Cakne — Brown Bot of Citnii^. 
15 
OCCURRENCE OF BROWN ROT IN WESTERN 
AUSTRALIA. 
Brown I?ot is tlie most sorioiis ])avasitio disoaso of citrus in the 
State. Though known as early at IDld it lias of late come into 
greater promiiienco especially since 1 D2 1. 
As tlio disease is very closely associated -with climate and soil 
moisture, a short review is given of the conditions iindiM' \vliich 
citrus' trees are grown. The total area of comnuu-cial citrus orchards 
in the State was 4,0f)9 acres in U)1^4. They may be conveniently divided 
into two jirincipal groui)s. The tirst and larger consists of isolat"d 
orcliards or gronjis of orchards on the coastal plain from tiu' neigh 
boiirhoo<l of Perth south to Harvey, the centre of greatf'st at'i'f'age. 
The second area occupit's strips of good soil in the wi'steni vallevs 
an<l foothills of the Darling Ibinges. The annua! rainfall in both 
areas vai'ies from about 55 to over 40 inches, falling principally be- 
tween A]i]-il and October. Sumnun- rain is erratic and unreliable, 
and on tlie average does not exceed 8 to 10 pei- cent, of the total. 
The wettest months are Juiu' and Julv. An occasional summer irri- 
gation (about three from January to Ajiril} is essential in most com- 
mercial orchards. In conse(pience they are mainly contiiuMl to areas 
wluu'e water can l)e obtaiiu’d by j)umping, oi‘ bv gravitation from 
private storage <lams. At Harvey there is a juiblic irrigatimi scheim’. 
On the Range area natural drainage is usually good, or tlie 
orchards can be readily drained ai'titicially into the valleys. At 
the same time as they occu]»y the valley sides and b(tttoms the 
actual watei‘ coming into the soil naturally, owing to si'opage ar.d 
s])rings. much exceeds tlie rainfall. During tiu' winter months the 
soil is often at the point of saturation for days and even weeks. 
Og the coastal area natural drainage is poolin' and more difficult 
to secui'e ai'tificially. Heia* again there is an accumulation of Avatiw 
1)V soakage from higher levels, causing the water tabh' to rise dose 
to soil level during wet periods before drainagi' i-an cope with the 
ijicoming supjily. River and creek side orchai'ds ar(\ of coursi', 
subject to occasional partial inundations for sliort periods. In bolh 
areas winter tenpieratures rarely fall to 27° V\ Summer temj.era- 
tures over 90° are common. 
(’itrus i>icking commences about June, and (>xt'mds into the 
summer, the ri^iening thus coinciding Avith the wet season. Oranges 
grown on the coastal plain are typically orange-yellow' when ripe 
AAith fine suiooth skins. Those on the range's ripmi later^ Ita'vc 
courser skins, and are a rich orange-red. They have distinctly 
better keejung qualities than the coastal plain oranges, whicii 
are rather liable to mould {PvniciUhun npp.). 
ib-owu Rot occurs more commonly in the Range area than on 
the coastal plain. During the past three seasons, when it has been 
