A Study of the Distribution of Economically Significant Weevils in the Deciduous Fruit Industry

Project Number
US ENT 17-A2

Project title
A study of the distribution of economically significant weevils in the deciduous fruit industry.

Project leader
Addison, P

Stellenbosch University. Department of Conservation, Ecology and Entomology

Team members
Addison, P
Addison, M F
Pringle, K L

Project description

Objectives and Rationale
It is proposed that an in depth analysis be undertaken to determine which abiotic and biotic factors play a role in causing damaging population levels in commercial orchards/vineyards. The objectives of this project will include: 1) determination of the influence of soil type on weevil distribution, 2) determining the influence of orchard floor management practices (eg, cover crops), 3) establishing the relative abundance of economically important weevil species and user-friendly keys for the identification of the species involved. The aim of this study will be to yield valuable information in developing improved weevil management related to both soil texture and cover crop variability (cultural control methods), as well as prioritizing the species that should be targeted for management purposes.

Farms with a history of weevil infestations will be selected in two-three regions (e.g. Ceres, Elgin and a coastal region). Monitoring will take place once per month, using weevil bands (double-sided cardboard bands) and plant (buds, leaves, stems and fruit) damage assessments. Collection of geographic and biological attributes will include: soil, slope, location, orchard design (nr. Trees/vines/ha, row spacing, irrigation, fertilization etc…), cover crop assessment (type, estimation of % cover, ratio between broad leaf and grass species). Weevil species (if occurring as mixed populations of various species) will be analysed using rank abundance curves which assess both species richness and evenness to determine level of dominance. Coupled with results from damage assessments, the data will indicate which species are of more economic concern for growers.

Key Results
There were nine weevil species found to occur in apple orchards and vineyards, all belonging to the family Entiminae (root weevils). Based on collected species during the survey, an illustrated morphological key was produced with species identification information. Most of the damage was attributed to P. callosus, with the remaining weevils contributing to some damage. The results further indicated that there was no significant (P = 0.05) relationship between either soil chemistry, soil bulk density, soil texture, ground cover percentage and weevil population. The time of application is important. A peak in adult populations were reached between November and December, after which the population dropped drastically from January up to May. Good monitoring practices are highly recommended to producers. It was recommended that monitoring should take place starting in early October and control should be applied as soon as weevils are noticed. Spraying should preferably be on the trunks and not on the leaves for best success.

Key Conclusion of Discussion
This study identified and recognized nine weevil species causing damage in vineyards and apple orchards in the Western Cape Province, South Africa, of which one was recorded for the first time in vineyards, as well as assessing the effect of abiotic and biotic attributes towards the population of weevils on these crops. The findings of this study aimed towards supporting the development of ecologically-based control strategies; which enable further research into sustainable and integrated approaches to the management of these weevils.

Recommendation to Industry / Key take-home message
Monitoring should take place starting in early October and control should be applied as soon as weevils are noticed. Abiotic factors were not found to play a role in this study, but should be assessed over a larger area, for a longer time period. Eremnus occatus was noticed for the first time in agricultural vineyards and ranked as the second most dominant weevil in vineyards, which would require a detailed future study as no previous literature on its biology and ecology exist. However, the drought which occurred during the time of sampling might have been a factor influencing the weevil diversity in vineyards.

Magagula, M, Addison, M F and Addison, P. The large scale spatial distribution of banded fruit weevil (BFW) (Phlyctinus callosus) (Schoeherr) damage in apple orchards. Paper presented at the ESSA and ZSSA Conference: 3 – 7 July 2017, Pretoria, South Africa.


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