Oidium Hevejs Report on the 1985 Outbreak of Hevfa Leaf
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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; <M oo 1 1 2 2 " ! S ; » *" i i 1 1 I I 1 - ! 1 1 I i 1 I ; i S1 10< INI O\ ' rv^i s ' i \i-->H 1— 30 ~ INI f, • CO '~~ P-I M ; 10 ——— i ——— CM ' ! . | Johore 1 2 7 2 2 i ; 14 Malacca 1 1 , • : 2 Negri Sembilan i 1 3 1 5 1 i 1 , 13 Selanffor 1 2 4 ! 2 1 1 2 132 : 1 20 Perak 4 3 5 3 1 ; . 16 Province i i I Wellesley 1 ! : ; ! 1 2 Kedah i ! 3 Pahang 1 1 ! ! 2 i Total I 4 5 15 1 17 6 i 1 7 0 8 2 65 • 1 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.