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 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. date of emergence for other crops prolonged cold period. A month with mean 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. Only the grey field slug is of economic importance on cereals and oilseeds.
The grey field slug is mottled grey and of medium size.
Economic importance Chemical control Slugs are most damaging to the four true-leaf stage (GS 1.4). Slug pellets are effective at the soil surface for 4–7 days, but only kill seeds and seedlings. Cereals are After these stages slug grazing actively feeding slugs. In mild, damp weather pellets only kill a vulnerable up to the fourth leaf does not generally threaten proportion of sexually active mature slugs. Juveniles often escape as stage (GS 14); oilseed rape to plant survival. they remain in the soil. Pellets have limited impact. Damage may resume within a month or, if conditions improve, weeks of treatment. Risk factors Action thresholds All cereal and oilseed crops, Such conditions allow access to Action thresholds for cereals are The threshold applies to particularly if grown on heavier, seeds and germinating seedlings based on slug numbers caught cereal crops. Slightly lower wetter soils and sown in loose, and also favour slug survival. in refuge traps – before or after numbers are probably worth cloddy seedbeds, are vulnerable. treatment. These can be made controlling in oilseed rape. from plant pot saucers or tiles, Trapping, and treatment if the Natural enemies baited with layers mash, or threshold is exceeded, is proprietary mats can be generally advised: Several predators eat slugs. purchased. Catches reflect before sowing if the field has Ground beetles are probably the numbers of slugs active on the a history of slug damage most common in arable fields. surface, not in the soil.Traps before sowing if wet weather only give useful information delays sowing in a prepared when mild damp night seedbed conditions encourage activity. following sowing if seedbed A catch of four or more slugs tilth is poor and further a trap generally justifies consolidation is not possible Cultural control treatment, provided conditions the crop is slow to emerge or remain favourable. to grow to GS 1.4 and when Cultivation in dry conditions consolidation prevents access to damage is visible. leads to physical damage and seed as well as encouraging desiccation. seed-to-soil contact, and rapid Cereal seed should be sown at germination. A Cambridge roller least 12 mm deep. For all is suitable. combinable crops soil Life cycle
There are two generations each year.
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Distinct spring (and autumn) Distinct autumn (and breeding peaks lead to two spring) breeding peaks overlapping generations at any time. lead to two overlapping generations at any time.
The grey field slug breeds year round exploiting any mild, damp periods. Mature adult slugs each lays up to 500 eggs.Typically many eggs and young slugs die from desiccation which keeps populations stable. If weather conditions are particularly favourable and mortality low, populations may increase to very high levels. Slugs feed opportunistically on a wide range of plant material changing from male to female as they mature.They are inactive in unsuitable conditions and resume feeding in mild, damp, still weather.
6 CEREAL PESTS Gout Fly Chlorops pumilionis
Larvae feeding in stems cause a ‘gouted’ appearance – swollen main stem and primary tillers with leaves puckered and torn above. In winter crops, damage is first seen in December, but mainly in January/February. Infested spring- sown crops show damage in June and July which prevents ear emergence from the flag leaf. Upper surface black with yellow beneath, Damage tends to be highest in sheltered fields three black stripes on thorax. near woodland.
Economic importance Cultural control
The pest is present across the tillers, with a developed crown Sow winter wheat and barley Sow spring crops as early as UK, but only causes economic root system can survive and in sheltered fields near practicable in areas where damage from the south coast to compensate for damage at lower woodland after late damage is prevalent. the midlands in wheat, barley levels of incidence.Where half September. and triticale. Incidence appears the crop or more is damaged, to be moving north. In 2002, yield losses range from 0.25 high levels of damage were seen tonnes/ha to total crop failure. Chemical control in early-sown crops as far north Shoots damaged by spring Chlorpyrifos and pyrethroid as Staffordshire and Lincolnshire. generations lose 30% of grain insecticides, used to control frit Winter damage kills affected yield on average. Late-sown fly and BYDV vectors tillers and any still dependent on crops suffer losses up to half of respectively, will give useful the mother plant. Unaffected their potential yield. control of the autumn generation where sprays are Risk factors applied before eggs hatch. In 2002, treatments after early Crops emerged by the end of south of England, late May in October were ineffective. September are at greatest risk the midlands. Crops at, or from the autumn generation. beyond, GS 37 by this time Action thresholds Late-sown winter and spring suffer little damage. Limited evidence suggests that crops are at greatest risk from Oats are immune, but gout fly treatment is economic in winter the spring generation. Egg-laying can attack couch grass. crops if eggs are found on more commences in mid-May in the than half of the plants at GS 12. No threshold exists for spring- Larvae feed by secreting Natural enemies sown crops. enzymes to break down surrounding tissues.This causes Larvae of the parasitoid wasps, no obvious damage to shoots. Stenomalus micans and As the stem extends this break Coelineus niger, feed inside the develops into a line of damage. gout fly larvae.They can kill 80% or more of gout fly larvae. Adult wasps are active slightly later than gout flies and could be vulnerable to late insecticide applications. Stenomalus micans Life cycle
There are two generations each year.
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Larvae Larvae Pupation Adult flies Larvae Larvae Adults shelter in Larvae feed. Adult flies feed. pupate in hatch. Eggs crawl into pupate hatch wooded areas and stem. laid on leaf sheath in leaf before hedgerows. uppermost and feed on sheath. harvest. Eggs laid on unfurled leaf sheath upperside of first leaf and beneath unfurled leaf. hatch in ear. 7–10 days.
7 CEREAL PESTS Wheat bulb fly Delia coarctata
Wheat bulb fly larvae attack shoots of wheat, barley and rye from January to April.They bore into plants, feed at the shoot base and eat through the central leaf which dies, causing the classic deadheart symptom. Larvae lack legs and are white to pale yellow with a blunt tail end.
Economic importance Chemical control
Yield loss depends on tiller destroyed.Well-tillered crops Tefluthrin seed treatments are density at the time of attack. generally withstand up to 100 effective with later sowings, but Crops still at the single shoot larvae/m2 without economic may not fully protect earlier- stage in February are most impact on yield. sown crops. Drill treated seed vulnerable and may be totally no deeper than 40 mm. Chlorpyrifos egg hatch Risk factors sprays are applied between the Egg start of egg hatch in January All cereals, except oats, can be crops (eg vining peas) if and its peak in February or attacked.Adults fly up to half a cultivated between mid-July March. Egg hatch is monitored mile from previously-attacked and mid-August each year to provide fields to lay eggs. They lay eggs row crops, eg sugar beet, information on timing and the on stubbles after cultivation and potatoes and onions but not need to add, or switch to, prefer freshly-turned soil. Under brassicas. dimethoate for later sprays. hot, dry conditions they lay eggs Frequency of attack depends on Dimethoate is applied when between row crops, especially if the population of vulnerable first deadhearts first appear in Larva hatching the foliage is wilting. wheats on the farm: March. It should be applied Eggs may be laid on: more than 25% – regularly before larvae move off to attack bare soil following fallows, 10–25% – occasionally other shoots in late March. Plant samples may be set-aside, or early harvested less than 10% – rarely. examined to determine Action thresholds numbers of larvae present Natural enemies Egg numbers can be estimated when deadhearts are first The main egg predators are Aleochara bipustulata may from soil samples. Each year found. Stripping off the outer ground beetles and their larvae. parasitise the pupae, and kill up ADAS forecasts (available leaf sheath can reveal a brown Small rove beetles, particularly to 50% of them. through Dow*) the proportion stain where larvae are feeding. of fields likely to exceed A small entry hole in the leaf Cultural control threshold levels: sheaf confirms that a larva has above 5 million eggs/ha – entered.The thresholds assume Avoid cultivating fields destined Early sowing reduces the damage inevitable, extra plant populations of at least 200 for wheat in late July and early impact of wheat bulb fly, but measures needed plants/m2: August.This reduces numbers of increases survival of larvae and 2.5–5 million eggs/ha (sowing 10% tillers attacked @ GS 20 eggs laid, especially if fields for numbers on the farm the next Sept–Oct) – damage likely 15% tillers attacked @ GS 21 oilseed rape, and other non-host year. less than 1.25 million eggs/ha 20% tillers attacked @ GS 22 crops, are worked at this time. (sowing Nov–Mar). Late sown onwards. crops may suffer damage.
Life cycle
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Larvae hatch and invade shoots of Adults feed on Eggs laid on wheat, rye and barley. saprophytic fungi on bare soil host plants. and Larvae attack 3–5 Larvae between further shoots. pupate at base of row crops. Overwinters as eggs. plants.
* Dow AgroSciences Technical Hotline – 0800 689 8899
8 CEREAL PESTS Yellow cereal fly Opomyza florum
Yellow cereal fly, like wheat bulb fly, causes ‘deadheart’ as larvae enter through the top of the shoot.The yellow cereal fly larva does not leave an entry hole; wheat bulb fly larva does.The larva, yellow and with a pointed end, looks similar to frit fly, but occurs later in the winter.
Economic importance Cultural control
Each larva damages only a single withstand a considerable Establish at least 200 shoot so economic impact is number of larvae by producing plants/m2 in vulnerable generally low. Most crops can compensating tillers. situations.
Risk factors Chemical control Crops at low plant populations sheltered fields close to Pyrethroid sprays applied to Action thresholds and early-sown crops in woodland are at greatest risk. control BYDV vectors also No action thresholds have been control yellow cereal fly. established. Natural enemies No treatments are recommended once larvae have The eggs and pupae are the predation by ground beetles. entered plants. most vulnerable stages to
Life cycle
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Eggs overwinter. Adult flies hatch. Flies move to early- sown wheat crops in Eggs hatch. Adults spend the summer in late September. Larvae enter and feed on wheat shoots. woodland. Larvae Eggs are Eggs overwinter. leave the laid at the shoots to base of pupate in plants. soil.
Arable and cropping and the environment – a guide assesses how any one management decision affects all other decisions in an integrated cropping system.
9 CEREAL PESTS Wireworms Agriotes lineatus Agriotes obscurus
Wireworms are the larvae of click beetles. Yellow larvae with distinct legs at the front and two dark spots at the tail, bite into stems at the soil surface causing a hole with tattered edges. By the time this is evident, wireworms have usually moved along rows to attack further shoots.
Economic importance Cultural control
Wireworms have become a cereal/ley rotations. Heavy Consolidate seedbeds to Consider including a spring more serious pest since the infestations can cause yield loss restrict movement. crop in the rotation. withdrawal of organochlorine of up to 0.6 t/ha in cereals. Control grass weeds. insecticides and the increase of Peas, linseed and flax are winter cropping.They can now more tolerant of damage than affect all winter cereal or winter other crops. Chemical control
Risk factors Seed treatment with tefluthrin Action thresholds or imidacloprid controls Populations can be very patchy Crops at highest risk are sown predominant winter cropping, moderate attacks. so estimating numbers is within two years of ploughing particularly with grass weeds, is difficult. Examining soil cores in out permanent pasture. at risk. the field for larger wireworms or However, any rotation with in the laboratory for smaller ones is costly and rarely Natural enemies justified. Use a seed treatment if The main natural enemies are wireworms exceed the fungi and parasitic wasps. threshold of 750,000/ha. Some residual damage is likely if numbers exceed 1.25 M/ha.
Life cycle
Wireworms have a 4–5 year life cycle.
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Adults active. Adults active. Egg laying.
Larvae feed. Pupae
Adult click beetles cause no economic damage.They live for about a year and lay eggs in grass fields. Larvae then feed for five years before pupating in the spring. Numbers increase over the years; highest populations occur in old permanent pastures.Wireworms feed in ploughed-down turf for about six months before moving to the surface to damage the next two crops.
10 CEREAL PESTS Leatherjackets Tipula paludosa Tipula oleracea
Leatherjackets (grey, legless larvae of cranefly, or daddy longlegs) feed below the soil surface making stems at the surface appear ragged. Stems break and keel over. Wireworms and other minor pests cause similar effects.
Economic importance Chemical control
Yield losses can range up to total infestation levels. Loss depends Chlorpyrifos is the only crop loss at the highest mainly on September rainfall. approved chemical.
Risk factors Action thresholds Assess leatherjacket numbers, Attacks on all cereals and move to feed on the new crop. before ploughing, by oilseeds frequently occur This leads to damage suddenly examining soil samples or following grass, where appearing some weeks after flooding plastic pipes, driven populations build up.Adults do crops emerge. into the ground, filled with not fly far and infestations take Dry September weather can brine. Proprietary brine-based some years to develop. Larvae reduce numbers considerably as testing kits are available. continue feeding in ploughed eggs and young leatherjackets Assess leatherjacket numbers, down turf.When it rots they are vulnerable to desiccation. in established crops if damage is seen, by scratching soil Natural enemies either side of crop rows. Treat with chlorpyrifos if: A range of viral, bacterial and • over 50 leatherjackets/m2 for protozoan diseases attack spring cereals (5 in 12 pipes) leatherjackets. Rooks are • 5 leatherjackets/m of row in A plastic pipe driven in the attracted to patches of spring cereals. ground is filled with brine. leatherjacket damage and may Lower levels may cause indicate infestations. Predatory significant damage in spring soil insects, eg ground beetles, oilseed rape and linseed. eat eggs and young larvae.
Cultural control