STRBAC P.1, KERESI T. 1,
SEKULIC R. 2, BACA F. 3
1 Faculty of Agriculture, Trg
D. Obradovica 8, 21000 Novi Sad, Yugoslavia
2 Research Institute of Field
and Vegetable crops, M. Gorkog 30, 21000 Novi Sad, Yugoslavia
3 Maize Research Institute,
Zemun Polje, S. Bajica 1, 11185 Beograd-Zemun, Yugoslavia
The study on efficacy of some insecticides in control of Western Corn Rootworm (WCR) larvae was carried out under four environmental conditions at Backo Dobro Polje (BDP) and Temerin (the region of southern Backa, Yugoslavia) during 1999 and 2000. The 4-replicate complete block design trials with long-term maize continuous crop were performed. The following products were tested: Ariba, 6.0 and 8.0 kg ha-1, Counter G-5, 20.0 and 25 kg ha-1 Cruiser 350FS, 0.6 and 0.9 kg per 100 kg seeds, Cruiser 350FS, + Force 20SC, 0.6+0.2 L per 100 kg seed, Gaucho 350FS, 1.0 L per 100 kg seeds and Talstar 10EC, 0.5, 1.0 and 1.5 L ha-1. Planting of maize was machine-operated; seed dressing and application of soil insecticides were done manually. Soil insecticides were distributed in 10-cm wide bands over the rows at the time of planting and incorporated to the depth of 5-6 cm. The following parameters were used in efficacy measurements: the number of emerged plants per hectare (at the 7-8-leaf stage), the percentage of "gooseneck" plants (at the beginning of imago emerging in the third decade of June) and the root damage rating (the end of June - beginning of July). Yield was measured in one location in both years. Some of insecticides were tested under four, three, two or even one environmental condition.
The planting rates amounted to 58,160 plants ha-1 and 33,306 plants ha-1 in BDP, and 44,310 plants ha-1 and 45,344 plants ha-1 in Temerin in 1999 and 2000, respectively. The results indicate the absence of the economic level of soil insects. Neither significant increase and/nor decrease in the number of plants per ha-1 over the insecticides tested was determined. Decreased germination in BDP in 2000 occurred due to dry spring. The percentage of lodged plants in the untreated check ranged from 11.32% in BDP, to 79.58% in Temerin in 1999. The corresponding values in 2000 amounted to 43.42% and 58.65% in BDP and Temerin, respectively. Although the coefficient of insecticide efficacy was rather law, the percentage of lodged plants was reduced by the majority of insecticides. The application rate of 0.9 L of Cruiser 350FS per 100 kg seed showed the best results. The four-year mean of the coefficient of efficacy (CE) in decreasing plant lodging amounted to 38.8%. The highest CE among all insecticides tested was 60.4% obtained with Cruiser 350FS in Temerin in 2000. The root damage rating (RD) indicates the same tendency in efficacy as in plant lodging.
The application rate of 0.9 L of Cruiser 350FS per 100 kg seed showed the best results. The average, i.e. highest CE of Cruiser 350FS was 20.2%, i.e. 41.5%, respectively, in Temerin in 2000. On the basis of the root damage rating, over 50% of the root system were damaged on the average. The only exception was registered with Cruiser 350FS and Cruiser+Force in Temerin in 2000 when the RD was 2.00 and 1.78, respectively. It is assumed that high temperatures in April and May of 2000 induce hatching of WCR larvae prior to sufficient development of the maize root system. The lack of available food at the time of larval hatching, particularly in Temerin, resulted in mass decrease of their population. As a consequence of a larval reduction, the levels of root damage and plant lodging were lower. Other insecticides expressed their efficacy in the lower extent in comparison to Cruiser 350FS.
Consideration of all results on efficacy of tested insecticides, as well as, the economic potential of Yugoslav farmers, indicate the application of Cruiser 350FS in rate of 0.9 L per 100 kg seed as the best choice for maize protection in the first year of monoculture. Achieved yield did not correlate to other criterion indicating insecticide efficacy. It is important to point out that the precipitation amount during the vegetation period in two years differs at the rate of 1 to 4. The first year (1999) was extremely favorable with 466 mm of precipitation, while the second one had only about 125 mm during the April-August period.