Pests, Diseases and Beneficials

Friends and Foes of Australian Gardens

F David Hockings AM

• Publisher: CSIRO PUBLISHING
• Year: 2014
• ISBN:
  9781486300235
• Topic: Biological Sciences
• Subtopic: Horticulture
• Index: Biological Sciences

Pests, Diseases and Beneficials helps gardeners to identify and deal with those common insects and small animals (such as bugs, beetles, caterpillars, thrips and mites) that are found in every Australian garden.

It offers clear descriptions and full colour images to aid in identifying insects or other organisms, and provides useful advice on how to recognise and treat problems. The book also covers feeding habits, life cycles and insect biology.

Based on the 1980 book Friends and Foes of Australian Gardens, this new work has been revised and expanded to include general garden situations as well as Australian native plants, and provides further information on plant diseases, harmless and beneficial fungi, bacteria and viruses, physiological disorders and problems caused by horticultural mismanagement.

Chapter 1

FRIEND OR FOE?

One of the really absorbing interests associated with gardening is the discovery of the large number of weird and wonderful insects and other small animals that have evolved with plants. They are not all pests and some are quite beautiful or else have a bizarre appearance.

Apart from the native creatures, a large number of introduced species, which include many pests, have become established here in Australia.

Some of these small native and exotic animals (they are not all insects) are quite specific to particular families of plants, some even to particular species, while others have a wide range of association. The larger creatures are usually fairly obvious, although some are remarkably well camouflaged.

Small insects such as aphids and planthoppers are not easily noticed, and the damage or abnormality they cause is more likely to attract attention before the creatures themselves are detected.

Still other creatures, such as mites, are so small that, even though you may look closely, you are unlikely to see them. Smaller mites such as broad mite and brevipalpid mite often do damage to the growing point or young fruit or the bark of young stems – damage which does not become evident until, after a period of growth, the damaged tissue tries to expand. By the time the damage is noticed, the mites may no longer be present. I call these cyclic mites.

Some pest damage is easily confused with damage caused by disease organisms (fungi, bacteria and viruses) or abnormalities from physiological causes. Physiological abnormalities are many and varied and may result from such factors as deficient or excess trace elements, sunburn, over-fertilising or accumulated salts. Herbicide damage has become very common and can also be confused with pest damage.

Garden pest and disease control chemicals are almost all quite specific for either pests or diseases (unless ‘catch all’ mixtures). Products specifically for use against small animal pests are, in almost all cases, quite useless against diseases and vice versa. Some are fairly ineffective against other than a particular group of pests or particular group of disease organisms. For example, sulphur has some effectiveness against mites as well as rust fungus, but is of little use against most insects or other fungal diseases or bacteria or viruses. Miticides are used against mites, but are of little use against insects.

It is pointless spraying or dusting with pesticide unless you know what pest you are dealing with, and it is essential to know if treatment is even necessary. It should be understood that not all of the small animals that can be found in gardens are pests. Many of them are harmless or beneficial in a variety of ways.

The beneficial and harmless creatures usually outnumber those that actually damage plants. Even of those that feed on plants, a significant number do so little damage that treatment or removal is rarely warranted, and they may have other virtues.

If a pesticide spray or dust is avoidable, the environment and your plants would be better off without it. I would never want a garden without insects – just imagine, no butterflies or bees!

Insects, like the nectar-feeding birds, have evolved along with the flowering plants. Bees, wasps, flies, beetles, moths and butterflies play a significant part in pollination and seed production of crop plants as well as bush plants.

Insects and the other small animals also play an extremely important part in the disintegration and decomposition of plant debris, animal wastes and the bodies of dead animals. This action is extremely important in disposal of litter, recycling of plant nutrients, and formation and improvement of soil.

It is therefore obvious that some understanding of the activities and feeding habits of the various small animals is most important if you are to identify whether they are harmful, harmless or beneficial.

A predator is a carnivorous organism that either captures and consumes its active prey or, more passively, consumes soft-bodied, relatively inactive prey such as aphids. A predator may have raptorial forelegs for seizing prey and sharp mouthparts for tearing the victim apart, or it may have a piercing style through which it injects a digestive fluid that predigests the contents of the victim – which are then sucked out.

Some predators use snares (spiders) or traps (ant lions), and some wasp predators capture and anaesthetise prey to provide food for their larvae.

A parasite is an organism that takes or steals its nutrition from another organism (the host). Its parasitism usually leads to death of the host.

A parasite can be classified as an ectoparasite (it feeds from outside the host), endoparasite (it feeds within the host), hyperparasite (a parasite on a parasite) or parasitoid (it does not kill its host – eggs are laid amongst or in the host eggs, or on food that may be eaten by the host).

As an aid to this understanding, the following two chapters show how these various small animals are grouped, the way the groups are related to each other, and how the members of these groups feed and multiply. It is important to realise that even within genera of pests there are frequently species that are parasites or predators of the pest species.

Chapter 2

CLASSIFICATION – THE IMPORTANCE OF SMALL ANIMALS

In times past, the world’s living entities have been classified into either the Plant Kingdom or the Animal Kingdom. However, some forms of bacteria, protozoa, fungi, slime moulds, water moulds and algae have exhibited some characteristics of both these kingdoms.

To deal with these anomalies five or six kingdoms are now recognised: Plantae, Animalia, Fungi, Protista and Monera. Monera is further divided into Eubacteria and Archeobacteria. Some of these changes relate to plant disease-causing organisms and others that can be found in gardens.

Kingdom Protista now includes the slime moulds (myxomycetes), water moulds (phytophthoras), and human disease organisms such as Amoeba, Plasmodium (malaria) and Giardia.

Kingdom Fungi contains food species such as mushrooms, truffles, morels, and useful species such as yeasts (bakers and brewers), penicillins (cheese, yoghurt and medicinal), and mycorrhizal and entomogenous fungi. Also there are many plant disease species as well as human-disease organisms such as Cryptococcus and Candida.

Kingdom Monera includes the bacteria and is sometimes divided into kingdom Eubacteria and kingdom Archaeobacteria.

Kingdom Eubacteria includes important decomposers and recyclers or symbionts in the gut of many animals to aid digestion (in termites, even in man). A couple that cause human diseases are Escherichia coli and Salmonella.

Kingdom Archaeobacteria includes species that live in extreme environments such as salt lakes, hot springs and undersea volcanic vents.

In the Animal Kingdom, the levels of classification are as follows: phylum, class, order (sometimes further divided into suborder and superfamily), family (sometimes subfamily), genus and species (sometimes further into subspecies and variety). At times taxonomists have rather flexibly used another level ‘higher taxon’ as an intermediate between main levels of classification.

The classification into groups called phyla (singular, phylum) applies to the simplest forms of organisms, the microscopic single-celled animals at the bottom of the evolutionary ladder, and equally to organisms of increasing complexity and evolutionary development, including humans.

The divisions of classification and the phyla into which some animals are placed vary slightly according to which authority is followed. According to some systems of classification, there are some 22 phyla of animals, but fortunately we are concerned here with only four phyla and with relatively few of the individual small animals in these phyla.

PHYLUM NEMATODA

NEMATODES OR ROUNDWORMS [ILLUSTR ATIONS 6, 108, 247]

This group was previously included in the phylum Aschelminthes. It includes the nematodes and consists of slender unsegmented cylindrical or sac worms, mostly small to microscopic in size. They reproduce by laying eggs and the sexes are usually separate. The young worms moult (grow a new cuticle or skin beneath the old, which is shed) as they grow.

Aschelminths include many marine and freshwater worms and many terrestrial and parasitic species such as the roundworms and hookworms, as well as nematodes and the Gordius or horsehair worms.

Nematodes are thread-like worms, although the mature females of some species are swollen or sac-like. They include many that are parasitic on or in other forms of animal life, including humans, and many that are parasitic on plants.

The majority of soil nematodes are microscopic, ranging in length from 0.5 mm to 2 mm. Different groups of nematodes feed in the following ways: as parasites of insects and other small animals (often of the larval stages); as predators on other nematodes; as feeders on fungi, bacteria, algae and moss; and as parasites of plants, causing loss of vigour, decline disease and, in some cases, spread of virus diseases. Many of the serious plant pest species are introduced to Australia.

Parasitic nematodes that attack plants below the ground may cause root galls, root rots, root lesions, damage to the surface or tips of roots, distortion or bunching of roots.

Parasitic nematodes that attack plants above the ground may cause distortion or death of growing points or flower buds, leaf or flower bud drop, galls or angular leaf spots.

The natural enemies of nematodes include: parasitic protozoans (single-celled animals) as either external or internal parasites; predacious nematodes that may swallow pest nematodes whole or puncture and suck out the contents; and parasitic and predatory fungi that either parasitise or actively capture nematodes. Other groups of worms as well as some mites and springtails also feed on nematodes.

Nematodes are of very great economic importance, perhaps even greater than is generally realised. There are many groups besides the more obvious root-galling (root knot) types. Being microscopic and mostly hidden under the soil, they are easily overlooked and the symptoms are often attributed to other causes such as root-rotting fungi or faulty nutrition. Some historical rural catastrophes such as the American ‘Dust Bowl’, recorded as having other causes, are now believed to have been the result of nematode infestation.

Nematode problems are best avoided by strict rejection of infested plants and soil. Expensive and very poisonous chemicals such as fenamiphos (Nemacur™) can be used to treat infested soil but kill other beneficial soil animals, can be harmful to plants and, if used close to harvest of edible plants, can render the plant parts poisonous. Leaf nematodes may be controlled by pruning and shifting plants to a drier environment.

Attempts at biological control of nematodes, using predatory species or nematode-feeding fungi and trap plants such as marigolds (which attract nematodes but in which they cannot reproduce), have been disappointing.

The best long-term solution is regular addition of organic matter as mulch. Organic matter promotes a large array of organisms that assist in decomposition and recycling nutrients. Some of the fungi and bacteria feed specifically on nematodes. A DOOR (‘Do Our Own Research’) trial carried out with hardwood sawdust mulch took about 10 months to be colonised by nematode-feeding fungi and bacteria and then gave complete control of nematodes.

The sawdust was pre-treated to prevent nitrogen drawdown by mixing in urea and moistening, then composting for six weeks. The mulch layer had to be topped up every six months to maintain the layer.

PHYLUM MOLLUSCA

This phylum of slugs and snails consists of soft-bodied animals, some of which have a single, bivalve or compound shell. They are o...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Acknowledgements
• Introduction
• Chapter 1 Friend or Foe?
• Chapter 2 Classification – the Importance of Small Animals
• Chapter 3 Plant Damage – by Mouthparts, Egg-Laying, Bites and Stings
• Chapter 4 Plant Diseases and Useful, Harmless and Beneficial Organisms
• Chapter 5 Dealing with Pests and Diseases
• Illustrations I Pests Associated with Flowers, Fruit, Seeds, Leaves and Shoots
• Illustrations II Less Harmful, Harmless and Beneficial Small Animals
• Illustrations III Pests Associated with Twigs and Small Branches
• Illustrations IV Pests and Beneficial Animals Associated with Trunks and Main Branches
• Illustrations V Pests Affecting Collars and Roots
• Illustrations VI Small Animals Associated with Soil, Compost and Shelter
• Illustrations VII Free-Ranging Small Animals
• Illustrations VIII Diseases Affecting Garden Plants
• Illustrations IX Harmless and Beneficial Other Organisms and Specialised Roots and Bark
• Illustrations X Parasitic Plants
• Illustrations XI Physiological Disorders
• Illustrations XII Horticultural Problems
• Appendix I: Control Chart
• Appendix II: Glossary
• Index