Crop Walkers’ Guide Outdoor Salads Lettuce & Celery Outdoor Salads Crop Walkers’ Guide GuideGuideIntroduction Every year, a significant proportion of the UK outdoor salads crop would be lost to invertebrate pests and diseases if growers did not monitor their crops and employ effective crop protection strategies. This Crop Walkers’ Guide is aimed at assisting growers, agronomists and staff in the vital task of monitoring outdoor salads. It is designed to help with the accurate identification of pests, diseases, nutritional deficiencies and physiological disorders within a crop. Images of key stages in the life cycles of pests and diseases are included along with bullet point comments to help with identification. It is impossible to show every symptom of every pest or disease, therefore growers are advised to familiarise themselves with the range of symptoms that can be expressed and be aware of new problems that occasionally arise. This guide does not offer any advice on the measures available for controlling pests or diseases as both chemical active ingredients and their approvals frequently change. However, having identified a particular pest or disease in their crop, growers should acquaint themselves with the currently available control measures. Grace Choto Research and Knowledge Exchange Manager (Field Vegetables) AHDB Horticulture Introduction 3 Outdoor Salads Crop Walkers’ Guide Contents Invertebrate Pests on Outdoor Lettuce SECTION 1 Aphid – Currant-lettuce 1.1 Aphid – Lettuce root 1.2 Aphid – Peach-potato 1.3 Cutworms 1.4 Flax tortrix moth 1.5 Leatherjackets 1.6 Silver Y moth 1.7 Slugs 1.8 Predators and Parasitoids on Outdoor Lettuce SECTION 2 Common stiletto fly larvae 2.1 Ground beetles and rove beetles 2.2 Hoverfly larvae 2.3 Lacewing larvae 2.4 Ladybirds 2.5 Parasitic wasps 2.6 Diseases on Outdoor Lettuce SECTION 3 BACTERIAL DISEASES Bacterial infection 3.1 FUNGAL DISEASES Bottom rot 3.2 Grey mould 3.3 Sclerotinia rot 3.4 4 Contents OOMYCETE DISEASES Downy mildew 3.5 VIRAL DISEASES Cucumber mosaic Virus (CMV) 3.6 Lettuce big vein associated Virus (LBVaV) 3.7 Ring Spot 3.8 Lettuce mosaic Virus (LMV) 3.9 Turnip yellows Virus (TuYV) 3.10 Nutrient deficiencies SECTION 4 Boron (B) 4.1 Calcium (Ca) 4.2 Copper (Cu) 4.3 Iron (Fe) 4.4 Magnesium (Mg) 4.5 Manganese (Mn) 4.6 Nitrogen (N) 4.7 Phosphorus (P) 4.8 Potassium (K) 4.9 Sulphur (S) 4.10 Zinc (Zn) 4.11 Physiological Disorders on Outdoor Lettuce SECTION 5 Bolting 5.1 Tipburn 5.2 Invertebrate Pests on Outdoor Celery SECTION 6 Aphid – Peach-potato 6.1 Aphid – Willow-carrot 6.2 Capsid bug 6.3 Contents 5 Carrot fly 6.4 Celery fly 6.5 Cutworms 6.6 Silver Y moth 6.7 Slugs 6.8 Predators and Parasitoids on Outdoor Celery SECTION 7 Hoverfly larvae 7.1 Lacewing larvae 7.2 Ladybirds 7.3 Parasitic wasps 7.4 Diseases on Outdoor Celery SECTION 8 FUNGAL DISEASES Leaf spot/late blight 8.1 Sclerotinia rot 8.2 Nutrient Deficiencies on Outdoor Celery SECTION 9 Boron (B) 9.1 Calcium (Ca) 9.2 Iron (Fe) 9.3 Magnesium (Mg) 9.4 Manganese (Mn) 9.5 Nitrogen (N) 9.6 Phosphorous (P) 9.7 Potassium (K) 9.8 Sulphur (S) 9.9 Physiological Disorders on Outdoor Celery SECTION 10 Bolting 10.1 6 Contents References SECTION 11 Acknowledgements 11.1 Photographic credits 11.2 Photographic credits 11.3 Photographic credits 11.4 Contents 7 Outdoor Salads Crop Walkers’ Guide SECTION 1 Invertebrate pests Lettuce 1 Lettuce Invertebrate pests Aphid – Currant-lettuce Nasonovia ribisnigri • Green to yellow-green body, • Aphids can walk quickly into the 1.4–2.6mm long with long black heart of lettuce causing a rapid jointed legs and dark diamond build up of colonies, especially in stripes across the dorsal part of Iceberg and Cos lettuce. the abdomen. • Overwinters on flowering • Migration starts in May but is blackcurrants and gooseberry a major risk during the return Transmits Cucumber Mosaic migration period of September Virus (CMV). to October when large numbers • Forecast available on AHDB can build up. Horticulture Pest Bulletin. Lettuce – Invertebrate pests 1.1 Aphid – Lettuce root Pemphigus bursariusAphis gossypii, Macrosiphum euphorbiae, etc. • Overwinters as eggs on Lombardy • Adults alight on the plant and poplar. Winged migration from move down to the roots to feed mid-June from galls formed on and reproduce. the poplar tree. • Examine plant roots to locate • Aphid characterised by white the feeding aphids and the or blue-white waxy filaments characteristic white waxy on abdomen and very short deposits. antennae. 1.2 Lettuce – Invertebrate pests Aphid – Peach-potato Aphis gossypii, Macrosiphum euphorbiaeMyzus persicae, etc. • A common aphid with a wide • Winged forms migrate from winter summer host range including hosts, in May and June, peaking lettuce, potato, sugar beet, in July. Look under the older, Brassicas and others. outer leaves for colonies as this is where they are first seen. • Colour varies greatly from pale yellow-green to dark green. • Transmits Lettuce mosaic, Immature forms can be pink. Cucumber Mosaic and Turnip Winged forms often with dark Yellows Viruses (TuYV). brown to blackish head with • Forecast available on AHDB a green or sometimes red Horticulture Pest Bulletin. abdomen. Lettuce – Invertebrate pests 1.3 Cutworms Various Agrotis spp.Aphis gossypii, Macrosiphum euphorbiae, etc. • Adults emerge in April and • First signs of damage are May from pupae in the soil. collapsing plants where the Populations can be monitored taproot is severed. Check the soil with pheromone traps. around the root to try and locate the caterpillars. • Adult moths can be distinguished by kidney-shaped marks on the • Can be confused with wing backs. leatherjacket attack. • Caterpillars feed on the foliage • Forecast available on AHDB before descending to feed on Horticulture Pest Bulletin. the roots. 1.4 Lettuce – Invertebrate pests Flax tortrix moth Aphis gossypii, MacrosiphumCnephasia euphorbiae asseclana, etc. • An infrequent pest, usually found • Caterpillar forms a silk web that around headlands or alongside sticks the leaf together. Pull apart hedges and woods. They mainly the leaf to find the pest. overwinter on deciduous trees and • Damage is normally only found in drop into the crop in the spring. late spring. Lettuce – Invertebrate pests 1.5 Leatherjackets Tipulidae spp. Aphis gossypii, Macrosiphum euphorbiae, etc. • Leatherjackets are the larvae of • They are normally only a crane flies or ‘daddy long legs’. problem where land has come out of permanent grass and on • Leatherjackets can be field margins. distinguished from cutworm caterpillars as they have no legs • First signs of damage are and no distinct head. collapsing plants where the taproot is severed. Check the soil around the root to try and locate the larvae. 1.6 Lettuce – Invertebrate pests Silver Y moth Aphis gossypii, MacrosiphumAutographa euphorbiae gamma, etc. • The most serious caterpillar pest are blown across the channel of lettuce, it can bore through from Europe. petioles as well as eating through • Monitor adult activity using the leaves. pheromone traps. The adult moth • Caterpillar has only three pairs of has a distinctive silver Y shape on pro-legs, a pale green body with the wing back. white longitudinal stripes. • Caterpillar forecast available on • Migration from April onwards. AHDB Horticulture Pest Bulletin. Large numbers arrive in the UK following southerly winds in the middle of summer, when adults Lettuce – Invertebrate pests 1.7 Slugs Various spp. Aphis gossypii, Macrosiphum euphorbiae, etc. • The common grey field slug is • Look in the top 25mm soil under the most often found. the plant for hiding slugs. Slugs feed on decaying organic matter • Damp moist soils are favoured in the soil as well as above ground by slugs. They will stop feeding when conditions permit. during very dry or cold frosty weather. • Symptomatic holes on the leaf can be confused with caterpillar damage – check for slime trails. 1.8 Lettuce – Invertebrate pests Outdoor Salads Crop Walkers’ Guide SECTION 2 Lettuce Predators and Parasitoids Predators and Parasitoids Predators Lettuce 2 Common stiletto fly larvae Thereva nobilitata • Stiletto fly larvae are thin, around • Larvae feed on worms, 25–30mm long, a creamy white insect larvae, leatherjackets colour and live in the soil. and wireworms. • They are commonly mistaken • Take care when handling them – for wireworms. These larvae they have very strong mouthparts are however legless whereas and can bite. wireworm have three pairs just behind the head. Wireworms are also normally of a darker golden brown colour. Lettuce – Predators and Parasitoids 2.1 Ground beetles and rove beetles Various spp. • Many species of ground beetles • Both adults and larvae feed on and rove beetles inhabit the other insects consuming a range soil and the soil surface around of adults, larvae and eggs. lettuce plants. • Some of the Carabid types such as • They are mainly black or dark Pterostichus melanius eat slugs. brown, are predatory and have powerful jaws. 2.2 Lettuce – Predators and Parasitoids Hoverfly larvae Syrphus ribesii • The currant hoverfly adults have a • Larvae are pale yellow, soft yellow and black striped body that bodied, about 12mm long, legless can, at a glance, be mistaken for and leech-like in appearance. a common wasp. Hoverfly though Each one can eat up to 500 have only one pair of wings to the aphids before pupating. wasps’ two. • Prior to pupation larvae attach • Adults feed on the nectar of themselves to a leaf, so, like many common flowers, especially lacewing larvae, they too can Compositae and Cruciferae. become contaminants. Lettuce – Predators and Parasitoids 2.3 Lacewing larvae Chrysopa perla • Adult lacewings are pearly • Larvae are plump, around 8mm blue-green with a wingspan of long, covered in bristles and about 20–32mm and are around have a cream body with brown 14mm long.