A.M. Dewar

Delayed control of weeds in glyphosate-tolerant sugar beet and the consequences on aphid infestation and yield†

An experiment was set up in 1998 to study the effect of glyphosate on the weeds and pests in glyphosate-tolerant sugar beet, in comparison with a conventional herbicide regime. Glyphosate at 1.08 kg ha−1 was first applied at the two- to four-leaf, 8- to 10-leaf and 12- to 14-leaf stage of the crop, followed by a second application at the same rate two to four weeks later. Weed growth did not affect sugar beet emergence or establishment, but, in untreated controls and the two later glyphosate treatments, weeds almost completely covered the ground, leading to reduction of root weight, sugar concentration and yield at harvest. The number of aphids (mostly Myzus persicae Sulzer) in the beet in June was significantly higher on plots treated with glyphosate at the two- to four-leaf stage than on untreated plots or plots treated later with glyphosate. Large numbers of the leaf curling plum aphid (Brachycaudus helichrysi Kaltenbach) colonised the weeds within untreated or later-treated plots. These were accompanied by predators and parasites which eventually caused substantial mortality in the aphid populations. There was evidence that glyphosate-treated weeds, although not in competition with the crop, were still able to provide sustenance for aphids. Very low levels of virus yellows were observed in the trial, and there were no significant differences between treatments. The results suggest that the latest application of the first glyphosate spray in a two-spray programme should be before the eight-leaf stage of the sugar beet to prevent weed competition reducing yield. Further studies on late control of weeds and insect diversity are being carried out. © 2000 Society of Chemical Industry

Weed control in glyphosate-tolerant maize in Europe.

Maize growing in the EU27 increased to over 13 million ha in 2007, most of which (>80%) was grown in just eight countries (France, Romania, Germany, Hungary, Italy, Poland, Spain and Bulgaria). The number of herbicides used to control the wide spectrum of weeds occurring in all these countries is likely to decline in the future as each current active ingredient is reassessed for toxicological and environmental safety under Directive 91/414/EEC. Glyphosate has already been approved under this directive. Glyphosate, applied alone or in combination with currently available residual herbicides to genetically modified varieties tolerant to glyphosate, can provide a viable, flexible and profitable alternative to conventional weed control programmes. Glyphosate usage with glyphosate-tolerant varieties also provides an environmentally sustainable weed control option as long as sufficient diversity of weed management options (crop rotation, chemical diversity, multiple cultural and mechanical practices, buffer strips) is maintained within the farm management system. Appropriate product stewardship measures will be required to maximise the long-term overall benefits of the glyphosate-based system. Specifically, care will need to be taken to manage potential weed shifts to more difficult-to-control species and to reduce the risk of selection for glyphosate-resistant weeds.

The adverse impact of the neonicotinoid seed treatment ban on crop protection in oilseed rape in the United Kingdom

This paper describes the consequences of the ban on neonicotinoid seed treatments on pest management in oilseed rape. Since the ban was implemented in December 2013, there have been serious crop losses in 2014, 2015 and 2016 owing to cabbage stem flea beetles, Psylliodes chrysocephala, and aphids, Myzus persicae, which have developed resistance to the alternative pyrethroid sprays that were employed to control them. This has resulted in increased crop losses, decreased yields and a substantial decrease in the area grown, leading to fewer flowering crops available in the spring, especially in the eastern region of the United Kingdom. This is likely to have an adverse effect on bees locally.

The adverse impact of the neonicotinoid seed treatment ban on crop protection in oilseed rape in the UK

This paper describes the consequences of the ban on neonicotinoid seed treatments on pest management in oilseed rape. Since the ban was implemented in December 2013, there have been serious crop losses in 2014, 2015 and 2016 owing to cabbage stem flea beetles, Psylliodes chrysocephala, and aphids, Myzus persicae, which have developed resistance to the alternative pyrethroid sprays that were employed to control them. This has resulted in increased crop losses, decreased yields and a substantial decrease in the area grown, leading to fewer flowering crops available in the spring, especially in the eastern region of the United Kingdom. This is likely to have an adverse effect on bees locally.

Onset of a decline in the quality of sugar beet as a host for the aphid Myzus persicae

The results presented in this paper suggest that sugar beet became less suitable as a host for aphids after late June and early July, when the plants were at the 10–12 leaf stage. This was indicated by a faster rate of aphid mortality and greater incidence of dark stomach deposits after this time. Increased aphid mortality coincided with a change in physiology of sugar beet leaves from being net sinks to sources of assimilate. Aphids which fed on older leaves, irrespective of plant age, suffered greater mortality than those feeding on young heart leaves. The incidence of dark deposits in aphid stomachs associated with this mortality was greater on outer than on inner leaves of old, mature and young plants. It is suggested that the incidence of the dark deposit is an indicator of declining plant quality. The consequences of this for the spread of beet yellowing viruses are discussed.

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.

The relationship between pellet size and the quantity of imidacloprid applied to sugar beet pellets and the consequences for seedling emergence

Abstract When imidacloprid was applied to sugar beet pellets at 90 g a.i. per unit of 100,000 seeds, the quantity of imidacloprid applied to individual sugar beet pellets was directly proportional to the size of pellet, resulting in lower dosing of some pellets and high dosing of others. This variability in application resulted in a slowing of germination in a laboratory experiment but had no effect on the rate of emergence in a field trial of young seedlings produced from large pellets compared with that from smaller pellets. However, there was a significant reduction in total number of seedlings emerging from large imidacloprid-treated pellets in a spring-sown field trial suggesting that additional phytotoxicity had occurred. Uptake of imidacloprid in leaf tissue was also greater in plants produced from large pellets. In a field trial at Brooms Barn, sown in the autumn, imidacloprid at 30, 60, 90 and 120 g a.i. per unit significantly slowed the rate of emergence of three varieties of sugar beet but there was no effect on pellet size. However, in contrast to the earlier trial, small pellets of two of the three varieties produced significantly fewer seedlings than large pellets, irrespective of the rate of imidacloprid applied, and there were no interactions between pellet size and rate of imidacloprid applied. Similar results were observed in another field trial in Norfolk where small pellets of one of the varieties, untreated, or treated with 30, 60 and 90 g a.i. of imidacloprid, but not 120 g a.i., produced significantly fewer seedlings. Small pellets of another variety produced the highest number of seedlings. Thus the variability in application of imidacloprid to sugar beet pellets can sometimes cause increased phytotoxicity to plants produced from large pellets, but this effect was not consistent with different varieties and different batches of the same variety.

The effect of host plant-induced stomach precipitate on the ability of Myzus persicae (Hemiptera : Aphididae) to transmit sugarbeet yellowing viruses

When Myzus persicae (Sulzer) feeds on healthy sugarbeet it develops a white precipitate inside its stomach which causes the stomach to enlarge. Infection of sugarbeet plants with beet yellows virus (BYV), but not beet mild yellowing virus (BMYV) results in further increases in stomach size. The influence of the white precipitate on the transmission of BYV and BMYV was investigated by rearing M. persicae on sugarbeet Beta vulgaris, Tetragonia expansa and Capsella bursa-pastoris, which are hosts for both BYV and BMYV, BYV and BMYV respectively, but the latter two hosts do not stimulate the formation of white precipitate in the aphids stomach. Aphids reared on BYV-infected T. expansa were significantly better vectors of BYV than those reared on BYV-infected sugarbeet, but aphids reared on BMYV-infected C. bursa-pastoris did not transmit BMYV more efficiently than those reared on BMYV-infected sugarbeet. The consequences of these results for the spread of beet yellowing viruses are discussed.

Comparisons of granular pesticides for the control of soil-inhabiting arthropod pests of sugar beet

Abstract From 1979 to 1991, surveys show that on average about 50% of the UK sugar-beet crop was treated with a granular pesticide applied in the seed furrow at sowing, and a further 10% with gamma-HCH spray worked into the seed-bed before sowing. Between 9 and 18% was treated with granules specifically to control a complex of soil-inhabiting arthropod pests such as springtails, symphylids, millipedes and pygmy beetle. Between 1978 and 1988 the efficacy of various granular insecticides was assessed in 24 field experiments situated where attack by these pests was expected. These experiments indicated that the replacement of aldicarb, largely by carbofuran or carbosulfan, in situations where soil pests were the main target, was justified. Furathiocarb and tefluthrin tested in the later experiments were, respectively, at least equal to, or better than, the best commercially available treatments.

Effect of established and novel aphicides on resistant Myzus persicae (Sulz.) on sugar beet under field cages

Abstract In caged field trials where currently approved insecticide sprays were applied to potted sugar-beet plants infested with mixtures of resistant clones of Myzus persicae , pirimicarb gave the best control of resistant aphids, leaving only a few highly resistant survivors. Deltamethrin plus heptenophos, ethiofencarb and demeton-S-methyl gave reasonable control after one application but relatively poor, if any, control after two sprays. The pyrethroids, cypermethrin and cyhalothrin, gave poor control of aphids after one spray and allowed a rapid increase in numbers of resistant aphids after two sprays. Of the novel insecticides tested, RH 7988 gave excellent control, while WL108477 gave poorest control of all resistant variants, but did not select for resistant variants. The results of the performance of approved products support current recommendations for aphid control in sugar beet in the UK.