Optimization of spray application technology in ornamental crops

Dieter Foqué

    Research output: ThesisDoctoral dissertation - Doctoral dissertationpeer-review

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    In Flanders, ornamental growers predominantly use handheld sprayers, e.g. knapsack sprayers and spray guns, instead of spray boom equipment for their plant protection needs. These handheld sprayers, however, have several drawbacks. In addition to the higher exposure risks for the applicator and the environment and the higher pressures and application rates with which these handheld techniques are often operated, spray gun techniques are also known to result in less uniform spray results and higher labor costs when compared to spray boom equipment. Growers increasingly recognize the advantages of spray boom equipment and this has resulted in increasing adoption of spray boom systems. Some growers still doubt the efficacy of spray boom systems, however, while others have questions about their use. This thesis aimed to address both doubts and questions by optimizing the deposition of spray liquids when using spray boom techniques in two important ornamental crops grown in Flanders: ivy (Hedera sp.) and bay laurel (Laurus nobilis). These tests were carried out under laboratory conditions. For ivy, a horizontal spray boom approach was used while a vertical spray boom system was used for bay laurel. In both cases, the (combined) effect of nozzle type, spray pressure, droplet characteristics, spray angle, spray volume and air support on spray deposition and penetration was studied. In addition, a horizontal and vertical spray boom prototype were built and compared to the performance of the traditionally used handheld techniques.
    Overall, the results of the experiments show that, ideally, these spray boom systems should be mounted with standard flat fan nozzles with a medium spray quality or air inclusion nozzles with a coarse droplet spectrum. These nozzles should be used within their recommended pressure range as higher working pressures result in smaller droplet sizes which have a smaller capacity to penetrate the crop canopy and are more susceptible to drift.
    The experiments also showed that plant architecture affects the optimal spray boom configuration and spray volume. Both for the laurel and the ivy crop, increasing the spray volume above the optimal one does not result in equally higher deposits. Therefore, these practices only result in higher losses to the environment.
    Of all horizontal spray boom configurations tested, the air-assisted medium droplet size extended range ISO 03 flat-fan nozzle at 3.0 bar with a 30° forward or a standard 0° spray angle at a spray volume of 1000 L ha-1 was found to be the most optimal one for the ivy crop considered in the laboratory trials. An air assisted coarse air-inclusion spray at 6.0 bar with a normal 0° or -30° backward spray angle at the same application was a valuable alternative. The same configurations but without air assistance also lead to high spray depositions within the canopy when compared to those of a normal 0° angled standard flat fan spray without air assistance. The use of air assistance, however, resulted in the most uniform spray distribution because of an improved spray penetration and a good coverage of the lower sides of the leaves (or abaxial side of the leaves) and the effect was most pronounced for a medium droplet size spray. Of the application rates tested, the spray volume of 1000 L ha-1 was the most appropriate as doubling the application rate from 500 to 1000 L ha-1 still lead to substantial improvements of the deposits, while a further increase to 2000 L ha-1 often lead to comparable results as observed for the 1000 L ha-1 application. The less favorable results for the 500 L ha-1 applications and of spraying 1000 L ha-1 in two passes could be the result of the higher application speed used.
    The results of the lab trials with the vertical booms also showed that using a spray volume adapted to the crop can significantly improve the spray results when using an appropriate spray application technology. Of the three application rates tested, 4900 L ha-1 ground surface proved to be the most optimal one to treat the considered, conically pruned bay laurel crop. From the wide range of vertical spray boom techniques tested, applications with an extended range standard flat fan nozzle with a medium spray quality without air support, directed straight toward the crop generally provided the best spray results in a bay laurel crop with a fixed spray distance to the stem of about 30 cm. The use of an adapted spray direction only proved to add value when a backward spray direction (-30°) or when an application with a forward spray direction (30°) was applied in two opposing successive runs. Although these two spray configurations did not lead to higher deposits than the previously mentioned technique, both spray applications improved spray uniformity in the canopy. The use of air support only resulted in a significant rise in the overall deposition values for the air inclusion nozzle and in a more uniform spray distribution for the extended range flat fan and the air inclusion flat fan nozzle with the standard 0° spray direction. In combination with a forward spray direction, the use of air support increased the differences in deposition between the front and the back of the plants. In general, however, air support did not have a positive effect on the spray deposition values or the penetration of the spray in the canopy. Most likely the air speed of the air assistance was too high. To improve the effect of air support, the air speed and volume should be adapted based on the crop and spray characteristics. In addition, the experiments demonstrated that vertical spray booms can be adjusted to the shape of the crop by simply changing the nozzle spacing.
    Throughout this thesis, it is shown that spray booms generally offer a more uniform coverage, result in higher deposition values and could allow for a reduction of the spray volume, the pesticide losses to the environment and the operator exposure risk. Therefore, they have a high potential to optimize spray applications in ornamentals. This is especially true for automated spray boom systems, but the experiments with the manually pulled spray booms illustrate that they could do just as well. Manually pulled spray booms are cheaper than their automated equivalents and they can easily be constructed by the growers themselves, which makes them easily adaptable to each grower’s needs.
    In conclusion, using spray boom systems instead of the predominantly used spray guns and lances in ornamental crops is possible and could be a big step forward toward a more sustainable use of crop protection products in ornamental crop production. This study showed the importance of a well-considered choice of nozzles and spray boom setting which is closely related to the plant architecture. Nozzle type and size, spray volume, spray pressure and spray angle as well as the use of air assistance significantly affects the spray deposition, crop penetration and uniformity of the spray.
    The findings of this thesis can therefore be an important tool to direct growers to a more efficient spray application technique, which will improve the bio-efficacy and the sustainable use of the available plant protection products.
    Translated title of the contributionOptimalisatie van spuittechniek in de sierteelt
    Original languageEnglish
    Place of PublicationGhent
    Print ISBNs978-90-5989-557-7
    Publication statusPublished - 2012

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