Chemical control of male Margarodes prieskaensis
INTRODUCTION
Margarodes are subterranean scale insect pests that attack plant roots. Of the 10 species known in SA, five attack grapevines while the rest mainly occur on grasses. Margarodes prieskaensis is widespread within the Orange River irrigation area in the Northern Cape around Pella, Blouputs, Kakamas, Keimoes, Upington, Groblershoop, Prieska, Douglas and Hopetown. The specie was recently also recorded on table grapes in Mpumalanga [Lephalale (Ellis-ras), Mokopane (Potgietersrus) and Groblersdal], and Southern Namibia near Noordoewer. Serious damage is being caused in table, raisin and wine grape vineyards on a variety of rootstocks. The feeding on the roots causes retarded growth and low yields, resulting in uneconomic production and eventual death of the vines. Young vines planted in infested soil can be killed within four years. As no pesticide is presently registered for the control of Margarodes and no biological control methods or resistant rootstocks are known, infested soils become unsuitable for economic grape production in the Northern Cape. M. prieskaensis is the only SA Margarodes specie that reproduces sexually with females and winged males, emerging once a year to the soil surface to facilitate mating. This opens the possibility to control this specie by using contact insecticides to kill the males. Without mating, no fertile eggs can be produced and as each female can lay up to 1 000 eggs per season, the population could decrease very rapidly. If the males could be killed with con-tact insecticides before mating, unfertile eggs would reduce the population significantly. All residue problems will also be solved because no leaves are present when males occur (June/July). A further positive action will be if the same product could also kill the females.
The aim of this study was therefore to evaluate different contact pesticides to control the males before mating. Applications were made directly to the males at the soil surface during June/July, when no leaves are present and no irrigation is applied.
CONTROL OF MALES WITH DIFFERENT INSECTICIDES UNDER SEMI-LABORATORY CONDITIONS
As Margarodes males are very small-winged insects, already registered insecticides to control similar small-winged pests like fruitfly, pumpkin fly, leafhoppers, etc. were evaluated. Seven insecticides were evaluated in total. Information on these products are listed in Table 1. Males were collected with small brushes in an infested vineyard at Klein Pella near Pofadder in the Northern Cape, and 6 – 10 individuals were placed in a plastic container (24 x 19 cm and 11 cm deep) and the bottom was covered with a 2 cm layer of soil.
Each insecticide was sprayed onto the males with small 1L hand spray guns at five presses per replicate, to standardise the volume of spray mixture per product. Directly after treatment, the container was covered with a plastic lid perforated with very small holes and placed in a shady area in the vineyard. After three hours it was investigated if the males were still alive, according to any movement. The whole process was repeated four times for each insecticide.
Table 1: Information on insecticides evaluated for control of adult males and females of M. prieskaensis
Table 2: Percentage control of males with different insecticides, under semi-laboratory conditions
RESULTS
The percentage control obtained with each insecticide is shown in Table 2. Fantastic control of 100% was obtained with Ultra Kill, as well as Divos. Mospilan also obtained almost 100% control.
Dursban and Decis gave good control of 80% and more. However, poor control was obtained with Delegate and Steward.
CONTROL OF FEMALES WITH DIFFERENT INSECTICIDES UNDER SEMI-LABORATORY CONDITIONS
To determine the effect of each of the seven different insecticides on the control of females, the same technique with the plastic containers was applied as for males. Five replicates per treatment were evaluated. The soil in each plastic container was sieved after treatment, to ensure that females did not move underground.
RESULTS
The percentage control obtained with the same sev-en insecticides is shown in Table 3. As in the case of males Ultra Kill as well as Divos also gave 100% control of females. Dursban and Decis gave good control of 84% to 88%. Mospilan gave average control of 72% while Delegate and Steward performed badly with only 25% control.
Table 3: Percentage control of females with differ-ent insecticides under semi-laboratory conditions
Table 4: Percentage control of males and females with different insecticides under semi-laboratory conditions
SIMULTANEOUS CONTROL OF MALES AND FEMALES
The average control of males as well as females per insecticide of five of the most successful products evaluated is shown in Table 4.
Excellent control of 100% was obtained with Ultra Kill, as well as Divos. Good control was also obtained with Dursban (88%), Mospilan (84%) and Decis (83%). Anyone of these insecticides could thus be used to kill males and females simultaneously during the mating process (Figure below).
Males are strongly attracted by females for mating on the soil surface. Female (right) males (left).
CONTROL OF MALES UNDER SEMI-COMMERCIAL CONDITIONS
Males were collected in a vineyard at the farm Raap en Skraap, situated 180 km from Klein Pella. Methods were the same as mentioned before, except that the plastic containers were not covered with a lid after treatment of the males.
The open containers were kept in the vineyard to maintain the weather conditions. After only 30 min-utes the males were evaluated for any sign of life. Two of the insecticides that gave 100% control under semi-laboratory conditions viz Ultra Kill and Divos, were evaluated and the results are shown in Table 5. Both products gave excellent control of 100% each.
CONTROL OF MALES UNDER COMMERCIAL CONDITIONS WITH TRACTOR APPLICATION
Two wooden frames were built with 5 cm wide strips, each comprising two squares of 20 x 30 cm. These frames were placed in the vineyard on top of areas where females occur on the soil surface. The two frames were placed in line and 2-3 metres apart from each other in the middle of the row. A tractor mounted with a herbicide spray applicator with eight spray heads was used to apply Divos insecticide at a dosage of 100 ml per 100 L water. The spray applicator was mounted at the back of the spray tank pulled by the tractor. The spray applicator covered the whole area between two rows, including half of each “bankie”. The tractor’s speed was very slow, driving over the wooden frames. This action was repeated for a second application.
RESULTS
Two hours after treatment all males in each square in the two wooden frames were collected to decide if they were dead or alive. The results are shown in Table 6. Although the number of males was rather low, all males were dead and 100% control of males was obtained with this commercial method of application. When the spray applicator is connected at the back of the spray tank the possibility exists that the movement and noise of the tractor could be the reason for males to be disturbed and to fly away before the insecticide could contact them.
Table 5: Percentage control of males with two different insecticides under semi-commercial conditions
Table 6: Number of live males before and after treatment, and percentage control with Divos under commercial conditions with tractor application
CONTROL OF FEMALES UNDER SEMI-COMMERCIAL CONDITIONS
Two wooden frames were built, each consisting of two squares 20 x 30 cm. The wooden strips were only 5 cm wide. These frames were placed in the vineyard on top of areas where females occur on the soil surface. The two frames were placed in line and 2 – 3 meters apart from each other. Ultra Kill insecticide was sprayed with small 1 L hand sprays on top of the females in each square of the frames. (No males were present at the time of treatment.) The four squares represented four replicates per treatment. All females present in each square were counted at 10h00 in the morning and the whole population was alive. At 11h00 all females were treated as mentioned above. Three hours after treatment no females were present on the soil surface, indicating that they had burrowed downwards. Females usually do this daily, returning to the soil surface the next day for mating. However, the following day again between 10h00 and 11h00, no females were present on the soil surface, indicating that all had died underground. The soil underneath one of the squares, originally with 131 females on the surface before treatment, was dug out to a depth of 15 cm and all the fe-males were found dead.
RESULTS
As shown in Table 7 the female population was exceptionally high, with an average of 103 females present per square of 660 cm2, with a maximum of 152. With only one spray treatment, 100% control was obtained in all four replicates.
CONTROL OF FEMALES UNDER COMMERCIAL CONDITIONS WITH TRACTOR APPLICATION
The same actions were applied with a herbicide spray applicator, as described for the commercial control of males. The same insecticide, Divos, at the same dosage and wooden frames were also used. The herbicide spray applicator also covered the whole area between rows, but was mounted in front of the tractor. This will solve the problem that males could fly away and females may move down into the soil before the chemical could reach them. The experiment was conducted at the farm Raap en Skraap, while the control of males with tractor application was done at the farm Klein Pella, 180 km from Raap en Skraap.
RESULTS
The females per square in the wooden frames were collected two hours after treatment to determine if they were alive. (There were no males present at that stage.) The results are shown in Table 8.
A high and even number of females were present in each square (replicate). All of these were dead after treatment and 100% control of females was obtained with this commercial method.
Table 7: Number of live females before and after treatment with Ultra Kill, and percentage control under semi-commercial conditions
Table 8: Number of live females before and after treatment with Divos and percentage control under commercial conditions with tractor application
CONTROL OF FEMALES WITH BODY NOT TOTALLY ON SOIL SURFACE
At the time of emergence of females to the soil surface for mating, a relatively high percentage of the population turnaround protruding only about 30% of the body length above the soil surface
(Figure below). The success of control by spraying only such a small body area was evaluated under semi-commercial conditions. A small area of the soil surface with both kinds of protrusion was sprayed with Ultra Kill and small hand sprays, as mentioned previously. Directly after treatment 20 individuals of each position were collected in four different glass containers. After four hours the females in each container were evaluated for any sign of life, and to determine the percentage control.
RESULTS
As shown in Table 9, the total dorsal body con-tact treatment produced 100% control at all four replicates. The same results were obtained, where only about 30% of the body length was treated. Chemical control of females with contact insecticides will thus not be negatively affected if females protrude only part of their abdomen above the soil for mating.
Females with only part of their body above the soil surface during mating
Table 9: Percentage control of females with Ultra Kill at different body contact coverage during treatment, under semi-commercial conditions
SUMMARY
Margarodes is an underground insect pest that attacks the roots and causes tremendous damage to especially grape vines. Underground chemical control and leaf coversprays usually cause residues in the grapes that are unacceptable for the export market of table grapes. No insecticide is presently registered for control and many hectares are presently taken out and replaced with other fruit cultivars. Margarodes prieskaensis occurs widely in the Northern Cape area and is the only margarodes specie that reproduces sexually with males and females that move from the roots to the soil surface for mat-ing. If males could be killed with contact insecticides before mating, unfertile eggs would reduce the population significantly. All residue problems will also be solved, because no leaves are present when males occur (June/July). A further positive action will be if the same product could also kill the females. Because of the urgency of the problem seven contact insecticides were evaluated over three seasons for the control of males, as well as females with four evaluation methods. Five of these pesticides gave very good control of 80% to 100% of males, as well as females. Two of these chemicals that gave 100% control were also evaluated by commercial tractor application and 100% control was again obtained of males and females. The results show clearly that excellent control of Margarodes males and females could be obtained by various contact pesticides. Also, that both stages could be killed by a single application. Further-more, with this method of control only one annual application of the chemical is required during June/July, when they are present on the soil surface. The time of application will also solve the problem of residues, because the chemical will not be taken up by the plant during this time of application.
ACKNOWLEDGEMENTS
Mr Wollie Wolmarans, Manager Klein Pella Farm, Karsten Group, Northern Cape.
Mr Hawie Moller, Manager Raap en Skraap and Karsten Group, Northern Cape for using their vineyards, machinery and regular provi-sion of labourers over a period of three seasons.
The funders of the research: Department Agriculture, Land Reform and Rural Development, Northern Cape South African Table Grape Industry Dried Fruit Technical Services
Contact: Dr André de Klerk: annette8@telkomsa.net