Developing a Management Plan for Reducing Thrips-induced Damage on Timothy Hay

Project Overview

Project Type: Graduate Student
Funds awarded in 2006: $10,000.00
Projected End Date: 12/31/2008
Grant Recipient: University of California, Davis
Region: Western
State: California
Graduate Student:
Major Professor:
Larry Godfrey
University of California, Davis
Major Professor:
Daniel Marcum
University of California

Annual Reports


  • Agronomic: general hay and forage crops, grass (misc. perennial), hay


  • Animal Production: feed/forage
  • Crop Production: application rate management
  • Education and Training: extension, on-farm/ranch research
  • Farm Business Management: budgets/cost and returns
  • Pest Management: biorational pesticides, chemical control, economic threshold, field monitoring/scouting, integrated pest management


    Timothy is one of the most important cool season grasses grown for hay. Thrips have recently been implicated in reducing hay quality. Producers have management options primarily limited to chemicals. Integrated pest management (IPM) issues such as sampling, basic ecology, economic threshold levels had not previously been studied in timothy. Sampling protocols and population dynamics were evaluated and a preliminary damage threshold was established in cooperation a local farm advisor and producers to establish an IPM program in California. This research, in combination with ongoing efforts, will improve the economic and environmental benefits of growing timothy in a sustainable system.


    Timothy (Phleum pratense L.) is a cool-season grass grown as a forage crop in the United States. Most timothy grass in California is grown perennially for hay production in the Intermountain areas above 900 m elevation. Because it is a high-value forage, it is grown with agrichemical inputs and it must be irrigated during the dry summer in California. In 2007, California retail prices for alfalfa hay fluctuated between $160 to $225 per ton, while prices for timothy remained consistent at $300 to $350 per ton (USDA AMS 2007). This hay has stable export markets, with a high demand in Japan, and stable domestic markets, with demands in natural beef (fed only grains and grasses) and horse (race and hobby) production.
    Timothy hay is largely purchased on aesthetic appearance. Visual appearance is considered the most important attribute for producers of timothy hay, followed by hay price (Curtis et al. 2007). “Brown leaf” is a condition that refers to dead leaves, usually in the lower canopy of timothy stands. These brown leaves are very obvious in a bale of hay, when compared to the rest of the green foliage, and cause a significant loss in marketability for the producer. Thrips have recently been implicated by producers as a major factor causing brown leaf and reducing yield in timothy hay and Anaphothrips obscurus Müller is the main thrips species found in California timothy (unpublished data). Other factors that may interact to cause brown leaf include mites (Tetranichidae and Eriophyidae), nutrient deficiency, especially nitrogen and potassium, seeding rates, plant senescence and disease.
    The grass thrips, Anaphothrips obscurus Müller, was first documented infesting fescue range grass in California by Bailey (1948). The resulting injury was referred to as “silver-top” (silvertop). In timothy, silvertop refers to A. obscusus-caused damage that occurs in the growing points of the plant, which can include dead or abnormal inflorescences and white patches on the leaves (Hinds 1900, Kamm 1971). In addition to silvertop, undesirable frass is left by the thrips on the leaves. Silvertop damage was insignificant in California, until 1999, following a mild winter. It has also been hypothesized that stress induced by thrips could be interacting with other factors to effect brown leaf in timothy.
    A. obscurus has a winged (macropterous) and non-winged (brachypterous) phenotype that has been studied in timothy and colonial bentgrass (Agrostis tennis Sibth. ‘Exeter’) and in both systems, macropterous phenotypes were more prevalent in the summer, when nights are shorter in the Northern Hemisphere (Köppä 1970, Kamm 1972). Kamm (1972) determined that photoperiod was one cue for phenotypic change in wing form, but other factors most likely influenced the dimorphism. Very limited pest management studies have been conducted in timothy. Hence, most basic arthropod ecology, including population dynamics, diversity, life histories, and biological control, is unknown. The need for such knowledge has increased with the demand for timothy hay, and the subsequent increase in acreage to meet this demand. For example, the number of timothy acres that were harvested in California increased by 46% from 1992 to 2002 (NASS 1997, 2002).
    Economic thresholds are defined as the pest density at which the cost of taking a pest control action equals that of the value of the crop loss. Establishment of economic thresholds is an important part of IPM, with over 100 economic thresholds published for arthropod pests in 43 commodities, as of 1993 (Peterson 1996). They provide a standard by which economically feasible treatment decisions can be made based on scientific data. Economic thresholds depend heavily on monitoring for both their establishment and implementation. Monitoring insect pests requires routine sampling. Because pests may be difficult to identify, spatially disparate, or cryptic, sampling may be time consuming, expensive and physically challenging (Norris et al. 2003). In addition, sampling methods measure pest density in different ways. Absolute sampling methods describe methods in which the target organism is measured by unit-area, whereas relative methods do not (Pedigo 1994). Hence, a realistic sampling regime must be established that is economically, practically feasible, and correlated to realistic pest densities in the field.
    There are no economic thresholds to indicate when thrips should be controlled. Although cultural controls such as field burning may control thrips (Hewitt 1914), it may decrease plant vigor if the timothy is not dormant when burned (Wasser 1982). Hence, the only options for managing arthropod pests in California timothy are the insecticides methidathion, cyfluthrin, and malathion. Long-term availability of methidathion is uncertain because it is registered under a special local needs label; moreover, both methidathion and malathion are organophosphate materials which are under regulatory scrutiny. Furthermore, in California, timothy treated with methidathion may only serve as horse feed. Because this thrips is multivoltine, with a short developmental time of 12-30 days (Hewitt 1914, Köppä 1970), malathion, which has a short residual period, is commonly applied 2 to 3 times more often than methidathion. This application frequency is economically and environmentally injurious and may lead to insecticide resistance.
    A pyrethroid was registered for use on grasses in California in September 2006 for armyworm control. This chemical was mainly used by growers in 2007 as another option for thrips management, but it is restricted to one application per year. Unfortunately, pyrethroid insecticides can flare Tetranychid mite populations (Reisig and Godfrey 2006, Godfrey unpublished data), but without sustainable control options, producers are forced to accept these unwanted consequences.

    Project objectives:

    Developing a management program to reduce brown leaf fits the goals of the Western SARE program. Our objectives included the development of sampling protocols for diagnostic evaluation of A. obscurus populations in timothy, correlating thrips numbers with damage, to establish an economic threshold, and studying some basic ecology (i.e. population dynamics) of this pest. We wanted to develop a sampling program that addressed Pedigo’s (1994) suggestions for choice of sampling technique and timing for thrips in timothy in California, USA. We restricted the sampling universe to timothy fields and did not directly address issues involving sample units, such as sample size, number, or collection pattern. In addition, we wanted to evaluate cost and precision in regards to sampling technique and timing. Finally, we wanted to study the impact of nutrient applications and plant density in regards to brown leaf, but we could not find a suitable location for this experiment. We hoped that studying thrips and correlating their levels to damage, that we could reveal one of the causes of brown leaf, enhancing grower knowledge. This will lead to more precise pest management methods and sustainable growing practices for timothy, increasing profits for growers, while protecting the environment.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.