The effect of spray application rate and airflow rate on foliar deposition in a hedgerow vineyard

Two experiments were performed in a hedgerow vineyard, in June (after end of blossom) and July (full vegetation development) to assess the influence of spray application rate and air output on the spray distribution from an axial-fan sprayer. Measurements were performed by fluorometry, using Brilliant Sulpha Flavine as a tracer. Increasing spray application rate and air output both led to higher losses to the ground and lower deposition on the foliage. However, differences were statistically significant only in the July experiment. Losses to the soil ranged from 34.5 to 36.8% for the lower spray rates (313-391 l/ha), and from 41.3 to 48.9% for the medium spray rate (648-782 l/ha) treatments. Losses due to drift outside the experimental plots and deposition on branches, shoots and poles ranged from 6.5 to 10.5% for the lower air output (7.0 m(3)/s), and from 7.8 to 19.8% for the higher air output (8.6 m(3)/s). The highest deposition on the foliage was recorded for the combination of a low spray rate and a low airflow rate (54.2 to 56.7%). Deposits per unit leaf surface were invariably lower in the middle (1.2 to 1.6 m high), denser part of the canopy. However, differences between heights were lower than in a previous experiment. (C) 1995 Silsoe Research Institute