Serpil KORNOSOR
University of Cukurova, Faculty of Agriculture, Department of Plant Protection
01330 Adana TURKEY
In Turkey, although it may vary each year, maize is grown in an approximate area of 600.000 ha, and is the thirdmost important crop following wheat and barley. With "The Second Crop Agricultural Research and Dissemination Project" administered by the Ministry of Agriculture in 1982, it was aimed to increase maize planting area to reach 700.000 ha by putting uncultivated irrigated land into use and starting maize production in the Southeast Anatolia. In Turkey, maize production area have fluctuated in size between 1980 to 1995. Since the start and the spread of second crop sowing in The Mediterranean and The Aegean Regions in 1983 and the sowing of productive variety of hybrids, maize production has doubled. In Turkey, maize is mainly grown in The Black Sea, Marmara, Aegean and Mediterranean Regions. Maize has been grown in large area in The Black Sea and Marmara Regions only as a first crop, and in The Aegean and Mediterranean Regions as a first crop until 1983 and as a first and second crop since then. Although, the maize sowing area is the largest in The Black Sea Region but it is quite low in production. On the other hand, the production is high in The Mediterranean Region but sown maize areas are 33% less in size compared to those in The Black Sea region. After the sowing of maize in large areas as a second crop, pest population has been increased. Although some research on maize pests has been carried out before 1983, since then, a lot of research has been done mainly on the biology, population development, and the natural enemies of the major pests Ostrinia nubilalis Hbn. and Sesamia nonogrioides Lef. in Faculties of Agriculture, Plant Protection Research Institutes and Agricultural Research Institutes. Pest and beneficial species have been determined in the maize agroecosystem which has a rich insect fauna in different maize growing region. There are differences as major pests between the first and the second crop of maize.
Main Pests on The First Crop Maize
In the seedling period, Gryllotalpa gryllotalpa L. (Orthoptera, Gryllotalpidae), wireworms Agriotes lineatus L. A. obscurus L. (Coleoptera, Elateridae) and cutworms Agrotis ipsilon Hufnagel, Agrotis segetum Denis & Schiffermüller (Lepidoptera, Noctuidae) which feed on the roots of the young plants, are all found to be harmful only for first crop maize, due to their seasonal appearance and climatic requirements. Among these pests, cutworms, which are considered to be the most economically important pest, have occasionally damaged the roots of plants at the beginning of the seedling period, causing the fields to rest or crops to be re-sawn. Seed and surface insecticides are applied in order to prevent their damaging to the plants.
Tanymechus dilaticollis Gyll. (Coleoptera, Curculionidae) was determined to be harmful only in The Black Sea Region in the seedling period in some years feeding on the leaves of the maize, and seed and surface insecticides are recommended to control this
In The Mediterranean Region, an increase in the population of Pseudaletia unipuncta (Haworth) and Acantholecania loreyi (Duponchel) (Lepidoptera, Noctuidae) which feed on the maize leaves has been observed, within the last ten years. These pests damage crops by cutting the tassels of maize cobs which have not yet completed their fertilization. Both species have effective larva parasitoids that decries 80% of their damage in the region.
In addition, Nezara viridula Linnaeus (Heteroptera, Pentatomidae) which cannot feed sufficiently in wheat fields moves to maize fields and causes considerable deformations on the cops.
Pests sucking the sap of crops, such as Rhopalosiphum maidis Fitch., R. padi L.. (Homoptera, Aphididae), Tetranychus cinnabarinus Boisduval, T. urticae (Koch) (Acarina, Tetranychidae) have seen but have also been kept control pressure by a rich natural enemy fauna. Problems occur in regions where insecticides are extensively used. by these plant sucking insects.
Stemborers do not cause economic loss in the first crop maize in The Mediterranean and Aegean Regions due to their low population.
In the Marmara and the Black Sea regions, Ostrinia nubilalis is parasitized with the larva parasitoids of Lydella thompsoni Herting (Diptera, Tachinidae) at 55-62 %, and with Trichogramma evanescens Westwood at 97.03 % as a natural parasitization, there is no need to apply insecticide. because of this chemical insecticides are not used. In conclusion, depending on the sawing time, there is no chemical application on the first crop maize in general.
Main Pests on the Second Crop Maize
Insects causing damage on the first crop maize, except pests which feed with roots of seedlings (for example Agriotes spp., Agrotis spp.),are harmful on the vegetation period of the second crop maize to a varying extent. Considering the crops, phenological development, in the Mediterranean Region, Spodoptera exigua are seen on maize crops at the four or five- leaf-stage, especially in those sowed with delay on the first half of July (1-15 July). In the region where intensive agriculture takes place, S.exigua has many hosts and its population starts increasing early June, and reaches the pick stage in July and August damaging the maize, clover, cotton, soybean, many arable plants and different weeds. Meanwhile, natural parasitism with larva parasitoids are quite high in maize in The Mediterranean Region. Damage is avoided by sowing the crops earlier than usual (for example from beginning to mid June). In regions where insecticides are widely used and sawing is late synthetic pyretroids are applied to control these pests..
After the height of the maize reaches 40-50 cm, O. nubilalis starts being seen, depending on the sowing time and population density increases and it , becomes the major pest. It is kept as a major pest until milky and maturity stage. 0. nubilalis population reaches its pick stage from late July till end of August and the population starts decreasing after early September.
Despite S. nonagrioides having a low population at the beginning of the vegetation period till early September, in other words towards the end of the season when the European Corn Borer population starts to fall, S. nonagrioides population reaches a high density and makes damages on the second crop maize severely, especially on the late sown maize.
Helicoverpa armigera Hbn. (Lepidoptera, Noctuidae) causes damage locally on the maize-cobs which have not yet fertilized by cutting their tassels, which encumbers the development of grains.
In some years Spodoptera littoralis Boisd. (Lepidoptera, Noctuidae) damages on maize beginning from the early August by eating the leaves and tips of the corn-cob in The Mediterranean Region.
Natural Enemies of Maize Pests
On the basis of regions the natural enemies of 0. nubilalis have been studied extensively. In these studies, the natural existence of Trichogramma has been noted and natural parasitization rate for each region and years, has been determined. This findings revealed that natural parasitization existed in the Black Sea Region at a level of 97.60 %,in the Mediterranean Region 2.30 -51.06% depending on the year and in the Aegean Region with T. brassicae, 2.60-% 100 %.
In the Black Sea and Aegean Regions, L. thompsoni has been found to be the most effective and widespread larva parasitoid. The percentage of this parasitoid is 4.54-65.34 % in the Aegean region, and 55.62 % in the Black Sea Region. As mentioned previously, due to the high percentage of parasitization by natural enemies, chemical control is not used to control 0. nubilalis in the Black Sea Region.
The egg parasitoid of S. nonagrioides, Platytelenomus busseolae (Gahan) (Hymenoptera, Scelionidae) has been commonly found in the Mediterranean region, and causing high percentage of parasitization depending on the year. Research reveals that in the years 1990, 1991, 1992 and 1993, instances of natural parasite were observed at levels of 56.80 %, 49.37 %, 38.63 % and 48.08 % , respectively. At the same time T. evanescens was found as a egg parasitoid of S. nonagrioides in low percentage. Field and laboratory studies related this are in progress. In The Mediterranean Region, studies that aims to determined the natural enemies of Lepidopterous pests are also in progress. It has been found that Meteorus oculatus, Cotesia rusficrus (Holiday) (Hymenoptera, Braconidae), Diadegma spp, Hyposoter deidymator (Thbg) and Campoplex sp. (Hymenoptera, Ichneumonidae) are involved effective parasitoids of A. loreyi and P. unipuncta. Apart from the previous studies in the Mediterranean Region, studies on the inundative release of T .evanescens and the biological control of 0. nubilalis have started.