground and by spring, the spots split and release the needle-like spores which can be carried by wind to infect the nearest host.

General control can be achieved by raking and composting fallen leaves in deciduous trees. Fungicides not recommended as a cost-effective form of treatment.

Reference :  Cornell University factsheet online

Magnesium deficiency - azaleas

Mg deficiency first shows up on older leaves. Leaves begin to yellow near the midrib and the yellowness enlarges until the only green remaining is near the tip and near the base of the leaf, giving it a characteristic V shape. Mg is a constituent of chlorophyll and the plant transfers Mg from old leaves to new leaves - thus new leaves remain green in mild cases. Mg is also moved to developing fruit, but leaf fall and crop size reduction can result in severe Mg deficiency. Problem is more likely on acidic soils, but can occur on alkaline soils as well. Can be corrected by spreading epsom salts (Mg SO4) around under plant and watering in or by dissolving in water and spraying onto foliage. 

Infectious variegation - camellia

Probably a virus that causes variable discolouration commonly on camellia spp. - small yellow marks here and there on leaves, groups of yellow marks or yellow leaf margins. It is uncommon for more than a few leaves to show this abnormality. The plant grows and flowers normally. Remove leaves showing symptoms if they are bothering, but symptoms will develop on other leaves from time to time. 

Pestalotiopsis - Gordonia axillaris

This fungus commonly affects camellia spp. and invades areas of leaf that are already damaged or sunburnt. The area becomes silvery grey and may have black pin-prick sized fruiting bodies. Adjust cultural practises to minimise leaf damage.