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Updated : 21/9/2014

Garden Pests

Cutworm

Introduction

The cutworm (Euxoa and Agrotis species) is a general feeder, and attacks almost any kind of succulent young plant with most damage occuring in spring. Cutworms cause what can possibly be considered the cruellest damage to your plants. After you've coddled seeds and watched them grow into sturdy little seedlings, you walk out to the garden one morning to find them laying on the soil, as if chopped down by tiny axes. This is telltale cutworm damage. Here's how to protect your plants from these pests.

Life-cycle

Eggs are laid in autumn and winter. Larvae emerge and mature. They remain as larvae in the ground, unprotected or in earthen cells, until the end of winter. The larvae rely on winter weeds as a food source. The over-wintering larvae pupate during August / September. The pupal stage lasts two weeks. Moths emerge. They fly at night and lay eggs on weeds and volunteer maize. Moths may lay over 1 000 eggs. Eggs hatch after one week. Larvae feed on the leaves of plants or weeds for a few days. Although they also feed during the day, they avoid direct sunlight. A few days after the second instar the larvae creep into the soil during the day, and emerge at night. When still small they feed on the leaves. Thereafter they start feeding on the stems of young plants. A second generation soon follows the first.

Control measures

  1. Winter tillage

    Tillage prior to August destroys winter weeds. Larvae exposed on the soil surface might be damaged, or taken by birds. Frost also kills them. The destruction of winter weeds prevents the larvae from feeding, and also denies the moth a site for oviposition.

  2. Use of herbicides

    The application of herbicides well before planting is a very effective method to control cutworm. minimum period of 35 days prior to planting is needed in order to starve the larvae. Weeds on contour banks and land perimeters must also be controlled.

  3. Chemical control

    This is essential at planting time, in addition to previous control methods. Sprays as well as baits are available, and it is often advisable to use both. The method used is that which best fits into the farming system. Refer to the latest "Guide . . . . . . . ." for currently-registered poisons.

  4. Physical Protection

    The best way to protect your plants from cutworms is to create a barrier around them. Cutworms are the most dangerous during the first few weeks of a plant's outdoor life, when the newly-emerged stems are still very tender. If you have planted Brassicas (cauliflower, broccoli, kale, etc.) they are most susceptible to cutworms. By making a point of putting barriers around your seedlings as soon as you plant them, you can ensure that your plants will be protected.

    Which type of barrier should you use? One of the simplest is a toilet paper or paper towel roll, cut into two to three inch pieces. Slip the cardboard ring over your plants, and make sure that at least half an inch or so is beneath the soil's surface. Eventually, these will start to fall apart, but by that point, your plant will be too large for the cutworms to do any damage.

    Another good option is to use a three inch wide strip of tagboard or lightweight cardboard, and form it into a ring. Slip it around your seedling, again, burying part of it in the soil.




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Tomato and Tobacco Hornworms
(Manduca quinquemaculata and Manduca sexta)

Introduction

A late instar tomato hornworm can chew a good-sized tomato plant to the ground overnight.

Description

Early instar caterpillars range in color from white to yellow. As they molt and grow, tomato hornworm caterpillars turn to green with 8 v-shaped white marks on each side of their bodies. Tobacco hornworms differ slightly, having 7 diagonal white marks down each side instead. Both tomato and tobacco hornworms have a hornlike projection on their last segments – thus the name hornworm. Both pests are the larvae of sphinx moths, fat-bodied moths with small forewings. Eggs are oval and green, and laid singly on leaf surfaces.

Life cycle

Both tomato and tobacco hornworms overwinter in the soil as pupae. In spring, adults emerge from the ground to mate and lay eggs. When garden crops are not yet available, the adult moths will lay their eggs on other solanaceous plants, including weeds like jimsonweed, nightshade, and horse nettle. Caterpillars feed on foliage, reaching maturity within 4 weeks. The larvae then drop to the ground and pupate. A second generation of moths in midsummer, just when tomatoes and other nightshade crops are beginning to flower. These second generation caterpillars tend to do the most damage in the garden, before pupating in the soil in fall.

Crops damaged

Tomatoes, potatoes, eggplants, and peppers. Caterpillars feed on foliage and sometimes on unripened fruit.

Signs and symptoms

Defoliation of host plants, especially near the top of the plants. As caterpillars get larger, defoliation accelerates and entire plants can be devoured quickly. Frass (black or green caterpillar droppings) on lower leaves or on ground under affected plant.

Control measures

  1. Hand pick caterpillars and drop them in soapy water to destroy them. This requires a good eye, as hornworm caterpillars are well camouflaged.
  2. Turn or till soil at the end of the season to disturb any burrowing caterpillars or pupae.
  3. Keep the garden free of solanaceous weeds that provide tomato and tobacco hornworms additional hosts.
  4. Apply Bacillus thuringensis when larvae are young.
  5. Attract beneficial insects, such as predatory wasps and lady beetles, that feed on eggs and young caterpillars.
  6. Braconid wasps parasitize hornworms. If you find a hornworm with white, cylindrical projections on its body, leave it in the garden. These are braconid wasp pupae, and more parasitic wasps will emerge from them and find other hornworms to parasitize.

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Aphids
(Family Aphididae)

Introduction

In moderate numbers, aphids don't do as much harm to garden plants as one might think. But once you start seeing sooty mold or curled leaves, it's time to act.

Description

Aphids are tiny true bugs with piercing, sucking mouthparts designed to suck the juices from plants. They are usually wingless and pear-shaped. You can recognize aphids easily by the pair of cornicles projecting from their hind ends – two tiny "tailpipes" that other soft-bodied insects lack. Aphids vary in color according to species and host plants.

Life cycle

The aphid life cycle is unusual in that females can birth live young, and do so without mating. Aphids overwinter as eggs, from which wingless females hatch in spring. These females give rise quickly to the next generation of Amazon aphids, and the cycle continues throughout the growing season. As fall approaches, aphids begin producing some males with which they mate. Only then do the female aphids rely on traditional reproductive methods, laying eggs that will carry her genes through the winter months.

Crops damaged

Nearly all garden crop. In particular, aphids prefer beans, peas, melons, cucumbers, pumpkins, squash, tomatoes, potatoes, and cabbage. Aphids can also transmit diseases to many of these crops.

Signs and symptoms

Curled or yellowed leaves. Stunted growth. Blackening on foliage (sooty mold).

Control measures

  1. Use a strong spray of water to knock aphids from sturdy plants.
  2. Attract beneficial insects to your garden. Most predatory insects will feast on aphids when they are present in high numbers. Avoid using broad spectrum pesticides that will kill beneficials along with pests.
  3. Don't over fertilize your plants. When you give your aphid-infested plants a nitrogen boost, you're actually boosting aphid reproduction and creating a bigger problem.
  4. Keep the garden free of weeds, and check for infested ornamentals near your vegetable garden that might harbor aphids.
  5. When possible, prune any heavily infested shoots from plants and destroy them, aphids and all.
  6. Apply neem oil, horticultural soap, or horticultural oil when appropriate. These products work on contact, so repeat applications will be necessary. Be sure to get the undersides of leaves where aphids may be hiding.

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Cyprus Aphids
(Family Aphididae)

Introduction

The cypress aphid, which has wreaked havoc among conifers in southern Africa over the past few years, is a pest which injects a toxin into the plant branches while sucking the sap for food. The first sign of damage is yellowing of the foliage, which later turns brown. Despite its brown appearance, however, the plant does not become dehydrated and remains pliable.

As with all the many aphid species, the cypress aphid does have many enemies, including the adult and larva stages of ladybird species, parasitic wasps, hover flies, praying mantis and chameleons.

The cypress aphid secretes a fair amount of honeydew and, if populations are very high, you might also find black sooty mould growing on the stems or leaves covered in honeydew. The control of ants nesting in the surrounding soil of plants will assist beneficial predators to control their prey more effectively. Ants, especially pugnacious and other ‘cocktail' ant species, protect insects like cypress aphids against their natural predators in return for honeydew.

The cypress aphid reaches its peak infestation during the cooler months of the year, starting from March until August with a drop in numbers as it becomes warmer in summer. Whilst most aphid species are found on young, new, sappy growth, the cypress aphids are found on the main stem as well as lateral branches and not necessarily on the end of branches or new leaf growth of conifers.

Cypress aphid populations are found in colonies ranging from a few to hundreds. These colonies are more hidden where they are found on the actual main or lateral stems of conifers and you need to look deeper inside the plant - as opposed to most common aphids which are easily detected on the end of developing branches and or flower stems.

Protect the predators

Once you start looking inside your conifers, you might come across ladybirds mating in the middle of winter. It is also not unusual to find a praying mantis having a feast. The biggest challenge is to safeguard these populations, while still bringing the aphid population under control.

Simply put, use organic formulations like Ludwig's Insect Spray or Pyrol and avoid applying them as a general full cover spray. Pull the lateral branches away from the main stem to expose the aphids, and without drenching, hold the spray nozzle against the stem or branches and, at low pressure, allow the spray mixture to run down the stem and branches. By doing so, a huge percentage of the aphids are destroyed with one treatment and, because there was no full body contact with the ladybirds or praying mantis, their lives are spared. Two to three treatments during the months of May, June, July and August will give your conifers maximum protection.

Spray solutions

Organic formulations such as Margaret Roberts' Organic Insecticide and Vegol, which contain canola oil and no pyrethrum, have no or a very low negative impact on adult ladybirds or other bigger-bodied predators when applied as a full cover spray due to the fact that the recommended dosage rates are mainly effective for controlling very small-bodied insects the size of aphids, whiteflies or red spider mite.

In the event of direct contact with canola oil formulations, it is very unlikely that adult ladybirds or praying mantis will be killed by means of suffocation. Adults and larvae of ladybirds can feed on prey covered with canola oil with no secondary poisoning possible. To enhance the build-up of ladybird populations, maintain host plants near those conifers with light infestations of aphids. These plants include fennel, dill, tansy, bishop's weed, angelica, Queen Anne's lace, golden rod, cosmos, dandelion, sunflower, crimson clover, hairy vetch, grains and indigenous grasses, buckwheat, butterfly weed, euonymus, rye, soapbark tree, buckthorn (Rhamnus spp.) and Robinia pseudoacacia.

This conifer is infested with cypress aphid. Ladybirds are natural predators of aphids

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Psylla

Introduction

Citrus psylla is the vector and transmitter of a major citrus disease known as Greening.

Description

Citrus trees have 3 normal growth flushes during the year: spring growth during August/September, followed by a second in November/December and the last during February/March. Lemons are, however, the exception since lemon trees form new leaves throughout the year. It is during these flushes that the trees are subject to psylla infestation. It is therefore important to examine the trees thoroughly during these periods to determine the degree of infestation and to organise control of the pest accordingly. The female lays easily discernible orange-yellow eggs on the edges of young leaves. When the eggs hatch, the young nymphs move to the underside of the leaves where they establish themselves to feed and cause pock-like malformation of the leaves. Control of the pest must be aimed at destroying the nymphs as soon as possible after they have hatched. Because all the eggs do not hatch simultaneously, it is essential to use a spray with a fairly long residual action. Keep your citrus safe from pests, the most common of which is citrus psylla. An infestation results in a swelling on the upper leaf caused by insects underneath the leaf. Citrus psylla affects mainly young trees.

Treatment

Spray with Biogrow’s eco-friendly Pyrol or Bioneem

BIONEEM : 1500ppm AZADIRACHTIN
The key insecticidal ingredient found in the neem tree is AZADIRACHTIN, a naturally occurring substance that belongs to an organic molecule class called tetranortriterpenoids. It is structurally similar to insect hormones called ‘ecdysones’ which control the process of metamorphosis as the insects pass from larva to pupa to adult. Metamorphosis requires the careful synchrony of many hormones and other physiological changes to be successful, and azadirachtin is an ‘ecdysone blocker’. It blocks the insects production and release of these vital hormones. Insects then will not moult, thus breaking their life cycle. Azadirachtin also serves as a feeding deterrent for some insects. Depending on the stage of life-cycle, insect death may not occur for several days. However, upon ingestion of minute quantities, insects become quiescent and stop feeding. Residual insecticidal activity is evident for up to seven days or longer, depending on insects and application rate. Bioneem is used to control a wide range of insects (up to 200 insect types) including white flies, leafminers, mealybugs, thrips, fruit flies, leaf hopper, red spider mite, weevils and many more. Azadirachtin is relatively harmless to insects that pollinate crops and trees, such as butterflies, spiders and bees; ladybugs that consume aphids; and wasps that act as a parasite on various crop pests. This is because neem products must be ingested to be effective. Thus, insects that feed on plant tissue succumb, while those that feed on nectar or other insects rarely contact significant concentrations of neem products.

PYROL : ACTIVE INGREDIENTS : PYRETHRINS 0.5% ,CANOLA OIL 89.5%
This product provides broad-spectrum control. It can be used as a dormant and growing season insect spray and kills all stages of insects, including eggs, on contact. It is a proprietary formulation consisting only of naturally occurring plant oils as active ingredients. It is truly an insecticide from plants for plants. It does not contain piperonyl butoxide as a synergist, and the active ingredients do not persist in the environment. This product will control insect pests such as : aphids, beetles (e.g., Colorado potato beetle. Flea beetle, Japanese beetle, asparagus beetle), caterpillars (e.g., gypsy moth caterpillars, tent caterpillar, diamondback moth larvae, leaf rollers), ants, mealy bugs, mites, leafhoppers, scale, whitefly, adelgids, plant bugs, fungus gnats, thrips, sawfly larvae, psyllids, spittlebugs, and phylloxera.

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Mealybug

Description

Mealybugs are soft-bodied scale insects found in moist, warm areas. Mealybugs are usually covered with a white powder. They feed on the juices of plants. Mealybugs are found on greenhouse plants, house plants and subtropical trees. Mealybugs may be identified by looking on the undersides of leaves and around leaf joints. They look like small balls of cotton. Small infestations may not cause severe damage, but severe infestation causes poor growth, misvormed leaves, yellowing of leaves, leaf loss and plants eventually die. Mealybugs also produce honeydew (similar to that produced by whiteflies and aphids). A black fungus grows on the honeydew.



Treatment

There are both chemical and biological control options. The key aspect of management is to detect the infestation before it becomes too difficult and costly to deal with. If an infestation is well-established, it will be necessary to spray chemicals at 10 to 14 day intervals. Do not use the same pesticide, or pesticide combination, more than three times in sequence




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Red Spider Mite

Introduction

Mites are not true insects but belong to the spider family. The best known of the mites is the red spider. The presence of red spider is one of the major disease related problems during summer in southern Africa. This pest is favoured by hot and dry conditions. They fed usually on the under side of leaves by means of sucking mouthparts. The eggs and mites are covered with a delicate web, which protects them from contact sprays. In recent years red spider has become a major problem in our nurseries. For control of red spider it is very important to understand the life cycle of the spider.

Life Cycle

Egg – larva – nymf – adult

Up to 20 – 30 short cycles per year are possible in a hot and dry greenhouse. Under ideal conditions this cycle can be as short as 8 – 12 days. Important is the fact that 75% of the adults are females and that one female can give rise to millions of spiders within a few months.

Treatment

When controlling red spider the following must be taken into consideration:
  • Red spiders can become resistant to chemicals and chemicals must be varied frequently.
  • Chemicals used for different parts of the life cycle must be used alternatively during different spraying sessions.
  • eep the humidity high during hot periods. (Wet the paths and use your climate control systems).
  • Spray on the underside of the leaves and use small droplets for effective coverage.


The ten golden rules for the control of red spider:

  1.  Vary the active ingredient of the chemicals.
  2. Spray for all the life phases.
  3. The interval in-between spray applications must be short enough to break the life cycle.
  4. Use the recommended concentrations.
  5. Spray 1500 litre water per hectare.
  6. Wet the underside of the leaves properly.
  7. Use small nozzles.
  8. Do not spray only the plants but also the rest of the greenhouse.
  9. Wet the paths and use the climate control systems to decrease the temperature and to increase the humidity.
  10. Remove moisture and nutrition stress.


Treatment

There are both chemical and biological control options. The key aspect of management is to detect the infestation before it becomes too difficult and costly to deal with. If an infestation is well-established, it will be necessary to spray chemicals at 10 to 14 day intervals. Do not use the same pesticide, or pesticide combination, more than three times in sequence


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White Fly

Ash Whitefly - Siphoninus phillyreae
Whiteflies cause direct damage to plants by sucking plant sap and removing plant nutrients, thereby weakening the plants. Damage may be more severe when plants are under water stress. In addition, they often produce large quantity of honeydew that leads to the growth of sooty mould on the lower leaves, blocking or reducing the photosynthetic capacity of the plants. The honeydew also contaminates the marketable part of the plant, reducing its market value or making it outright unsaleable. Infested plants may wilt; turn yellow in colour, become stunted or die when whitefly infestations are severe or of long duration.

Monitoring and decision making
For early detection inspect for adults and eggs. They are usually found on young leaves. Watch out for whiteflies flying up when the crop is disturbed. It is important to identify the whitefly and the type of damage caused, as well as the stage of the crop for making decision. Small numbers of whiteflies do not cause major direct plant damage to healthy, mature plants and therefore do not justify any chemical intervention. Control measures can be justified if large numbers of whiteflies are present during the early stages of the crop. However, where virus transmission is involved, as is the case of the tobacco whitefly on tomatoes, sweet potato or cassava, even small numbers of whiteflies may need to be controlled.

Major species of whiteflies in Africa:
  • The greenhouse whitefly (Trialeurodes vaporariorum)
  • The tobacco whitefly or sweet potato whitefly (Bemisia tabaci)
  • The spiralling whitefly (Aleurodicus dispersus)
  • The citrus woolly whitefly (Aleurothrixus floccosus)
  • The cabbage whitefly (Aleyrodes proletella)
How to indentify whitefly:
All whiteflies are best identified by their pupae, small immobile structures 1.5 mm long, usually clustered on the underside of the leaves of its host. Ash Whitefly pupae characteristically appear to have greyish bands on a pale/whitish body. Adult Ash Whitefly have slightly mottled wings but otherwise are a pale whitish whitefly indistinguishable from many other different species.

Immature stages of the citrus woolly whiteflyAdults of the citrus woolly whitefly (Aleurothrixus floccosus) have wings all white in colour. Eggs are in a circle or half a circle. The immature stages are covered by abundant, dirty-looking, flocculent white wax, which gives them a woolly appearance. They usually form large dense colonies covered with cotton-like secretions on the lower leaf surface.
 
Which plants are hosts:
In order of preference (i.e. plants most likely to be attacked):
Members of the Oleaceae, including many species of Fraxinus (e.g. Claret ash, Golden ash etc), Olea (Olives) and Phillyrea.
Members of the Rosaceae including many species of Crataegus, Malus, Prunus, Pyrus (eg Hawthorn, Apple, Plum, Pear)
Puniaceae: Punica granatum (Pomegranate)
A variety of other plants, including various species of citrus, magnolia, and crepe myrtle, are likely to be occasional hosts for this pest.
The life cycle:
Development only occurs between temps of 10° and 30°C with optimal temps between 20-25°C. Winged adults lay eggs on underside of leaves. Nymphs emerge, rarely moving more than one centimeter. The nymphs feed on tree sap until pupation. Pupation occurs in situ with larvae on undersides of leaves.

Harmful Whitefly in SA

Neem (Azadirachta indica)
Neem-based pesticides are reported to control young nymphs, inhibit growth and development of older nymphs, and reduce egg laying by adult whiteflies. They also reduce significantly the risk of Tomato Yellow Leaf Curl Virus transmission. Efficacy of neem-based pesticides can be enhanced by adding 0.1 to 0.5% of soft soap.
For more information on Neem click here.
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