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

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

Summary

Project goals reached in 2006-2007 involved identification of sampling protocols for diagnostic evaluation of thrips, viz. Anaphothrips obscurus, populations in timothy, thrips ecology, correlating thrips and Tetranychid mite numbers with damage for an economic threshold, and exploring field burning as an alternative management practice to reduce thrips levels. Winged thrips are formed in the spring and summer and disperse in the summer and fall before the timothy is harvested; reduced-winged forms most likely overwinter in the fields. Monitoring untreated grower fields elucidated thrips population dynamics, and another thrips species, Frankliniella occidentalis, was found when the timothy flowered.

Objectives/Performance Targets

My objectives listed in the proposal included the development of sampling protocols for diagnostic evaluation of A. obscurus populations in timothy, correlating thrips numbers with damage, and studying some basic ecology of this pest. I wished to reveal the causes of brown leaf by studying thrips, nutrient applications, and plant density, to enhance grower knowledge. I also hoped that this would lead to more precise nutrient and pesticide applications and sustainable growing practices for timothy, increasing profits for growers, while protecting the environment.

Accomplishments/Milestones

In 2006-2007, although several candidate fields were analyzed for nutrient deficiency, we could not find a suitable location for a study that would incorporate nutrient application and plant density because none of the candidate fields were nutrient deficient. Hence, we shifted the project goals from this objective to a magnified focus on population dynamics and wing polymorphism, alternative control measures, such as burning, and development of an economic threshold.
In 2006-2007, we were able to develop and identify sampling protocols for A. obscurus. As an added benefit, the exploration of these methods revealed some of the basic ecology of this pest in the form of wing polymorphism and population dynamics. We found that the beat cup method, which involves beating timothy within a cup and counting the dislodged thrips, was a quick, consistent, and cost effective sampling method in comparison to other absolute counting methods, such as direct observation and tiller washing. We will repeat this experiment in spring 2008 to have a full two years of data for publication.
In addition, this method was consistent across different fields in 2006. We tested the beat cup method against direct observation across 16 grower fields on two sampling dates. The coefficient of variations for each method were calculated for each field on each date and were not significantly different from one another (F= 0.00; df= 1, 45; P = 0.9526). This experiment was repeated in 2007, but data have not been analyzed.
We also found that winged thrips are formed in the spring and summer and disperse in the summer and fall before the timothy is harvested. We knew that winged forms were dispersing in the summer and fall because we caught more thrips on sticky cards as the timothy matured. Sticky cards were placed xx inches above the canopy and as such captured only winged thrips. Finally, reduced-winged forms most likely overwinter in the fields, because no winged forms are found in the fields until late spring.
We successfully manipulated a range of thrips populations using pesticides in plot studies in both 2006 and 2007. We found that some chemical management for thrips may flare Tetranychid mite levels. The highest mite levels that we observed impacted yield, but thrips never impacted yield. Both thrips and mites significantly affected timothy hay qualtiy. Work remains to correlate these damage levels to economic threshold levels. When this is accomplished, growers can decide if treatment is justified.
In addition, we established plot studies in two fields in 2007 to see if burning could reduce thrips levels. One field had low thrips levels and no thrips were found in plots two weeks after burning. There were <1 thrips per plot in unburned plots. The other field had higher thrips levels, and there were significantly lower thrips in burned versus unburned plots (F= 25.99; df= 1, 38; P = <0.0001) two weeks after burning. This study will be repeated in 2008 to see if burning can be used as an alternative management tactic to chemical applications.
Finally, we monitored untreated grower fields in 2006-07 to study thrips population dynamics. Adult thrips were keyed to species, but only the 2006 data have been analyzed. We found that thrips population levels varied throughout 2006, with the first generation of nymphs hatching from eggs in late spring. Moreover, we found that another thrips species, Frankliniella occidentalis, co-occurs with A. obscurus around the time that timothy flowers. This leads us to believe that F. occidentalis may be feeding on timothy pollen.

Impacts and Contributions/Outcomes

Basic ecology of thrips is unknown in timothy. It is important for growers to understand the dynamics of thrips populations in their fields so that they can predict what will happen with more certainty. This research provides producers of timothy hay in the intermountain region of California with important knowledge regarding arthropod management. For example, a new chemical was registered for use on timothy in 2007, which was targeted at thrips management. Our research, in 2006, incorporated this chemical in experiments manipulating thrips levels for establishing an economic threshold. We discovered that this chemical could flare Tetranychid mite populations and informed growers of this unwanted consequence in winter 2007. It is hard to estimate what positive impact this information may have had, but Tetranychid mite problems were not widespread in timothy in 2007.
Finally, sampling methods are a cornerstone of a sustainable pest management program. Producers must have consistent and inexpensive ways to measure pest levels. This is why we have focused on this as an integral part of our research. Furthermore, once an economic threshold is established, growers can judiciously weigh treatment options and may be able to avoid chemical treatment. We are also trying to develop field burning as an alternative method to chemical control. Hopefully, this can lead to a more sustainable timothy production system.