Pest Management in Cereals and Oilseed Rape – a Guide
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Pest management in cereals and oilseed rape – a guide Autumn 2003 Contents BYDV vectors 4 Grey field slug 6 Gout fly 7 The impact of pests on yield and quality can be more variable than that of many diseases. Wheat bulb fly 8 However, they do pose a serious threat to UK crops and can reduce yield by 10% or more, Yellow cereal fly 9 sometimes much more. Wireworms 10 With increasing concerns about the environment, there is a need to balance pest Leatherjackets 11 control against encouraging other insects which Summer aphids 12 can actually benefit the crop. Orange wheat blossom midge 13 Integrated strategies seek to use cultural control options, encourage natural enemies and only use Peach-potato aphid 14 crop protection methods when they are fully justified – usually by the use of thresholds. Cabbage aphid 14 Developing such strategies depends on a sound Cabbage stem flea beetle 15 understanding of pests, their life cycles and their natural enemies.This guide brings together the Other flea beetles 16 latest knowledge from research funded by Defra and HGCA. Wessex flea beetle Turnip flea beetle Jon Oakley, a leading entomologist, has gathered here information that will be invaluable to Large striped flea beetle growers who seek to minimise pest damage, Pollen beetle 17 maximise the marketability of their crops and enhance the environment on their farms. Cabbage seed weevil 18 Brassica pod midge 18 Other pests 19 Frit fly Thrips Professor Graham Jellis Saddle gall midge Director of Research HGCA Rape winter stem weevil Cereal ground beetle Cabbage stem weevil The Home-Grown Cereals Authority (HGCA) has provided funding for some of the projects on which this guide is based but has not conducted the research or written this guide. While the authors have worked on Biological and cultural control 20 the best information available to them, neither the HGCA nor the authors shall in any event be liable for any loss, damage or injury Further information 23 howsoever suffered directly or indirectly in relation to the booklet or the research on which it is based. Front cover: Gout fly and parasitoids on wild flowers Reference herein to trade names and proprietary products without in a field margin. stating that they are protected does not imply they may be regarded as pest management in cereals and unprotected and thus free for general use. No endorsement of named oilseed rape – a guide products is intended, nor is any criticism implied of other alternative, but unnamed products. 2 Effective pest control ➤ Assess the risk of infestations. ➤ Minimise pest risk by cultural means. ➤ Maximise the effects of natural enemies. ➤ Only use treatments if economically justified. General principles of pest management For pests Yes Order that seed Have these seed treatments pests caused Yes treatment may control damage in Has risk (eg cabbage previous No of pest stem flea beetle, crops? increased? wireworm, No Do not use seed wheat bulb fly) treatment For pests Yes Plough early, or use desiccant that Does cultivations previous crop BEFORE SOWING may control or stubble (eg green bridge regrowth No BYDV, increase risk? leatherjackets, frit fly) Do slugs pose Yes Sow deeper and Monitor a particular roll after sowing using traps threat? Control (eg is there a of slugs history of slug Yes Apply problems, does Are slugs above molluscicide the weather threshold? No No EMERGENCE favour the pest?) FROM SOWING TO SOWING FROM Consider Monitor for No Will pest levels Yes treatment at pests that Is there a exceed correct timing affect growing risk of threshold? No crops imminent (eg pollen beetle, attack? No AFTER Are natural wheat blossom Yes midge, gout fly) enemies present? EMERGENCE No Yes 3 BYDV VECTORS BYDV Two different aphid species transmit barley yellow dwarf luteovirus (BYDV) to cereals and grasses in the UK. Very low populations, which may go unnoticed, can cause economic damage. In autumn most aphids probably come from grasses, especially perennial ryegrass.Virus may also come from other cereal crops and volunteers. Grain aphid Bird cherry-oat aphid Sitobion avenae Rhopalosiphum padi The aphids may be green, The aphids are green to red or brown with black dusky brown with rust red legs. patches at the rear. Transmits: The MAV and Transmits: The PAV and PAV strains of BYDV. RPV strains of BYDV. Economic importance Economic importance The grain aphid is the main and northern Britain. Losses can The bird cherry-oat aphid is the west England and in warm BYDV vector in eastern, mid be up to 2.5 t/ha. main vector of BYDV in south- autumns elsewhere. Risk factors Risk factors Winter crops: In mild winters Spring crops: After mild Winter crops: Crops sown Spring crops: After mild significant spread may occur in winters BYDV may be early,particularly in a warm winters BYDV may be any crops exposed to transmitted to late-sown crops autumn, are most susceptible to transmitted to late-sown crops migrations of the winged by winged aphids. bird cherry-oat attack.These by winged aphids. aphids.These can continue into conditions allow aphids to breed November and infect later sown rapidly before frosts kill them. crops. Life cycle Life cycles The grain aphid is mainly 50% of the aphids) of -8ºC. The asexual strain The sexual strain asexual feeding on cereals and Grain aphids survive on crops – overwinters on cereals – overwinters as eggs on bird grasses all year round.The aphid through most winters. Numbers and grasses. cherry trees. is more frost-resistant than the increase during mild spells Aphids are frost-susceptible, the Most wild bird cherry trees are bird cherry-oat aphid with a when further BYDV spread LT50 being -0.5ºC. In colder found in northern Britain LT50 (lethal temperature for may occur. winters survival of this strain is although they occur across restricted to milder coastal the UK. districts. Eggs of bird cherry-oat aphid are very frost-resistant. Bird cherry trees are not infected by BYDV,so spring migrants are initially virus-free. Aphids of the sexual strain do not transmit BYDV within winter cereal crops. 4 BYDV VECTORS Both species Natural enemies Ground beetles and spiders may attack aphids in the autumn and Grass banks and grassed field margins may assist predator survival, winter and parasitoids can be active in mild weather. Minimum tillage but can also harbour infective aphids. Grassed areas should be leaves more predators, but increases the risk of ‘green bridge’ transfer. considered in large arable fields of 20 ha or more. ‘Green bridge’ transmission Warm, moist soil conditions facilitate aphid movement through weedy stubbles to new cereal crops.The aphids can feed on new soil.‘Green bridge’ transmission is most likely in south-west crop roots, and transmit virus directly without appearing above England, on early-sown crops and in mild, damp autumns. ground level to provide a control opportunity. Any cereal aphid Aphids can transfer directly from grass or ploughed-down grass or species present may transmit virus – often the RPV strain of BYDV. Cultural control 1. Clean stubble before preparing seedbed. 2. Leave at least five weeks between ploughing and sowing the new crop. 3. Consider applying a desiccant herbicide if cultivation to sowing interval is less than five weeks. 4. Delay sowing by a week to reduce BYDV spread by up to half. 5. Choose a moderately resistant spring barley variety (see HGCA Recommended Lists) if growing crops after mild winters or in milder districts. Chemical control Applying a seed treatment incorporating Spray timing imidacloprid (Secur) can provide about six BYDV starts to spread within the crop 1. Calculate ‘T sum’ by subtracting 3ºC from weeks’ protection, less at very low seed when the second wingless aphid generation the daily mean temperature and adding rates. It may not replace the need to spray. emerges. Spread, initially slow, accelerates as the result to the running total. In mild seasons the threat of aphid the third wingless aphid generation 2. If ‘T sum’is 170 (second generation could infestation may continue through the winter. appears. Aphid breeding is governed by be starting) A pyrethroid spray will kill most wingless temperature, so a ‘T sum’system of – consider a tank-mix insecticide if aphids. accumulated day degrees above 3ºC can be treating the crop for another purpose. Chemical control is ineffective on spring- used to predict best spray timings. 3. If ‘T sum’is 340 (significant spread sown crops. Temperature accumulation should be imminent) started from: – apply a spray treatment as a priority. Action thresholds M six weeks after sowing for imidacloprid- A crop should suffer little yield loss from No satisfactory thresholds for treatment treated crops fresh BYDV infection after GS 31 or after a exist. M date of emergence for other crops prolonged cold period. A month with mean M one week after application for pyrethroid- daily temperatures below 5ºC will severely treated crops. reduce grain aphid survival. An example of the effect of date of crop emergence on need to spray in a mild winter 26 Nov Early emerged crops are most at risk of BYDV infection. Decisions on whether to 19 Nov t n treat crops emerging in September must e ix be made by the start of October. The 12 Nov treatment window is wider for later- tm m emerging crops. 5 Nov a k e 29 Oct r tan Use ‘T-sum’ (see above) for specific t locality. 22 Oct o n rity 15 Oct 8 Oct high prio Date of crop emergence Date of crop 1 Oct 24 Sept 17 Sept too late Sept Oct Nov Dec Jan Feb Mar Month 5 CEREAL & OILSEED RAPE PESTS Grey field slug Deroceras reticulatum Many slug species are found in arable fields.