T. KERESI, P. STRBAC, D. LATKOVIC
Faculty of Agriculture, Novi Sad, Yugoslavia;
R. SEKULIC
Institute of Field and Vegetable Crops, Novi  Sad
F. BACA
Maize Research Institute, Zemun Polje, Belgrade, Yugoslavia

Since it has been realized that the chemical control of the Western corn rootworm (Diabrotica virgifera virgifera Le Conte) is complicated and uncertain, it became important to determine which agrotechnical measures permit continued growing of corn in monoculture.

With this objective in mind, we have studied the effect of fertilization systems and corn hybrids on the harmfulness of the WCR. Experiments were conducted in 2000-2001, in the vicinity of Novi Sad, in a trial with corn monoculture established in 1951. The trial includes three fertilization variants (1. NPK, 2. crop residues + NPK, 3. manure + NPK) and the non-fertilized control and several maize hybrids of different maturity groups (FAO 300, 500, 600, 700). WCR damage was assessed via plant lodging, root damage and yield reduction.

In dry 2000, plant lodging were significantly higher in variants 2 and 3 (52.4 and 61.1%) than in the control (37.6%), while the situation was reverse in wet 2001. In the first year, plant lodging was most intensive in FAO groups 300 and 600 and least intensive in FAO 700. In the second year, the most intensive lodging occurred in FAO group 600 and the least intensive in FAO 300.

In both experiment years, root damage (on the scale 1-6) was largest in the control (4.57 and 4.91) and lowest in variant 2 (3.35 and 4.15). The differences were significant in the first year and non-significant in the second. In 2000, root damage ranged in the hybrids from 4.07 to 4.31, with non-significant differences. In 2001, FAO groups 300 and 500 experienced significant damages (4.74 and 4.63, respectively) in relation to the two hybrids in FAO group 600 (4.16).

In 2000, the highest yield (2.74 t/ha) was obtained in variant 2, which is significantly higher than in the control and variant 3 (1.18 and 1.25 t/ha). Yields of FAO groups 700 (2.45 t/ha) and 600 (1.96-2.08 t/ha) were significantly higher than those of groups 300 and 500 (1.00 and 1.49 t/ha). The yields in 2001 will be assessed in October.
Because of the extremely opposite weather conditions (particularly rainfalls) in 2000-2001, relevant conclusions may be expected on the basis of long-term data.