Scientific development and practical mastering methods for improving the effectiveness of weed control system is an important task in modern agriculture. It contributes to solving not only partial local aspects, but can become an integral part of the soil protection system of agriculture in Ukraine as well.

By their technical efficiency, agrotechnical measures for weeds control are dominated by variants with chemical methods of weeds control. This advantage of herbicides in comparison with agrotechnical measures is the consequence of the timeliness loss during realization of agrotechnical measures of fight, which arises up at unfavorable weather conditions and considerable loading on the soil-forming units in the farm.

It is necessary to apply more effective methods of weed control in corn crops in production with bringing of certain herbicides, which in combination with agrotechnical methods ensure elimination of almost all weeds in sowing of corn.

The purpose of the research was to determine the effects of weeds control measures on growth, development and weediness of corn crops.

Field experiments were conducted during 2013-2016 yrs. in the experimental field of the Bila Tserkva National Agrarian University, which is located in the Central Forest-steppe of Ukraine.

The two-factor experiment was carried out according to the following scheme: Factor A. Corn hybrids: 1. DP Pyvycha (FAO 180) 2. DP Galateia (FAO 260) 3. Monica 350 MV (FAO 350) 4. Bystrytsia 400 MV (FAO 400). Factor В. Measures for controlling the number of weeds: 1. Biological weediness (control). 2. Mechanized crop care (post-harvest harrowing and two inter-row cultivations). 3. Applying of soil herbicide Harnes (2.5 l/ha) before the emergence of stairs. 4. Applying of post-stairs herbicide Master Power (1.25 l/ha) in a 3-5-leaves stage in corn. 5. Compatible application of Harnes (2.5 l/ha) + Master Power (1.25 l/ha).

Among the investigated weeds control measures in the initial period (10-11 leaves stage), the mechanized care of crops had considerable advantage, and further there was no significant difference between the experimental variants. The highest indexes of plant height were recorded in the hybrid Bystrytsia 400 MV using herbicide Master Power (1.25 l/ha) – 242.0 cm. When combined with a soil herbicide Harnes (2.5 l/ha), this index decreased on 0.4 cm.

The area of the leaf surface varied depending on the corn's biotype and the degree of weediness of the crops. At the same time, despite the variability of this corn index under the impact of the investigated factors and weather conditions, the morpho-biological characteristics of hybrids were stable throughout all years of research. So, depending on the variant of the experiment, the area of leaf surface in the flowering stage was: in the hybrid DP Pyvycha 21,4-40,5 thousand m²/ha, DP Galateia – 23,7-40,1 thousand m²/ha, Monica 350 MV – 25,6-48,5 thousand m²/ha, Bystrytsia 400 MV – 28,1-51,2 thousand m²/ha.

In the flowering stage of corn, there were no significant differences between the variants with different measures of protection against weeds. Thus, when the mechanized crop care, the area of leaf surface of the hybrid DP Pyvycha amounted to 41.0 thousand m²/ha, DP Galateia – 46.0 thousand m²/ha, Monica 350 MV – 49.4 thousand m²/ha, Bystrytsia 400 MV – 51.8 thousand m²/ha.

In our researches, the use of agronomic and chemical weeds control measures contributed to the reduction of unproductive loss of moisture from the soil by weeds. This allowed using it effectively by corn for a longer period. The reserves of productive moisture in the meter layer of soil in these variants amounted to 74.3-87.6 mm, which is higher than in the control variant on 20.9-22.3 %.

When natural weediness, corn hybrids used 127.0-158.9 m³/t water, and when carrying out weeds control measures, the amount of moisture, that used for the formation of corn biomass, was 60.9-98.0 m³/t.

From sowing to a 5-6 leaves stage of corn, high efficiency ensured the applying of soil herbicide Harnes (2.5 l/ha). The remaining amount of weeds in the 5-6 leaves stage of corn was insignificant and amounted to 12.3-13.0 pcs/m². Indexes of the Harnes (2.5 l/ha) use effectiveness improved significantly after the sowing of the insurance herbicide Master Power (1.25 l/ha) – the amount of weeds decreased to 5.5-6.1 pcs/m².

On average, over the years of research, the best phyto-sanitary condition of corn crops was in the variant compatible application of Harnes (2.5 l/ha) + Master Power (1.25 l/ha). At the same time, in this variant the number of weeds in the kernel milk-wax stage of corn depending on the hybrid decreased to a minimum – 6.1-6.5 pcs/m². The decrease in weediness compared with the control variant was 95-96 % – number of weeds and 80-86 % – their weight. Such double application of soil and post- stairs herbicides provides high technical efficiency of their action – 89.6-95.3%.

The weediness of corn crops is influenced by the degree of potential impurity of sowing and the effectiveness of weeds control measures. The degree of weediness and the processes of phytocoenosis formation of weeds don’t dependent on the corn hybrid.

Key words: corn, hybrids, weediness, plant height, herbicides, chemical method, mechanized crop care.