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Horticultural Industry in Kenya and Plant protection strategies : 

Horticultural Industry in Kenya and Plant protection strategies By Harun Murithi

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Agriculture accounts for about 24% of Kenya’s GDP An estimated 75% of the population depend on the sector either directly or indirectly. The Horticulture industry is the fastest growing agricultural subsector in the country and is ranked third in terms of foreign exchange. Fruits, vegetable and cut flower production are the main aspects of horticultural production in Kenya.

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Horticulture in Kenya is mainly rain fed though a number of farms, especially the ones growing horticultural crops for export, also use irrigation. The sub-sector generates over USD 300 million in foreign exchange earnings The Horticultural Crops Development Authority (HCDA) is a parastatal established by the Government with the aim of developing and regulating the horticultural industry.

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As the volume of production and export increases, there are constraints being felt both at production level and marketing level. At production level, the rising costs of inputs especially fertilizers and other agrochemicals most of which are imported are challenges the farmer is faced with. Freight costs are also rising steadily while air cargo space on scheduled flights. Losses due to pest and diseases amounts to millions of money. Plant protection is an important factor in horticulture

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Horticulture is divided into 3 main areas: Floriculture Olericulture Pomology

Common Pests in Horticulture : 

Common Pests in Horticulture Diamond Back moth Leaf miner Mites

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Thrips, Mango Fruit fly American Boll worm Aphids

Two-spotted spider mite Tetranychus urticae : 

Two-spotted spider mite Tetranychus urticae

Description : 

T. urticae is extremely small, barely visible with the naked eye as reddish or greenish spots on leaves and stems; the adults measure about 0.5 mm. The red spider mite, can be seen in greenhouses and tropical and temperate zones spinning a fine web on and under leaves. The red spider mite is extremely polyphagous. It lays its eggs on the leaves, and it poses a threat to host plants by sucking cell contents from the leaves cell by cell, leaving very tiny, pale spots or scars where the green epidermal cells have been destroyed. Description

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The two spotted spider mite is oval in shape, about 1/50 inch long and may be brown or orange-red, but a green, greenish-yellow or an almost translucent color is the most common The body is separated into two distinct parts: (1) the gnathosoma and (2) the idiosoma. The gnathosoma includes only the mouthparts. The idiosoma is the remainder of the body and parallels the head, thorax and abdomen of insects. After hatching from the egg, the first immature stage (larva) has three pair of legs. The following nymphal stages and the adult have four pairs of legs. The 2 spot

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All mites have needle-like piercing-sucking mouthparts. Spider mites feed by penetrating the plant tissue with their mouthparts and are found primarily on the underside of the leaf. All spider mites spin fine strands of webbing on the host plant — hence their name. Webs may constricte the plant and interfere with development

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Adult female and her eggs. Females, Larvae and eggs The twos potted spider mite prefers the hot, dry weather but may occur anytime during the year

Life cycle : 

Life cycle Developing mites pass through egg, larval, protonymph, and deutonymph stages, with periods of quiescence in between

Damage and Managemnet : 

Damage and Managemnet They damage plants by piercing leaf cells and sucking out the contents, which causes the cells to collapse and die It is estimated that 18 to 22 cells are destroyed per minute. Continued feeding causes a stippled-bleached effect and later, the leaves turn yellow, gray or bronze This damage is usually most conspicuous as pale-coloured spotting visible on the upper surface of the leaves. In heavy infestations the mites remove nearly all the chlorophyll, and leaves eventually die and fall off

Management : 

Management Examine the undersides of the leaves closely for mites, cast skins and webbing. Regulating the Humidity in green house Chemical control- Miticide Biological control

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Predators are very important in regulating spider mite populations and should be protected whenever possible. Important genera include the predatory mites: Amblyseius, Phytoseiulus; the lady beetles-Stethorus the minute pirate bugs,Orius the thrips, Leptothrips; lacewing larvae, Chrysopa.

DiamondBack moth (Plutella xylostella)- cabbage moth : 

DiamondBack moth (Plutella xylostella)- cabbage moth It is one of the most important pests of cole crops in the world and will usually only feed on plants It is the most destructive insect pest of brassica crops throughout the world It was the first insect that was found to have developed resistance to the biological pesticide Bt toxin in the field. The adult moths get their name from the diamond-shape markings that are formed when their wings are folded at rest

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Geographical Distribution of the Diamondback moth in Africa (red marked) Throughout the world diamondback moth is considered the main insect pest of brassica crops, particularly cabbages, kales, broccoli and cauliflowers.

Life History : 

Life History

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The moths have a narrow appearance and are about 1 cm or ½ inch long. They are gray or brownish with white marks on the front margins of the forewings Females tend to deposit eggs (about 160) in the depressions created by leaf veins or where the leaf petioles clasp the stem. Small green larvae hatch within a few days and enter the leaves to feed on, or "mine", the internal tissue. After feeding inside the leaf for about a week, the larvae move to the outside of the leaf. Eggs are tiny, flat and oval in shape, they are yellowish and less than 1 mm in size. Caterpillars are pale yellowish-green to green covered with fine, tiny scattered, erect hairs Pupae are 5 to 6 mm long. Pupae are initially light green and turn brown as the adult moths become visible through the cocoon

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The smooth, pale yellowish-green larvae commonly cut holes or feed on the outer tissue of leaves or seed pods. Larvae feed for 10 to 30 days, depending upon food supply and temperature, to reach a mature length of about 12mm. Pupation takes place in delicate white, open mesh cocoons attached to the leaves, stem and seedpods of the host plant. Depending on environmental conditions, the pupal stage lasts from 5 to 15 days.

Damage : 

Damage When larvae are small, damage is seen as small irregular holes in the leaves. If the larvae are numerous, they may eat an entire leaf, leaving only the veins. When the crop matures, larvae feed on the outer green tissue of the pods, leaving plants with a whitened appearance when viewed from a distance.

Management : 

Management Crop rotation , use of resistant varieties enhancement of soil quality, water management , monitoring screening, mechanical barriers Introduction of predators and pathogens Biopesticides and physical mreasures It is difficult to get insecticide contact with the diamondback caterpillar because its feeding sites are under leaves and within the plant tissue.

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