Apple pests and dieases All infrmatin taken frm Garden Organic web site except sectins n canker and greenfly and ther aphids. Apple Scab and Pear Scab Scab is a widespread fungal disease f apples and pears. Causing mainly blemished fruit, its effects are tlerated by gardeners, thugh cmmercially, fruit may be unmarketable. The disease is caused by tw clsely related fungi; Venturia inaequalis affecting apples and related rnamental species such as Pyracantha, Ctneaster, Viburnum and Srbus, and Venturia pirina, affecting nly pears. Typical symptms Apples Leaves: brwny/green bltches appear first n the underside f leaves in spring. As leaves unfld, bth surfaces may shw symptms. Yung lesins are velvety brwn t live green and have feathery, indistinct margins. These may expand and run int each ther, mainly alng the veins and may develp a blistered appearance. When infectins are numerus n yung leaves, they becme curled, dwarfed and distrted. Leaves may drp prematurely. Sme crab apple species may have mre severe symptms, the variety 'Jhn Dwnie' is very susceptible t scab. Fruit: dark spts n the skin lk much like thse n the leaves initially. As the fruit enlarges, these then develp int brwn crky patches. A severe infectin can cause fruit t crack if the apple is still grwing. These wunds may cause the fruit t rt thrugh a secndary infectin. Twigs: small blister like swellings burst t prduce brwn/green pustules in spring. The cracked bark may then prvide sites fr further infectin by the fungus causing canker. Pears Leaves: scabby spts similar t thse n apples appear n shts, leaves, fruit and buds. Fruit: dark brwn sptting can be mre severe than n apples, causing infected fruit t grw defrmed and deeply cleft. Twigs: cnspicuus swellings which later burst. Infectin ccurs frequently n bud scales. Life cycle The fungus verwinters in fallen infected leaves, fruit and in infected twigs. In the spring, given a mist envirnment, spres released frm these surces are blwn r splashed nt newly emerging leaves causing infectin. As the fungus develps, further spres are prduced and the infectin cntinues t spread thrughut the grwing seasn. Scab attacks are wrst in cl, wet perids in spring and early summer. Page 1 f 10
Preventin and cntrl Treatment is the same fr apples and pears, althugh it needs t start earlier in the seasn fr pears because sht infectins are mre serius. Garden hygiene: Remve badly infected fruitlets during thinning in June and remve mature fallen fruits in the autumn. Remve all fallen leaves in the autumn and cmpst them. If this is impractical, mw the grund belw the trees t shred the leaves and increase the rate at which they are taken dwn int the sil. Watering fallen leaves with diluted urine, r any ther high nitrgen liquid (nettle brew, liquid manure) will als help t kill the spres and speed up the decmpsitin rate. Cultural cntrl: Pick-ff and destry any leaves and fruit left n the tree in the winter. Prune-ut and burn diseased twigs. Prune trees regularly t maintain an pen centre. This will increase air circulatin and rapid drying f leaves which in turn discurages scab develpment. Resistant varieties: Bth apple and pear cultivars vary cnsiderably in their resistance t scab. They can als lse their resistance with time. Cntact a specialist fruit nursery fr details f current resistant varieties. Sme scab resistant apples are: Ashmead's Kernel Ellisn's Orange Frtune Discvery Egremnt Russet Grenadier Kidd's Orange Red Limelight Lrd Derby Red Devil Reverend Wilkes Saturn Sunset Winter Gem Resistant pears: Buerre Hardy Bristl Crss Catillac Grham Jargnelle Cnference is partially resistant. Susceptible varieties: Sme apples that are particularly susceptible t scab: Cx's Orange Pippin Gala James Grieve Laxtn s Superb Susceptible pears: Williams Bn Crétien Page 2 f 10
Apple Pwdery Mildew Apple pwdery mildew, Pdsphaera leuctricha, is a serius and cmmn fungal disease f apples. It als infects pear, quince, peach, medlar and the rnamental, Phtinia, but with less serius effects. The disease can reduce bth vigur and crpping. Typical symptms A white pwdery cating appears first n leaves and shts, as well as flwer buds in spring. Blssm may be affected, causing it t wither and drp. Leaves are distrted, becming narrw and flded, turn brittle and then fall. Early infectins may mark the fruit skin with a 'russet' effect. Life cycle The fungus verwinters in buds. Spres are prduced in spring n emerging leaves, flwers and shts and spread by wind. Infected flwers will nt set any fruit. The develpment f this disease is affected by climatic cnditins. A harsh winter will reduce the risk f infectin; it spreads mst rapidly in summer when warm, sunny days are accmpanied by humid nights. Preventin and cntrl Pruning: In winter, prune ut any shts and buds that have been infected with mildew. Shts will appear silvery/grey, and buds distrted. Cut back t several buds belw the infectin. In spring, carefully remve infected leaves and shts. Prune directly int a bag t prevent spres frm spreading. Check trees weekly thrugh the seasn and carry n cutting ut infectin. On small trees this can be a very effective methd f cntrlling mildew, if dne thrughly. Prune trees regularly t permit gd air circulatin. Prunings shuld be buried in an active cmpst heap r sent t yur lcal cuncil s green waste recycling centre. Cultural cntrl: Mulch in spring with bark, cmpst r straw under trees t stp sil drying ut. Water trees in dry weather. Avid applying t much nitrgen (hrse manure, cmpst etc) in the grwing seasn; excess vegetative grwth is mre susceptible t infectin. Variety chice: Varieties vary in their degree f resistance t mildew. Avid susceptible varieties when planting new trees. Trees we have fund t be less susceptible t mildew are: Allingtn Pippin Arthur Turner Brwnless Russet Curt Pendu Plat Crawley Beauty D'Arcy Spice Discvery Early Victria Frtune Glden Nble Grenadier Jupiter King Edward VII King f the Pippins Lrd Derby Redsleeves Rev. W Wilks Uptn Pyne Wrcester Pearmain Page 3 f 10
Glden Reinette Susceptible t mildew: Cx's Orange Pippin Crispin Glden Delicius Jnathan Lane's Prince Albert Chemical cntrl - a last resrt: u sulphur has traditinally been used t cntrl mildew, and is accepted under rganic standards. It is nt harmless t the envirnment, hwever, and shuld nt be used regularly. Sme varieties are particularly sensitive t sulphur and will nt tlerate it. Beauty f Bath, Cx's Orange Pippin, and Newtn Wnder will be damaged by sulphur. If yu cannt get infrmatin abut a particular variety, test spray a single sht and lk fr scrching r leaf fall within 24 hurs. Ptassium bicarbnate is an effective fungicide which has recently gained fficial gvernment apprval under the Cmmdity Substance Apprval Scheme (26 July 2005) hwever this might be shrt lived due t the phasing ut f the Eurpean pesticide regulatins apprvals, and any prducts under this scheme culd be banned. Currently it des nt have rganic apprval in the EU r UK. But there is nthing t stp rganic gardeners, wh are nt selling prduce with an rganic lg, giving it a try alngside the ther cultural practices recmmended t. Until then, ptassium bicarbnate can be used t cntrl pwdery mildew. A maximum dilutin f 20g/litre (apprx 3z per galln) is allwed. Hwever, a regular spray f a weaker slutin (2.5-5g/litre) at 7-10 day intervals seems t wrk better. Always d a spray test n a few singular leaves, as bicarbnate may scrch leaves. This has been reprted in a previus issue f The Organic Way, Issue 182 Bitter Pit This is nt a disease, but a cmmn disrder f apples. It can shw up when the fruit is still n the tree twards the end f the seasn, but mst cmmnly appears during strage. Typical symptms The first signs are widespread shadwy spts shwing just belw the fruit skin. These frm int dark, slightly sunken areas r pits, up t a few millimetres in diameter. Directly beneath each pit a small patch f the fruit tissue turns brwn and crky in appearance, and similar brwn patches eventually develp scattered thrugh the apple flesh. When the cnditin is severe it affects the entire apple, giving it an unpleasant bitter taste. Hail damage causes similar symptms n the skin, but withut brwn spts inside the fruit. What is the cause? Page 4 f 10
Bitter pit is due t a deficiency f calcium and/r an excess f ptassium r magnesium within the apple fruit. The cnditin develps when the mvement f calcium int grwing fruits is disrupted, and varius cmplex factrs can bring this abut. Water stress at critical times in the grwing seasn appears t be a majr factr cnnected with bitter pit, and high applicatins f nitrgen-rich fertilisers and manures als seem t aggravate the cnditin. As an essential plant nutrient, calcium des nt mve very readily within the apple tree. In cnditins when it is needed rapidly, it is directed t leaves and shts in preference t the fruit. This means that even when sil calcium levels are abundant (few sils are deficient in calcium), there can still be a deficiency f calcium and bitter pit symptms in the fruit. Bitter pit is usually wrse in seasns with wide fluctuatins in rainfall and temperature. It is mre cmmn in yung, vigrusly grwing trees. In mature trees it is mst likely t ccur in larger fruits, and in fruits picked befre they are fully mature. Preventin and cntrl Bitter pit can usually be prevented with careful management. The aim shuld be t maintain cnditins that allw steady, unifrm grwth thrughut the seasn as this will avid rapid fluctuatins f calcium in the trees. Avid water stress: Keep the tree mulched, applying the mulch early in the seasn when sil misture levels are still high. In very dry seasns, irrigate t stp the sil drying ut. Crrect feeding: Avid ver-feeding, particularly with nitrgen-rich materials. Variety chice: Sme varieties, especially large fruited cking varieties, are particularly susceptible. These include Bramley's Seedling, Edward VII, Hwgate Wnder, Newtn Wnder and Mertn Wrcester. Calcium sprays: Cmmercial grwers prvide extra calcium t the fruit by using a fliar spray r pst-harvest dip. This is nt a very practical methd fr the dmestic gardener as the spraying, with calcium chlride, needs t be very thrugh and carried ut every 10 days frm June nwards t be effective. Acid sils: Apply lime t raise p H t abut 6.5. This will help t make calcium available t the rts. Late summer pruning Carry ut late summer pruning n vigrus/mature trees. There is evidence that summer pruning can be beneficial as it reduces cmpetitin fr calcium between fruit and shts. It shuld be dne in August when extensin grwth has slwed dwn and terminal bud frmatin is visible. When late summer pruning is practised nly minimal winter pruning is required. Cut ut all vertical ne year ld shts, i.e. any upward r dwnward pinting shts. Remve sme tw year ld wd where new grwth arising frm it is very vigrus. Remve any 'water shts', ie new shts that have arisen in respnse t branches being remved (unless a replacement branch is needed t fill a gap). Page 5 f 10
Cut ut mst new grwth, leaving nly a few side shts that lie in a fairly hrizntal plane. Cping with bitter pit D nt pick immature apples if yu want t stre them as these are mre prne t develping bitter pit in stre. Check stred fruit regularly and use up any that shw early bitter pit symptms. If bitter pit is a serius, recurrent prblem d nt even try string the apples; use the fruit as sn as it is picked s that the disrder des nt have time t develp. A few pits n the skin at picking time can be remved by peeling and shuld nt affect fruit quality. Preserve the fruit by cking, freezing, bttling, etc. Knw yur apples - if bitter pit always tends t develp in yur maturing fruit while still n the tree, save the fruit by picking it early, still green, t use fr cking and preserving. Brwn rt Brwn rt is a cmmn fungal disease causing damage t many types f fruit trees. The same symptms are caused by tw different species f fungi, Mnilinia fructigena, infecting apple, pear, almnd and quince and M. laxa n plum, peach, aprict, cherry and nectarine. Typical symptms The fungus causes brwn patches and rt n fruit, ften accmpanied by blssm wilt, spur blight and wither tip f shts and flwers. Fruit: Sft brwn patches enlarge t engulf the entire fruit, either n the tree r in strage. The fungus can spread quickly in strage, infecting undamaged fruit by cntact. White spre bearing pustules may appear n the brwn patches, ften in cncentric rings. Fruits shrivel and becme mummified. They may drp r remain attached t the tree. Blssm wilt: In spring, blssms turn brwn and wilt. They usually remain attached t the twig. In wet weather, fungal spres multiply and spread quickly, causing mre flral infectins. Spres can spread t spurs resulting in canker develpment n the twigs. Spur blight: Leaves wither n the spur. This may develp int a small canker having tufts f grey fungal grwth. Wither tip: Leaves wither and develp brwn lesins, tip drps. Aphids may be present. Life cycle Spres verwinter in mummified fruit r in twig and branch cankers. In spring, spres are released t be carried n the wind, by insects r by rain-splash. Blssms and yung Page 6 f 10
shts are the first t becme infected. The fungus spreads quickly int the spur r branch t frm canker. The fungus enters fruit via wunds r cracks created by frst, hail, birds, r insect pests. Careless picking and handling at harvest allws entry f spres that cause pst harvest lsses in strage. Infectin is accelerated in ht and humid cnditins tw t three weeks prir t harvesting. Preventin and cntrl Garden hygiene: Remve all rtting r mummified fruits frm trees and cllect up fallen fruit frm the grund. Burn r take t the lcal recycling centre. Keep area under trees free f vegetatin. Cultural cntrl: Prune ut wither tip and spur blight as sn as it ccurs. In winter, cut ut cankers and brwn lesins n stems and branches. Strage: Avid damaging fruit during harvest. D nt stre bruised and stalk-less fruit. Use clean cntainers fr strage f fruit. Check stres regularly and remve any fruit with signs f rt. Fliar feed: Use seaweed extract as a fliar feed t bst the trees resistance having a beneficial effect. Apply it every 10-14 days frm bud-burst t green cluster stage and then again frm petal fall t early August. Canker A fungal disease that affects twigs and smetimes-larger branches. Usually eneters weak r damaged wd Preventin and cntrl Prune ut as much affected wd as pssible, preferably remving at least 5cm f gd wd t. Avid ver pruning trees as this prmtes weak sappy canker prne grwth. Prune t prmte gd air circulatin and remve damaged & rubbing wd. Always make cuts as clean as pssible The benefits f dispsing f infected wd is debatable as the disease spreads by wind blwn spres ver great distances Cdling mth The larva r caterpillar f the cdling mth (Cydia pmnella) is a serius pest f apples. It ccasinally attacks pears. Typical symptms Page 7 f 10
Cdling mth larvae, als knwn as apple maggts, eat int maturing fruit. A single larva enters each fruit thrugh the eye if the fruit is small, but therwise near the stalk. It initially frms a small cavity belw the skin, and then after a few days it burrws int the cre leaving a prminent, red-ringed, entry hle blcked by dry frass (maggt drppings). A large prprtin f the fruit flesh can be eaten away and the cavity becmes filled with brwn frass. After feeding fr abut 4 weeks, the larva escapes thrugh a small unplugged exit hle. Damaged fruits tend t ripen and drp prematurely. Cdling mth damage shuld nt be cnfused with apple sawfly damage; sawfly als burrw int the fruit but they prduce masses f black, wet frass which is pushed t the utside. Sawfly damage als usually ccurs earlier in the seasn in May r June, n yunger fruits. Descriptin f pest The larvae are pinkish-white with mttled brwn heads, 18-20mm lng. The adult mth is mttled grey-brwn in clur, abut 8mm lng and with a wingspan f 15-22mm. It has a large characteristic brnzy-black bltch near the tip f the wings. The adults fly at night, s are seldm nticed. Life cycle The female mths lay single eggs n fruits and leaves in June/July. The eggs hatch 10-14 days later and tiny larvae immediately burrw int the fruit and feed fr abut a mnth. They then leave the fruit and crawl dwn the trunk t spin a ccn under lse bark, tree ties etc. Larvae that reach this stage by the end f July may emerge as adults the same seasn t give a secnd infestatin during August and September. The majrity will nt emerge until the fllwing spring. Preventin and cntrl Encurage natural cntrls: Make yur garden a friendly place fr a range f helpful creatures by aviding harmful sprays and prviding suitable wildlife habitats. Grw flwers that attract beneficial insects. Small, simple flwers are best, such as members f the Umbelliferae and Cmpsitae families, as well as the pached egg plant (Limnanthes duglasii), Cnvlvulus triclr and Phacelia tanacetiflia. Encurage birds t yur trees by prviding them with sme fd in the winter. Blue tits are especially adept at searching ut and cnsuming the verwintering mth ccns. D nt kill earwigs, they will eat cdling mth eggs. Other methds: Always pick up and remve windfalls sn after they have fallen and remve leaf litter in the autumn. Remve any tree ties in the autumn in case they cntain ccns. Replace with new nes. Trapping: Phermne traps fr cdling mths are available t buy. They cntain minute quantities f female cdling mth phermne, attractive t male mths which are then trapped n a sticky base. Hang the traps in trees frm mid May t September. Each trap will prtect up t 4-5 trees. Once trapped, the males are n lnger available fr mating and the females cannt therefre prduce fertile eggs. Anther apprach is t trap the pupae f the mths by prviding a suitable site fr them t pupate. Cut a 50cm strip f large-cre crrugated cardbard. Wrap rund Page 8 f 10
the trunk s the crrugatins are vertical, abut 45cm abve grund level. Put the traps in psitin in July, remve and burn them in the autumn. This methd is mst effective n smth trunks. If yur neighburs als have fruit trees, try and encurage them t d the same, therwise yur effrts will have limited effect. Chemical cntrl - a last resrt: Spraying is the least satisfactry methd f cntrl fr cdling mth. The timing must be exactly right fr it t have any effect. Yu have t catch the caterpillars during the brief perid befre they disappear int the apple, but as the eggs hatch ut ver a relatively lng perid there is n single best time t d this. A derris spray will kill caterpillars nly by direct cntact, therefre is f limited effectiveness and may kill beneficial insects t. The phermne trap described abve can be used t detect when the first mths are present; this is likely t be in mid June. Start spraying abut 10 days after the first mths are caught and then weekly fr abut 4 weeks. Greenfly & ther Aphids Mstly a prblem n yung trees where new grwth is distrted by attack Preventin and cntrl Encurage natural cntrls. Manually squash clnies. Pinch ut wrst affected shts Lcalised spraying f affected areas nly as a last resrt Wlly Aphid A cmmn pest f apple trees, the wlly aphid (Erisma lanigerum) als infests rnamental crab apple, ctneaster, hawthrn, pyracantha, srbus and ther related plants. Typical symptms In spring and summer, white fluffy utgrwths ccur n tree stems and branches. This sticky "wl" is a prtective wax secreted by the breeding clnies f the aphid. The aphids feed mainly n spurs and branches, particularly where the bark is brken. Little damage is dne t mature trees, althugh irregular swellings r galls may develp n twigs and branches; these nly becme a prblem if they crack pen and allw entry f Page 9 f 10
disease rganisms such as apple canker. In yung trees, galling caused by wlly aphids can cause serius disfigurement. Descriptin f pest A small, purplish-brwn aphid, densely cvered with white, waxy fluff when mature. Often mistaken fr a fungus r mildew attack. If tuched, the aphid clnies squash t an unpleasant sticky mess, while the disease mildew disintegrates t a white dust. Life cycle Yung aphids (waxless) verwinter in cracks and under lse bark n trees and shrubs. They becme active and start feeding in late March/April and by May, breeding clnies are established under masses f cnspicuus fluffy white wax. Several generatins ccur during the seasn. Only a few winged aphids are prduced s mst spread is by wingless aphids crawling, r being blwn, frm tree t tree. Fr this reasn the prblem may nt spread far, but will persist n the same trees frm year t year. Survival f this species des nt invlve eggs; it is yung wingless aphids that verwinter and carry n the lifecycle int the fllwing year. Preventin and cntrl Encurage natural cntrls: Make yur garden a friendly place fr a range f helpful creatures by aviding harmful sprays and prviding suitable wildlife habitats. Grw flwers that attract beneficial insects. Small, simple flwers are best, such as members f the Apiaceae (Umbelliferae) and Asteraceae (Cmpsitae) families, as well as the pached egg plant (Limnanthes duglasii), cnvlvulus and Phacelia tanacetiflia. A small chalcid wasp (Aphelinus mali) is a parasite n the wlly aphid and can give effective cntrl if allwed t flurish. Originally intrduced in the 1920s, it is nw naturalised and is cmmn in suthern England. Parasitised aphids will have a tiny hle in the back if the wasps are active, in which case avid spraying. Hand picking: Try t deal with the aphids as sn as they are visible, befre numbers build up scrape ff the white wlly clnies, r attack them with a stiff brush. Cultural cntrl: Prune ut and burn severely infected branches, particularly if there are signs f canker. Chemical cntrl - a last resrt: Spraying with insecticidal sap can be effective but may need t be dne several times. Try spraying at 1 r 2 day intervals, and repeat 2-3 times. A high vlume, high pressure spray is necessary t get thrugh the prtective waxy cat. Page 10 f 10