Associations of wheat with pea can reduce aphid infestations.

Increasing plant diversity within crops can be beneficial for pest control. In this field study, the effects of two wheat and pea associations (mixed cropping and strip cropping) on aphid populations were compared with pure stands of both crops by observations on tillers and plants. Pea was more susceptible to infestations than wheat. As expected, the density of aphid colonies was significantly higher in pure stands during the main occurrence periods, compared with associations. Additionally, flying beneficials, such as not only aphidophagous adult ladybirds but also parasitoid, hoverfly and lacewing species that feed on aphids at the larval stage, were monitored using yellow pan traps. At specific times of the sampling season, ladybirds and hoverflies were significantly more abundant in the pure stand of pea and wheat, respectively, compared with associations. Few parasitoids and lacewings were trapped. This study showed that increasing plant diversity within crops by associating cultivated species can reduce aphid infestations, since host plants are more difficult to locate. However, additional methods are needed to attract more efficiently adult beneficials into wheat and pea associations.

Unusual occurrence of cocoons in population of Haplodiplosis marginata (Diptera: Cecidomyiidae) in Belgium.

The saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), is a phytophagous species that develops in saddle-shaped galls on stems of wheat Triticum vulgare, barley Hordeum sativum, rye Secale cereale, and some other species of Poaceae. Only one generation develops per year. Full-grown larvae leave galls and drop onto the soil where they remain up to the springtime of the following year. Larvae do not usually spin cocoons. However, formation of cocoons by larvae was observed in populations developing in western Europe: in England in 1954, in the Netherlands in the 1960s, and in Belgium in 2011. On the basis of our analysis, a part of the larval population forms cocoons as protection against unfavorable weather conditions, especially drought.

Study on the sensitivity of three oat varieties to the saddle gall midge, haplodiplosis margina ta (von Roser) (Diptera: cecidomyiidae).

The saddle gall midge, Haplodiplosis marginota (von Roser, 1840) is a univoltine pest of cereals which occurs in Europe. The larvae feed on stems and attractive saddle-shaped depressions, driving to important yield losses when the galls are numerous. After 40 years without any reporting, large populations of H. marginata and important damage have been observed since 2010 in wheat crops in Belgium, especially in the Flemish Polders where clay soils and intensive farming of cereals favour heavy infestations. According to some research conducted in the 1960s during the last outbreak, oat (Avena sativa L.) is known to be one of the less favourable hosts to the saddle gall midge. Our study was performed in order to assess the host sensitivity of three oat varieties currently grown in Belgium: EVITA, EFFEKTIv and FREDDY. Therefore, oat varieties were sown on infested soil in two separate enclosures in a glasshouse. In the first enclosure, only the three oat varieties were grown; in the second one, these three oat varieties were grown together with two varieties of spring wheat: GRANNY and KWS CHAMSIN. TWO parameters were measured: the percentage of leaves with laid eggs, and the number of galls per stem. The percentage of leaves with eggs showed that the infestation was significantly lower on oats when they were in presence of wheat. The egg infestation was also significantly higher on wheat than on oat, which means oat is a much less favourable host plant than spring wheat for egg laying. Oat varieties were significantly different from each other regarding the number of galls per stem, but with very little damage compared to wheat. The FREDDY variety even seemed to be completely resistant to saddle gall midge, as no galls were observed although there was a similar percentage of leaves with eggs for the three oat varieties. Cropping oat could thus contribute to reduce infestations of H. morginato.

Integrated management of wild chamomile (Matricaria chamomilla L.) populations by tillage.

Nowadays, environmental, health and economic concerns encourage reviewing our weed management in agriculture. Integrated pest management is one key element in the development of weed management strategies less dependent from herbicides. To reach this goal, impact of different methods of tillage (Combinations of stubble cultivator and moldboard plow) on biology and dynamic of wild chamomile populations was studied in experimental plots of experimental farm of Gembloux Agro-Bio Tech. In summer 2012, wild chamomile densities were significantly lower in plots tilled with a moldboard plow. The use of a stubble cultivator did not significantly affect M. chamomilla density. In addition, we found higher wheat yields in plowed plots, indicating that the decrease in M. chamomilla densities reduces competition for wheat. These results show well long run impact of plowing and his effect on densities of wild chamomile and the seedbank.

Silky bent grass resistance to herbicides: one year of monitoring in Belgium.

Silky bent grass (Apera spica-venti (L.) P. Beauv.) is a common weed of cereal crops widely spread in Northern and Easthern Europe (Germany, Czech Republic,...), Northern Asia, Siberia and Canada. Up to now, no resistant case has been detected in Belgium but some chemical weeding failures have been observed in Wallonia fields. During summer 2011, 37 seed samples of Apera spica-venti were collected in Wallonia and submitted to resistance tests in controlled conditions. Three modes of action were tested: acetyl coenzyme-A carboxylase inhibitors (pinoxaden and cycloxydim), acetolactate synthase inhibitors (mesosulfuron+iodosulfu-ron, pyroxsulam and sulfometuron) and photosynthesis inhibitors (isoproturon). One susceptible standard population was included in the test in order to validate it and to permit wild populations classification according to "R" rating system developed by Moss et al (2007). Most of populations were susceptible but some populations showed resistance to at least one of the three tested modes of action.

Study of factors influencing the germination of Apera spica-venti(L.) P. Beauv. in controlled conditions.

Apera spica-venti (L.) P. Beauv. is a common weed of cereal crops widely spread in Northern and Eastern Europe, Northern Asia, Siberia and Canada. Given the ability of Apera spica-venti to grow and develop in Wallonia and lack of scientific knowledge of its biology, germination tests were performed on four populations. These laboratory tests were carried on according to the standards of the International Seed Testing Association (ISTA) in order to study three key factors (composition of water solution, presence/absence of pre-chilling and temperature) influencing the germination of the seeds. Germination tests showed that a solution containing 2 g/L of KNO3 and alternating night/day temperatures between 10 degrees C and 30 degrees C favorably influence the germination of Apera spica-venti. These results in controlled conditions are a premise for greenhouse and field tests.

Effect of mechanical weeding on wild chamomile (Matricaria chamomilla L.) populations in winter wheat crop (Triticum aestivum L.).

Currently, economic, agronomic and environmental concerns lead to reduce the use of herbicides. Mechanical weeding can help to reach this objective. Dynamics and biology of wild chamomile (Matricaria chamomilla L.) populations were assessed as well as dynamic of winter wheat (Triticum aestivum L.) for four level of application of a weeder-harrow (0, 1, 2, 3 treatment(s)). After each treatment, an effect of mechanical weeding on wild chamomile density was observed. Density of wild chamomile decreased significantly with intensification of mechanical weeding. A third treatment allowed eliminating late emerged plants.

Chemical control of Haplodiplosis marginata von Roser (Diptera: Cecidomyiidae).

The saddle gall midge, Haplodiplosis marginata (von Roser), has been detected in Belgium since 2010, after several decades without any reporting. It had indeed caused serious damages between 1965 and 1970. This insect is a European cereal pest whose larvae feed on stems and engender saddle-shaped depressions, resulting in yield losses. Face with the resurgence of this pest, it was decided to study its spatial distribution and, because serious damages were observed in some regions, to develop effective curative control. To date, chemical protection seems to be the only immediate solution in case of heavy emergences. Experimentation was conducted in a highly infested field (Meetkerke, Belgian Polders), according to a randomized complete blocks arrangement with four replications. Foremost, a lambdacyhalothrin-based insecticide was used to evaluate efficiency of several protection schemes, ranging between one and four spray(s). The large spread of flights observed during the 2011 spring allowed to highlight the effect of treatment date on the attack intensity and also on the galls distribution along the stem, on the different internodes: the lower internodes were protected by the early sprayings, while last sprayings induced reduction of galls number on the upper internodes. Moreover, several insecticides already registrated in cereals against aphids were compared for their efficacy against saddle gall midge. Studied pyrethroids have shown a very good efficacy, ranging between 75% and 87%, when applied twice with a 2 weeks interval. To be efficient, insecticide applications must thus be synchronized with the flights and egg-laying periods. Monitoring the phenology of flights is thus essential as part of integrated pest management against saddle gall midge.

Dynamic of black-grass populations depending on the sowing time of winter wheat.

Currently, economic, agronomic and environmental concerns, lead to reduce use of herbicides. This reduction can be help by cultural measures like delay of the sowing date. Four sowing dates of winter wheat from 15th of October to 26th of November were tested. Dynamic of black-grass (Alopecurus myosuroides Huds.) populations and their reproduction rate were assessed as well as dynamic of winter wheat for each date. Delay of sowing could significantly reduce reproduction rate of black-grass. It was shown that the emergence rate (pl/m2), but also number of ears per plant and number of seeds per ear of black-grass decreased significantly with the sowing date. This reduction of seeds production already is from sixty per cent for a delay of two weeks sowing.

Crossing abilities of ALS target-site resistant black-grass (Alopecurus myosuroides Huds.).

Black-grass crossings were conducted outdoor for two successive years in a way to determine the percentage of resistant black-grass that can be engendered in one generation, after the introduction of one target-site resistant individual. After germination, plants were genotyped and couples of resistant and susceptible individuals were formed, then planted outdoor and enclosed with a pollen-proof cloth to avoid any external pollen contamination. Seeds were collected and tested in glasshouses with herbicide spraying. DNA analyses were also performed on surviving plants to distinguish hetero- from homozygotes. The resistance level of the progeny seems to be fairly high and Mendelean distribution is generally confirmed. The offspring of self-crossings was also observed to assess the facultative autogamy ability, according to the genotype and the presence of mutant ALS alleles (position W-574).

Detection of ACCase target-site resistant Alopecurus myosuroides Huds. (black-grass) in Belgian populations.

Black-grass is a common grass weed, widely spread in Northern Europe and also in Belgium. For ages, it has been an increasing problem in industrial crops, especially winter cereals. The first case of resistance in Belgium was reported in 1996 by Robert Bulcke (Eelen et al., 1996). Yet the resistance mechanism was not specified. Since then, no more information was published about the evolution Belgium, while research continued in the United Kingdom and in France. Moreover, during the last decade, progress in molecular biology allowed to highlight the mechanism of target-site resistance. A simple PCR method allows to detect the mutation conferring resistance to herbicide. After two years of resistance monitoring in Belgium, mostly in the Walloon part, some populations have been clearly identified as highly resistant to ACCase inhibitor. These populations have been tested by molecular biology so as to detect the single nucleotide polymorphism (SNP) involved in this case. The method employed was the Polymerase Chain Reaction Allele Specific Assays (PASA: Délye, 2002a) for the mutation Ile-1781-Leu that confers a target-site resistance to ACCase inhibitors. Those analyses were performed on plant material issued from bioassays, either in glasshouses or in Petri dishes. Leaves have been collected from plants which survived a fenoxaprop-P treatment applied in a glasshouse single dose assay. Seedlings from resistant populations grown in Petri dishes containing either fenoxaprop-P or cycloxydim provided the second type of sample. Ile1781 mutants were discovered within three populations. Each mutant plant was heterozygote. Five of those samples have been sequenced to confirm PASA results and everyone was matching. Moreover, they were all issued from Petri dishes containing cycloxydim, known to be unaffected by enhanced metabolism, confirming that theses populations are indeed target-site resistant.

Treatment influence on herbicide resistance level of Belgian Alopecurus myosuroides populations (black-grass).

Black-grass is a common grass weed, widely spread in Northern Europe and also in Belgium. For ages, it has been an increasing problem in industrial crops, especially winter cereals. Therefore, farmers started to spray herbicide intensively and soon cases of failure occurred for different molecules and different modes of action. Black-grass populations have been tested in greenhouses to assess the influence of an herbicide treatment as to the resistance level regarding three different herbicides: chlortoluron, fenoxaprop-P and mesosulfuron+iodosulfuron. Black-grass seeds were collected in field trials in six locations in Belgium, on individuals which have survived the herbicide treatment. Each population comes from trial plots, measuring 2 meters wide by 5 meters long and characterized by a single or a combination of products. Herbicides sprayed were isoproturon, flufenacet+diflufenican, ACCase inhibitors and ALS inhibitors. Seeds were also collected in the untreated plots. The population present in these last ones corresponds to the former population, before the herbicide selection pressure was applied. In the glasshouse assay, this population was used as the standard population to compare with other populations issued from the same field. The 'R' rating system was set up with this population to assess the evolution of resistance level, year in, year out. Rothamsted and Peldon populations were also included as cross-reference. Each field population presented different behaviours towards herbicide applied in greenhouses and some cases of resistance can be highlighted. Generally, a reduction of treatment efficiency between field and greenhouse results was clearly visible for the whole of studied active ingredients. Indeed, a distribution shift of the populations towards higher resistance classes could be observed. This is particularly remarkable for active ingredients sharing the same mode of action. For example, it has been found that populations already sprayed with fenoxaprop-P on the field showed a higher resistance level to fenoxaprop-P than to mesosulfuron in the greenhouse test.

Inter- and intra-guild interactions related to aphids in nettle (Urtica dioica L.) strips closed to field crops.

A field experiment designed to assess the biodiversity related to nettle strips closed to crops, and more particularly the aphid and related beneficial populations, was established in experimental farm located in Gembloux (Belgium). Margin strips of nettle (Urtica dioica) closed to wheat (Triticum aestivum), green pea (Pisum sativum) and rape (Brassicae napus) fields were investigated. The diversity, abundance of aphids and related predators were analysed according to the plant crop species and the differential pesticide application (treated plot and control). Insects were visually observed every week during all the cultivation season. Two main families of aphidophagous predators were found in all field crops and nettle, the Coccinellidae and Syrphidae. The diversity of the aphidophagous predators was shown to be higher on nettle than in field crops, particularly the Chrysopidae, the Anthocoridae and the Miridae. However, a striking difference of ladybird abundance was observed according to the aphid host plant. In one side, Coccinella septempunctata was much more abundant on Acyrthosiphon pisum infested green pea than on the other host plant species. At the opposite, higher occurrence of Harmonia axyridis was observed on the aphid infested nettle plants than on the crop plants. In particular, none of H. axyridis was found in wheat crop. Also, more than only a significant positive correlation between predator and aphid abundance, specialised relations between particular aphid species and some so-called generalist predators was determined in the fields. Finally, intraguild interactions between the aphidophagous predators was assessed and shown that only a significant negative correlation between Episyrphus balteatus and H. axyridis related to the nettle aphid, Micrlophium carnosum, was observed. The relative distribution of the ladybirds, namely C. septempunctata and H. axyridis according to the host plant, nettle strips and crop plots was discussed in relation to integrated pest management approach.

Individual and combined effects of dosages of azoxystrobin and epoxiconazole in wheat.

The effects of single fungicide applications on Mycosphaerella graminicola (septoria leaf blotch) control and winter wheat yield were evaluated in field trials conducted in central Belgium between 2000 and 2004. Individual applications of 25, 50, 75 and 100% of the manufacturer's recommended dose rates of azoxystrobin and epoxiconazole, and all the combinations of these treatments, were made at GS 39 in 2001 to 2004 and at GS 59 in 2000. Disease assessments were made at growth stage 75, some 7-8 weeks after the last applications. Between 2000 and 2003, no significant difference was observed for disease control between the products when applied alone. With regard to the dose responses, the differences between the recommended dose rates and the 50% reduced dosages were not important. In 2004, azoxystrobin was less effective than epoxiconazole. This was probably the result of strobilurin-resistant isolates of M. graminicola reaching an occurrence of 32% before fungicide application. The combination of different dosages of azoxystrobin and epoxiconazole revealed that there was very little synergy between these products when applied in a single application. The combinations of these products were better than individual applications only when high dosages of both compounds were used.

First detection of resistance to QoI fungicides in Mycosphaerella graminicola on winter wheat in Belgium.

A total of 740 Mycosphaerella graminicola strains were isolated between 2000 and 2002 from winter wheat F1 or F2 leaves showing Septoria leaf blotch lesions (SLB) collected mainly at the soft dough stage in fungicide trials, analysing at 12 locations in Belgium the possibilities and risks associated with the use of epoxiconazole and azoxystrobin at various doses, mixtures and application dates. Fungicide sensitivity tests were performed in microtitre plates on potato dextrose broth amended with various concentrations of azoxystrobin. A wide range of sensitivity to azoxystrobin was observed, with EC50 values ranging for 735 strains between 0.002 to 0.7 microg/ml, the highest frequency gradually shifting from EC50 classes 0.01 and 0.02 microg/ml azoxystrobin in 2000 to EC50 classes 0.02 and 0.04 microg/ml in 2002. No clear selection effect of particular fungicide use strategies was observed. Among the 382 strains isolated in 2002, five originating from 2 locations, showed azoxystrobin EC50 values >1 microg/ml. On medium amended with 100 microg/ml salicylhydroxamic acid (SHAM), 58% of the 2002 strains were strongly inhibited, which affected adequate azoxystrobin ED50 determination. This suggests widespread occurrence of M. graminicola strains relying in vitro on the alternative respiration pathway. In the presence of SHAM, strains 339 and 880 showed azoxystrobin EC50 values of 3 and >30 microg/ml, respectively. This high level of resistance to a QoI fungicide was confirmed by analysing mycelium growth inhibition on PDA. Cross-resistance to trifloxystrobin and kresoxim-methyl was demonstrated. Greenhouse assays on wheat plants revealed that control of QoI resistant strains by azoxystrobin is decreased, compared to control of sensitive ones. This highlights the risk of resistance to QoI fungicides also in M. graminicola populations, although up to now no decrease in field performance was noticed. It is recommended to delay build up of QoI resistance by an integrated approach, combining optimised fungicide use with the choice of SLB resistant cultivars and the application of farming practices promoting stubbles break down and so the reduction of the teleomorph stage.

Lessons from the year 2001 Mycosphaerella graminicola epidemic on winter wheat in Belgium.

Infection by Mycosphaerella graminicola (anamorph Septoria tritici) was monitored between April and July 2001 on F6 to flag leaf in 11 farmers' fields or fungicide trials. Data were analysed by mean of the decision support system "Proculture" which links an automatic weather station of the PAMESEB network to a particular field, simulates plant development with adjustment by one phenological observation during the stem elongation and analyses superposition of emerged leaves and infection events (http://www.fymy.ucl.ac.be/proculture). Several climatic events favourable for the infection and dissemination of M. graminicola occurred between October 2000 and March 2001 and allowed build up of a large amount of inoculum on the lower leaves at the end of the winter. The start of stem elongation was associated with frequent rainy periods during April, causing early infection of F5, F4 and up to F3 in some precocious fields. Dry weather with only a few local showers during most of May and June slowed down spread of infection to the upper leaves, leading to absence of M. graminicola infection of the flag leaf in 9 out of the 11 fields. Yield increase by a single fungicide spray ranged from 800 to 2200 kg/ha. A second treatment was cost effective in none of the fields. The interest and limitation of the decision support system for understanding M. graminicola epidemic and for guiding decision on spray timing are discussed.

[Attempt to elaborate an explanating model of adolescents' contraceptive behavior]. / Essai d'elaboration d'un modele explicatif du comportement contraceptif des adolescentes.

PIP: Of the 3 main currents of literature seeking to explain adolescent pregnancy, the medical and demographic currents have essentially produced descriptions of behaviors, attitudes, and opinions, while the psychological current has produced primarily hypotheses interpreting sexual and contraceptive behavior in terms of predispositions. This work seeks to develop an explanatory framework for adolescent sexual and contraceptive behavior in which situational variables would be included. The explanatory variables utilized in the framework were informative and sociological variables, beliefs associated with side effects of contraceptive methods, social support for contraceptive use, norms associated with heterosexual behavior, ability to foresee future consequences, future prospects, perceptions of pregnancy and its consequences, and evaluation of the risk of pregnancy. A semiclosed questionnaire exploring the different model variables was orally administered to 186 female secondary school students in Liege, France. The data were subjected to a discriminant function analysis which permitted assessment of the role of each explanatory variable in determining contraceptive behavior. 53% of the respondents did not use contraception. 91% of those using contraception used pills. 5 types of contraceptive behavior were noted: 1) 20% of the sample were sexually active and had always used contraception 2) 20% were sexually active and used contraception but had not always done so 3) 13% were sexually active but had never used contraception 4) 40% were not sexually active and did not use contraception, and 5) 7% were not sexually active but used a contraceptive. The variables explained 75% of the difference between adolescents who used and did not use contraception, and 39% of the difference between adolescents ever exposed to risk of pregnancy or never exposed. The principle variables explaining use or nonuse of contraception were stated in declining order of importance. Girls having sexual relations under 17 years of age were much less likely to use a contraceptive method. 3 dimensions of norms associated with sexual behavior were relevant: adolescents using contraception had a more positive attitude toward sex, were less affected by aversion to programming or planning sexual activity, and had a more flexible sexual morality. Adolescents using contraception had parents and other associates who were more likely to approve of pill use, and they had less fear of the side effects of pills. Adolescents not using contraception tended to be under 17, with rigid norms associated with sexual behavior, weak social support for pill use, and beliefs in the negative effects of pills. Sexually active adolescents not using contraception tended to come from larger families, to have more unfavorable views of condoms than other adolescents, to have less social support for use of condoms than other adolescents, to want to have a child within the next 2 years, and to come from the lower social classes.^ieng