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Block Reference: #c9297dfc-06fe-11ec-b845-6751476a704b
Date and time: Fri, 27 Aug 2021 06:19:50 GMT
Figure 1. Seed production and 1000 seed weight after paraquat, ammonium-glufosinate, iodosulfuron-methyl and clethodim application for seed inviabilization of Italian ryegrass in different phenological stages. Same lowercase letters compare the herbicide effects in the different stages, and uppercase letters compare the herbicides in each stage by Duncan´s test (p<0.05). * significant effect for control without herbicide by Scheffé test (p<0.05).
*Means followed by the same uppercase letter (column) and lowercase letter (line) do not differ by Duncan´s test (p<0.05). ns = not significant (p<0.05). (1) Favorable effect to control without herbicide compared to the herbicides applied by Scheffé test (p≤0.05). (ns) = not significant by Scheffé test (p<0.05).
For the seed viability, the analyzes were carried out in a seed laboratory using the completely randomized experimental design with four repetitions. A sampling from each treatment was performed, and 50 seeds were placed in each transparent boxes (11.5×11.5×3.5 cm), containing two sheets blotter paper, previously moistened with distilled water in an amount to 2.5-fold the paper weight. The boxes were put in a chamber of Biochemical Oxygen Demand (BOD) for 14 days at alternating temperature 20/30 o C in dark/light, and 8 h of photoperiod, according to the Brazilian Rules for Seed Testing (Brasil 2009). Seed viability was evaluated at 14 days after starts the germination testing, based on the germination percentage, abnormal seedlings, dead seeds, percentage of dormant viable and non-viable seeds. The non-germinated seeds were analyzed in a 1% tetrazolium solution after longitudinally cut of embryo and imbibition at 30 o C of temperature for 6 h, with check-in in a stereo microscope (Brasil 2009).
Pre-harvest herbicide application reduces the Italian ryegrass seed viability
Lower germination percentages were found for all herbicides applied, regardless of the phenological stages evaluated compared to the control, in which the germination was of 89% (Table 2). Herbicides application at pre-spike and anthesis stages caused strong reduction in germination (decreases greater than 98%), except for iodosulfuron-methyl applied after the anthesis stage, with the germination of 21% (Table 2). In wheat plants, recent studies have been reporting the negative effects on seed germination after paraquat and glyphosate application due to the oxidative damage of membranes caused when herbicides are applied in the pre-harvest (Bellé et al. 2014, Perboni et al. 2018). The increase of dead seeds occurred for all herbicides applied in the pre-spike and anthesis stages, with decreases greater than 98%, except for iodosulfuron-methyl applied at anthesis in which dead seeds were only 76% (Table 2). Furthermore, late herbicide application reduced the percentage of dead seeds, especially for iodosulfuron-methyl applied at grain filling, with 66% of dead seeds. Herbicides are chemical substances that modify several physiological processes, affecting grain filling and seed quality, especially for applications performed before seed maturity (Jaskulski and Jaskulska 2014). Wheat burndown with ammonium-glufosinate, clethodim or paraquat can reduce the initial growth of seedlings due to the incomplete formation and lower seed weight (Krenchinski et al. 2017).
Figure 2. Effect of herbicides on Italian ryegrass seeds after application in the grain filling, demonstrating the absence of embryo.
Herbicides caused strong reduction on the seed number produced plant -1 , especially for applications in the pre-spike stage, causing full reduction in the seed production compared to the control (Figure 1A). Paraquat and ammonium-glufosinate applied up to the anthesis stage were more efficient to reduce seed production compared to the control without herbicide, whereas iodosulfuron-methyl and clethodim reduced by 90 and 92% the seed number produced plant -1 , respectively.
The pesky Palmer Amaranth weed can produce as many as a million seeds per plant, but only a small percentage of those seeds will sprout and grow into a pain-in-the-field. Owen says from an ecological perspective, it depends on whether a weed seed is in a “safe site” to germinate.
“Weed seeds such as the velvet leaf, very hard-seeded coat, will last a long time. Foxtail seeds, which don’t have a hard seed coat, are less likely to survive more than a couple of years. There are many things that attack weed seeds. There’s disease, there’s climatic conditions, there’s insects, and all kinds of things that will affect them,” says Owen. “Those generally are what is going to determine just how likely a weed seed is going to survive.”
Mike Owen is a weed scientist at Iowa State University. He says weed seeds that have a hard seed coat are more likely to survive the trials and tribulations that occur when they fall into the soil.
“Factors that are involved are obviously temperature of the soil, sunlight to some degree. Nutrients and things like that really don’t affect it,” he says. “The depth obviously will impact because sometimes in tillage, for example, you may cause the weed seed to get the appropriate sunlight exposure, but then because of that tillage you bury it too deep.”
We all have weeds that we just can’t seem to get the upper hand on. Their weapon against us is seed longevity. Most annual weedy grass seeds die after two-to-three years, but some broadleaf weed seeds can remain viable for decades.
Careful weed management over time will reduce the number of viable seeds in the soil, and make your life in the garden or field a little easier.