Sampling plans for aphids and their parasitoids in blueberry fields in Argentina

Densities of aphids (Aphis gossypii and A. spiraecola) and mummified aphids at different phenological stages of a blueberry crop were estimated for the purpose of developing sampling plans. Our data set comprised 99 samples taken during the period 2006–2008 in four fields in Buenos Aires Province, Argentina. Estimation of population density based on the proportion of sample units infested by individuals was investigated. We also calculated the minimum number of sample units to estimate the density of individuals on buds and buds + flowers using enumerative sampling. The relative precision of both methods was compared. Moreover, an enumerative sequential sampling protocol was developed. The presence–absence sampling plan gave density estimates with large variances (as measured by confidence intervals and large standard errors). The aggregation of mummies was similar on buds and buds + flowers, so the required number of sample units for density estimates was the same. Relative precision of estimates was much lower for the presence–absence sampling than the enumerative sampling, even at intermediate densities. An enumerative sequential plan would be the most appropriate and useful method in management plans for aphids and mummified aphids in blueberries.     

Spatial characteristics of white mould epidemics and the development of sequential sampling plans in Australian bean fields

To improve sampling efficiency and precision in the assessment of white mould (caused by Sclerotinia sclerotiorum) disease incidence on bean (Phaseolus vulgaris), the spatial characteristics of epidemics were characterized in 54 linear transects in 18 bean fields during 2008–2010 in northern Tasmania, Australia. The incidence of diseased pods and plants was assessed prior to harvest. Distributional and correlation‐based analyses indicated the incidence of diseased pods was characterized by a largely random pattern at the individual plant scale, with some patches of similar disease levels on pods occurring at a scale of 1·5 m or greater. Collectively, these results suggested epidemics may be dominated by localized sources of inoculum. Sequential sampling approaches were developed to estimate or classify disease incidence above or below provisional thresholds of 3, 5 and 15% incidence on pods near harvest. Achieving prespecified levels of precision by sequential estimation was possible only when disease incidence on pods was greater than approximately 4% and sampling was relatively intense (i.e. 10 pods evaluated on each of at least 64 plants). Using sequential classification, correct decisions on disease status were made in at least 95% of independent validation datasets after assessment of only 10·1–15 plants, depending on classification threshold and error rates. Outcomes of this research provide the basis for implementing more efficient sampling and management strategies for this disease in Australian fields.     

Dispersion patterns and sampling plans for the pea aphid,Acyrthosiphon pisum (Harris), on grass pea,Lathyrus sativus L.

From 2009/2010 to 2010/2011, flight patterns and spatial distribution of pea aphids were studied in northwestern Ethiopia. Yellow traps were used and legume fields sampled. Trap catches varied between years (lower in 2009/2010 than in 2010/2011), locations and months in the growing season. At Woreta, peaks were observed in January (20–70 per trap) and at Wondata in October and November (60–80 per trap). Also, pea aphid numbers were more on fallow land than on other land-use systems (a maximum of 41,000 in December 2010/2011 and 25,000 in January 2009/2010 per 100 plants). Taylor's power law coefficients, i.e., b values, were significantly greater than 1 on grass peas planted after fallow; the corresponding r² values ranged between 0.87 and 0.94. Coefficients were inconsistent on grass peas planted after teff and undersown in maize. The optimum sample size n (number of yellow traps) required in relation to the mean densities of the pea aphid was more or less the same for the three levels of accuracy (D = 0.2, 0.3 and 0.5). At D = 0.5, numerical sample size curves showed 10 traps as mean number of aphids per trap approached 4 or 5, which is practical and affordable. Some additional work at more locations may be required to validate these sampling plans before wider use.     

Integrated management of Thrips tabaci (Thysanoptera: Thripidae) on onion in north‐western Italy: basic approaches for supervised control

BACKGROUND: Thrips tabaci Lindeman (Thysanoptera: Thripidae) is a major pest on onion, Allium cepa L., worldwide. In 2010, research was conducted in a commercial onion field in north‐western Italy in order (i) to evaluate the efficacy of different insecticides and of the SAR activator acibenzolar‐S‐methyl, (ii) to correlate thrips infestation levels with bulb size and weight at harvest and (iii) to implement a reliable thrips sampling method. Efficacy of the three active ingredients spinosad, lambda‐cyhalothrin and acibenzolar‐S‐methyl on local thrips populations were also evaluated in laboratory bioassays. RESULTS: During field surveys, the highest and the lowest thrips infestations were observed in plots treated with lambda‐cyhalothrin and with spinosad and acibenzolar‐S‐methyl respectively. The effectiveness of spinosad was also confirmed in laboratory bioassays. At harvest, bulb size and weight did not significantly differ between treatments. A high correlation with visual inspection made plant beating a suitable sampling method for routine practice, enabling a good estimate of thrips infestation. CONCLUSION: Damage caused by thrips is often not severe enough to warrant the frequent pesticide applications the crops receive in north‐western Italy. The use of spinosad and acibenzolar‐S‐methyl is suggested as an alternative to conventional insecticides for the preservation of natural enemies. Copyright © 2011 Society of Chemical Industry     

Differential reproduction of Meloidogyne incognita and M. javanica in watermelon cultivars and cucurbit rootstocks

The suitability of watermelon cultivars and cucurbit rootstocks as hosts to Meloidogyne incognita and M. javanica was determined in pot and field experiments. Meloidogyne incognita showed higher reproduction than did M. javanica on watermelon and cucurbit rootstocks. The watermelon cultivars did not differ in host status when challenged with these two species and supported lower nematode reproduction than the cucurbit rootstocks. Rootstocks Lagenaria siceraria cv. Pelops and Cucurbita pepo AK15 supported lower reproduction than did the squash hybrid rootstocks (C. maxima × C. moschata). Egg production increased (P < 0·05) with a rising initial inoculum level (Pi) in the non‐grafted Sugar Baby but the reproduction factor Rf (eggs per plant/Pi) was similar at two Pi levels. The total egg production in the plants grafted onto squash hybrids RS841 and Titan was greater (P < 0·05) at the higher Pi, but the Rf values were lower. The development of field‐grown non‐grafted watermelon plants was significantly stunted in plots where nematodes were detected at planting. However, no differences were observed in plots with grafted plants. In plots with nematodes, non‐grafted and Titan‐grafted plants had similar yields that were higher than that of RS841‐grafted plants. In the commercial plastic houses with grafted watermelon, the average Rf value was 42‐fold, confirming the high susceptibility of squash hybrids as rootstocks for grafted watermelon. The Titan–Sugar Baby combination was tolerant to M. javanica.     

Spatial dispersion and binomial sequential sampling for the potato psyllid (Hemiptera: Triozidae) on potato

BACKGROUND: The potato psyllid is a serious pest of potatoes. Sampling plans on potatoes for the potato psyllid have yet to be developed, thus the authors' objectives were (1) to determine the most efficient within‐plant sampling unit, (2) to determine the spatial dispersion of potato psyllids in potato fields and (3) to develop a binomial sequential sampling plan for this pest. RESULTS: Significantly more potato plants were infested with potato psyllids on the edges of the field, and significantly more plants were infested with psyllids on the ‘top’ and ‘middle’ of the potato plant. Significantly more psyllids were also found on the undersides of leaves. The potato psyllid has an aggregated distribution in potato fields. Binomial sequential sampling plans were developed for three action thresholds representing 0.5, 1 and 5 psyllids per plant. The average sample numbers for these action thresholds were between 12 and 16 samples, depending on the action thresholds. However, based on the shape of the operating characteristic curve, the 0.5 and 1 sampling plans were more reliable than the 5 psyllids per plant plan. CONCLUSION: The binomial sequential sampling plans are useful for detecting potato psyllids at low levels of infestation, which will be useful for pest management purposes. Copyright © 2011 Society of Chemical Industry     

凉山烟田烟粉虱(MED隐种)成虫空间分布型及序贯抽样技术

运用2种回归方法和8个聚集度指标对四川凉山烟田烟粉虱盛发期种群的空间格局进行了研究。结果表明,烟粉虱种群呈聚集分布,聚集强度不随种群密度的变化而变化,其聚集原因是由环境因素所导致;通过种群密度与聚集度指标相关性分析表明,用平均拥挤度(m*/m)、负二项分布指标(K)及久野指数(CA)分析烟粉虱空间分布型更具说服力;并利用空间格局参数确定了理论抽样数和序贯抽样模型。     

Distribution pattern and sequential sampling plan for spotted pod borer,Maruca vitrata (Fabricius) (Lepidoptera: Crambidae) on pigeon pea,Cajanus cajan L

Spatial distribution of legume pod borer, Maruca vitrata (Fabricius) (Lepidoptera: Crambidae) on Pusa 992 pigeon pea cultivar during kharif (rainy season) 2011 and 2012 was analyzed through Taylor's power law (TPL) and Iwao's mean crowding (IMC) regression. M. vitrata exhibited an aggregated distribution pattern on the crop. The pooled data for the two years fitted well to the TPL (a = 1.05, b = 1.19, R² = 0.967) and the IMC (α = ?0.17, β = 1.124, R² = 0.99). The optimal sample sizes with the TPL parameters increased with an increased precision level. Based on the TPL parameters, the decision lines of sequential sampling for M. vitrata were determined to be d = 3n ± 2.5√n. The sequential sampling plan would economize decision-making for an effective management of M. vitrata.     

白星花金龟在玉米田的空间分布和抽样技术

应用平均拥挤度指标、扩散指数等6种聚集度指标以及Iwao回归法、Taylor幂函数法等方法分析了白星花金龟种群在玉米田空间分布特征。结果表明:白星花金龟种群呈现聚集分布特征,并且聚集程度较高;分析拟合了白星花金龟在玉米田中的理论抽样数学模型。     

Practical experiences with a system for site-specific weed control in arable crops using real-time image analysis and GPS-controlled patch spraying

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post‐emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site‐specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on‐line weed detection using digital image analysis, computer‐based decision making and Global Positioning System‐controlled patch spraying. In a 2‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site‐specific weed management will not result in higher infestation levels in the following crops.     

Spatiotemporal variation in airborne sporangia of Phytophthora infestans: characterization and initiatives towards improving potato late blight risk estimation

This study investigated the value of using real‐time monitoring of Phytophthora infestans airborne inoculum as a complement to decision support systems (DSS). The experiment was conducted during the 2010, 2011 and 2012 potato production seasons in two locations in New Brunswick, Canada. Airborne sporangia concentrations (ASC) of P. infestans were monitored using 16 rotating‐arm spore samplers placed 3 m above the ground. The first cases of late blight (2010 and 2011) were detected 6–7 days after the first ASC peak, and all samplers captured their first sporangia within the same week (at 3‐ and 9‐day periods). The cumulative ASC curve and the risk curves from two DSS (PLANT‐Plus and Pameseb Late Blight) had the same shape but different magnitudes. In both locations, the negative binomial distribution fitted the data better than the Poisson distribution, which is indicative of heterogeneity, and based on Taylor's power law, the heterogeneity increased with increasing ASC. Therefore, the present results suggest that spore‐sampling network devices may be a suitable approach for early detection of incoming inoculum and, when combined with DSS, represent a potential aid for targeting the optimal time to apply a disease‐control product. In this context, cumulative ASC can be a counterweight to the DSS risk estimate: a high risk combined with significant ASC will trigger fungicide spraying. Moreover, spore sampling can be used to assess the efficiency of management strategies by means of examining the area under the inoculum progress curve.     

Combining mechanical rhizome removal and cover crops for Elytrigia repens control in organic barley systems

Mechanical weed control of perennial weeds in organic crop production over long post‐harvest periods is incompatible with the establishment of cover crops for improving soil quality and preventing nutrient leaching. We suggest a new concept that comprises uprooting and immediate removal of vegetative propagules located within the plough layer to allow for quick re‐establishment of a plant cover. A field experiment comparing the effects of conventional practices (stubble cultivation) with different combinations of rotary cultivation (One, Two or four passes) and cover crops (none vs. rye‐vetch‐mustard mixture) on Elytrigia repens rhizome removal, shoot growth and suppression of a subsequent barley crop was examined in two growing seasons. Four passes with a modified rotary cultivator, where each pass was followed by rhizome removal, reduced E. repens shoot growth in barley by 84% and 97%. In general, the cover crop developed poorly and did not affect barley or E. repens. Barley yield was only affected by treatments in the first season, where yield was negatively correlated with E. repens shoot biomass. The concept has potential for the control of severe E. repens infestations, but future research aimed at identifying more effective smother crops and less intensive methods of rhizome removal is needed.