Weed contamination is one of the factors limiting the increase in maize and sorghum production. Weeds block 35-60 % of all growth factors in the crops as they affect moisture formation and nutrient provision.

Hence, the most important issue in crop production is weed control aimed at improving the nutrient and water regimes of soil, and ultimately at optimizing plant growth and improving yielding capacity.

Research concerning the rational and environmentally safe weed control in the joint production of maize and sorghum for silage has not been carried out to date. Therefore, it is necessary to study weed control techniques in joint production of maize and sorghum for silage.

The aim of the research was to determine the yielding capacity of maize and sugar sorghum joint growing by the way of selecting the most efficient weed control technique.

The field trials were carried out during 2012-2015 on the research field of BTNAU, located in the central Forest Steppe zone of Ukraine.

In the trial medium-early maize hybrid DN Galatea and sugar sorghum hybrid Dovista were grown. The trial plan included the following options for weed control: 1. Biological weed contamination (control). 2. Mechanical weed control. 3. Application of herbicide Dialen Super – 1.25 l/ha in the phase of 3-5 leaves of plants. 4. Application of herbicide Prymeхtra TZ 500 Gold SC – 4.5 l/ha in the phase of 3-5 leaves of plants. 5. Application of soil herbicide Dual Gold 960 EC – 1.6 l/ha prior to crop germination.

The analysis of the data obtained indicates that the maize plants in the flowering stage boosted leaf area by 0.26-0.27 m²/plant and the sorghum plants in the phase of panicle appearance – by 0.04 m²/plant compared to the control after applying the post-germination herbicides Dialen Super and Prymeхtra TZ Gold. It should be noted that difference in the leaf surface area of the crops in variants with herbicides was not observed. During the growing season the leaf surface area in maize was 28.3-52.6 % higher compared to sorghum.

The largest area of leaf surface was shown in the variant of maize and sorghum joint growing with the use of mechanical weed control; the total leaf area in one maize plant was 0.57 m², and in sorghum – 0.14 m² in the second accounting period.

In average, the lowest weed contamination was recorded in the variant with mechanical weed control – 19.6 pcs./ m², the highest was in control variant – 95.6 pcs./m².

Maize and sorghum spraying with herbicides at recommended doses ensured the eradication of 58.6-69.5 % weeds. Insufficient efficiency of chemical control is explained by the selective action of the herbicides under study, namely their poor performance in annual grass weeds that contaminated sugar sorghum and maize areas significantly.

Mechanical weed control ensured the eradication of 80.1% weeds in average. The reduced level of weed contamination in maize and sugar sorghum ensured better conditions for plant growth.

The analysis of dry matter distribution of in plant parts indicates that its highest index is in the maize cob (60.5-68.2 %) and sugar sorghum panicle (51.6-60.5 %). In stems, the dry matter is 20.6-27.1 %; 15.7-18.4 %, and in leaves 11.2-13.2 %; 23.8-30.1 % in maize and sugar sorghum respectively.

Worsening conditions in maize and sugar sorghum growing with the significant weed contamination reduce the photosynthetic productivity and reduces yielding capacity.

In case of mechanical weed control application, excluding weed destruction, certain damage to maize and sugar sorghum plants was observed, which led to the decrease in plant stand density and green mass yield formation, which comprised
70.1 t/ha on average over the four years.

The use of post-germination herbicides Dialen Super and Prymeхtra TZ Gold ensured the increase in green mass yielding capacity up to 23.5 and 26.2 t/ha, dry matter – 7.2 and 8.1 t/ha, compared with the contaminated areas. Increase in the yield of green mass, in case of soil herbicide Dual Gold 960 EC application, was 20.0 t/ha prior to control.

Thus, we came to the conclusion that weed contamination greatly affects the growth and yielding capacity in maize and sugar sorghum, particularly in the early stages of vegetation. The study showed that the application of herbicides is the best weed control technique that contributes to improving the yielding capacity in maize and sugar sorghum joint growing.

Key words: maize, sugar sorghum, joint growing, yielding capacity, dry matter, herbicides, mechanical weed control.