g62-encyclopaedia-of-pests-and-natural-enemies-in-field-crops

Pest thresholds: quick referencePest thresholds: quick referenceOilseed rapeField beansCabbage seedweevil(p. 19)Cabbage stemflea beetle(p. 21)Weevils per plant during flowering:– Northern UK: 0.5– Elsewhere: 1Adult feeding thresholds:– >25% leaf area eaten at the cotyledon–2 leaf stage– >50% leaf area eaten at the 3–4 leaf stage– The crop is growing more slowly than it is beingconsumedBruchid beetle(p. 17)Pea and beanweevil(p. 25)Black beanaphid(p. 45)Treatment should be applied when, during flowering:– Adults have been found in the crop– The temperature has reached 20°C on two consecutivedays– Beans have developed the first pods on the lowest trussesSpring field beans:– An average of 30 or more weevils on any one recordingdayPollen beetle(p. 27)Mealy cabbageaphid(p. 59)Leatherjackets(p. 99)Slugs(p. 163)Thresholds for control of larvae:Yellow water trap:– >35 beetles/trap caught in total between earlySeptember and the end of OctoberPlant dissection:– >2 larvae per plant– 50% of petioles damagedBeetles per plant at the green to yellow bud stage:– If there are fewer than 30 plants/m 2 : 25– If there are 30–50 plants/m 2 : 18– If there are 50–70 plants/m 2 : 11– If there are more than 70 plants/m 2 : 7% of plants infested before petal fall:– Winter oilseed rape: more than 13%– Spring oilseed rape: more than 4%Prior to cultivation:– More than 50 leatherjackets per m 2– More than 5 leatherjackets in 12 pipes– More than 5 leatherjackets per metre of rowSlugs per refuge trap, prior to cultivation:– In cereal crops: 4– In cereal stubble: 1Slugs (p. 163)PeasPea and beanweevil(p. 25)Pea aphid(p. 61)Pea midge(p. 105)Pea moth(p. 141)Early flowering until pod formation:– 10% of plants infested: Immediate treatment is justified– 5% of plants infested: Treatment can help prevent virusinfection1 slug per refuge trap, prior to cultivationSpring-sown peas:– An average of 30 or more weevils on any one recordingday% plants infested, May to July:– Combining peas: 20% or more– Vining peas: 15% or moreIf more than 500 midges are caught on one trap (placedby the third week of May), susceptible pea crops in thenear vicinity should be examinedDry harvested peas for human consumption:– 10 or more moths caught in traps (placed by the middleof May and examined at two-day intervals) on twoconsecutive occasionsVining peas:Traps are just used to determine if moths are present.Growers should be guided by the factory fieldsman aseven very small infestations can lead to rejectionVining peas:– Cumulative catch exceeds 50 moths by the first podstage (GS204)Silver Y moth(p. 143)Slugs (p. 163)1 slug per refuge trap, prior to cultivation13Encyclopaedia of pests and natural enemies in field cropsEncyclopaedia of pests and natural enemies in field crops14