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Keeping inoculants on the seed

If microbial inoculants are to be effective as seed treatments they need to remain attached to the seed until they arrive in the soil. Some products, such as mychorrizal fungi inoculant, can have a fairly large particle size, and does not stick to seed very well, particularly smooth seeds such as beans.

The last thing we want to see is accumulated inoculant at the bottom of the seed hopper when we get done planting.

When you apply seed treatments yourself, lightly spray a sugar-water solution onto the seed before the inoculant is applied. This serves to make the seed slightly sticky, and microbial powders remain strongly attached to the seed.

2020-04-11T15:39:36-05:00April 13th, 2020|Tags: , |

Impacts of glyphosate residue on seed germination

Some new research1 describes the impact of pre-emerge glyphosate applications on seedling development and yields, and the impact of prior year appplications. The conclusion: you certainly want to avoid any application until well after seedling emergence, and prior year applications are probably impacting your current yields. It seems we need to begin using alternatives immediately.

The article itself is a great read, here are a few excerpted highlights:

  • The seed germination of faba bean, oat and turnip rape, and sprouting of potato tubers was delayed in the greenhouse experiments in soils treated with GBH (glyphosate based herbicide) or with pure glyphosate.
  • The total shoot biomass of faba bean was 28%, oat 29% and turnip rape 58% higher in control compared to GBH soils four weeks after sowing.
  • Grazing by barnacle geese was three times higher in oats growing in the GBH soils compared to control oats in the field. 
  • Our results indicate that the use of GBH, as well as surfactants and other ingredients of commercial herbicide products, have different effects on the seedling establishment of seed- and vegetative-propagated crops.
  • In all the studied seed-propagated crops, germination was faster, and in turnip rape and oats the total germination percentage was higher in the C soils compared to the pure G- or GBH (Roundup)-treated soils.
  • seed-propagated crops with limited endosperms as an energy source are likely to be exposed to GBH residues in soils following water imbibition at the beginning of the seed germination.
  • Our results suggest that the use of GPH may have unintended and undesirable consequences for farmers. The speed of germination and early growth may be crucial for the plants, depending on the abiotic and biotic environmental factors. Especially in spring, earlier individuals may benefit from moisture and a lack of competition. Thus, delayed germination and weakened growth of seed-propagated crops in GBH-contaminated soils may invalidate the intended crop protection if targeted weeds get a head start in early spring.
  • The use of GBH may increase the yield loss caused by flea beetles and further challenge spring-planted oilseed rape and turnip rape cultivation
  • Glyphosate can enhance the attractiveness of plants to vertebrate herbivores. In the field experiment, the oat plants growing in GBH-treated experimental plots experienced heavy barnacle geese grazing while the adjacent plants in C plots were only mildly grazed. 
  • Glyphosate is known to inhibit the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the shikimate acid pathway, thereby interfering with the production of tryptophan, phenylalanine or tyrosine, which are precursors of proteins and other molecules, including growth promoters (e.g., indoleacetic acid, IAA) or secondary compounds with known importance for plant defense against herbivores (e.g., tannins, anthocyanins, flavonoids, and lignin.
  • Overall, the effect of pure glyphosate was weaker compared to that of the commercial formulation (Roundup Gold) containing the same amount of glyphosate. This supports other studies suggesting that other ingredients in GBH, such as surfactants, solvents, and preservatives, could also cause adverse effects on non-target organisms.
  • Our results clearly demonstrate that the use of GBH has detectable effects on crop plant germination and growth, and their quality to herbivores, even though we used field-realistic concentrations of GBH and the experimental plants were introduced into the soil after a two-week withholding period.
  • In contrast to seed-propagated crops, GBH treatment boosted the growth of vegetatively propagated potatoes, and glyphosate appeared to accumulate in the potato tubers. This leads to the critical question of whether the residues in potatoes have consequences for the subsequent year’s yield.
  • These results emphasize the importance of a more comprehensive understanding of the effects of GBH on the productivity of crop plants and their chemical ecology, affecting their pest and pathogen resistance and thus the need for crop protection.
  1. Helander, M., Pauna, A., Saikkonen, K. & Saloniemi, I. Glyphosate residues in soil affect crop plant germination and growth. Sci. Rep. 9, 19653 (2019).

 

2020-03-16T13:54:09-05:00January 14th, 2020|Tags: , , , , |

Effective Seed Treatments

For direct-seeded crops, seed treatments are the least expensive and highest return application a grower can apply. 

Seed treatments can contain bacterial inoculants, fungal inoculants, microbial biostimulants, plant biostimulants, and trace minerals. The most effective treatments usually are a synergistic stack that contains ingredients from several or all of these categories. 

Trace mineral seed treatments are most important with poor quality seed that is small in size and light in weight (most commercial corn seed). High-quality seed often contains enough of the more common trace minerals. 

Many seeds, at least those grown on healthy parent plants, vector their own symbiotic endophytic microbes, both bacteria and fungi. In addition to those microbes vectored on the seed, seedlings also recruit symbiotic fungi and bacteria from the soil, particularly mycorrhizal fungi, as well as others, even some of the same species they carry along on the outside of the seed. 

Applying mycorrhizal fungi and other bacterial inoculants as a seed treatment is generally an effective delivery method to achieve early root colonization, particularly for monocots, where the seed remains in the ground. 

For dicotyledon plants, I have always wondered how effective it is to treat the seed when the seed is soon pushed up and out of the ground. Many growers have used seed treatments on these crops effectively, but I suspect we may get better responses from applying them in-furrow right with the seed when the option exists.

One other thought, applying a fungal inoculant on fungicide treated seed doesn’t seem like the brightest idea under the sun. We know the crop does benefit because this is a (surprisingly) common combination. How much bigger might the benefits be if the fungicide was removed and the beneficial fungi permitted to flourish.

2020-03-16T13:53:28-05:00January 13th, 2020|Tags: , |
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