Thomas G. Chastain

An often asked question is whether there is a benefit to application of irrigation in late summer or early fall (mid-August until the end of September) in grass seed crops such as perennial ryegrass and tall fescue in the Willamette Valley.  Our  research and extension team in seed crops conducted studies over a broad range of years to determine whether irrigation in this period is helpful for these seed crops.

Big gun
Big gun style irrigation system in grass seed field (TG Chastain photo)

Some of our perennial ryegrass work was done in the very dry years of the early 1990s. Those years were as dry as our recent multi-year drought in western Oregon. What we found was that in two cultivars of perennial ryegrass, there was no effect of 2 inches of irrigation water in August and September on seed yield over a three-year period.

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Thomas G. Chastain

Here’s a new article from our seed production research and extension team on spring nitrogen and seed yield in winter canola.  Field trials were conducted in the Willamette Valley over a 3-year period at OSU’s Hyslop Farm.  This work was led by Brock Ferguson and is the first study to be published on winter canola in the seasonally wet environment of western Oregon.

Winter canola flowers and buds (TG Chastain photo)
Winter canola flowers and buds (TG Chastain photo)

This article appears in the most recent issue of Agronomy Journal and can be found at the link below:

Ferguson, B.T., T.G. Chastain, C.J. Garbacik, B.T. Chastain, and D.J. Wysocki. 2016. Spring nitrogen and cultivar affect seed production in winter canola (Brassica napus L.). Agron. J. 108:1124-1131.

Key findings of the article:

  • Spring nitrogen increased seed and oil yield in winter canola except when the crop was lodged as a result of high spring rainfall.
  • Seeds m-2 was the most influential factor in determining seed yield in winter canola.
  • Seed oil content was high but was inversely related to the rate of spring N applied.
  • Seed yield and oil yield were maximized at 100 lbs N/acre while minimizing lodging losses.


Thomas G. Chastain

The Willamette Valley does not expect much rain during harvest of grass seed crops.  The production practices for grass seed crops in the region have evolved to take advantage of the dry conditions that are prevalent during harvest.  But when rain falls during the harvest season, questions arise regarding the effects of this late precipitation on seed yield and quality of grass seed crops.

Seed Field
Aerial view of windrow harvested Willamette Valley grass seed field.

For grass seed crops that are at the pre-harvest stage during precipitation events, rain is usually not a problem and even after the crop is cut, the worst consequence is that the crop will take more time to dry down to reach combine seed moisture in the swath.  However, if the delay in drying is too long, grass blades can grow up and through the swath making combining operations difficult.  Tall fescue seems to be particularly problematic with regard to post-swathing leaf growth.  When grass blades grow back up through the swath, some farmers recut the swath to facilitate combine harvesting but some seed losses can be expected in this operation due to shattering.  If the crop is swathed onto wet soil and remains there for an extended period, there can be some losses in yield and quality as a result of the action of fungi and other pests.

The potential for damage to seed crop yield and quality is dependent on the intensity and duration of rainfall.  Excessive rain after the grass seed crop is swathed can be a problem, especially in July and early August (for later maturing crops).  First, the action of the falling rain in some circumstances can be sufficient to cause shatter losses of seed in the swath.  Secondly, if rain is persistent and is accompanied by high humidity, then seed can sprout, thereby reducing the quality and marketability of the seed.  These late season high rainfall events are not very common and that is why the seed industry has few artificial drying facilities in the region.  Pre-harvest sprouting of grass seed was observed in the Willamette Valley in 1983 and again in 1993.  Light rainfall after swathing of the crop is not generally a problem.

Thomas G. Chastain

In order to maximize harvest efficiency and seed yield, using the appropriate timing for harvest is essential. Seed moisture content is the most reliable indicator of seed maturity and harvest timing in grass seed crops.

Since pollination and seed maturation are not uniform processes in grass seed crops, a range of seed maturity can be found in a single field. Harvesting within the correct range of seed moisture contents will maximize seed yield and minimize losses of seed during harvest. Seed moisture content is also an important factor in the storage of harvested seed. High seed moisture content reduces longevity of seed in storage and reduces seed quality.

To optimize the timing to swath grass seed crops and to maximize the quantity of seed harvested, seed growers must balance cutting late-maturing seeds too early with cutting early-maturing seeds too late. Cutting too early at high seed moisture content shortens the seed fill period leading to immature seed and reduced seed size or weight. Cutting too late at low seed moisture content can reduce yield as a result of seed shattering losses.

The table below shows the seed moisture content range recommended for swathing of grass seed crops:


Recommended seed moisture for swathing (%)

Moisture loss per day (%)

Annual ryegrass






Tall Fescue (forage)



Tall Fescue (turf)



Perennial ryegrass



Chewings fescue



Creeping red fescue



Kentucky bluegrass



Illustrated instructions on how to conduct a seed moisture test in grass seed crops and guidelines for seed moisture contents for best harvest efficiency can be found in OSU’s publication EM 9012. Here’s a link to the publication:

Using Seed Moisture as a Harvest Management Tool

A video showing step by step instructions on collecting seed and methods to test moisture content of seed is linked below:

Seed moisture and harvest video

Oregon State University is offering an online course (CROP 460/560) in seed production starting in September 2016.  This course is the online version of OSU’s long running seed production course but is now being made available to a wider audience via OSU’s Ecampus electronic delivery program.

OSU Ecampus Photo The Ecampus seed production course has been developed in cooperation with Alyssa DuVal, a colleague and former graduate student in OSU’s Department of Crop and Soil Science.  The course is split into two units – the first addresses seed production as a genetic delivery system, biological principles of seed production, seed production economics, seed conditioning, and other topics.  The second unit covers management practices and methodologies for producing a variety of seed crops ranging from grasses and forage legumes to vegetables and native plants.

The seed production course is open to both undergraduate (CROP 460) and graduate (CROP 560) students.  The course runs from September through December 2016.

For more information on the undergraduate and graduate courses follow the links below:

CROP 460 Seed Production

CROP 560 Seed Production

More information about Oregon State University’s Ecampus course offerings can be found at this link:

OSU Ecampus