Optimising fungicide use by varying application according to crop canopy characteristics in wheat

Abstract

A two-year study was conducted to determine the interactions between spray application variables and crop canopy structure so as to explore the potential for improving the performance of fungicides applied to cereal crops.  The work involved a review of methods of sensing crop canopy characteristics that concluded that reflectance radiometry to determine a vegetative index, particularly at early stages of growth, was an appropriate method that could be developed commercially.

Field experiments then used radiometry to define areas of high and low crop canopy density and treatment plots based on spray application variables were defined in each area.  In the first seasons work, only deposits were measured at two growth stages using a tracer dye technique.  In year 2, sites in different parts of East Anglia used a T2 fungicide applied at the later growth stage and with a different dye to measure both deposit distribution and fungicide efficacy.

Results from experiments conducted in the first year's trials showed large differences in mean deposit levels at the two growth stages with deposits per unit of leaf weight at growth stage 39 43% less than those at growth stage 32.  At a given growth stage, there was some variation in deposit levels and distribution between the areas of high and low crop canopy density but these were not statistically significant.  Total deposit levels at both growth stages were increased by an average of 13% by angling nozzles at 45o to the vertical and by 38% by using a volume rate of 100 l/ha compared with 200 l/ha applications. The largest differences were measured at the earlier growth stage.  Higher deposits were consistently measured when applying a fine spray.

Results from the second year's experiments also showed no difference in mean deposit levels per unit of leaf weight in the areas of high and low canopy density.  Deposits were again higher from the low volume (100 l/ha) applications compared with applications at 200 l/ha but no differences were established from using angled nozzles or a fine spray quality.  No differences in levels of disease control between treatments in high and low crop canopy areas were measured.

Results from the project indicated:

(i)         that there may be the potential to improve the use of fungicides by matching applications to crop growth stage although some further experiments are required to confirm that efficacy can be maintained under such conditions;

(ii)        there is currently little to be gained from spatially variable applications of T2 fungicides in cereal crops based on measurements of crop canopy characteristics;

(iii)       that savings in pesticide use can be achieved by changes to spray application parameters including adjustments to account for canopy characteristics: in wheat, increased crop deposits could be obtained particularly at early stages of growth by using volume rates of 100 l/ha applied with conventional nozzles systems and by angling the nozzles;

(iv)       reflectance radiometry is an effective and relatively low cost way of characterising crop canopy characteristics particularly at early growth stages (before GS 32).