Abstract: Field studies were conducted for the determination of infestation ratio for Spiny Bollworm (SBW) and Pink Bollworm (PBW) examining the blind bolls of cotton in the periods of 1999-2001. In this study, Stoneville-453 type cotton, widely grown in Harran Plain, was used. The blind bolls on the cotton plants were collected after the harvest. The pests larvae were identified as PBW and SBW in the split blind bolls and their populations were calculated. The ratio of infested bolls was determined and this ratio, through an equation developed for this study, was used for the prediction of infestation in the fields. At the end of study, field infestation ratio in Harran Plain was predicted as 11.81, 14.28 and 14.12% in 1999, 2000 and 2001, respectively.
INTRODUCTION
The Pink Bollworm, Pectinophora gossypiella (Saunders), is distributed worldwide. P. gossypiella was first described from larvae recovered from infested cotton bolls in India in 1843[1]. The first report on cotton infestation in North America occurred in 1911 in Mexico, presumably from Egyptian cotton seed shipments[2]. In the United States, Pink Bollworm was first detected in Robertson Country, Texas in 1917[1]. In Turkey, PBW was first found by Karman[3] in Southern Turkey. In the study area, PBW was first found by Ozpinar et al.[4]. Although it was a new pest for the area, the damage of which was economically important[5].
The Spiny Bollworm (SBW), Earias insulana Boisd., is widely distributed in Africa and Mediterranean causing a considerable damage in cotton growing areas such as Israel[6], Syria[7]and Turkey[8]. On the other hand, SBW, first found by Kiray[8] in Southern Turkey, is also a major pest for cotton plants and it causes economically considerable damage. The first study in Harran Plain to determine the development of population and damage was conducted by Ozpinar et al.[4], they found that the damage was prevalent in all cotton growing areas especially the most contaminated area in the plain was Akcakale.
The aim of study was to determine the infestation ratio of the pests by examining blind bolls in Harran lain and to predict the probable injury in cotton fields.
MATERIALS AND METHODS
This study was conducted in Harran Plain during 1999 through 2001 years. There are few methods to calculate the level of infestation ratio of PBW and SBW in cotton plants. These methods are commonly used to identify the infestation ratio by counting the eggs, larvae, and the rosetted blooms. Counting and monitoring procedures required at least a three month period of time for each pest. The findings obtained from the calculations were used to control the infestation in growing cotton plants.
The method, proposed in the this study diverges from the preceding methods with respect to two important points. First, it provides economy of time since the researchers do not have to monitor the pest population for such a long period of time. Second, and more important, it yields data, which will help the researcher predict the level of probable infestation that is likely to occur during the following season.
In this study, the infestation ratio of PBW and SBW where predicted on Stoneville-453 cotton plants by examining blinds bolls.
After the crop harvest, at least 100 blind bolls from the each of 10 fields, which are in certain distance (approx. 3 km) from each other, were collected three times of each years. The number of total and blossomed bolls were counted and recorded from the each of 20 cotton plants that were randomly selected. The bolls were splited in the laboratory and examined if they were infected with PBW and SBW larvae. The infestation ratio of the bolls was determined and then the infestation ratio of the field was calculated, considering the infestation ratio of the collected bolls and the number of total and blossomed bolls, with the equation given below.
| (1) |
| ILF | : | Infected Levels of Field (%) |
| NIB | : | Number of Infected Bolls (Piece) |
| NCB | : | Number of Collected Bolls (Piece) |
| TB | : | Total Bolls (Piece) |
| OB | : | Open Bolls (Piece) |
RESULTS AND DISCUSSION
This study, yielded data showed that SBW and PBW pests caused considerable damage in the sample bolls. When the ratio of the damage was expanded field-wide, it was found that the ratio of infestation was over the economic threshold (5%). Since the literature lacks studies conducted with blind bolls, we think that the present study is a new and significant one in this field. The data related to the field infestation ratio can be used for the prediction of the level of the probable damage that is likely to occur during the following season.
The infestation ratio of the fields, from where the samples had been collected, was found with the and the results were presented in Table 1.
When the Table 1 is examined, it was seen that the highest level of infestation occurred in Yardimci (13.78%), while the level of infestation was the lowest in Parapara (2.60%) in 1999. Although there was a general decrease in the infestation levels in the year 2000, the highest level of the infestation was, again, in Yardimci (14.28%), whereas there was no infestation in Yenice. The infestation ratio of PBW and SBW in 2001 ranges between 3.94 and 19.08%, and as it is seen, the infestation levels in 2001 are higher than those occurred in the preceding two years.
| Table 1: | The infestation ratio of the fields obtained from the infestation ratio of the sample blind bolls collected from Harran Plain in the years of 1999-2001 |
NCB: Number of Collected Bolls NIB: Number of Infested Bolls TB: Total Bolls OB: Open Bolls ILF:Infected Levels of Field | |
Qureshi and Ahmed[9] proposed that SBW caused an economic injury when the infestation level reached to 10%. Singh and Sandy[10], Purahit and Deshpande[11] reported that SBW caused an economic damage when the level of infestation was 5% and they suggested that the chemical application should be done at that level. The infestation levels that were found in the plain in 2001 were considered to be higher than the threshold and thus, it is advised that chemical application should be done in the area.
The means of the transition of the pests from one season to the next and the source of infestation are the blind bolls left in the fields after the harvest. In this study, we investigated the ratio of the infestation of PBW and SBW in Harran Plain by calculating the infestation ratio of the sample bolls and expanding the findings to the infestation ratio of the whole field.