Plant Issues

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Cotton Leafhoppers and Jassids

Amrasca devastans

Caused by insect

Factors –

a- Nymph and adult leaf hoppers feed on leaves.

b- Outer leaf parts appear yellowish or burned and tend to curl upwards.

c- Leaves are similar and feature mosaic pattern.

Hosting body – cotton

Identifiable traits

The affected leaves turn yellowish, then brownish starting from the margins and migrating to the midrib. Leaves gradually show signs of curling before drying completely and shedding. Severe incidences result in “hopper burn” injury and death of leaves, eventually leading to the stunting of young plants. The fruiting capacity of the plants infested at later stages of growth is significantly affected and in many cases cause lower yields and poor quality of the fibres. Before becoming necrotic, leaves may show higher trichome density on the lower side of leaves and a hardening of the tissues. These traits confers some degree of resistance against the insect in that it makes ovoposition and movement more difficult. However, it has a negative effect on the agronomic performance.

Inducing factors

Both nymphs and adults of Amrasca devastans suck the plant sap and introduce salivary toxins that damage the tissue and impair photosynthesis in proportion to the amount of feeding and the number of insects. First and second generation of nymphs feed near the base of the leaf veins, older nymphs get distributed all over the leaves but feed chiefly from the lower side. Environmental factors such as moderate to high temperatures (21 to 31 ˚C), moderate to high humidity ranges (55 to 85%) either early in the morning or late in the evenings, and hours of sunshine affects positively the populations of this insect. Low temperatures and strong winds have a negative impact.

Organic remedies

Generalist predators of cotton leaf hopper are the common green lacewing (Chrysoperia carnea), species of the genus Orius or Geocoris, some species of Coccinellids and spiders. Make sure to promote those species and avoid use of broad-scale insecticides. Apply spinosad (0.35ml/L) when first symptoms occur.

Chemical remedies

Always consider an integrated approach with preventive measures together with biological treatments if available. Insecticide formulations based on malathion, cypernethrin (1 ml/L) or chlorantraniliprole + lambda-cyhalothrin (0.5 ml/L) can be applied. They may however also affect in severe cases and in a timely manner. Seed treatment with insecticides can also help to suppress leaf hopper populations on crop for 45-50 days.

Extra remedies

Plant resistant or tolerant varieties (several are available on the market). Monitor the orchards regularly for signs of cotton leaf hoppers. Maintain a balanced fertilization and especially do not apply excessive nitrogen.

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Black Citrus Aphid

Toxoptera aurantii

Caused by insect

Factors –

a- Distortions of twigs and inflorescences and curling, rolling or folding of leaves.

b- Leaves turn black in presence of honeydew that is readily colonizes by sooty mold.

c- Downgraded quality of fruits and poor vigor in trees.

d- Tristeza virus is a possible infection.

Hosting body – Citrus and Mango

Identifiable traits

It affects all citrus trees in all growth stages. The aphids have long piercing mouthparts which they use to suck the sap on shoot tips and young leaves, which leads to distortions of twigs and inflorescences and the curling, rolling or folding of leaves. They feed on sweet plant phloem, they excrete excess sugar in the form of honeydew. When this honeydew falls onto the leaves, it readily colonized by sooty mold fungi which make the leaves turn black. In result, this limits photosynthesis and has consequences on the vigor of the tree and the quality of the fruits. Tristeza virus is other causing factor which causes damage to citrus trees, which aphids carry.

Inducing factors

Symptoms are caused by the adults and nymphs of the black citrus aphid Toxoptera aurantii. They often co-infect citrus trees and other cultures together with another related species of aphid T. citicida, commonly known as brown citrus aphid. Adult aphids exist in two forms, either with or without wings. Winged aphids can fly a distance of up to 30 km and are found when they become too numerous or when food supply reduces or becomes limited. They have a dull brownish to black body with a length of about 1.5 mm. These black citrus aphids have a simple life cycle and a high reproduction rate that can lead to rapid and severe infestations. Favourable temperature range for development, survival and reproduction varies from 9.4 to 30.4 ˚C. The honeydew attracts ants, which in turn protect the aphids from natural predators. They are considered a vector of the Tristeza disease of citrus and the zucchini yellow mosaic virus.

Organic remedies

Predators include many species of hoverflies, lacewings and ladybirds that can attack aphids at all stages of development. Two commonly used coccinellids against this pest are adults and larvae of Cycloneda sanguinea and Hippodamia convergens. Some culture-specific parasitic wasps may also be available for citrus in the area of interest. The fungus Neozygites fresensii can be important check on aphid populations during humid weather. Ants can be killed with boiling water or with solutions containing natural pyrethrins. Insecticidial solutions can also be used against aphids, for example solutions based on soap, detergent soap, neem or chilli extracts.

Chemical remedies

If available, always consider an integrated approach with preventive measures together with biological treatments. Several insecticides can be used to control aphids but their effectiveness depends on a timely application, for example before the leaves curl or populations become too large. Commercial products containing petroleum oil can be sprayed on the underside of leaves, so that they directly contact the aphids. Synthetic pyrethroids are also likely to be effective against aphids and ants, but can have a negative impact on natural enemies, too.

Extra remedies

Select seeds from healthy plants or from certified sources. If possible, plant in an area free of this pest, and isolated geographically. Keep monitoring fields regularly to assess the incidence of a disease or pest and determine their severity. Remove infected plant parts or hand-pick the aphids manually. Check weeds in and around the fields. Do not over-water or over-fertilize. Control ant populations that protect aphids with sticky bands or nets. Do not transport citrus trees between different farms or areas. Control the use of pesticides, as those can affect negatively the populations of beneficial insects. Prune the branches of your trees or remove the bottom leaves or your plants to favour the ventilation of the canopy.

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Bitter Rot

GLOMERELLA CINGULATA

Caused by fungus

Factors –

a- Small, brown, sunken lesions surrounded by a red halo appear on fruits.

b- The brown rot expands from the surface to the core of the fruit, forming a V-shaped pattern.

c- A few of these lesions enlarge and show small, black dots on their middle.

d- The decaying apple dries up and forms a so-called mummified fruit.

Hosting bodies – Apple and Cherry

Identifiable traits

Its primary symptoms appear during the spring as small grey or brown flecks on young fruits.

As soon as summer starts, these flecks have developed into small, sunken, brown lesions, sometimes surrounded by a conspicuous red halo. As soon as the conditions become favourable to them, a few of these lesions enlarge further and show small, black or dark brown dots on their middle. As time passes, the brown, watery rot expands from surface to the core of the fruit, forming a V-shaped pattern (cylindrical rot pattern around the core are typical of another disease of apple, bot rot). This decomposes the decaying apple and dries up and usually remains hanging on the branch, forming a so-called mummified fruit. Infections are characterized by small purple flecks that later enlarge to irregular necrotic areas of the leaves. Leaves that are affected severely turn yellow and eventually shed. The contagion of the disease to shoots will compromised flowering the following season. All varieties of apple are susceptible to bitter rot.

Inducing factors

The symptoms on leaves and fruit are caused by two different sexual stages of the same pathogen. The spots on leaves and fruit are the results of the colonization of the tissues by the sexual form Glomorella cingulate. Colletotrichum gloeosporiodes is the asexual form and is the causal agent for the fruit lesions later in the season. Infected wood and mummified fruits are the overwintering sites of the fungus. During the spring, it starts growing and produces spores that are released by rain splashes and dispersed by wind. As temperature elevates

(25˚ C) and prolonged periods of leaf wetting favoured the life cycle of the fungus and infection development, but are more common in the latter half of the season. Epidemic proportion and immense loss can be reached during prolonged periods of wet warm weather during fruit growth.

Organic remedies

An antagonist, Metchnikowia pulcherrima T5-A2, was uses in combination with heat treatment to control bitter rot on ‘Golden Delicious’ apples under controlled conditions. These treatments still needs to be tested in the field trials depending on their productivity.

Chemical remedies

If available, always consider an integrated approach with preventive measures together with biological treatments. Spraying every fortnight with preparations based on dinathion, copper or sulphur can generate effective results if a good sanitation program is followed. If periods of warm, wet weather occur, it is imperative to spray more frequently than every 14 days.

Extra remedies

Make sure entire field is properly sanitised. At low incidence, monitor the orchards and remove diseased fruit from the tree during the growing season. Infected parts (wood and tress residues) must be removed and destroyed after harvest. Alternatively, mow dead braches on the ground in order to increase the rate of decomposing. Plant fortifier can be applied to keep the plan resistant against such infections. Maintain a balanced fertilization program.

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Hairy Caterpillars

Hairy caterpillars

EUPROCTIS FRATERNA

Factors –

a- Defoliation of the mango trees caused by reddish brown, hairy larvae with single tufts on each end.

b- Young pupil larvae are covered with whitish hair.

c- The moth is bright yellow with darker lines and black dots on forewings.

Hosting body – MANGO

Identifiable traits

In the early stage of hairy caterpillars have long white hairs coming from the flanks of their body. Their main feed is leaves of mango trees in groups and several other tree species.

The developed/mature larvae feature a red head covered with white hair and a reddish brown body. Larvae pupate in a cocoon of hairs on branches and leaves and also have a single tuft in the head. The moths are bright yellow and has forewings with transversal lines which are dark and black dots near the edge of wings.

Inducing factors

They are similar to two species of caterpillars with similar features which damages leaves and defoliation. The females lay yellow, circular, flat eggs in clusters on the lower surface of leaves. Their laid eggs are suspicious because they are covered with yellow brown hair and scales over them. These larvae hatch generally between 4-10 days. They feed for about 13 to 29 days on tree leaves until they convert to a cocoon. In between 9-25 days in a silk cocoon the adult moth hatches. During winter season the larvae may perform dormancy.

Organic remedies

Burning torches can be used to terminate/decimate them as they feed in tight groups. Sprays of neem (Azadirachta indica L.) and dhatura (datura stramonium L.) extracts controls caterpillar populations and reduces it. The bacterium Bacillus thuringiensis is a microbial pesticide which kills the caterpillar by crippling the gut.

Chemical remedies

If available, always consider an integrated approach with preventive measures together with biological treatments. Insecticide sprays containing cyphermethrin, deltamethrin, fluvalinat are effective against hairy caterpillars.

Extra remedies

Regular monitoring of the orchard for eggs, larvae, moths and cocoons. Find, collect and destroy the caterpillars, cocoons and egg clusters in minor cases. Adult moths can be controlled using light traps.

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American Bollworm

American bollworm has been identified to attack more than 180 host plants. These host plants include beans, maize, tomato, legumes etc. It has caused so much damage to the fields and has developed resistance to so many insectides that it has been popularly given the name of a global pest.

In the moth phase they are brownish yellow in color with a black spot on the fore wings and a broad black patch on the margin of the hind wing. Larvae are green when they are young and their color varies when the larvae grows in size. The eggs are laid only singly on the leaves and are white in color.

They hatch in a time span of 3 to 4 days. The new larvae feed on the leaves after hatching and attach the near by bolls by keeping half of the body inside the bolls and half of its body outside.

The larval period is of around 25 days long whereas the pupal period is around 10 days long.

Some of the damage symptoms are as follows:

The squares which are affected by the American bollworm shows flaring up with its brackets spread out.

Holes can be seen on the squares by the internal tissues which are being fed by the larval and hollowed by it.

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Aphids

Aphids basically belong to Aphidoidea Family. They are small sap-sucking insects like greenfly and blackfly. However, they are not harmful to crops in early stage or in small or moderate numbers. Aphid’s infest severe damage to leaves and shoots and also causes damage to plant growth.

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Alternaria Blight

The symptoms of Alternaria blight usually occur in summer and are depicted by the presence of angular or circular spots of around 4 to 7 mm in diameter. In some bad cases, the spot become 3 cm in diameter.

Black lesions are also present on leaves. Leaves can wither and fall on severe infestation. Minute brown or black spots can appear on immature fruits. The spots are about 3 mm in diameter and are surrounded by a red tint on mature fruits. This infection reduces the quality of the produce.

The symptoms arise are due to a group of three different fungi of alternaria. During favorable conditions, they come out of hibernation from the soil and produce spores that are carried by the rain or wind. Nutrient deficiency, high humidity, high temperatures, dew formation and sunny days are some of the important factors that are responsible for the development of alternaria.

Some of the characteristics of alternaria can be confused with that of Botryosphaeria dothidea. Rub the leaves to tell if the late blight is caused by alternaria alternata or not.

Biological Remedies

Apply a paste of garlic on the leaves and fruits for biological control . You can also use solutions based on Bacillus subtilis which is found to be lethal to fungus. One should always start treatment against this disease before the fruits get ripened in the early summer.

Chemical Methods of Control

Product enriched with entities such as copper, maneb, thiophanate-methyl are found to be effective in curing alternaria. The timing of the application of the treatment, age of the tree, and the quantity of the dose determine the effectiveness of the treatment.

To promote aeration of plantation, one must not plant the trees closely. Proper care should be taken to remove weeds from the field. As soon as the first symptoms are visible, one must cut the affected parts and burn them. At the time of infancy, prune the trees to get fully aerated fields.
During fruit ripening, one must not irrigate the fields using sprinklers. Once the crop is cut from the field, destroy the remaining harvest by burning it. Above all try not to compost parts of these plants as they may carry over this disease to another season.

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Angular Leaf Spot

Angular Leaf Spots are very easy to distinguish since the plants suffering from this develop leaf spots that follow leaf veins. It is caused by bacteria such as Pseudomonas syringae (cucurbits) and Xanthomonas fragariae (strawberries) that survive in seeds and plant debris.

Symptoms

Once water soaked-spots appear on leaves, they spread rapidly when conditions get moist and ambient temperature is around 24-28 degree celcius. These spots expands upto a point they fill the area between leaf veins completely, but do not cross each other. Occasionally, older spots dry out and tear apart, leaving a hole at its place. On fruits, the spots appear as perfectly circular and water soaked and comparatively smaller than those on the leaves. The spots become powdery white and may crack the fruit open once the disease spreads. This contaminates fruits and causes fruit rot.

Biological Remedies

Use garlic solutions and hot water for around 30 minutes on infected seeding material. Use dehumidifiers in greenhouses to control night time humidity. It has also been found out that Pentaphage is lethal to Pseudomonas syringae, and organic copper fnngicides can slow the spread of the disease.

Chemical Control Measures

Pesticides containing copper hydroxide are most effective when the temperature is above 24 degree celcuis and the foliage is wet and are sprayed on a weekly basis. It is NOT recommended to spray the field on a hot day since it can seriously harm the plants.

Other Preventive Measures

Use furrow irrigation instead of sprinklers and avoid overwatering the field. Furthermore, do not sow crops in the field that have had cucurbits for at least 2 years.

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