Daniel B. Marcum

Thresholds, Injury, and Loss Relationships for Thrips in Phleum pratense (Poales: Poaceae)

ABSTRACT Timothy (Phleum pratense L.) is an important forage crop in many Western U.S. states. Marketing of timothy hay is primarily based on esthetics, and green color is an important attribute. The objective of these studies was to determine a relationship between arthropod populations, yield, and esthetic injury in timothy. Economic injury levels (EILs) and economic thresholds were calculated based on these relationships. Thrips (Thripidae) numbers were manipulated with insecticides in small plot studies in 2006, 2007, and 2008, although tetranychid mite levels were incidentally flared by cyfluthrin in some experiments. Arthropod population densities were determined weekly, and yield and esthetic injury were measured at each harvest. Effects of arthropods on timothy were assessed using multilinear regression. Producers were also surveyed to relate economic loss from leaf color to the injury ratings for use in establishing EILs. Thrips population levels were significantly related to yield loss in only one of nine experiments. Thrips population levels were significantly related to injury once before the first annual harvest and twice before the second. Thrips were the most important pest in these experiments, and they were more often related to esthetic injury rather than yield loss. EILs and economic thresholds for thrips population levels were established using esthetic injury data. These results document the first example of a significant relationship between arthropod pest population levels and economic yield and quality losses in timothy.

Spatial Dependence, Dispersion, and Sequential Sampling of Anaphothrips obscurus (Thysanoptera: Thripidae) in Timothy

ABSTRACT The spatial distribution and dispersion of Anaphothrips obscuras (Müller) (Thysanoptera: Thripidae) was examined with the goal of establishing a sequential sampling plan for this pest in timothy, Phleum pratense L. (Poaceae). Approximately 16 different California timothy fields were sampled twice yearly from 2006 to 2008 using direct observation and the beat cup method. For direct observation, the number of thrips on each leaf of the plant was counted. For the beat cup method, tillers were tapped into a cup and dislodged thrips were counted. Samples were separated by ∼3 m in 2006 and 2007 and exactly 3 m in 2008. Spatial autocorrelation of intrafield population distribution was tested for significance in 2008 using Morans I, but autocorrelation was not detected. The population dispersion was assessed by Taylors power law and was determined to be aggregated and density-dependent. Intraplant population dispersion and distribution for each year were also evaluated for adults, larvae, and total thrips. All lifestages were highly spatially dependent and more thrips were found near the top of the plant than the bottom. Direct observation proved to be a more accurate and precise method than the beat cup method, especially when thrips abundances were greater than one. However, the number of samples required to provide an accurate level of precision was unrealistic for both methods. A sequential sampling plan was evaluated, but was not practical for the beat cup method because few thrips were found using this method. Because there was no spatial autocorrelation at sampling distances of 3 m, samples can be taken at intervals at 3 m to obtain spatially independent population abundance estimates.

Grass Thrips (Anaphothrips obscurus) (Thysanoptera: Thripidae) Population Dynamics and Sampling Method Comparison in Timothy

ABSTRACT Sampling studies were conducted on grass thrips, Anaphothrips obscurus (Müller) (Thysanoptera: Thripidae), in timothy, Phleum pratense L. These studies were used to compare the occurrence of brachypterous and macropterous thrips across sampling methods, seasons, and time of day. Information about the population dynamics of this thrips was also revealed. Three absolute and two relative methods were tested at three different dates within a season and three different daily times during four harvest periods. Thrips were counted and different phenotypes were recorded from one of the absolute methods. Absolute methods were the most similar to one another over time of day and within seasonal dates. Relative methods varied in assessing thrips population dynamics over time of day and within seasonal dates. Based on thrips collected from the plant and sticky card counts, macropterous individuals increased in the spring and summer. Thrips aerially dispersed in the summer. An absolute method, the beat cup method (rapping timothy inside a plastic cup), was among the least variable sampling methods and was faster than direct observations. These findings parallel other studies, documenting the commonality of diel and diurnal effects on sampled arthropod abundance and the seasonal effects on population abundance and structure. These studies also demonstrate that estimated population abundance can be markedly affected by temporal patterns as well as shifting adult phenotypes.

Binomial and Enumerative Sampling of Tetranychus urticae (Acari: Tetranychidae) on Peppermint in California

ABSTRACT The two-spotted spider mite, Tetranychus urticae Koch, is an economic pest on peppermint [Mentha x piperita (L.), ‘Black Mitcham’ grown in California. A sampling plan for T. urticae was developed under Pacific Northwest conditions in the early 1980s and has been used by California growers since ≈1998. This sampling plan, however, is cumbersome and a poor predictor of T. urticae densities in California. Between June and August, the numbers of immature and adult T. urticae were counted on leaves at three commercial peppermint fields (sites) in 2010 and a single field in 2011. In each of seven locations per site, 45 leaves were sampled, that is, 9 leaves per five stems. Leaf samples were stratified by collecting three leaves from the top, middle, and bottom strata per stem. The on-plant distribution of T. urticae did not significantly differ among the stem strata through the growing season. Binomial and enumerative sampling plans were developed using generic Taylors power law coefficient values. The best fit of our data for binomial sampling occurred using a tally threshold of T = 0. The optimum number of leaves required for T. urticae at the critical density of five mites per leaf was 20 for the binomial and 23 for the enumerative sampling plans, respectively. Sampling models were validated using Resampling for Validation of Sampling Plan Software.

Plant quality and conspecific density effects on Anaphothrips obscurus (Thysanoptera: Thripidae) wing diphenism and population ecology.

ABSTRACT Factors that influence thysanopteran wing diphenism are not well known. In these studies, the impact of food quality, mediated through nitrogen addition, and conspecific density was explored on the wing diphenism of an herbivorous thrips species (Anaphothrips obscurus Müller) (Thysanoptera: Thripidae). In the first study, nitrogen was added to timothy grass (Phleum pretense L.) (Poales: Poaceae) transplants, and naturally occurring thrips populations were caged on the plants. Thrips abundance and foliar nutrients were assessed every 2 wk. A separate factorial experiment in growth chambers explored the impact of both plant nitrogen addition and thrips abundance on wing diphenism. Thrips density was manipulated by adding either 3 or 40 thrips to potted and caged timothy. Thrips abundance and foliar nutrients were measured 58 d after treatment placement. Plant quality directly affected thrips wing diphenism independent of thrips density in both experiments. Near the end of the field cage experiment, density may have indirectly impacted wing diphenism. In both experiments, plant quality and thrips density interacted to affect thrips population abundance. Plant quality alone can affect thrips wing diphenism, but it remains unclear whether density alone can affect thrips wing diphenism. This is a unique and understudied system that will be useful to examine generalized theories on the negative interaction between reproduction and dispersal.

Assessing Nitrogen Fertilization Needs for Irrigated Orchardgrass in the Intermountain Region of California

Nitrogen fertilization is a critical component of maximizing yield for grass hay production. However, the steady increase in fertilizer price along with concerns for off-site N movement make prudent use of N important. On-farm studies in northeastern California were conducted in irrigated orchardgrass to examine the influence N fertilizer rates and application times have on forage yield, forage quality, soil nitrate, and economics for retail hay. N rates up to 400 lb/acre increased annual yield and net return in a three-cut system. N fertilizer also increased crude protein. Applying fertilizer in split applications gave higher yield, crude protein, and economic return for second and third cut compared to a single fertilizer application at grass green-up. Apparent N recovery decreased with increasing fertilizer rate and ranged from 80 to 38%. N fertilizer did not influence forage neutral detergent fiber. At the highest N fertilizer rates, forage NO3-N at first and second-cut was above 1500 ppm. Fertilizing with N at 600 lb/acre/season elevated fall soil NO3-N at the 24 to 36-inch soil depth compared to the control at multiple sites. Split applications of N fertilizer are imperative to maximize yield, crude protein, and economic return, but excessive N fertilization can increase the likelihood of high forage nitrate and nitrate accumulation below the root zone. Introduction Orchardgrass (Dactylis glomerata) is a popular irrigated grass species grown in the intermountain region of California. Orchardgrass is desired for hay, and it produces high quality forage with proper irrigation and fertilization. Most intermountain orchardgrass fields are managed with efficient irrigation systems (center-pivot, wheel-line, or laser-leveled flood) and cut for hay three times per season. Grass hay prices are high — hay for horses often brings a price greater than dairy-quality alfalfa (4) — making grass hay more valuable than pasture. With high fuel, fertilizer, and energy costs, producers must maximize yield and production efficiency to be Fig. 1. Unfertilized orchardgrass (right) and orchardgrass fertilized with 100 lb N per acre at grass green-up (left) at first-cut harvest. 18 June 2008 Forage and Grazinglands profitable (2). N fertilization is necessary to obtain high grass yields, but applying too much or too little N has negative economic or environmental consequences. Several studies have examined N fertilization of cool-season perennial grasses (2,3,8,10). These studies showed that forage yield increases with increasing N rate, but apparent N recovery (ANR) decreases with high N rates. They also found split applications of N usually produce higher yields compared to applying all the N in early spring. Discrepancies between published studies emerge with optimal N fertilization rates, application timings, and ANR and are likely the result of differences in climate, soil, and management between experiments (9). Management practices, cutting schedules, economics, and soils in the intermountain region of California differ greatly from previous N fertilization research published in the literature, especially since many of these studies were conducted under rain-fed systems east of the Mississippi. Thus, our objective was to determine the optimum N fertilization rate and timing to maximize yield, N use efficiency (NUE), ANR, and returns for orchardgrass grown for retail hay in the intermountain region of California. N Fertilization Study The study was conducted at four orchardgrass sites (McArthur, Ft. Jones, Doyle, and Lookout) in 2005 and two orchardgrass sites (Montague and Susanville) in 2006. Sites’ soil and climate attributes are shown in Table 1. The experiment at every site was a completely random design with 4 replicates and 8 N fertilization treatments. Plot size was 20 by 20 ft. Soil samples were collected at each site before initiating the experiment, and sites were fertilized with phosphorus, sulfur, or potassium if the pre-treatment soil test suggested a deficiency. Watermark soil moisture sensors (Irrometer Co., Riverside, CA) were buried at an 8-inch depth at all sites before N treatments were applied to measure soil moisture throughout the growing season. Table 1. Site soil and climate attributes. N treatments were applied by hand in the form of urea (46-0-0) at the rates listed in Table 2. Treatments totaled 100, 200, 300, 400, or 600 lb of N per acre for the entire season. N application rates at grass green-up in March were 0, 100, 200, or 300 lb/acre. Split application rates after first and second cutting were 0, 50, 100, or 200 lb/acre and were applied immediately before the first Site Soil type Mean annual temperature (°F) Mean annual precipitation (inches) Elevation (feet) Doyle Calpine sandy loam Aridic Haploxerolls 50.6 11.4 4275 Ft. Jones Stoner gravelly sandy loam coarse-loamy, mixed, active, mesic Typic Haploxerepts 50.5 20.6 2747 Lookout Modoc sandy loammesic Vitritorrandic Durixerolls 48.5 15.8 4144 McArthur Esperanza loam fine, smectitic, mesic Pachic Argixerolls 50.6 19.1 3311 Montague Montague clay fine, montmorillonitic, mesic Typic Chromoxererts 51.7 19.5 2634 Susanville Mottsville gravelly loamy course sand mixed, mesic, Torripsammentic Haploxeroll 49.4 14.3 4258 18 June 2008 Forage and Grazinglands irrigation after first and/or second harvest. All fertilizer applications were incorporated into the soil with rainfall or irrigation ≥ 0.5 inch within one to two days of application. The first harvest occurred when grasses were in the flowering stage, and the second and third harvest occurred 40 to 50 days after the previous cutting. Drought stress occurred in mid-summer at the Doyle, Lookout, and Ft. Jones sites in 2005. Therefore, the crop at these sites was only harvested twice, once at flowering and again in early fall. Yield was measured by harvesting a 3by 20-ft strip at a 3-inch stubble height from each plot with a Carter Harvester (Carter Mfg. Co. Inc., Brookston, IN). Forage samples were oven-dried at 140°F for dry matter (DM) determination and forage quality analysis. Dried forage samples were analyzed for total extractable nitrate N (NO3-N), total N (N), total crude protein (CP) and neutral detergent fiber (NDF) using University of California ANR Analytical Lab preparation and analyses methods (UC ANR Analytical Lab, Davis, CA) (7). In the fall after the last cutting, soil was sampled for NO3-N at three depths: 0 to 12 inches, 12 to 24 inches, and 24 to 36 inches. Soil cores were taken from 10 random locations in each plot for three fertilization treatments (unfertilized, 100-100-100, and 200-200-200). Soil was air-dried and analyzed for NO3-N using University of California ANR Analytical Lab methods (UC ANR Analytical Lab, Davis, CA). Yield, forage quality, and soil nitrate data were analyzed by analysis of variance (ANOVA) followed by a comparison of treatment means using Fischer’s least significant difference (LSD) at P ≤ 0.05. Regression analysis was used to determine the relationship between first-cutting yield and N fertilizer rate applied in early spring (SAS Institute Inc., Cary, NC). Site data were pooled for analysis if a site by treatment interaction was not significant at P ≤ 0.05. Influence on Forage Dry Matter Yield and NUE Both N fertilizer rate and application timing had a significant effect on orchardgrass yield (Table 2). First-cut harvest produced more forage than secondor third-cut harvest (Table 2). First-cut orchardgrass yield increased rapidly from 0 to 100 lb N per acre, however the yield response diminished at rates above 100 lb N per acre (Fig. 1). At the moisture-stressed 2-cut sites, orchardgrass yield almost doubled from 0 to 100 lb N per acre, but the yield increase from fertilization lessened from 100 to 200 lb N per acre, and leveled off at fertilizer rates above 200 lb N per acre (Fig. 1). At 3-cut sites, the relationship between first-cut yield and fertilizer was similar to 2-cut sites, but yield at 3-cut sites increased slightly from 200 to 300 lb N per acre (Fig. 1). Applying N fertilizer in split applications produced higher secondand thirdcut yield compared to applying all N at grass green-up (Table 2). Second-cut yield was 0.26 to 0.66 ton/acre higher if fertilizer was applied at 100 lb N per acre in early spring and 100 lb N per acre after first cutting (100-100) compared to 200 lb N per acre in early spring (200-0) (Table 2). Second-cut yield was 0.15 to 0.78 ton/acre higher if fertilizer was applied at 200-100 compared to 300-0 (Table 2). Split applications of N fertilizer were essential for increasing third-cut yield. Even at the highest single N rate (300 lb/acre), yield did not differ from the unfertilized plots if fertilizer was only applied in early spring (Table 2). In contrast, applying fertilizer in split applications at 100-50-50, 100-100-100, or 200-100-100 increased third-cut yield by at least 190% compared to unfertilized plots (Table 2). 18 June 2008 Forage and Grazinglands Table 2. The effect of nitrogen rate and application time on orchardgrass yield and nitrogen use efficiency. x N use efficiency represents lbs of additional forage for each lb of applied N. It was calculated as [(total yield at Nx – total yield at N0) * 2000 ÷ lb N per acre applied at Nx], where x = N rate > 0. y N fertilizer treatments shown as lb of N per acre applied: at spring green-up – after first cut – after second cut. Orchardgrass sites 100% Dry matter yield (tons/acre) N use efficiencyx (lbs) 1st cut 2nd cut 3rd cut Total 2-cut 0-0y 1.51 0.88 2.39 100-0 2.71 1.11 3.82 29 100-50 2.75 1.68 4.43 27 200-0 3.05 1.50 4.55 22 100-100 2.82 1.96 4.78 24 300-0 3.13 1.66 4.79 16 200-100 3.13 2.15 5.28 20 200-200 3.08 2.27 5.36 15 LSD (P = 0.05) 0.27 0.28 0.42 4 3-cut 0-0-0 1.93 0.91 0.41 3.26 100-0-0 3.22 1.31 0.54 5.08 35 100-50-50 3.29 1.77 1.22 6.28 30 200-0-0 3.42 1.29 0.49 5.20 18 100-100-100 3.25 1.95 1.37 6.58 22 300-0-0 3.86 1.37 0.55 5.78 17 200-100-

First report of damping-off of wild rice in California caused by Pythium torulosum.

During 1994, damping-off of wild rice (Zizania palustris L.) in a single field in eastern Shasta County, CA resulted in near total stand failure. Since then, the disease was observed in at least 11 other fields with varying levels of stand loss. In all cases, the affected wild rice was grown as a volunteer crop following one or more years of wild rice production. Symptoms included a dark red discoloration and necrosis of the primary root followed by seedling death. When the red discoloration was limited to secondary roots, the plants often survived. Pythium torulosum, readily recovered from symptomatic roots by isolation on PARP media, was identified by morphological structures produced on grass blades in water (homothallic with smooth-walled oogonia, plerotic oospores, monoclinous antheridia, and inflated filamentous sporangia) and a 99.2% internal transcribed spacer sequence similarity of the rDNA (1). To complete Kochs postulates, inoculum of two isolates of P. torulosum grown on moistened cornmeal/sand (2%/98% [v/v]) for 3 weeks at 25°C were combined and mixed into sterilized sandy loam soil at a rate of 30 cm3 inoculum per liter of soil. Sterilized noninfested soil was used as a control treatment. Twenty wild rice seeds (cv. Franklin) were sown in each of four replicate 20-cm-diameter pots in each treatment. Plants were submerged in water and maintained in a greenhouse at 18 to 25°C. After 8 weeks, plants stands were reduced 50% in infested pots; dry weights of infected plants were reduced by 45% relative to the controls. The fungus was reisolated from symptomatic plants but not from the plants grown in noninfested soil. The experiment was repeated with similar results. To our knowledge, this is the first report of damping-off of wild rice caused by P. torulosum. Reference: (1) C. A. Levesque and W. A. M. DeCock. Mycol. Res. 108:1363, 2004.

Biology of Mint Root Borer (Lepidoptera: Crambidae) and Control Options on California Peppermint

Mint root borer, Fumibotys fumalis (Guenee), larvae cause damage to peppermint by feeding on rhizomes belowground. This species can cause significant economic damage and occurs throughout all peppermint-growing regions in Washington, Oregon, Idaho, and California. Until 2009, managing economic populations was limited to fall or spring tilling, and postharvest application of the organophosphate insecticide, Lorsban. The recent registration in California of the reduced risk insecticides chlorantraniliprole, indoxacarb, methoxyfenozide, and spinetoram on peppermint potentially improves management tactics by including preharvest applications. A degree-day model, available through the Oregon State University, Integrated Plant Protection Center (OSU IPPC), provides information that could be used for applying preharvest insecticides targeting vulnerable life stages. In 2010 and 2011, large delta sticky traps baited with mint root borer sex pheromone were placed in commercial peppermint fields in Shasta and Siskiyou counties and used to validate the OSU IPPC model under California conditions. Moth capture data indicated that the OSU IPPC model did not provide a reliable prediction of emergence, peak flight, and 90% flight. In 2010, observed peak flight varied 10-25 days earlier than predicted by the OSU IPPC model. Observed 90% flight occurred ∼2 weeks earlier than predicted in Shasta County and nearly 1 month earlier than predicted in Siskiyou County during 2010 and 2011, respectively.