PROTECTION OF SWEET CORN FROM OSTRINIA NUBILALIS HBN. AND HELICOVERPA ARMIGERA HBN.

O. nubilalis and H. armigera regularly occur and cause significant damages in corn crops in Serbia, particularly under global warming conditions. Several measures are applied against these pests (crop rotation, tolerant and resistant hybrids, monitoring, forecast, chemical measures). Larvae damage stem, panicle and ear, which favour development of saprophytes and secondary infections by mycotoxin producing, pathogenic fungi. The aim of the paper was to test the efficacy of the insecticides azadirachtin and indoxacarb in sweet corn protection against the mentioned pests. The trials were conducted in 2014 at two localities (Becej B. and PoIjanice P.) on sweet corn, hybrid Enterprise according to standard OEPP methods (PP1/13; 1/152; 1/135). Products on the basis of azadirachtin (10 g a.i./I of product) at a rate of 0.4 and 0.5% and indoxacarb (150 g a.i./I of product) at a rate of 0.25 I/ha, were applied. Treatments were conducted on the 5th of August with tractor sprayers (high clearance). The plot size was 5000 m². Three assessments were made. The first one prior to treatment, on 25 randomly selected plants per replicate, and the number of O. nubilalis and H. armigera egg masses and larvae on silk was registered. In the second assessment (18th of August), on 20 randomly selected plants per replicate, the number of damaged plants and the number of vital larvae was registered. In the third assessment, immediately before harvest (28th of August, i.e. 12th of September) on 20 randomly selected plants per replicate, the number of plants broken below ear (fallen on the ground), damaged ears and vital larvae, was determined. Results are presented as means, efficacy (E%) according to Abbott and significance of differences by LSD test (5%). At B locality egg masses of O. nubilalis were registered on ear silk on 13-19% of plants and larvae on 3-7%, and larvae of H. armigera on 2-4%. At P locality egg masses of O. nubilalis were present on 34-40.8% of plants. After 13 days from treatment, at B locality the percentage of damaged plants was 3.8-7.5% and at a significantly lower level compared to control where 40.0% of damaged plants was recorded. Vital larvae of O. nubilalis were present on 1.3-31% of plants, depending on the insecticide and application rate, and in the control on 41.3%. At P locality the percentage of damaged plants per treatment ranged from 20 to 46.3% depending on insecticide and application rate, and in the control 63.8%, and the presence of vital larvae of O. nubilalis on 16.3-21.3% of plants, and in the control on 53.5%. Immediately before harvest, at B locality azadirachtin efficacy, depending on application rate and counted parameters, was 88.5-92.5%; 66.7-72.9% and 69.1-75.2%. Efficacy of indoxacarb in general was 75-100%. At P locality, efficacy of azadirachtin depending on application rate and counted parameters, was 77.8-88.9%; 66.5-83.3% and 44.1-74.6%, while efficacy of this insecticide in general amounted 91.5-100%.

PHYTO-INDICATORS IN DETECTION OF LINDANE RESIDUES IN WATER.

Intensive use of pesticides, especially insecticides, in agriculture during the past several decades has already led to contamination of surface and underground waters and sediments in some regions, thus presents a serious problem for the environment. Lindane was one of frequently applied insecticides for soil treatment. In Serbia, it has been in use since 1944, but in the period 2001-2007 its use was restricted only to timber treatments. In 2009 an international ban on the use of lindane in agriculture was implemented under the Stockholm Convention on Persistent Organic Pollutants. However, due to a long-term use and persistence, its residues can be present in underground water and sediment, thus present a potential risk for incorporation in food chains. According to Directive 2008/105/EC it is listed as one of the priority water pollutants, whose presence is mainly detected by chemical methods. However, biological tests are gaining in importance in the last few years and since some plant species are highly sensitive to certain pollutants. This work aimed to assess potential of white mustard (Sinapis alba L.), cucumber (Cucumis sativus L.) and barley (Hordeum vulgare L.) as phyto-indicators of water contamination with lindane. The effect of lindane (rates 0.1 µg a.i./L--maximal allowable concentration (MAC) in water; 0.2; 0.5; 1 and 2 µg a.i./L) was assessed on physiological (germination energy and germination- %) and morphological parameters (root and shoot lengths, fresh and dry weights) of tested species. Assay was carried out using slightly modified filter paper method recommended by ISTA Regulations book (2011). The experiment was set in four replicates. Data were processed using Duncan's multiple range test for determining the differences between treatments for confidence interval 95%. Results of bioassay indicate that germination energy (70.75%) and germination (79.00%) of white mustard were significantly inhibited by lindane applied at MAC rate compared to the control (79.75, 82.00%, respectively). Physiological parameters of other test species were not affected by this insecticide. Lindane inhibited root elongation of barley seedlings at 2 µg a.i./L (20-fold MAC) and of cucumber at 0.5 µg a.i./L (5-fold MAC). Only fresh root weight of barley was inhibited by lindane at MAC quantities. Based on presented results, valid and reliable indicators of lindane presence in water can be considered germination energy and germination of white mustard and fresh root weight of barley seedlings.

CONTROL OF DIABROTICA VIRGIFERA VIRGIFERA LE CONTE IN MAIZE SEED TREATMENT.

During the last decade of XX century, Diabrotica virgifera virgifera Le Conte became an important introduced harmful species in maize production in the northern Serbia region. The aim of this work was to assess the efficacy of imidacloprid based insecticides formulated for seed treatment in the control of D. v. virgifera. Experiments were set at two localities (Curug--two-year maize culturing; Becej--four-year maize culturing) in 2013, according to OEPP (PP 1/212(1) 2004) method. Imidacloprid based insecticide (600 g a.i./L) was applied at rates 0.36; 0.55; 0,7 and 0.8 L/100 kg of maize seeds (hybrids NS 5041 and NS 640 Ultra). The degree of maize root damage was determined according to scale 1-6 (http://www.ent.iastate.edu/-pest/rootworm/nodeinjury/nodeinjury.htm). A number of damaged plants was also registered and expressed in percents, as well as the development of adventitious roots. Significance of differences between root damages and number of damaged plants between treatments was tested using ANOVA. Regardless on localities and applied rates, maize roots in treatments with imidacloprid were significantly less damaged by larvae D. v. virgifera (1.1-1.4) compared to the control (3.7-4.1). Also, a significant reduction in percent of damaged plants (5.0-20%) was registered compared to the control (90-97.5%). At both localities in treatments with imidacloprid adventitious roots were well developed in 60.5 to 91% of plants compared to the control were it was the case in 10-27.5% plants. It is important to emphasize that roots were significantly more developed in treated variants compared to the control. Based on the obtained results it can be concluded that imidacloprid, regardless on its future status and restraints/limitations in maize seed treatment, provided efficient protection of maize roots from D. v. virgifera larvae, even at rate twice lower (0.36) than recommended (0.8 L/100 kg seeds), which justifies the application of lower quantities of imidacloprid in practice.