PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Pest cycle
The LIFE CYCLE. of an insect is the stage or succession of stages in growth and development
that occurs between the appearance or re-appearance of the same stage, eg the adult.
The PEST CYCLE describes where each stage of the life cycle occurs, eg host, seed, soil, the
length of each stage, the number of generations, its seasonal occurrence and so on. The range of
insect pest cycles is almost infinite so that only a few common examples of where stages may occur
are presented. Many insects spend some part of their life cycle in the soil.
HOST ONLY
HOST,
HOST DEBRIS,
LITTER, ETC
Codling moth
larva in fallen
fruit
HOST AND SOIL
Pupa of scarab
grub in soil
WHY IS
KNOWLEDGE OF
THE PEST CYCLE
IMPORTANT?
SOME INSECTS SPEND NEARLY ALL THEIR LIFE in a close parasitic
relationship with their hosts with perhaps only very short stages occurring
away from the host, eg
Bean weevil (seeds)
Black scale (stems, leaves)
Green peach aphid (buds, leaves, shoots)
Longtailed mealybug (leaf bases, flowers, fruit)
Twospotted mite (mainly leaves, herbaceous stems)
SOME INSECTS CONTINUE TO DEVELOP
IN SEED, HOST PLANT DEBRIS, LITTER, eg
Citrus gall wasp (in galls of pruned stems)
Codling moth larvae (in fallen fruit)
CATERPILLARS OF MANY MOTHS
AND BUTTERFLIES MAY PUPATE
on host plants, host plant debris or on
general litter:
Cabbage white butterfly
Codling moth
Life cycle of the
cabbage white butterfly
DEBRIS FROM SOME PLANTS MUST BE DESTROYED, eg
Prunings of citrus containing mature citrus gall wasp larvae and/or pupae
should be burnt to prevent adult wasps from emerging.
LARVAE OF MANY INSECTS feed on or in leaves and other plant parts but
pupate in the soil, eg
Corn earworm, grapevine moth
Pear and cherry slug
Steelblue sawfly
EGGS, LARVAE, NYMPHS AND ADULTS of some insects may occur in or
on the soil but feed on roots, stems, trunks, seed and other plant parts, eg
African black beetle
Cutworms and armyworms
Mole crickets
FOR IMPLEMENTATION OF EFFECTIVE CONTROL MEASURES, eg
Planning IPM (Integrated Pest Management) programs (page 39). After
identifying the pest, knowledge of the pest cycle is essential as the pest
scout needs to know where to look for the pest, eg on leaves or bark.
Does the seed or other propagation material need to be treated?
Could sanitation and other non-chemical methods be useful controls?
When should pesticides be applied? When the pest is under the bud
scales during winter or when it is feeding on the new leaves in spring?
Insects and allied pests - Plant damage 35