云杉矮槲寄生的侵染对青杄光合与蒸腾作用的影响

 云杉矮槲寄生(Arceuthobium sichuanense)属半寄生性多年生种子植物,是青海省云杉天然林毁灭性生物灾害之一。本研究首次报道了云杉矮槲寄生在自然条件下可以侵染青杄,并对健康与染病青杄(Picea wilsonii)针叶形态及其光合日变化进行了测定。结果表明:1)染病青杄的针叶长度和宽度显著小于健康青杄(P＜0.001),而染病青杄的针叶比叶面积(SLA)显著大于健康青杄(P＜0.001);2)云杉矮槲寄生的侵染显著降低了青杄叶片的净光合速率、蒸腾速率以及气孔导度(P＜0.05),但不影响其胞间CO₂浓度(P =0.32);3)冗余分析(RDA)表明,云杉矮槲寄生的侵染导致青杄对不同环境因子的依赖程度发生变化,健康青杄表现为环境CO₂浓度(CO₂)＞空气温度(T_air)＞叶片温度(T_l)＞蒸汽压亏缺(Vpd)＞空气相对湿度(RH)＞光合有效辐射(PAR),而染病青杄则出现T_l＞RH＞T_air＞PAR＞Vpd＞CO₂,且T_l成为影响染病青杄叶片光合与蒸腾作用(P_n、T_r)的主要环境因子,且染病青杄对RH和PAR变化的响应更加敏感。此外,染病青杄叶片的水分利用率(WUE)显著低于健康寄主(P＜0.05)。因此,云杉矮槲寄生的侵染可降低青杄对环境的适应能力,从而加速寄主的衰老死亡。     

Pest and disease control on intensive apple trees by overhead mobile spraying

In 3 year field experiments on pest and disease control by mobile overhead spraying of intensive Cox's Orange Pippin apple trees, overhead booms applying 1125 litres/ha and overhead mist-blowing equipment applying 562 litres/ha, each spraying two complete rows from one alley in half the normal time, were compared with conventional automatic mast spraying at 2250 litres/ha and with conventional mist-blowing at 562 litres/ha. The overhead boom application of demeton-S-methyl (0.0036% a.i.) with azinphos-methyl (0.0165% a.i.) or of fenitrothion (0.031% a.i.) at the green cluster stage gave control of the applegrass aphid, Rhopalosiphum insertum, virtually equal to that obtained by conventional application of the same insecticides. Similarly, the overhead mist applications of conventional quantities of insecticides gave equal control, but not when applying one-quarter of the normal amount of insecticides. The conventional methods generally gave better control of apple sucker, Psylla mali. In 1971, when the incidence of apple scab, Venturia inaequalis, was only moderate, the overhead boom method gave equal control to conventional spraying with both dodine/captan (0.03% a.i. and 0.094% a.i.) and benomyl (0.025% a.i.) programmes: in 1972 and 1973, when the scab incidence was heavier, the overhead boom spraying was again equal to the conventional method with the benomyl programme but was less effective with the dodine/captan programme. The overhead mist applications gave control only when the scab incidence was light. Repeated applications of dinocap emulsion (0.025% a.i.), included in the fungicide programme in 1971, gave as good control of the active stages of fruit tree red spider mite, Panonychus ulmi, when applied by the overhead methods as by conventional spraying, but application of the benomyl programme gave poor control. Mobile overhead spraying of small intensive apple trees is a promising method but needs further development before becoming fully acceptable.     

溴氰虫酰胺对香蕉田间黄胸蓟马的药效及其残留规律

采用10%溴氰虫酰胺可分散油悬浮剂（OD）,按有效成分75 g/hm2的剂量,于香蕉抽蕾初期施药1次,比较了喷雾、灌根和埋药3种施药方式下溴氰虫酰胺对黄胸蓟马的防效,并通过超高效液相色谱-串联质谱法（UPLC-MS/MS）,分析了溴氰虫酰胺在香蕉果实、花瓣及土壤中的消解动态和最终残留。药效试验表明:喷雾法与灌根法对黄胸蓟马均具有良好的防治效果,防效分别为78%和74%,而埋药处理的防效较差,仅18%。残留检测结果表明:喷雾和灌根处理组,溴氰虫酰胺在果实、花瓣和土壤中的消解半衰期分别为6.5、14.0、8.5 d和16.0、5.7、8.0 d;在香蕉收获前7 d采样,果实中未检测到溴氰虫酰胺残留,其在土壤中残留量为0.028 mg/kg。研究表明,采用喷雾与灌根法施用溴氰虫酰胺可有效防治香蕉田黄胸蓟马,且其在香蕉上使用较安全,属于易降解性农药。     

稻飞虱和纹枯病化控的策略及复合指标研究

采取田间小区和网室盆栽试验,研究稻飞虱和纹枯病混合发生的化控策略及复合防治指标。结果表明,水稻孕穗期(7月上中旬)用高效、长效、安全药剂扑虱灵和粉锈灵混合防治的“治前控后”化防策略保产效果最佳。试验证明,稻飞虱和纹枯病对水稻有明显的交互作用。组建了稻飞虱(白背飞虱、褐飞虱)虫量(X_(1-2))、纹枯病病株率(X_3)的复合为害损失及动态经济阈值模型。经田间小区、大田应用检验,不仅防效高,保产效果好,而且减少施药次数,保护了天敌,三大效益显著。     

喷雾法施用线虫大面积防治荔枝拟木蠹蛾

荔枝拟木蠹蛾(Arbela dea Swinhoe)是南方荔枝、木麻黄等主要的钻蛀害虫,作者利用拟木蠹蛾昼伏夜出的习性,用大蜡螟幼虫诱测和回收喷雾荔枝拟木蠹蛾粪道上的线虫(Steinernema carpocapsae Agriotos),不同温度、不同粪道大小对线虫存活影响的测试结果表明,应用1×10~3/ml线虫剂量喷雾拟木蠢蛾挂在树上的粪道,粪道上便有足够数量的线虫和时间使寄主感染。1995年喷雾法施用线虫防治荔枝拟木蠹蛾260hm~2,防治效果在85％～100％,平均为94.28％,有效地压低了田间的虫口密度。解决了树冠嫩枝受害后人工难以注射及倒置斜垂坑道的虫口防治效果差的矛盾,也使利用病原线虫防治害虫这一有效的生物防治手段更容易为果农所接受。     

Pest and disease control in blackcurrants and apples by the use of overhead irrigation sprinklers

In field experiments on the effectiveness of overhead irrigation spraying of crop protection chemicals, an oscillating bar sprinkler was compared with hand spraying in post-harvest applications of protective fungicides mancozeb (0.096% a.i.) with zineb (0.022% a.i.) for the control of blackcurrant leaf spot, Pseudopeziza ribis. Twin-jet rotating sprinkler nozzles were compared with conventional automatic spraying of Cox's Orange Pippin apple trees in the application of a malathion emulsion (0.125% a.i.) for the control of apple-grass aphid, Rhopalosiphum insertum and also in applications of pre-blossom dodine emulsion (0.03% a.i.) and post-blossom captan suspension (0.09% a.i.) for control of apple scab, Venturia inaequalis. All applications were made at a nominal rate of 2250 litres/ha (200 gal/acre). On blackcurrants, the hand spraying gave much better control of leaf spot and was shown by fluorescent tracer assessment to give more cover on the lower surfaces of the leaves than the sprinkler. On apple, the rotating sprinklers gave almost as good control of apple-grass aphid and apple scab as the conventional automatic spraying. The malathion deposit levels, determined by g.l.c., on the flower trusses were also comparable, though the liquid volume distribution from the irrigation nozzles was uneven.     

Overview of development of an anti-attractant based technology for spruce protection against Ips typographus: From past failures to future success

We describe a series of experiments on the protection of Norway spruce (Picea abies (L.) Karst.) logs and standing trees against Ips typographus L. (Coleoptera: Scolytidae). The tested protective materials were applied 1) at point sources and 2) area-covering using zeolite-based dispensers. We performed 11 terrestrial and one aerial application (using a helicopter) between 1992 and 2001. We gradually replaced polyethylene-bag verbenone dispensers by composite dispensers releasing verbenone and non-host volatiles (NHV: green leaf volatiles, trans-conophthorin, and C8-alcohols). Many experiments did not give statistically significant results, due to the low number of true replicates and the spatial heterogeneity of beetle attacks. The protection of horizontal objects like logs or lying trees with anti-attractants was not always successful. In the future, positive results can be expected with an area covering spray applied by zeolite dispensers containing mixtures of verbenone and NHV. A similar approach could probably be used in aerial spraying of anti-attractants.We have succeeded in our attempt to protect zones of standing spruce trees from I. typographus attacks. We used dispensers with a combination of verbenone and a full blend of NHV compounds. The protection is not complete, but in both 2000 and 2001, the treatment significantly decreased the probability of the insect attack on trees by 60–80%.     

Enhancement of Postharvest Disease Resistance in Ya Li Pear (Pyrus bretschneideri) Fruit by Salicylic Acid Sprays on the Trees during Fruit Growth

The Ya Li pear (Pyrus bretschneideri) trees were sprayed three times with 2.5 mM salicylic acid (SA) around 30, 60 and 90 days after full flowering. The fruit were harvested at commercial maturity (about 120 days after full flowering), inoculated with Penicillium expansum, and incubated at 20 °C, 95–100% RH. The results showed that resistance to the pathogen of the mature pear fruit was remarkably enhanced by the SA sprays. Disease incidence in the SA-treated fruit was 58.0% or 26.5%, and lesion diameter on SA-treated fruit was 58.4% or 29.0% lower than that in/on fruit without SA treatment (control) on day 12 or 17 after incubation, respectively. The SA spray applied to the trees around 30 days after full flowering notably enhanced accumulation of hydrogen peroxide in the young fruit. Meanwhile, activities of defense enzymes, including peroxidase, phenylalanine ammonia-lyase (PAL), chitinase or β-1,3-glucanase in the young fruit from SA-treated trees was 29.5%, 60.0%, 24.4% or 35.7% higher than that in the control fruit 4 days after the SA spraying. Furthermore, after harvest, activities of PAL, chitinase and β-1,3-glucanase were still significantly higher in the mature pear fruit from the trees sprayed three times with SA than those of the control fruit. Activities of the antioxidant enzymes including catalase and ascorbate peroxidase in the young fruit were significantly reduced by SA spraying. However, the activity of another antioxidant enzyme, glutathione reductase in the young fruit was significantly enhanced by SA spraying. These results suggest that enzymes exerting their functions in different ways may be coordinately regulated by SA in the pear fruit. Our study indicates that treatment of SA sprays on the trees may provide further protection against postharvest disease of Ya Li pear fruit in practice and could be used as an alternative and economical approach to reduce application of chemical fungicides.     

Influence of weather on the efficacy of dichlorprop-P/MCPA and trihenuron-methyl

The influence of weather on the efficacy of dichlorprop-P/MCPA and tribenuron-methyl on annual weeds in spritig barley was studied in the field during 4 years at six locations in southern Sweden. The herbicides were applied at one-eighth to three-quarters of the full dose at three application times with approximately 6-day intervals. Weather stations, placed in the experiments, recorded climatic data, Maximum herbicide efficacy was obtained when spraying 1 week after the cotyledon stage with half or three-quarters of the recommended dose. Dose-response curves were estimated and the ED₈₀ doses were calculated. On average, the herbicide dose required to obtain an effect of 80% was about 40% of the recommended dose. The influence of weather was analysed for seven different periods: 7 and 2 days before and after herbicide application, 1 day before and after application, and the day of herbicide treatment. The most pronounced eftects of weather were found for the day of and the day before herbicide application, revealing the strong influence of weather on herbicide uptake and plant metabolism. High air tetnperature and low global radiation during the day of treattnent reduced the ED₈₀ dose of dichlorprop-P/MCPA, whereas the ED₈₀ dose of tribenuron-methyl increased. For both herbicides, precipitation and high soil temperature increased the ED₈₀ dose, which reflects the importance of rain on herbicide uptake and the effect of soil temperature on plant growth. The R² values were higher in the analyses of dichlorprop-P/MCPA than of tribenuron-methyl, indicating that the effect of dichlorprop-P/MCA was more weather-dependent than that of tribenuron-methyl. Separate analyses of the ED₈₀ doses for Brassica napus L., Chenopodium, album L. and Stellaria media (L.) Vill. generally resulted in increased R² values. but otherwise gave results similar to those for the total weed population. Although the analyses revealed significant effects of indivtdual weather factors on herbicide efficacy, it was not possible to discern a consistent and causal relationship between weather and herbicide performance.     

寄主植物上喷药对大螟产卵选择性的影响

为明确稻田适量喷施保护性农药是否影响周边香根草对水稻螟虫的诱集效果,通过室内盆栽试验测定了在水稻和香根草上分别喷施氯虫苯甲酰胺对大螟成虫趋性及产卵选择性的影响。结果表明:在水稻上喷药后第1天,栖息在香根草上的大螟雌、雄成虫总量分别为4.2头和3.8头,显著高于水稻上雌、雄成虫的总量1.00头和0.60头;在水稻上喷药后1~3 d接入大螟,在水稻上不产卵,直到第6天才出现卵块;喷药后6 d和12 d接入大螟,在香根草上的卵粒数分别为287.2粒和309.2粒,显著高于其在水稻上的57.2粒和81.4粒,约为水稻上的5.0倍和3.8倍。在香根草上喷药后1~3 d接入大螟,成虫选择水稻居多,在香根草上的产卵量为0;喷药后6 d接入大螟,成虫对2种寄主植物的选择性无显著差异;喷药后12 d接入大螟,在香根草上的成虫数量为9.8头,约为水稻上的2.5倍,产卵量也约为水稻上的1.9倍,二者均差异显著。表明香根草喷施氯虫苯甲酰胺后其对大螟的诱集作用有一定影响,但这种影响会随着施药时间的延长而逐渐减弱。     

苗圃毛白杨由锈病引起的生长量损失估计

1983—1985年,通过定株系统观测,对毛白杨幼苗由锈病造成的生长量损失做了数理分析,提出3个数学模型,可试用于计算不同病情(x)对单株胸径增长量(y)的影响,并可做为研究防治苗圃锈病的经济效益和防治指标的参考。用于1年生养干苗的模型为:y_1=0.2998e~(-0.08481x) 用于2年生养干苗的模型为:y_2=0.4208e~(-0.0457x2) 用于3年生养干苗的模型为:y_3=0.7913e~(-1.0282x3)     

Tolerance of two Bifora radians Bieb populations to ALS inhibitors in winter wheat

BACKGROUND: Bifora radians, an annual weed in winter wheat, is distributed mainly in the Mediterranean area, Asia Minor and the Caucasus. It infests winter-sown crops of the Central Anatolia and Middle Black Sea regions of Turkey. Field experiments in heavily B. radians-infested fields were conducted over 3 years in Samsun, Turkey, to determine the response of B. radians to ALS-inhibiting herbicides, because growers had complained of a decrease in herbicide effect. RESULTS: The efficacy of ALS inhibitors on a putatively tolerant population sprayed annually with ALS inhibitors and an adjacent allegedly sensitive population was estimated at the ED₅₀ and ED₉₀ response levels. The recommended rates of herbicides controlled 90% of the weed (ED₉₀) in the sensitive population at the early stage of B. radians development, but not in the tolerant population. The relative potencies (ED_x(tolerant)/ED_x(sensitive)) of herbicides on the two populations were estimated by assuming years as being random effects. The relative potency was on average about 1.7, irrespective of the ED_x levels. CONCLUSION: Although the relative potencies were not large, they were large enough to be noted by growers. In field experiments it would be important to establish tools demonstrating when farmers recognise loss of herbicide efficacy. There has been no indication of evolution of resistant biotypes so far, but continuous spraying favours biotypes with increased levels of tolerance. Copyright © 2011 Society of Chemical Industry     

柑橘溃疡病菌的侵染过程及噻森铜对溃疡病的防治效果

为高效精准防治柑橘溃疡病,本研究对不同成熟度柑橘叶片接种溃疡病菌Xanthomonas citri subsp.cirri后的发病情况进行观察,并在显微镜下观察溃疡病菌侵染叶片的过程,并对不同浓度、不同施用方法下噻森铜的室内防治效果和田间防治效果进行测定,对施用噻森铜后土壤、叶片和果实中的残留进行测定.结果 表明,溃疡...     

赤霉素缓解Mn~(2+)对草甘膦拮抗效应的研究

为探索能够减轻或消除Mn2+对草甘膦拮抗效应的方法,以高羊茅为试材,将赤霉素(GA3)与草甘膦和硫酸锰(Mn2+质量分数为0.1%)混用,研究了赤霉素对Mn2+降低草甘膦药效的缓解作用。结果表明:赤霉素+草甘膦+硫酸锰处理组高羊茅比同剂量草甘膦+硫酸锰处理组叶色更黄,萎蔫更严重,与同剂量草甘膦单剂处理组比较接近,其中加入50 mg/L赤霉素处理组缓解草甘膦拮抗效应的效果最好。赤霉素+草甘膦+硫酸锰处理组高羊茅的干、鲜重及叶绿素含量均低于草甘膦+硫酸锰处理组,而丙二醛和莽草酸含量均明显高于草甘膦+硫酸锰处理组。处理后第6天,赤霉素+草甘膦+硫酸锰组莽草酸含量分别比草甘膦+硫酸锰组增加了49.8%(加入50 mg/L赤霉素)和28.8%(加入30 mg/L赤霉素),差异显著;处理后第2天,赤霉素+草甘膦+硫酸锰组丙二醛含量分别比草甘膦+硫酸锰组增加了54.1%(加入50 mg/L赤霉素)和52.9%(加入30 mg/L赤霉素),差异显著。研究表明,将赤霉素与锰肥和草甘膦混合喷施,将有可能在一定程度上缓解Mn2+对草甘膦的拮抗效应,保证草甘膦的除草效果。     

河西走廊棉田主要害虫发生动态及植物源杀虫剂防治技术

为了解甘肃省河西走廊棉区5种常见害虫的田间种群消长动态,明确防治适期并提出以植物源药剂为主的棉花害虫绿色防控技术,于甘肃省敦煌市和瓜州县棉田连续3年采用人工调查和性诱剂诱捕器监测棉蚜Aphis gossypii、棉叶螨、棉蓟马Thrips tabaci、烟粉虱Bemisia tabaci及棉铃虫Helicoverpa armigera的发生动态,同时开展以植物源农药为主的不同类型杀虫剂的田间药效筛选试验,建立科学防控用药技术流程。结果表明,棉蚜全年有6月中旬和7月中下旬2个发生高峰期,建议防治适期为7月上中旬;棉叶螨全年有7月上旬和7月下旬（2017年除外）2个发生高峰期,建议防治适期为6月下旬和7月中旬;烟粉虱全年只有8月中旬至9月中下旬1个高峰期,建议防治适期为8月上中旬;棉蓟马全年只有7月上旬至8月上旬1个高峰期,建议防治适期为7月上旬;棉铃虫1年发生3代,幼虫在7月下旬、9月上旬和9月中旬各有1个发生高峰期,成虫在7月上中旬、8月中下旬和9月中旬各有1个高峰期,建议防治适期应为7月上旬。软皂水剂、藜芦碱、苦参碱、啶虫脒和吡虫啉可用于防控棉蚜,药后14 d防效达76.93%~91.25%;藜芦碱、苦参碱、矿物油、软皂水剂、松油、阿维菌素、阿维·哒螨灵、螺螨酯和硅藻土+有机硅助剂可用于防控棉叶螨,药后10 d防效达72.39%~92.81%;软皂水剂、藜芦碱、印楝素、硅藻土+有机硅助剂、阿维菌素和噻虫嗪可用于防控烟粉虱,药后7 d防效达65.84%~84.29%;除虫菊素、苦参碱、多杀霉素、噻虫嗪和吡虫啉可用于防控棉蓟马,药后14 d防效达72.92%~90.93%。表明在该地区棉田主要害虫防治适期,建立以植物源农药替代传统化学药剂的防控技术,可用于我国河西走廊棉区棉花害虫的绿色防控。     

Early detection of squash silverleaf and chemical control of Bemisia tabaci using imidacloprid

Squash silverleaf induced by the geographical variant Middle East-Asia Minor 1 (MEAM1) of Bemisia tabaci (Gennadius) is an economically important disease of Cucurbita pepo L. in tropical and warm temperate regions of the world. Therefore, both early detection of disease severity and judicious use of insecticides are important for minimizing economic losses. Therefore, the aims of this study were to use chlorophyll fluorescence to detect squash silverleaf early and determine the best protocol for imidacloprid application. The results showed that chlorophyll fluorescence was positively correlated with disease severity of whitefly-infested plants. Foliar spraying was suitable for application to control MEAM1 in the high risk region because it could be rapidly implemented against whitefly infestations and because it has a high knockdown rate. Soil application was slow-acting but had a long-lasting effect and was suitable for implementation during the initial stage of a whitefly outbreak. Considering the overall insect control potential and the risks to the environmental contamination and human health, 0.3 g L^?1 imidacloprid is the recommended concentration using the two application methods.     

Image‐based thresholds for weeds in maize fields

Recent development of site‐specific weed management strategies suggests patch application of herbicides to avoid their excessive use in crops. The estimation of infestation of weeds and control thresholds are important components for taking spray decisions. If weed pressure is below a certain level in some parts of the field and if late germinating weeds do not affect yield, it may not be necessary the spray such places from an economic point of view. Consequently, it makes sense to develop weed control thresholds for patch spraying, based on weed cover early in the growing season. In Danish maize field experiments conducted from 2010 to 2012, we estimated competitive ability parameters and control thresholds of naturally established weed populations in the context of decision‐making for patch spraying. The most frequent weed was Chenopodium album, accompanied by Capsella bursa‐pastoris, Cirsium arvense, Lamium amplexicaule, Tripleurospermum inodorum, Poa annua, Polygonum aviculare, Polygonum persicaria, Stellaria media and Veronica persica. Relative leaf cover of weeds was estimated using an image analysis method. The relation between relative weed leaf cover and yield loss was analysed by nonlinear regression models. The competitive ability parameters and economic thresholds were estimated from the regression models. The competitive ability of weed mixtures was influenced by the increasing proportion of large size weeds in the mixtures. There was no significant effect of weeds which survived or established after the first herbicide application, indicating that early image analysis was robust for use under these conditions.     

Eradication campaign for Rhynchophorus ferrugineus in Cyprus1

Rhynchohorus ferrugineus (red palm weevil) was first recorded in Cyprus in September 2006 on 4 palm trees (Phoenix canariensis) in a hotel garden in the coastal area of Lemesos. All infested plants from the first point of outbreak were removed and burned. Intensive monitoring showed that R. ferrugineus was present in the areas of Limassol, Larnaca and Paphos. In the Famagusta area a consignment of palm trees was found to be infested and measures for the destruction of the consignment were taken. From the results of monitoring, the areas of Limassol, Larnaca and Paphos were placed under close supervision and infested zones and buffer zones were created. In the area of Famagusta there was no trapping of adult insects, however a demarcated area was created and will remain under close supervision for a period of 3 years. The establishment of demarcated areas was carried out according to the provisions of the EU Decision 2007/365/EC. The measures taken in the infested and buffer zones were mainly the application of chemicals through the crown of the susceptible palm plants and the removal of heavily infested palms. Since burning proved not to be an efficient method, the heavily infested palm plants were buried in approved areas, after chemical spraying. In addition the NPPO, of Cyprus has taken measures in training all plant health inspectors in the identification and handling of infested palm trees and public awareness about R. ferrugineus. Surveys continue throughout Cyprus with the use of pheromone traps and eradication measures continue within the demarcated areas with the aim of eradicating of this pest.     

硅酸钠对葡萄炭疽病的防治效果

为探讨硅酸钠在室内和田间对葡萄炭疽病的防治效果,以巨峰葡萄为材料,对葡萄炭疽菌孢子萌发、菌丝生长速率及室内和田间防治炭疽病效果等进行测定。结果表明:不同浓度硅酸钠对葡萄炭疽菌的孢子萌发和菌丝生长均有抑制作用,且随浓度升高抑制作用增强;室内接种炭疽病菌5 d后,15、20和25 mmol/L硅酸钠对葡萄炭疽病的防治效果分别为30.58%、44.37%和52.71%,且抑制效果差异极显著;田间最后1次喷药10 d后,15、20和25 mmol/L硅酸钠对葡萄炭疽病的防治效果分别为66.94%、67.16%和73.46%,喷施10%苯醚甲环唑6次的防治效果为76.84%,喷施3次的防治效果为64.29%;25 mmol/L硅酸钠与喷施6次苯醚甲环唑的防治效果差异不显著,但与喷施3次苯醚甲环唑的差异极显著。研究表明,在生长季可利用硅酸钠与常规药剂交替使用来防治葡萄炭疽病。     

Variation in MCPA-resistance in Ranunculus acris L. subsp. acris and its correlation with historical exposure to MCPA

In seven field experiments in which the effect of MCPA on Ranunculus acris subsp. acris in dairy pastures in New Zealand was studied, control varied between sites from 93% to 11% reduction in ground cover. To determine if the populations varied in resistance to MCPA, seedling progeny were sprayed with a range of doses of MCPA in a glasshouse. The LD₅₀ values ranged from 0.36 kg MCPA ha^?1 to 1.5 kg MCPA ha^?1 confirming the existence of genetic variability in resistance between the populations. Correlations between the LD₅₀ values and the control of the populations in the field, suggested that the differences in resistance contributed to the differences in control. A correlation between the LD₅₀ values and historical exposures of the populations to MCPA suggested that selection for resistance had occurred. No evidence of a difference in competitive ability between the least and the most susceptible biotypes was detected, suggesting that resistance would not decline if spraying ceased.