Drought Affects Seed Size and Your Novel Endophyte Tall Fescue Renovation Practices

The impact of the drought and heat conditions on seed production in Oregon’s Willamette Valley was outlined in a report written by Drew Denman on July 15.  Drew pointed out that seed production in 2021 will be reduced by 40-50% as a result of the climatic conditions.  Reduced seed yield raises concerns beyond the availability of seed.  Seed size is also impacted by the drought conditions during seed production in Oregon.  One of the major impacts that poor growing conditions have on seed production is seed size.  A common measurement of grass seed size is called the “Thousand Seed Weight”, which is as the name implies, the weight in grams of 1000 seed from a seed lot. I selected five random seed lots that were submitted for quality analysis (endophyte and ergot alkaloid presence) for 2021 and retrieved the corresponding seed from those varieties that were harvested in 2020.  These seed comparisons were from different varieties and different companies, but the identity of each has been kept anonymous.  The data for the samples is in table 1.  On average the seed size of the seed harvested in 2021 is 13% smaller than the seed harvested in 2020.  So, what are the implications of having smaller seed on seed quality and agronomic practices?  Issues that you may have questions about are outlined below with explanations and suggestions for your cultural practices.

Seed Quality:  Seed quality is of major concern because it can be the determining factor as to whether you will have a successful stand following your renovation process.  The major issues that are important to the novel endophyte seed industry are endophyte presence, zero ergot alkaloids in those seed (the novel trait), seed size, germination, seedling vigor, and their implications towards a successful stand establishment.  There is some good news and not-so-good news on drought impact on novel endophyte tall fescue seed quality. 

  • The good news:
    • Drought and heat generally do not have an impact on the germination rates of the seed (1).  Therefore, seed viability is not changed by conditions experienced in the Willamette Valley this year.
    • Drought and heat can often increase the amount of dormancy in seed (2).  This means that some seed will germinate after sowing while others will germinate later after sowing.  This is a strategy plants use to hedge against the possibility of having temporary favorable conditions for establishment only to be followed by poor conditions that might prove lethal to establishing seedling plants.  Thus, dormancy can be a good trait for the seed to have to hedge against poor establishment conditions.  
    • Presence of endophyte and ergot alkaloids in the novel tall fescue varieties are remaining true to form.  Endophyte levels are testing the same in the 2021 seed as they did in the 2020 seed.  Novel varieties are maintaining their alkaloid-free trait in 2021.
    • Effective seeding rates are higher when seed are smaller.  While your seeding rate is based upon a rate of pounds per acre, your effective seed rate (number of seeds per acre) increases because there are more seed per pound.  On average, seed in 2021 will be planting 13% more seed per acre than seed from 2020.  For example, on average seed from 2020 planted at 12 lbs/A would result in approximately 51 seeds per ft2, while seed from 2021 planted at the same rate would result in 58 seeds per ft2.(3) This might seem trivial, but the result is an extra 305,000 seeds per acre!
  • The not so good news:
    • Small seed generally are not as vigorous as large seed (3).  Seed have two major physiological structures – the embryo and the endosperm.  The embryo is the portion which will eventually develop into a plant, and the endosperm is the part of the seed that stores the energy that will drive germination and early seedling growth.  The picture below illustrates the structures of a grass seed (caryopsis). Note the size of the endosperm relative to the embryo.

During seed production, the size of the embryo is not affected by drought as much as the endosperm.  Thus, there is less energy in smaller seeds to drive the seedling development and the energy supply runs out faster than in larger seed.  This means that the seedling plant becomes totally dependent upon photosynthesis earlier during seedling development than seedling plants from larger seed, which continue to get energy from the endosperm.  Seedling plants with lower vigor are more susceptible to death resulting from unfavorable environmental conditions than more vigorous plants.  Fortunately, germination dormancy and increased effective seeding rates are hedges against stand failure.

Impact of Small Seed on Agronomic Practices:  The physical and biological characteristics of small seed can dramatically impact success in the renovation/establishment phase.  Thus, it is important to pay attention to detail and use sound practices to provide the greatest probability of success.  Items that you want to pay close attention to are:

  1. Weed control.  Smaller seeds that portend plants with reduced vigor are less competitive with other plant species than seedling plants from larger seed.  Thus, make sure you follow good weed control practices and establish your Novel endophyte tall fescue into to a weed-free environment.  If you are planting using no-till practices, follow re-entry restrictions on herbicide labels but seed as soon as possible once those re-entry periods have passed.  Time your herbicide application so climatic and soil conditions are good for tall fescue establishment.  If you use tillage, time Novel endophyte planting as soon as possible following your last seedbed preparation step.  Remember, it is not just the germinated weeds that you contend with because if there are germinated weeds there is an abundance of other weed seed that have begun the germination process and will have a head start on the seedling plants you are trying to establish.  Weed control is easier on the front end of planting than once the tall fescue seed has started to germinate.
  2. Equipment Calibration.  Small seed flow through planting equipment much easier than large seed.  Using charts to set equipment for seeding is only a starting point for planting.  It is HIGHLY LIKELY that if you use a chart and do not calibrate your planting equipment that you will over-plant and you will run out of seed before you finish your acreage.  Chris Teutsch, at the University of Kentucky, has an excellent video on grain drill calibration that will assist you in performing that step on your equipment.  Follow this link (https://grazer.ca.uky.edu/file/grain-drill-calibration) for that presentation.  Make sure the depth of your planter is also adjusted properly as small seeded crops are sensitive to depth of placement in the soil.  If planted too deep they will either a) not get the proper light signals to germinate, or b) germinate but run out of stored energy reserves (from the endosperm) before the developing plants are able to survive from their own photosynthesis.


  1. McDonald, Miller B. and Lawrence Copeland. Seed Production: Principles and Practices.  Chapman and Hall Publishers, New York.
  2. Copeland, Larry O. and Miller B. McDonald. Seed Science and Technology. (3rd ed). Chapman and Hall Publishers, New York.
  3. Buckner, Robert C. and Lowell P. Bush. Tall Fescue. American Society of Agronomy, Madison, WI.

~ Nick Hill, Agrinostics Ltd. Co.

The Alliance for Grassland Renewal is a national organization focused on enhancing the appropriate adoption of novel endophyte tall fescue technology through education, incentives, self-regulation and promotion.  For more resources or to learn more about the Alliance for Grassland Renewal, go to www.grasslandrenewal.org

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