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

A field experiment in the cultivation of spring barley was carried out in the period 2007-2009 at the Experimental Farm in Czesławice (central Lublin region) on grey-brown podzolic soil derived from loess (soil quality class II). The study involved 3 rates of herbicides, growth retardant and fungicides (100%, 75%, 50%) as well as different adjuvant types (oil, surface- active, mineral adjuvant). Plots without any adjuvant were the control treatment. Conventional tillage was used, while mineral fertilization was adjusted to high initial soil nutrient availability. A hypothesis was made that the reduction of pesticide rates by 25-50%, with the simultaneous addition of adjuvants, would allow health, weed infestation and lodging of spring barley to be maintained at a level similar to that obtained under the conditions when maximum rates are applied without any adjuvant. It was also assumed that particular adjuvants could show different interactions with the tested groups of crop protection agents. It was proved that the application of full recommended rates of pesticides gave the best values of the indicators relating to weed infestation, health and lodging of spring barley. However, thanks to the addition of adjuvants to the spray solution, the application of pesticide doses reduced by 25% produced similar results. A higher reduction of pesticide rates (by 50%) had an adverse effect on the traits in question. In such case, there was noted higher weed infestation of the spring barley crop, compensation of some weed species, and increased stem-base infection by the fungal disease complex. On the other hand, less radical changes were observed in the case of spring barley lodging. The above-mentioned situation occurred in spite of the fact that the action of pesticides was aided by adjuvants. From the group of adjuvants under comparison, the oil adjuvant Atpolan 80 EC showed the best interaction with the crop protection agents under consideration