OIDIUM HEVEJS
REPOR THN TO E 1985 OUTBREA HEVFF KO A LEAF MILDEW
BY F. BESWSY
Durin earle gth y par f 193o t 5 Malay s experienceaha retura d n to more normal weather conditions. The easterly winds following1 e north-easth t monsoon rains brought with the mperioa f verdo y bright, dry weather during most of January and the first half of the month of February. A period of drought coming at this early part of the year is considered ideal from the point of view of inducing the fall of old leaves and production of new ones—a natural function observed in all deciduous trees, even in tropical regions, and known locally in connection with rubber agriculture as "wintering." a consequenc s A f thio e s pronounced y weatheperiodr f o d r wintering was early in practically every part of the country, the exceptions being some local coastal areas, especially the Bindings and Matang, where local weather conditions appear to be affected e closbyth e proximit e Hija th Bubd f an uo y u mountainse th d an , Labu—Port Dickson district where again local weathe s affectei r d by nearby n thesmountainsi s e wa district t I . s from whice th h earlier report of the presence of the disease arrived. The winter ing generally was sharp and even, while in the northern districts refoliatio s almoswa n t complete befor e weatheth e r broken I . the central and southern States up to 50 per cent of the trees had obtained their new leaves by the middle of February and it was thought that Malaya would escap e Leath e f Mildew disease entirely. However e 14t f Februarth o h n o , ydistinca t changn ei e directioth f winno d occurre d severadan l dull cloudy days with light rains followed, giving opportunit e funguth r develoo t ysfo p and attack the young leaves of the late-wintering trees. This dull weather continued for several weeks, but intervals of bright sunny weather speede e refoliatioth p du prevented an n d the disease from attainin a gvirulenc y sufficien o caust ty an e serious defoliation. a consequenc s A f thieo s intens eved an en winterinw ne e th g foliag s brighteri e , more evemord an n e dense whil e numbeth e r of seed pods set is greater throughout the country than has been e cas r somth fo e e yeare returth snormaf o i t npast d an ,l climate is maintained ther s everi e y reaso hopo t n e thaimprovemene th t t
49 so
e foliagith n f rubbeo e r tree n Malayi s a wil e continueb l d next year. Whereas last yea e earliesth r t reporte diseasth f o se were receive n Marchdi , this year (1935) reports were receiven i d February, whil e greatesth e t numbe f reporto r s were received during late February and early March when the weather was dull and showery. Later the weather became brighter, with the con- seqtience thafurthew fe t r reports were received except froe mth coastal districts of Selangor where, owing to the peaty nature of the soil, wintering had been later and more desultory. In practic- ally every case the reports indicated a very mild attack with slight leaf-fal late-winterinn o l g trees only. Referenc Tablo t e e I e grapth d h an will indicat e tim th f efirst-notice o e d leaf-faln i l the various States and the number of reports received during- the season.
TABLE I Oidium Hevetz 1935 Reports received Weekper from each State.
February March April
• 00 o\ — -- ir;
During March the writer visited every rubber-growing district west of the main range and full notes were made of the conditio e foliagth extend f no an evirulencd an tlea e th f f mildeeo w disease at that time. These notes together with observations and 51 WUMBE F QEPOETBO S EECEIVED PER. WEEK PERIOD.
information supplie y estatb d e managers e fore basith th mf o s district reports given below. While'on thi sdistricte touth f o r diseassa e resembling Oidium leaf mildew n thii t s bu instanc, e cause t a firs y whas b td wa t e leath thoughf e mitb o et t Tarsonemus translucens, s presenwa t in several districts and in some of the low-lying coastal areas was entirely responsibl e smalth r l efo amoun f leaf-falo t l taking place in the mature rubber. Microscopical investigation showed this smal Thripa l insece b a mites o t t reportA specieno . n d o t an s this new pest of rubber trees is given elsewhere in this Journal.
JOHORE e beneficiaTh l e earleffectth f yo swinterin d refoliatiogan n were obvious throughou e wholth t f thio e s Stat particularld ean y in the central districts where the trees are well grown; by mid- March the trees had completely refoliated. The top foliage wras very good quitan d e healthy, whil n onli e y rare instances wa s Oidium observes usuallwa d yd an confine e toweth o t rd branches of a few backward trees. The rubber trees nearer the coast are not so vigorous as e morthosth en i e central districts and, thoug e foliagt th hno s i e so good, little evidence of leaf-fall caused by the disease could be found. Dense planting in some of the small-holdings in coastal areas give e impressioth s t firsa nf ver o t y dense foliage. 52 North central Johore proved interesting in that, while the older mature rubber had wintered early and obtained a good new foliage, several fields of young rubber and some immature rubber which were observe e winterinb o t d g rather latd caughha e a heavt y infection, givin ga pal e mosaic appearanc e leavesth o t e. The e loca spreae diseasth th lo t f rain do e n thi ei du s e districb y ma t r miso t causee closth ey db proximit f Mounyo t Ophir (4187 ft). e occasionaTh l field f rubbeo s re abandone th see n i n d lalaiuj areas around Yang Pend Aye an t greporte rno Itae ar md upon here.
MALACCA
In the northern part of the territory where, owing (o impoverishment of soil, the rubber is poor and stunted, almost 100 per cent early wintering had taken place with the result that a new foliage, free of disease, and in appearance the best seen in the district for many years, developed. e morth en I central district e rubbeth s r improve d areaan s s may be found where the foliage is dense and of a glossy dark green colour showing little evidenc f mildewo e , thoug n closeo h r inspectio e lowerth n , heavily-shaded branches were observeo t d lie infected. e undulatine rubbeth Th n a r g country inland around Tampin, Kemuning and Ratang Malaka had, following a severe wintering, developed a better and healthier-looking foliage than has been the case for many years. Occasional areas of young rubber which had developed new leaves rather late were seen to be infected with the mildew fungus. e southerth n I n coastal district e territorth f o s y als oa grea t improvemen e foliagth s f noticeableo twa e e crowTh . n foliage was in almost every case of good colour and free of disease while in the lower branches traces of infection and slight leaf-fall were observed. Contrary to last year'the rubber in the coastal areas n bettei seemee b r o t conditiod e nJasi th tha n i n district. Around Jasin wintering appeare havo t d e been latd irregularan e , e facth possiblt o that e a secondart ydu y winterin Augusn gi s wa t experienced in 1934. Most of the late-wintering trees had Oidium in the lower and middle branches but only a slight leaf-fall was evident. This situatio e proximit th s possiblni o t e f Mounyo du t Ophir. The Asahan district appears to have been protected by the sam d wintere eha n extremel a hilld t an a sd y early period an d accordin o informatiot g n e treemanth f s o ydevelope leaw ne df in January. The district is now practically free of leaf-fall and 53
on only rare occasion e funguth s s wa s foun t alla d . The foliage is a great improvement on last year.
NKGRI SKMBJXAN The coastal distric f thio t s varyina Stat d eha g typ f foliageo e due apparently to variations in soil nutrition and water supply. e graveSomth d quartf o an el z soils bore rubbe f ratheo r r poor foliage in which a considerable amount of disease and leaf-fall s presenwa t caused bot y Thripsy Oidiub b h d man . Here again a secondary winterin s experiencewa g d durin e droughth g f o t August last. A great improvement was noticeable further south where an early and even wintering had resulted in an excellent foliage. Occasional patche n gravello s y soils weree b see o t n affected by the mildew disease but in very few cases was leaf-fall observed. Similarl e Lukuth n i yt area n stuntei , d rubben o r badly-drained flats disease evidencen i th , s ewa . Porn I t Dickson, Lingg Sengkand ian g districts some fields were las s lata a td o e t year desultorba e observes du a , e b yo dt winter- ing. A secondary wintering in August last again appeared to be responsible. considerablA e improvemen s observewa t d more inland an d also towards the Lubok China districts where such leaf-fall as was observed was found to be due to Thrips. Inland, Siliau & Rantau districts had experienced a severe early winterin undulatine th n go hilld gan y land wit hconsequena t good e flatfoliageth sn O severa. l fields were observe o bt de infected sufficiently to cause leaf-fall from the middle and lower branches. Seremban, Lab Nilad uan i districts showe verda y good foliage with only occasional late-wintering trees carrying a light infection with slight leaf-fall from the lower branches. n thesI e district a considerabls e amoun f sulphuo t r dusting had been carried out, but the effects of the disease have been so slight this year that no visible improvement to the foliage had been obtained by four weekly rounds of sulphur dusting. Through- out these districts Thrips werew observene e active th b n o t do e shoot whorld an s f leaveo s botn i s h mature and young areasn I . e Nilath i district some small area f badlo s y diseased foliage were observed whic y hav ma heo loca t beee l du ncondition s affecting the wintering and refoliation. In the Gemencheh district an early even wintering had in nearly every case led to a good healthy crown of foliage, whereas in Johol considerable areas of late-wintering trees had been attacke e foliag t eveth dbu o ns e showe dgreaa t improvemenn o t last year. 54 SBI/ANGOR The rubber generally on the higher ground in this State had vera y earl intensd yan e wintering, wit resule hth t that mucw hne foliag s obtainewa e d befor e finth ee weather e middlbrokth n i ee of February. In the more fertile, watered valleys wintering was not so early and in such areas the late-wintering trees could be observed in late March to be suffering from a mild attack of Oidiu e loweth mn ri branches. In the coastal districts the wintering was not so severe and infection, causin a gscarcel y noticeable leaf-fall s observedwa , , together wit a hfalf youn o l g leaf cause y Thripdb . sp s e southerTh n coastal district contains areas wher foliage th e e looks poor on account of poor soil conditions. Further inland around Kajang, Kuala Lumpur and Kuala Kubu the wintering was generally very early but, owing to the presence of mists aroun e foothillsth d e late-winterinth , g trees were attacke n Marci d earld an h y April. e foliagEveth o s ne this year can be said to be more dense and of a deeper and brighter colour than in 1934. Further north towards Tanjong Malim the improvement in foliage was maintained; trees on the hilly land wintering early had developed an excellent foliage but again those in the valleys were suffering a mild attack, actual leaf-fall being confined to the lower branches of late-wintering trees. The northern portion of Selangor also showed a general improvement though in several places the activity of Thrips pest s notedwa . f noto s Iei t that this yea greatese th r t number (20 f reporto ) s were received' from Selangor, but it is gratifying to note that in most case outbreae sth s describe mila kwa f o d s naturda e confined smalo t l Statee areath f so . greae Thith y bornts s i b increas t eou e in numbe f seeo r d pods whic e evidenhar t upo e maturnth e rubber.
The tree's in the district north of Tanjong Malim had experi- ence severda e early winterin developed gan dgooa d foliage th y eb en f Marchdo ; Trolak generally showe da grea t improvemenn o t last year .and the quality of the foliage seemed to vary with suit- ability of-'soils. Contrary to last, year there were scarcely any signs of leaf-fall due to Oidium Ileveae. e undulatinTh g groun f Sungkao d i bore rubbe f heavyo r , foliage and was practically free of disease. Further north from Bidor throughout the Kinta district the quality of the foliage varied with that of the soil. Trees on the 55
hills bearing excellent foliage practically fre f diseaso e e wern i e evidenc ee alluviawhilth n o e l flate foliagth s e though poos wa r healthy. Other occasional area n rico s h flat land showe- ex n a d cellent foliage, but new shoots and whorls of leaves were found to be infected. The trees in'the Kinta district as a whole showed a great improvement in foliage over previous years. e foliage Ipoh-Chemoth Th n i e r district though better than last year was, owing to the alluvial nature of the soil, only of medium density. Very little evidenc f diseaso e e coul e foundb d , even the young clearings were looking very healthy. Sungei Siput and Padang Rengas districts showed a much better foliage which appeared to have escaped attack completely although new shoot growth proved on close examination to be infected. Here also an early, severe wintering had taken place. North Perak, owing to the configuration of the land showed extremely variabl ea hiltreesid the foliagelone of e had s On . wintered d earlobtainean y n excellena d t foliagee whilth n o e other side late wintering and consequent attack of leaf mildew had occurred. Further variatio n qualiti n e f du foliago y s wa e directly to soil conditions, the substratum in some places being solid rock. Leavin e territor th e hill gth o t s y wes f Gunono t g Semanggol and Gunong Bubu more normal conditions were a foun d an d gradual improvement had taken place until on the flat peaty soils a very heavy dense canop f foliagyo s generalwa e . .Further sout e winterinhth beed gha n upse y locab t l climatic effects due to the proximity of G. Bubu. Wintering was patchy and, though some areas had developed a fairly good foliage, others showe a dheav y infection with resultant heavy leaf-fall. This e worsth distric s t wa observet d durin e tourgraduath A g . l improvement took place further e P>ruasoutth n i hs districtt bu , wintering had been patchy and some 5 to 10 per cent of trees in the early stages of refoliation were observed to be heavily infected. improvemene Th s continue wa t rubbee th n Sitiawandn i i r , where winterin s morgwa e evecompleted nan , thoug mann hi y casee th s lower branche d beeha sn attacke d sufferean d d considerable leaf- fall. e canopEveth s somewhao s nwa y t better than tha f laso t t year. Lower Perak, which has rarely shown any evidence of leaf- fall, has this year remained practically free of mildew disease.
PROVINCE Wi&uCSLEY Conditions here were similar to those of last year and though e foliag e slightl th b s sai o dwa t e y heavie sligha r t attac f leako f 56 milde d beewha n experience n i mid-Februaryd , bu a complet' t e recovery had taken place in both the old and the young rubber. At the time of the visit slight infection of new whorls of leaves was noted. On the poorer hilly land near Bakap some areas of poor rubber were observe carro dt ymoderata e infection causing mild leaf-fall. Further inland the rubber is planted on rising ground intersected by padi land goon e i whols th s d an n ewa conditioo d showed an n d signo n f havino s g been attacked.
KKDAH -In South Kedah the Temp and Serdang districts appeared lo have escaped attack completely. Difficulty was experiencen i d findin e slightesth g te fungutracth f o ee nes th evew n shooo n t foliage. The conditions of the foliage varied entirely with the general cultural conditions. Further south towards Bandar Bahru, thoug uppee hth r foliage s .goodwa , distinct sign f infectioo s d leaf-fale lowean nth n i rl branche s notedwa s . Kulie th n mI distric e treeth tbot n i s h large estat smalld ean - holding a dens d eha s canop f deeo y p green foliage. Secondary growth on lower branches was attacked by the Oidium fungus. Similarl Lunae th n yi s district early winterin resulted - gha ex n di cellent foliage which appeare o vart d y only accordin e soith l o t g conditions. Around Padang Serai early wintering had resulted in a strong dark green foliage in most of the rubber areas. Secondary growth appeared to be attacked by both Oidium and Thrips. Kuala Ketil and Lubok districts also showed a great improvement on the foliage of last year, thouglate-winterinw fe a h g tree d beeha sn caught by the disease following the break in the weather just after the middl f Februaryeo youne Th . g rubber trees, late wintering trees, growtw ne ann e refoliateo hth d d trees were here showe b o t n affected by both Oidium Heveae and Thrips. The foliage in the Kuala Muda and Sungei Patani districts was considere r cen some pe b t0 o bette5 edt rprevioue thath n ni o tw s years; early winterin hare treee th dth n f ssoilo go s enabled themo t escape attack during refoliation, resulting in good well-shaped dark green foliage. Grass-covered fields invariably born a inferioe r foliage. The improvement continued further north to Gurun, the most northerly point visited. Her foliage eth e was s usuala , , very heavy and as a result of the excellent shade Oidium, Thrips, spider and Helminthosporium leaf spot were observed in the new growths