• 
• 

Articles

July 2010

Wynboer - Pests & Diseases

Chemical control of margarodes in the Orange River irrigation area

INTRODUCTION
Margarodes (ground pearls) is a subterranean insect pest and five species are currently known to attack grapevines in South Africa. Serious damage is caused in practically all regions where grapevines are cultivated. Margarodes prieskaensis is widespread in the Orange River irrigation area in the Northern Cape, and table, raisin and wine grapes that have been grafted on various rootstocks are infested and killed. It is the only margarodes species in South Africa that reproduce sexually, with females and males appearing on the soil surface to mate (De Klerk, 1985).

The life cycle of M. prieskaensis is as follows (De Klerk & Vermeulen, 2007):

The larvae feeding on the roots are covered by a hard wax layer which forms a round cyst. During April male pre-pupae develop out of the cysts and move upwards in the soil to form pupae just below the surface. The pupae develop into winged males which appear above the soil during June/July.

During the same period when the males appear, adult females develop out of the cysts and move directly to the soil surface. After mating the females move back into the soil to lay their eggs in the vicinity of the roots. When the eggs hatch, the larvae move to the roots, penetrating them with their mouthparts to feed and secrete layers of hard wax to form new cysts.

Damage caused by M. prieskaensis is on the increase in the Orange River area and is spreading to Mpumalanga and even Namibia, and since there are no known control measures, a field trial was conducted to test various insecticides for the chemical control of the pest.

MATERIAL AND METHODS
The trial was conducted over a period of three years in a heavily infested Sultanina (Thompson Seedless) vineyard on Ramsey under micro-irrigation on the farm Klein Pella belonging to Karsten Boerdery along the Orange River near Pofadder. The vines were twelve years old, trellised on a gable system with plant spacing 3,0 m x 1,8 m. Infested data vines were identified in August 2005, based on the occurrence of females on the soil surface. The trial was set out in a randomised block design with five single vines per treatment. The soil in an area of 1,4 m x 1,4 m (2 m2) around each vine was levelled and surrounded by embankments 100 to 150 mm high to form the treatment plots. Insecticides in a soluble formulation were dissolved in 10 litres of water and evenly applied to the surface of each plot with a watering-can and spray head. Insecticides in granular form were distributed evenly over the surface of the plot, shovelled lightly into the soil and washed in with 10 litres of water. A soil fumigant was administered using a manual soil fumigation pump at a depth of 200 mm. After each application all insecticides were washed into the soil with a further 10 litres of water. The insecticides, and their respective formulation, brand name and dosage are indicated in Table 1. The text refers throughout to the brand name of the product that was evaluated.



To control pre-pupae, four insecticides with contact action and a fumigant were administered in April, when pre-pupae occur, and evaluated two to three weeks later. Five insecticides with a systemic action were applied post-harvest in January. This specific time was chosen because the systemic insecticides have a very long safety period, and this is also the time of the year when the new generation cysts start feeding and translocation in the vines remains sufficient to distribute the insecticides into the root system.

For control of females the contact insecticides were applied during June/July and evaluated two to three weeks later when females generally occur on the soil surface. Systemic insecticides which were applied in January and the fumigant in April to control pre-pupae were also evaluated for the control of females.

During evaluation the entire area of the plot (2 m2) around the treated vine was trenched manually to a depth of 80 - 120 mm, and all pre-pupae and females were collected and counted. After each observation the individuals were returned to and distributed over the surface of the plot. Insecticides were applied and evaluations done in 2006, 2007 and 2008 and if a treatment was repeated, the same plots were used. The number of live pre-pupae and females per site were statistically analysed to determine whether significant differences between treatments occur.

RESULTS
A high infestation of margarodes occurred at all the control plots. Maximum numbers of 66 females and 296 pre-pupae were found per m2 on the soil surface. The percentage control with regard to the untreated control was calculated per annum and the average percentage control is indicated in Table 1. The contact insecticides Dursban and Crop Guard produced no or poor control of pre-pupae as well as females. The contact action of Nemacur was not successful either. Excellent control of pre-pupae was obtained with Rugby in 2006 and the treatment was repeated in 2007 and 2008. The average control was 85,8%. Rugby was nevertheless not very successful in the control of females.

The fumigant Telone II was applied once only, in 2006, and provided excellent control of pre-pupae as well as females for three consecutive years. The average control of pre-pupae and females was 94,8% and 87,4% respectively. Telone II is phytotoxic and all treated vines died within three months. The odd pre-pupae and females that still occurred at the treated plots each year could possibly have come from cysts occurring so deep in the soil that they could not be reached by the fumigation gas.

The systemic insecticides Curaterr and Counter as well as the systemic action of Nemacur was not successful for the control of pre-pupae nor females. Actara at 2,4 ml/m2 applied once in 2007 provided excellent control over two consecutive years. The average control of pre-pupae and females was 83,2% and 85,0% respectively. In 2008 the dosage was reduced to 2,0 ml/m2 and 1,2 ml/m2. A dosage of 2,0 ml/m2 also produced good control of pre-pupae (76,6%) as well as females (80,2%). At 1,2 ml/m2 the control of pre-pupae as well as females was poor.

Confidor at a high dosage of 15 ml/m2 was applied once only, in 2007, with excellent control of pre-pupae and females in 2007 as well as in 2008. The average control exceeded 90% for each developmental stage. A reduced dosage of 3,0 ml/m2 in 2008 also resulted in excellent control of pre-pupae (95,0%) as well as females (80,2%). A dosage of 1,5 ml/m2 obtained 98,3% control of pre-pupae. Although not statistically significant, control of females (70,9%) was not as good at 1,5 ml/m2 as at a dosage of 3,0 ml/m2.

SUMMARY AND RECOMMENDATION
The results clearly show that the contact insecticide Rugby, at 25 ml/m2, results in effective control of pre-pupae. Applications should be done in the last week of March or the first week of April. Control of pre-pupae which develop into males will prevent the females from producing fertile eggs, resulting in a decreased population. Rugby, however, did not control females successfully.

Telone II at a dosage of 15 ml/m2 produces excellent control of pre-pupae as well as females and should be administered at the end of March, beginning of April before pre-pupae occur. In view of the fact that Telone II is phytotoxic, it can only be used when an infested block has to be replaced or when a few infested vines in a block can be removed.

Excellent control of pre-pupae as well as females was obtained using Actara and Confidor. A dosage of 2,0 ml/m2 for Actara and 3,0 ml/m2 for Confidor appears to provide adequate control. Further trials are necessary, however, to confirm these dosages. Systemic products should be applied post-harvest in January when the new annual populations of cysts start feeding and translocation in the vines is still active.

Seeing that only a certain percentage of cysts develop into pre-pupae or females each year, and cysts may occur in the soil for years without feeding, follow-up treatments are necessary. The occurrence of pre-pupae and females on the soil surface should therefore be determined regularly after a treatment.

The results show furthermore that Dursban, Crop Guard, Nemacur, Curaterr and Counter administered in the particular formulations and dosages resulted in poor or no control of pre-pupae.

Rugby and Telone II are registered for control of nematodes on vines while Confidor is registered for the control of grapevine mealybug. Actara is in the process of being registered for the control of mealybug on vines. None of these insecticides are currently registered for the control of margarodes and at this stage they cannot therefore be recommended.

ACKNOWLEDGEMENTS
Winetech, Dried Fruit Technical Services and the South African Table Grape Industry for financial support over a period of four years. Karsten Boerdery for the use of their vineyard and other infrastructure at Klein Pella. The support of Mr Goosen, general manager; Mr Bouwer, farm manager; Mr Cloete and Mr Kordom, block monitors at Klein Pella and Mr and Mrs Van Aarde, technical advisors, Karsten Boerdery. The technical assistance of Ms Du Toit of the research division Plant Protection, ARC Infruitec-Nietvoorbij. All contributions are gratefully acknowledged.

AUTHORS
André de Klerk & Roleen Carstens, ARC Infruitec-Nietvoorbij, Stellenbosch

For more information contact Dr André de Klerk at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

REFERENCES
De Klerk, C.A., 1985. Occurrence of South African species of Margarodes Guilding (Homoptera: Coccoidea: Margarodidae) with special reference to vine infesting species. Phytophylactica 17, 215 - 216.
De Klerk, C.A. & Vermeulen, A.K., 2007. Life cycle of Margarodes prieskaensis (Jakubski) (Homoptera: Coccoidea: Margarodidae) on table grapes in the Northern Cape, South Africa. Extended abstract of research poster delivered at the 5th International Table Grape Symposium, November 2007, pp 139 - 141.