Integrated Pest Management Model for Kenya

J. G. Mwangi - Manager, National Cypress Aphid Project, Kenya

Introduction

Integrated pest management (IPM) is defined as the optimization of pest control in an economically and ecologically sound manner (Apple 1979). It is a recipe of biological, cultural, genetic, mechanical and chemical tactics used individually or in combination to maintain pest damage below the economic injury level* while providing protection against hazards to humans, animals, plants and the environment.

Components of the Kenyan IPM are enumerated as follows:

1. The extent of damage by Cinara cupressi will be shown.
2. The management units are emergency control, genetic control and biological control.
3. Development of appropriate technologies for the aforementioned management units.
4. Development of reliable monitoring techniques.
5. Development of a descriptive and predictive model.
6. Establishment of economic thresholds.
7. Technology transfer is ongoing through extension seminars, local papers, radio and televison.

With the exception of item 1, these activities are yet to be carried out and that crystallizes the bulk of the Kenyan IPM as will be described in the subsequent text.

* Economic injury level is defined as the lowest pest population density which will cause economic damage (Stern et al 1959).

Extent of Damage

In Kenya, so far, the most severely affected tree is Cupressus lusitanica. Kenya, which has the largest area of industrial forest plantations of Cupressus lusitanica is planted on about 86,000 ha. Out of this, about 5,153 ha have been infested by the aphid to variable damage levels ranging from slight to severe.

Damage levels for other members of the Cupressaceae, Juniperus procera, Thuja occidentalis and Callitris robusta has, in the first year of attack, been slight in most parts of Kenya. It is not known whether this will be the same after the second year of attack. Juniperus procera, which covers about 200,000 ha, mainly in water catchment areas, is currently a great source of national concern.

Emergency Control

The activities of this management objective comprise identification and survey of the infested areas, screening and application of pesticides and salvage.

Ground surveys are ongoing but are inadequate because of the lack of adequate transport. Aerial

survey, using low-flying aircraft techniques is intended to begin in September 1991 through FAO funding. Both aerial and ground surveys for identification of infested areas is scheduled to be completed within eight months of the project.

Screening of locally available pesticides has been carried out and relative toxicities (LC₉₀) determined (Fig. 1). These are categorized in the broad spectrum range and selective, environmentally friendly aphicides are yet to be screened. Chemicals are currently being used to control the aphid on people’s hedges and nurseries. Plans are also to use chemicals in high-value seed orchards and arboretums but not in conventional plantations because this would be prohibitively expensive and socially and environmentally unacceptable.

Fig. 1. Relative toxicity of pesticides tested against Cinara cupressi (LC₉₀ - 24 hrs. ppm. ai.)

Various modes of pesticide application have been tested at the Kenya Forestry Research Institute (KEFRI). Soil applications of systemic pesticides have failed to produce good results.

Regarding the tools for pesticide applications, high-volume back-mounted warm fog generators were tested. Results show that fog generators reduced the man hours for spraying by two thirds. The fog, which is a carrier of active ingredients, rises to the top of the crown and drifts to cover all portions of the tree. Motorized sprayers need a lot of water and spray droplets cannot reach the tops of tall trees.

Salvaging of severely damaged plantations is ongoing but guidance on the criteria for salvage is urgently needed by resource managers. It is suggested that a two year observation of the damaged trees should be done before salvage is recommended. This is because some trees recover after the first year of infestation.

Biological Studies

Biological control may offer a long term solution to the aphid problem. Ecobiological studies are a prerequisite to biological control. These studies are short term and are intended to be completed within the next three years.

Aphid population studies are ongoing at Muguga and the results obtained so far are shocking all resource managers. The results show that population density is highest during the hot, dry season and lowest during the season of heavy rains (Fig. 2). The decline in population density results in some recovery of damaged trees. This recovery is probably not sufficient to carry a tree through another dry period. At the time of writing this paper, many Kenyans were complacent that the evident recovery of trees was an indicator that the aphid was not a threat to trees any more. They were yet to learn that this was not true.

Fig. 2. Population trends of Cinara cupressi, Mugug, Kenya (November 19900 - April 1991)

Another activity which is ongoing is exploration of natural enemies in Europe by IIBC. A Kenyan is already in Europe working with IIBC in this progamme. Further exploration in North America and other places is yet to be carried out. Exploration is intended to continue up to the fourth year but mass rearing and release will start in the second year.

Examples of natural enemies that may be explored are Pauesis cupressobii and P. juniperorum (Hymenoptera: Braconidae), which have been found attacking Cinara juniperi. Aphidus sp, also a parasitoid, has been found attacking Cinara cupressi in Germany.

Silicultural Tactics

Silvicultural control has already been recommended to resource managers. This consists of thinning to reduce the density of trees and resultant shady conditions which the aphid seems to prefer; restricting planting of cypress to rich, deep soils in cool areas; and planting of alternative species, for example Grevillea robusta, which are not attacked by the aphid.

Better than the aforementioned would be to seek trees which have some degree of genetic tolerance or resistance to aphid feeding. A compendium of activities has been planned for this objective. The expected result would be to have a substantial stock of strains of cypress resistant to attack by the aphid which would be made available to foresters and farmers for planting.

Monitoring and Evaluation

All activities will be monitored and evaluated during the five year period of this project. This will ensure proper accountability on success or failure of each activity and changes may be instituted at the appropriate time.

References

Apple, J.L., 1979. Integrated pest management - a programme of research for the State Agricultural Experiment Station and the colleges of 1890. A study conducted by the Intersociety Consortium for Plant Protection.

Stern, V.M., R.F. Smith, R. Van den Bosch and K.S. Hagen. 1959. The integrated control concept. Hilgardia 29:81.