Safety Of Seed Coating Agents To Maize And Its Effects On Major Diseases And Pests In Corn Field

Maize is the largest grain crop in China at present, besides serving as food for human and livestock, which is also an important industrial raw material. Seed coating agent plays an important role in controlling plant diseases and pests, ensuring high and stable yield of maize with strong targeting, lower amount of pesticide use and high utilization rate of pesticides. But some side-effects have appeared with the large scale application of seed coating agent, such as inhibiting the growth of crops, injuring beneficial organisms, so how to safely use the agent is an issues that must be solved. In 2013, a trial was initiated in Xuchang, to evaluate the effects of seed dressing with 8 kinds of maize seed coating agent using three dosages(the recommended optimal dose and its 1.5 times, 2 times doses, respectively) on maize emergence, growth, yields and its main pests using Zhengdan958, a maize hybrid with widely application in Henan province. And as a representative, the effects of 20% thiram·carbofuran FSC on antioxidative metabolism were investigated. Based on the experiment in 2013, we studied the effects of 600 g/L imidacloprid FSC on nutrient substances, secondary metabolism substances of maize plant and its main pests in 2014. In addition, the host-feeding and oviposition behaviors of Ostrinia furnacalis were analyzed and the activities of enzymes were measured. The main results are showed as follows:1. Through observation and survey in greenhouse, we found that seed coating agents we tested influence the time of seedling emergence of maize by promoting or delaying effects, but have no disadvantage to final emergence of seedling. The inhibition is positively related to the dosage, among which the inhibition of flowable concentration for seed coating is greater than that of the powder.2. In the field test, all of the 8 kinds of seed coating agents have no obvious adverse effects on maize and have a good preventing effect on target pests. The rate of emergence of maize treated with seed coating increased by 6.04%-11.25%. Twenty days after sowing, all treatments promoted the growth of maize, with increasing of plant height, root numbers, fresh(dry) weights and root-shoot ratio, especially the appropriate root-shoot ratio and seedling shape were obtained in all treatments. In the field plot with seed coating by those containing carbofuran, imidacloprid and thiamethoxam, the underground pests and aphids were reduced, but the corn borer had a trend of increasing. Tebuconazole and thiram have no control effects to corn crown rot and head smut. The yields of treatments are better than or equivalent to the control, with no significant difference among doses, and yield-increasing effects of thiram·carbofuran were slightly better than neonicotinoids.3. The effects of recommended dose and its 1.5 times and 2 times dose of 20% thiram·carbofuran FSC on the chlorophyll content and root vigor in seedling period as well as the activities of antioxidant enzymes in different growth periods were studied in field plot experiment. The results showed that the recommended dose of 20% thiram·carbofuran FSC increased the chlorophyll content, 1.5 times and 2 times doses reduced the content 10 days after sowing, but at 20 days after sowing, all treatments increased the chlorophyll. 20% thiram·carbofuran FSC can increase the root vigor in seedling, and cannot change the activities of antioxidative enzymes in leaf and root, which suggest that seed coating play a part in maintaining or adjusting plant growth even though under the 2 times of the dose.4. Nutrient substances and secondary metabolism substances were analyzed in seedling stage, bell stage, tasseling stage and booting stage of maize treated with 600 g/L imidacloprid FSC seed coating. The result indicate reducible carbohydrate and tannins contents increased, while total contents of sugars and phenols reduced in seed coating plants comparing with the control in seedling stage. In bell stage, the reducible carbohydrate content in the leaves of seed coating plant declined, while tannins and total phenols increased. Up to tasseling stage and booting stage, the contents of secondary metabolism substances and sugars increased significantly.5. The effects of seed coating with 600/L imidacloprid FSC on population dynamics of main pests and natural enemies in corn fields were surveyed systematically. The results showed that the damage of leaf-chewing pests reduced at the earlier stage of maize, and the population quantity of corn aphids decreased obviously in the whole growth period. For Propylaea japonica, a main enemy of the aphids, its population dynamics is in accordance with the aphids. From pustulation period to harvest, the damage of boring insects, O. furnacalis and Conogethes punctiferalis, present an aggravating tendency with increasing of larva, tunnel length and damage rate. Meanwhile, the yield and its indicators decreased, which imply the damage caused by boring insects is the main reason of yield loss.6. The influence of seed coating by 600 g/L imidacloprid FSC or artificial diet added the agent on the oviposition behavior and the growth and development of O. furnacalis were studied. The result revealed the host-preference of newly hatched larvae were identical between the leaves from seed coating plant and that from the control, while the eggs laid on the former significantly higher than that on the latter. When using the artificial diet added with the agent to feed the larva, we found that the growth and reproductive capacity indexes of corn borer increased than that the control.