The effect of reduced rates of crop protection agents and adjuvants on productivity, weed infestation and health of spring barley (Hordeum sativum L.)

A field experiment on the cultivation of spring barley was carried out in the period 2009–2011 at the Experimental Farm in Czesławice (central Lublin region) on grey-brown podzolic soil derived from loess (soil quality class II). The study included 3 rates of herbicides, growth retardant and fungicides (100%, 75% and 50%) as well as different types of adjuvant (oil, surface-active, mineral). Plots without adjuvant were the control treatment. A hypothesis was made that the reduction in rates of crop protection agents by 25–50%, with the simultaneous addition of adjuvants, would allow spring barley productivity to be maintained at a level similar to that obtained under the conditions when recommended rates are applied without adjuvant. It was also assumed that particular types of adjuvant would show different interactions with specific groups of crop protection agents. It has been proved that a rational reduction in rates of crop protection agents is up to a limit of 25%, especially when an adjuvant is added to such reduced rates. This allows spring barley productivity to be maintained at the level obtained after the application of full rates (without adjuvant). But a further reduction in rates of crop protection agents by 50%, in spite of the interaction of adjuvants, results in a significant deterioration of all spring barley yield components, since such conditions lead to increased occurrence of agricultural pests (weeds, fungal diseases) as well as increased crop lodging. Among the group of adjuvants tested in the present experiment, the oil adjuvant Atpolan 80 EC showed the best interaction with crop protection agents used