Control of grassy weeds in annual canarygrass

There are currently no herbicides registered in Argentina for the selective control of grassy weeds in annual canarygrass (Phalaris canariensis L.). The principal grassy weeds are darnel ryegrass (Lolium temulentum L.) and wild oats (Avena fatua L.), which cause grain yield and quality losses. The potential of diclofop-methyl and clordinafop-propargyl for their control was assessed through greenhouse and field trials, in which crop phytotoxicity and weed control efficacy were evaluated. It was found that (i) field application of clordinafop-propargyl resulted in severe crop damage, except for low doses that did not affect the species to be controlled; (ii) although field application of diclofop-methyl resulted in a certain degree of phytotoxicity on wild oats, these effects were insufficient for efficacious control; and (iii) field and greenhouse application of diclofop-methyl between 200 and 500 g a.i. ha⁻¹ revealed differences between crop sensitivity and that of darnel ryegrass. In this range, crop phytotoxicity in the greenhouse was less than 20% compared to more than 60% in the weed, and in the field only slight crop phytotoxicity symptoms were observed. As in the greenhouse, field application resulted in significant phytotoxic effects upon darnel ryegrass, high efficacy levels, a low survival rate amongst treated plants and a notable reduction in seed production by surviving plants. Only the highest dose (500 g a.i. ha⁻¹) in one of the field trials resulted in a significant reduction in crop grain yield. Hence diclofop-methyl application appears to offer a promising means for controlling darnel ryegrass.     

A comparison of insecticide treatments for the control of frit fly in seedling ryegrass

Laboratory experiments gave useful indications of the effectiveness of insecticide treatments to control larvae of frit fly ( Oscinella frit L.). Lightly infested field experiments provided confirmatory evidence. Several seed treatments, insecticide granules combine-drilled with the seed and post-emergence sprays were very effective. The feasibility of delivering granules with seed must be confirmed for each granular formulation. Post-emergence sprays were most effective if applied at approximately the time of oviposition but several also gave a strong residual effect if applied earlier and a remedial effect if applied after larval establishment in the seedlings. More detailed conclusions are discussed.     

Improving ryegrass establishment with microencapsulated fonofos insecticide

The impact of various fonofos treatments on autumn-sown Italian ryegrass was assessed in 11 small-plot experiments. In nearly all of the experiments there were responses in the number of seedlings establishing, crop vigour or (where it was measured) herbage yield in the following spring. Few pest species were recorded in the experiments but plant attack by frit fly larvae was observed in most cases. In field-scale studies at 10 locations there was no evidence that sowing seed treated with fonofos presented any hazard to wildlife. Glasshouse tests showed that the fonofos seed treatment used had no marked phytotoxic effects.     

Seasonal distribution of stem-boring larvae including frit fly (Diptera: Oscinella frit L.) and pest damage in perennial ryegrass

Changes in the population of stem-boring Dipterous larvae (including Oscinella frit ) were examined weekly for a year on plots of perennial ryegrass ( Lolium perenne cv. S24). The herbage net regrowth rate of these plots and of plots receiving the pesticide, phorate, was also monitored. Herbage net regrowth rates were greatest in April and October. At the same times the differences in net regrowth between treated and untreated plots were greatest, thus indicating the periods of the greatest loss of production due to pest damage to the sward.
Populations of stem-boring larvae fell below 100 m⁻² for only 4 weeks in the year and were maximal in autumn and early winter. Larval mortality exceeded 50% during the winter period. A correlation was found between larval activity and sward damage.     

The effect of cereal incorporation on the fermentation of spring-and autumn-cut silages in laboratory silos

The effect of adding ground oats and barley on the ensiling characteristics of autumn-and spring-harvested ryegrass was studied in laboratory scale silos.
The addition of oats or barley at rates of 13 or 53 kg t⁻¹ of grass significantly improved the fermentation of late autumn ryegrass silage in the first year. Ammonia N levels were reduced from over 20% of total N to 11% or less. Similar addition to autumn-cut ryegrass higher in soluble carbohydrate content in the second year also significantly reduced pH and ammonia levels but all silages were well fermented. Addition of cereals to spring-cut ryegrass containing over 20% soluble carbohydrate had no effect on fermentation. Cereal addition increased silage DM and decreased silage fibre content in all experiments.
The results are discussed in relation to the potential advantage of cereal addition in the ensiling of grass crops.     

Investigation into the apparent failure of chemical control for management of western flower thrips, Frankliniella occidentalis (Pergande), on plums in the Western Cape Province of South Africa

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes russetting, pansy spot and silvering damage on plums. Despite routine insecticide applications for thrips control, some plum producers report economic losses due to pansy spot damage, pits and holes that render fruit unfit for export. Six commercial plum orchards in two climatic regions in the Western Cape Province, South Africa, were monitored to determine (1) why current management practices based on monitoring and insecticide applications failed to prevent damage in some orchards, and (2) whether WFT is responsible for pitting damage. Western flower thrips was the dominant thrips species in all orchards, though low numbers of Frankliniella schultzei Trybom also occurred. Blue sticky traps were more efficient for monitoring WFT and F. schultzei than yellow traps. Insecticide applications early in bloom and unfavourable weather conditions for thrips flight contributed to very low numbers of WFT on sticky traps during the flowering and fruit set periods. Flower dissections, however, revealed varying levels of oviposition damage to ovaries and fruitlets. Dissections confirmed that WFT enter flowers to lay eggs in the ovaries and other flower parts before petals are fully open. No consistent significant relationship between sticky trap counts and WFT oviposition damage to plums were found, therefore no treatment threshold level could be recommended. Insecticide applications during bloom limited thrips feeding damage, but were too late to prevent oviposition damage. Some oviposition sites developed into typical pansy spots, whilst others formed holes or pits that increased in size as the fruit matured. After insecticide applications ended, and as air temperature increased, WFT populations increased. Weeds and wild vegetation in and around orchards provide a continuous source of potential infestation for as long as the fruit remains attractive and vulnerable to WFT. As oviposition damage by WFT can occur before flowers open, and because of the risk to pollinators when insecticides are applied during flowering, a purely chemical control strategy does not appear to be feasible. A new approach to WFT management is required.     

The control of leatherjackets, Tipula paludosa Meig., in grassland by early application of insecticide

To determine whether leatherjackets might be controlled by application of a pesticide in summer, before oviposition by crane flies, chlorpyrifos was applied to perennial ryegrass (Lolium perenne) swards on dates from July to September in anticipation of leatherjacket infestation. Subsequent winter population estimates showed that leatherjacket numbers had been reduced by at least 85% by 0·72 kg chlorpyrifos ha^-1 applied on 13 July, and by 0·60 kg ha^-1 applied on 3 August or later.
The significance of leatherjacket control by pesticide application on these dates is discussed in relation to previously recorded effects of pesticide treatment on other known pests. It is concluded that control of all common arthropod pests of proven significance in established grassland may be achieved with one application of pesticide.     

The impact of granular formulations of phorate, terbufos, carbofuran, carbosulfan and thiofanox on newly sown Italian ryegrass (Lolium multiflorum)

The effect of applying granular formulations of phorate, terbufos and carbofuran to grass at the time of sowing at a range of dose rates ‘in furrow’ (i.e. drilled with the seed down the coulter tube into the drill row) or broadcast was assessed at two sites in each of two years. The effects of carbosulfan and thiofanox were assessed at one site in one year. All of the chemicals except thiofanox enhanced yield in one or more experiments by a sufficient amount to be economically viable. Much of the yield benefit seemed to derive from the control of frit fly larvae. Earthworms are an important component of the grassland fauna and checks were made of the effects of the chemical on their numbers. Their populations were affected initially in some experiments by phorate, terbufos and carbofuran, but their numbers recovered subsequently. There was a trend for treatments made ‘in-furrow’ to make more economic use of the pesticides compared with broadcasting them.     

Tiller size/density compensation in temperate climate grasses grown in monoculture or in intercropping systems under intermittent grazing

Oat and ryegrass intercropping in pastures is widely used in regions with subtropical climates. The aim of this study was to evaluate the tiller size/density compensation mechanisms in monoculture and intercropping swards of black oats (Avena strigosa Schreb cv. IAPAR 61) and annual ryegrass (Lolium multiflorum Lam. cv common) under intermittent grazing. Treatments (black oat, annual ryegrass and their mixture) were assigned according to a complete randomized block design with four replicates. Ryegrass, oat and intercropped pastures were grazed when the swards reached a height of 17, 25 and 23 cm, respectively, and with a level of defoliation of 40%. The aerial biomass was determined with a rising plate meter, and the tiller population density (TPD) was estimated by counting tillers in three 10 cm diameter PVC rings per paddock. The mass per tiller was estimated based on the aerial biomass and the TPD of each paddock. Total herbage production did not differ among treatments, with values around 7400 kg DM ha^?1. TPD decreased and mass per tiller increased linearly in the monoculture treatments. Tiller size/density compensation was observed in the three plant communities (treatments) according to the self‐thinning rule. In addition, no relationships were found when each species was analysed individually in the intercrop treatment. The results suggest that species in grass mixed swards adjust their population to keep a relatively constant leaf area index (LAI) over the grazing seasons, and that would help pastures to stabilize herbage production.     

Model of wheat yield response to application of diclofop-methyl to control ryegrass (Lolium rigidum)

A general model of crop yield response to herbicide application is proposed. The model includes three components: the effect of herbicide dosage on weed density, the effect of surviving weed density on crop yield and the effect of herbicide directly on the crop. The model is used to estimate the response of wheat yield to application of diclofop-methyl to control ryegrass (Lolium rigidum) in Australia. It is found that the competitiveness of ryegrass plants surviving treatment is reduced by the treatment and that the proportion of yield loss at a given ryegrass density is not independent of the absolute weed-free yield. The response function is used to calculate economic thresholds and optimal herbicide dosages.     

圆纹广翅蜡蝉产卵规律及温度对越冬卵发育的影响

为了阐明圆纹广翅蜡蝉（Pochazia guttifera Walker）产卵对茶树的为害规律及温度对其越冬卵发育的影响,通过五点取样法,系统调查了圆纹广翅蜡蝉产卵对茶树的为害情况,并研究了16、19、22、25、28℃恒温对圆纹广翅蜡蝉越冬卵发育的影响。结果表明,圆纹广翅蜡蝉成虫喜欢在直径为(0.23±0.04)cm的茶树幼嫩枝条上产卵,产卵刻痕在枝条上的为害长度为(1.36±0.59)cm。在茶园周围有较多寄主林木且管理较为粗放的马鞍山茶叶试验场阶梯茶园内,茶树枝条的受害率为13.35%,显著高于其他茶园。此外,越冬卵的发育历期,随着温度的升高逐渐缩短,28℃处理的越冬卵发育历期为(28.75±7.03)d,若虫初孵时间较早,孵化率较高。温度与圆纹广翅蜡蝉越冬卵发育速率关系满足方程y=0.001 9x–0.022,越冬卵的发育起点温度为11.58℃,有效积温为526.32 d·℃。本研究对信阳茶区圆纹广翅蜡蝉越冬种群发生期的预测预报和防控策略的制定具有重要的指导意义。     

Tolerance to frost and ice encasement in cultivars of timothy and perennial ryegrass during winter

Ice encasement causes major winter damage in grasslands in coastal areas of Northern Scandinavia and may also affect grass performance in a future changing climate. Changes in ice‐encasement tolerance (LD50), frost tolerance (LT50) and water‐soluble carbohydrate (WSC) content were investigated in different cultivars of timothy and perennial ryegrass sampled at three sites with contrasting conditions. Timothy endured ice encasement for 40 d more than ryegrass (maximum LD50 63 vs. 20 d), and a cultivar originating from 69°N tolerated significantly longer periods in ice than a cultivar from 59°N. A similar relationship between cultivar origin and tolerance was observed for ryegrass. The higher LD50 in timothy compared with ryegrass seemed to be associated with a lower rate of change in WSC content during ice encasement, but no apparent relationship was found between WSC content at the start of encasement and plant survival in ice. A significant linear relationship was found between LD50 and LT50 of plants sampled in the field. A differing decline in frost tolerance during ice encasement for the species indicated that timothy is more resistant to dehardening under ice than ryegrass. This study contributes data and functional relationships needed to develop models of grass performance during winter.     

Effects of pasture age on the genotype and phenotype of perennial ryegrass

Limited persistence of perennial ryegrass (Lolium perenne L.) in dairy pastures is a significant issue in parts of New Zealand. The contribution of plant genetic background to this problem is not well understood. Temporal changes were investigated in genotypic and phenotypic composition of two perennial ryegrass cultivars (Nui SE and Alto AR37, older and newer cultivars respectively) sown as fields plots at three locations. Samples from survivor populations collected annually over 6 years from each location were established in a field nursery, analysed by simple sequence repeat (SSR) markers and assessed for vigour, leaf morphology and tiller number. SSR-based estimates of the statistic G′_ST indicated no significant (p > .05) genetic differentiation between survivor populations and plants grown from remnant seed (ex-seed) after 5 years, and no significant change (p > .05) in within-population genetic diversity for either cultivar at any location. SSR analysis of endophytic fungus (Epichloë festucae var. lolii) type revealed only limited ingress of off-type ryegrass volunteers into plots at two locations. Vigour scores of survivor plants were not significantly (p > .05) different among plants collected from different locations and ex-seed plants. Leaves on ex-seed plants were longer (p < .001) than those on the survivor plants after four but not 6 years and may reflect a short-term response to climatic conditions experienced in the field nursery. Our results suggest that the reported poor ryegrass persistence is not driven by changes in population genetic structure and that the sown cultivars survived and remained true to type.     

The effects of treading by dairy cows during wet soil conditions on white clover productivity, growth and morphology in a white clover–perennial ryegrass pasture

Single pugging events, which involve remoulding of the soil around the hooves of livestock during treading, of moderate or severe pugging intensity were imposed in plots in a long‐term white clover‐ryegrass pasture during spring, by using dairy cows at varying stocking rates (4·5 cows 100 m^?2 for 1·5 or 2·5 h respectively). Changes in the growth and morphology of white clover were investigated over the following 12 months. Defoliation at approximately 3‐week intervals was carried out by mowing. Annual herbage production was reduced following moderate and severe pugging proportionately by 0·16 and 0·34 compared with the non‐pugged control treatment. The corresponding decreases in white clover production were 0·09 and 0·52 respectively. Annual perennial ryegrass production was reduced by 0·37 under severe pugging. Pugging had an immediate adverse effect on growth of white clover which persisted for up to 156 d, and coincided with a large decrease in the proportion of white clover in herbage over the same period (e.g. 0·40 vs. 0·12, in control and severely pugged treatments, respectively, on day 112). In comparison, recovery in ryegrass growth was apparent after 50 d in severely pugged treatments, indicating that white clover is more vulnerable to severe pugging than perennial ryegrass. Analysis of individual white clover plants extracted from turves (300 mm × 300 mm) showed that direct hoof damage, fragmentation and burial of stolons were the major factors which reduced white clover production, rather than the changes in soil physical properties measured. Morphological characteristics associated with plant size (e.g. stolon length, growing points, and leaf numbers) all decreased under pugging. The situation had reversed by late summer, with larger plants dominating pugged plots, and coincided with the recovery of the proportion of white clover in herbage. Strategic pasture management practices, such as restricted grazing and the use of stand‐off pads when soils are overly wet, are suggested as means of minimizing treading damage to pasture and reducing negative impacts on the growth and productivity of white clover.     

信阳茶区柿广翅蜡蝉越冬种群的发生与为害规律

不仅调查了粗放和精细两种管理模式茶园内柿广翅蜡蝉越冬产卵刻痕对茶枝的为害情况,还调查统计了其越冬产卵时对茶枝直径的选择情况,以及在茶枝上越冬产卵部位、产卵刻痕长度和相应的着卵量。研究表明,两个粗放管理茶园内茶枝的受害率（9.86%、13.79%）均显著高于精细管理茶园,柿广翅蜡蝉成虫偏向于在直径为0.20~0.30βcm的茶枝上产卵越冬,而且产卵刻痕顶端至茶枝芽头的平均距离为7.22βcm,产卵刻痕长度平均值为1.35βcm。此外,柿广翅蜡蝉越冬产卵刻痕长度（x）与刻痕内着卵量（y）之间呈显著正相关关系,满足方程：y=17.83x+1.12（F=3β652,df=1β145,R²=0.96,P<2.2×10^-16）。建议每年10月初到次年3月下旬,应及时剪除受越冬卵刻痕为害的茶树嫩枝条并加强茶园管理,以实现柿广翅蜡蝉越冬种群的区域性控制。本研究为信阳茶区柿广翅蜡蝉越冬种群的预测预报和生态防控提供了理论依据,对减少茶园农药用量以及提高“信阳毛尖”的产量和品质具有非常重要的意义。     

The productivity of oats and berseem clover intercrops. II. Effects of cutting date and density of oats on annual forage yield

Annual forage yields of intercrops of berseem clover (Trifolium alexandrinum L.) and oats (Avena sativa L.), as affected by timing of initial harvest and sowing rate of oats, were investigated. Berseem clover was intercropped with oats at 0, 30, 60, 90 and 240 plants m^?2 of oats in 1999 and 2000 in Alberta, Canada. Cutting date treatments involved initial harvest at 10‐d intervals between 35 and 88 d after planting (DAP), and one or two subsequent harvests of regrowth. Total intercrop dry‐matter (DM) yield averaged 12·9–13·3 t ha^?1 with proportions of 0·21–0·43 of berseem clover in the forage. Treatments with an initial cut at the silage stage of oats (76 DAP in 1999, 88 DAP in 2000, at about soft‐dough stage of oats) had greater yields of oats, lower yields of berseem clover, and lower proportions of berseem clover in total annual yields than treatments with an earlier initial cut. Total crude protein (CP) yield was greater with an initial cut at 65–66 DAP than with a silage‐stage initial cut. With an initial cut at 35 DAP (before stem elongation of oats) or after 65 DAP (after heading of oats), yield potential of oats was sometimes reduced compared with silage‐stage treatments, but this was balanced by a greater yield of berseem clover. The impact of harvest timing on total yield decreased as the proportion of berseem clover in the intercrops increased. With decreasing density of oats, DM yield of first‐cut intercrops and total DM yield of oats decreased, while regrowth and total DM yields of berseem clover increased. Intercrops with oats at 60 plants m^?2 had equal or greater total DM and CP yields than intercrops with 240 plants m^?2 of oats. For intercrops with oats at 60 plants m^?2, with initial cuts at 65–66, 75–76, or 88 DAP, yields of regrowths were 0·30–0·35, 0·16–0·26 and 0·09 of the total yield respectively. Oats–berseem clover intercrops showed potential to manipulate the pattern of annual forage yield and to provide flexibility of harvest without reducing annual yields.     

The productivity of oats and berseem clover intercrops. I. Primary growth characteristics and forage quality at four densities of oats

Berseem clover (Trifolium alexandrinum L.) was sown as an intercrop with oats (Avena sativa L.) at 0, 30, 60, 90 and 240 oats plants m^?2 in May in 1999 and 2000 in Alberta, Canada. Forage yield and quality were measured at 10‐d intervals between 35 and 88 d after planting (DAP). Yield is defined as the biomass above 6 cm of the soil surface. The dry‐matter (DM) yield of berseem clover in sole crops increased by 5–10 g m^?2 d^?1 between 35 and 55 DAP and then increased by 21–28 g m^?2 d^?1 between 55 and 75 DAP. The DM yields of oats sown at 240 plants m^?2 increased by 26–28 g m^?2 d^?1 over the whole period from 35 to 75 DAP. Oats were the dominant component in the intercrops, even at low densities of oats. Berseem clover grown with 60 oats plants m^?2 received only 0·24 of the incident light when shading by oats peaked at 65 DAP. DM yields of berseem clover in intercrops with 60 oats plants m^?2 averaged 0·14–0·32 of the yields of berseem clover sole crops. Between 35 and 88 DAP in 2000, the crude protein (CP) concentration of berseem clover sole crops declined linearly from 310 to 180 g kg^?1 DM, and the CP concentration of oats exhibited a quadratic response, declining from 350 g kg^?1 DM at tillering to 110 g kg^?1 DM at the soft dough stage. The mean CP concentration of berseem clover in intercrops with 60 oats plants m^?2 was 25 g kg^?1 less than in berseem clover sole crops, indicating that competition by oats reduced the CP concentration of berseem clover. At later sampling dates, CP and DM yields of intercrops with oats at 60 plants m^?2 equalled those with oats at 240 plants m^?2. The addition of berseem clover to oats in intercrops at 60 oats plants m^?2 reduced the neutral‐detergent fibre concentration by 30 g kg^?1 DM compared with oats alone. Oats were very competitive as a companion crop for berseem clover. Adding berseem clover to oats increased forage quality and may provide for increased intake and digestibility of forage to support higher livestock productivity.     

A preliminary study on the effects of a transgenic corn event on the non-target pest Dalbulus maidis (Hemiptera: Cicadellidae)

The inclusion of the cry gene in corn may produce direct effects on non-target pests. Our research was focused on the relationship between Bt corn germplasm, expressing the cry1F protein to control the fall armyworm [Spodoptera frugiperda (Noctuidae)], and a non-target pest, the corn leafhopper [Dalbulus maidis (Cicadellidae)]. The aim of this contribution was to elucidate if Bt corn plants have influence on the oviposition preference of the leafhopper and to evaluate the effect of the transgenic plant on the hatching rate of egg. Female corn leafhoppers were released in cages each containing two potted plants in the V2 stage: a Bt germplasm and the corresponding isogenic hybrid. Laid eggs were counted and the number of hatched nymphs recorded. D. maidis females oviposited and laid more eggs in Bt plants. The egg hatching rate was negatively affected by the Bt germplasm. In addition, a field study was conducted in order to determine the abundance of D. maidis adults in Bt corn and the corresponding non-Bt isoline. Two corn plots sown with the same germplasms as used in the laboratory bioassays were sampled weekly. In the field, the population of the corn leafhopper was higher in the Bt corn plot than in the non-Bt isoline. Possible hypotheses for the differences in abundance of the vector in the field are: a) that pleiotropic effects of Bt corn could attract adults; b) the existence of a possible direct competition between the corn leafhopper and the target pest in order to utilize the whorls of corn plants as refuge and feeding sites, so the high populations of the vector could be due to the large supply of healthy whorls in the transgenic plot; and/or c) a differential attack of natural enemies occurring in non-Bt plots.     

Nitrogen Uptake by Faba Bean from 15N-Labelled Oilseed-Rape Residue and Chicken Manure with Ryegrass as a Reference Crop

Abstract

The effects of soil amendment with oilseed-rape residue (OSRR) and chicken manure (CM) on the growth and nitrogen (N) uptake of faba bean (Vicia faba L.) were assessed in a pot experiments with Italian ryegrass (Lolium multiflorum Lam.) as a reference crop. A ¹⁵N isotope dilution method was used to estimate the amount of N derived from the residue (OSRR and CM) and from atmosphere through N₂ fixation in the plants. Dry weights (DW) of shoots and whole plants were heaviest in the plants grown on the soil amended with CM (CM plants) followed by the plants grown on the soil amended with OSRR (OSRR plants) and control plants in this order. There were significant differences (p<0.05) in dry weight between CM, OSRR and control plants. DW of roots was also increased by amendment with either CM or OSRR in faba bean, but it was decreased in ryegrass. The amount of total N in both roots and shoots were increased by application of either CM or OSRR in both faba bean and ryegrass. The amount of N₂ fixed by faba bean cultured on 1.2 kg soil amended with 10g residue (CM or OSRR) was 85.9 mg pot-¹ but total N in faba bean derived from OSRR and CM was 192 and 374 mg pot-¹, respectively. The percentage of N derived from atmosphere to total N in faba bean plants ranged from 15.9 to 26.5%. The amount of N taken up by faba bean and ryegrass plants from CM were larger than those from OSRR by 81.0 and 54.3%, respectively. Soil N balance was calculated as the difference between the amount of N applied (including fixed) and taken up by the plants. The N balance of soil amended with OSRR after cultivation of faba bean was 72.2% higher than that of the soil amended with CM, and that after cultivation of ryegrass was 89.9% higher.     

Methods for Surveying Stable Fly Populations

Stable flies are among the most important pests of livestock throughout much of the world. Their painful bites induce costly behavioral and physiological stress responses and reduce productivity. Stable flies are anthropogenic and their population dynamics vary depending on agricultural and animal husbandry practices. Standardized sampling methods are needed to better identify the factors controlling stable fly populations, test novel control technologies, and determine optimal management strategies. The current study reviewed methods used for a long-term study of stable fly population dynamics in the central Great Plains. An additional study compared the relative size of flies sampled from the general population with that of flies sampled emerging from substrates associated with livestock production. Flies developing in livestock associated substrates are significantly larger than those in the general population indicating that other types of developmental sites are contributing significant numbers of flies to the general population. Because efforts to identify those sites have yet to be successful, we speculate that they may be sites with low densities of developing stable flies, but covering large areas such as croplands and grasslands. The stable fly surveillance methods discussed can be used and further improved for monitoring stable fly populations for research and management programs.