Pests & Deaseases Details

1. Glycaspis brimblecombei; anew devastating pest of eucalyptus Psyllids are plant-juice sucking homopterans in the insect family Psyllidae. Redgum lerp psyllid nymphs (immatures) form a conical covers called a "lerps," which are small white, hemispherical caps composed of solidified honeydew and wax. Lerps on leaves can be up to about 1/8 inch in diameter and 1/12 inch tall and resemble armored scales Fig.1. Nymphs enlarge their lerps as they grow, or they move and form a new covering. The yellow or brownish nymphs resemble a wingless aphid, and spend most of their time covered beneath a lerp. Adults are about 1/8 inch long, slender, and light green to brownish with orangish and yellow blotches. Adults occur openly on foliage and do not live under lerp covers. Females lay tiny, yellowish, ovoid eggs singly or in scattered groups. Females prefer to lay eggs on succulent leaves and young shoots Fig. 1. Population increases often coincide with new plant growth. However, all psyllid life stages can occur on both new and mature foliage. Development time from egg to adult varies from several weeks during warm weather to several months during prolonged cool temperatures. This insect has several generations each year. All stages can be present throughout the year, although in lower numbers during the rainy season and cool weather. Psyllid nymphs and adults feed by sucking plant phloem sap through their strawlike mouthparts. High redgum lerp psyllid populations secrete copious honeydew and cause premature leaf drop. Extensive defoliation weakens trees, can increase tree susceptibility to damage from other insects and diseases affecting eucalyptus, and contributes to premature death of some highly susceptible species. Cultural practices: The species of eucalyptus primarily determines whether psyllids will be abundant. Cultural practices and overall tree health also influence populations and the extent to which trees are damaged. Providing adequate irrigation and limiting nitrogen can reduce susceptibility to damage. Chemical control: Contact insecticides are known to be ineffective against the nymphs of G. bramble combei as they are protected by the whitish covers. Systemic insecticides have been used with some success, but their use is of limited value in plantation forestry due to the high cost, pollution of environment and other related health hazards. Pesticides can also lead to pest resurgences (emergency of new pests). Biological control: As a long-term management option, we intend to introduce a parasitic wasp Psyllaephagus bliteus (Hymenoptera, Encyrtidae) for biological control of the pest. The parasitoid has been successfully released in South Africa , Brazil and many other countries and has positively impacted on the populations of G. Bramblecombei. Details
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4. Cassava brown streak disease • Vein clearing on leaves • Brown streaks on stems • Necrotic tissues on roots • Use CBSD-free planting materials • Plant tolerant varieties (Nase 1, Nase 3, Nase 14 and TZ 130) • Rogue infected plants Details
5. Cassava bacterial blight • Drops of creamish exudates on stems • Lesions between leaf veins on the lower surfaces of the leaves • Dying of the shoot from the tip (‘die-back’) • Rapid defoliation • Always get planting material from CBB-free plants and/or tolerant varieties (e.g. Nase 3 and Nase 14) Details
6. Cassava mosaic disease • Leaf wrinkling • Stunted young plants • Reduction in leaflet size • Leaf Chlorosis • Plant tolerant varieties e.g. TME 14, NASE 14, NASE 15, ASE 19, NAM 130 • Use clean planting material • Quarantine • Rogue out infected plants • Do not plant in previously infected fields • Create awareness Details