Rain-induced removal of copper from apple leaves: Influence of rain properties and tank-mix adjuvants on deposit characteristics at the micro scale

Application of copper fungicides is an integrative component in the control of apple scab. As shown in the past, tank-mix adjuvants might reduce the rain-induced removal of active ingredients. The aims of this study were a) to characterize the impact of defined rain amount on the removal of Cu-oxychloride (Cu-Ox) and Cu-hydroxide (Cu-Hyd) from apple seedling leaves, b) to examine the influence of ethoxylated seed oil adjuvants on deposit properties at the micro scale and their possible influence in reducing the fungicide erosion from the leaves, and finally c) to evaluate the influence of previous adjuvant application on the rainfastness of copper ions. Losses of Cu-Hyd and Cu-Ox from seedling leaves exposed to 5 mm heavy rain reached almost 80% of the original Cu load. Wash-off extent of Cu-Ox could be reduced by using the rapeseed oil ethoxylate RSO 5 (47%), the linseed oil ethoxylate LSO 10 (47%), or the soybean oil ethoxylate SBO 10 (40%). However, in case of Cu-Hyd, none of the adjuvants was able to increase the tenacity of the copper on the leaves. Rainfall removed the bulky deposits and induced changes in the typical shape of the crystals. Furthermore, a reorganization of the spatial distribution of the remaining active ingredient (a.i.) was induced, which was very often embedded in a thin layer of adjuvants. In general, the adjuvants had a significant impact on droplet spread, whereas the area effectively covered with the a.i. was affected to a lesser extent. For both Cu-Hyd and Cu-Ox rewetting of the original deposit under controlled conditions resulted in an increased spread area but reduced the area effectively covered with Cu. Our results showed no clear relationship between the area covered by Cu ions and their adhesion to the surface, i.e. rainfastness. Finally, our studies indicated that previous spray treatments might influence the rain-induced removal of copper.     

Control of late blight in organic potato production: evaluation of copper-free preparations under field,growth chamber and laboratory conditions

In order to replace copper fungicides in organic potato production, 53 copper-free preparations (CFPs) based on natural compounds, including plant extracts and microorganisms, and five copper preparations were evaluated for their potential to control Phytophthora infestans, the pathogen that causes late blight of potatoes. In in vitro assays, 30% of the CFPs inhibited indirect germination of sporangia, 26% mycelial growth and in growth chamber experiments, 21% efficiently reduced foliar blight of tomato plants. In micro-plot field trials with applications twice a week, the copper preparations were the most effective and reduced foliar blight by 99%. Of the CFPs tested, Oekofluid P, Mycosin and other sulphuric clays, and C-2000 reduced late blight the most, from 63% to 37%. In small-plot trials in 2001, 2002 and 2004, 27 CFPs with different formulations and four copper preparations were examined. In 2004, copper preparations at full and reduced rates and sulphuric clays were applied either weekly or according to the decision support system Bio-PhytoPRE. With Bio-PhytoPRE, copper preparations reduced foliar blight of potatoes by 23–77% and increased tuber yield by 2–28%, depending on the copper rate applied and year. With CFPs, maximal efficacy was 17% and no effect on tuber yield was observed. In vitro and in vivo trials showed that the rainfastness and the persistence of CFPs was low compared with copper preparations. This indicates that the failure of CFPs under field conditions is probably due to a lack of stability under prevailing environmental conditions and not to a lack of efficacy. Until stable formulations for CFPs are developed, an optimised and restricted use of copper fungicides using a decision support system could help to control late blight in organic potato production and to reduce copper input into the environment.