Influence of Concentration and Time of Kaolin Application on Agronomic Traits, Canola Aphid (Brevicoryne brassicae L.) and Its Natural Enemies

Canola is one of the most important sources of vegetable oil. It is a valuable oil crop plant the second-highest produced in the world, following soya. In dry farming areas with heavy cereal production, canola becomes crucial as an alternative to cereals. Due to its adaptation to Iran's climate, its cultivation has received much attention. Kaolin is a non-toxic aluminosilicate (Al4Si4O10 (OH)8) clay mineral that is used in organic farming as a foliar solution. Kaolin spray reduces leaf temperature through rising leaf reflectance, which decreases the transpiration rate more than the photosynthesis of plants grown at high solar radiation levels. The application of kaolin was reported to protect plants against drought stress. Kaolin efficacy in reducing temperature and mitigating environmental stresses can also affect fruit-quality parameters. Several studies also showed an increase in the yield of different crops after kaolin application, particularly under water stress conditions. It is also used to prevent crop insect damage, plant sunburn, and heat stress. Kaolin does not interfere with the leaf gas exchange by creating a porous coating. According to other research, this substance can change the insects behavior. The kaolin particles stick to the insects' tarsi, reducing their movement ability, feeding and laying eggs. Considering the importance of increasing oil production, in this study, the effect of different concentrations and time of kaolin application on canola aphid and its natural enemies and yield and yield components were examined to determine the best conditions for using kaolin on rapeseed.

The field experiment was carried out on Hydra 401 canola variety field in Mahdasht, Karaj, Iran, during 2017-2018. Canola seeds were planted in a depth of 2–3 cm. The first irrigation was done two days after planting, and then irrigation was done seven days apart. Phosphate and urea fertilizer were added to soil as required during the experiment based on the soil test results. The experiment was conducted as a factorial randomized complete block design with four replications and 16 treatments. Experimental factors were kaolin concentration (0, 3, 6, and 9 percent) and the Phenological stages of canola (germination, rosette, budding, and flowering). Field sampling was performed to determine agronomic traits, including seed yield, biological function, harvest index, and 1000-seed weight. Fifteen plants were also selected from each plot. Their pests (Brevicoryne brassicae L.) and natural enemies (Coccinella septempunctata L., Hippodamia variegata Goeze, Chrysoperla carnea Stephens.) were sampled. Samplings were performed one day before the treatments, on the third day of treatments, and once a week from insects (pests and natural enemies). This study was conducted under natural contamination conditions to adapt to field conditions. No aphids were manually added to the treatments for infection. Insects were counted and recorded in all areas of the selected plant. Mean data were used for analysis. Data analysis was done using Design Expert 10 software.

The results showed that kaolin could increase agronomic characteristics in canola. In the current study, the highest seed function, biological function, and harvest index were observed in 6% treatment about 1888.87 kg.ha-1 in the rosette stage, 3038 kg.ha-1 in the rosette stage, 66.77% in the budding stage, respectively. The highest 1000-seed weight was determined in 3% treatment about 3.90% in the rosette stage. Results of kaolin application on cabbage aphids revealed that this mineral could help to reduce the canola aphid population so that the lowest population was observed at the germination stage in 9% treatment with an average of 31.33 aphids. The results also showed that kaolin affects natural enemies and reduces their population.

The results of this study revealed that kaolin affects agronomic characteristics like seed function, biological function, harvest index, and 1000-seed weight. Kaolin was also could control the cabbage aphid population. Kaolin also had adverse effects on the studied natural enemies. It seems that using kaolin at the 6% concentration due to the canola phenological stage can increase the production of this plant in the country.