Onions (Allium cepa) are herbaceous biennial plants and can be propagated anywhere in South Africa. However, the main production areas are located in the Northern and Western Cape, Free State, North West, Limpopo and Mpumalanga Provinces mostly under pivot irrigation.
An annual watering requirement of about 400 – 600 mm is needed during the growing season. Due to this type of irrigation, coverage and retention of the agricultural chemicals during spray application are of the utmost importance. The moist conditions not only make the plants susceptible to fungal and bacterial infections, but harder to cover the plant surface as well.
In relation to the latter the trial was conducted to confirm the ability of Nu-Film P to improve the deposition of agri-chemicals during sprays on onion leaves.For evaluation purposes a fluorescent pigment and a newly developed mobile phone application called Dropsight (www.dropsight.ag) was used.
Materials and Methods
The site used during the trial is located in the Swartwater area of Limpopo. It consisted of a 10 ha onion field at three leaf developmental stage propagated under pivot irrigation. A boom sprayer with a 2000 L tank was calibrated to 500 L water/ha and used to apply the spray mixture. The spray mixture consisted of 1 L iprodione fungicide/ ha iprodione and 4 L foliar feed/ ha. To determine deposition, a fluorescent pigment (UView) was added to the spray mixture at a rate of 2%. The untreated control consisted of the spray mixture and fluorescent pigment without Nu-Film P and was applied first (Figure 1). Thereafter, 300 ml Nu-Film P/ ha was added to the spray mixture and fluorescent pigment and applied (Figure 2). The untreated and Nu-Film P treated plot consisted of approximately 2 ha each.
Figure 1: Spraying of the standard onion plot with a boom sprayer calibrated to 500l/ha during April 2022 near Swartwater, Limpopo province.
Figure 2: Spraying of the Nu-Film P added onion plot with a boom sprayer calibrated to 500l/ha during April 2022 near Swartwater, Limpopo province.
After the sprays dried off, 15 onion plants were randomly sampled from each plot and the middle leaf of each plant used for analysis. The analysis consisted of placing each leaf in a black photographic box (LeafLab) lined with UV lights. Using a cell phone, images were taken of the fluorescence on the onion leaves in the photographic box (Image 3A & B). Each of the 15 leaves per treatment were pictured separately and using the DropSight mobile application the %FPC was determined for each leaf. The %FPC relates to the amount of leaf surface covered with fluorescent pigment.
Figure 3. Fluorescent pigment observed after images were taken of onion leaves placed in the photographic box (LeafLab), A) Leaves from onion plants removed from the standard treated plot and B) Leaves from onion leaves retained from the plot containing Nu-Film P sprayed during April 2022 near Swartwater, Limpopo province.
Results and discussions
The results received from the DropSight application indicated that when Nu-Film P was added to the spraying mix the average %FPC was 1.86% compared to 0.95% of the standard treatment without Nu-Film P. This either suggests a higher retention of active due to the waxy nature of onion leaves or a better deposition of active. Either way, the results do show that when Nu-Film P is added to a spraying mix there is almost a doubling of active available on each leaf, when you accept that the pigment observed relates to the amount of active deposited.
Figure 4: The average %FPC data received from the DropSight application after images were downloaded of leaves collected from the standard and Nu-Film P treated plots respectively and subjected to analysis.
Written by: Charl Kotze