19, 2 Lee: Citrus-canker Control 161 
the dry season, with the result that such foliage matured and 
hardened during the dry season without incurring danger from 
reinfection. This matured foliage then entered the rainy season 
with the danger of infection very much minimized, and only in 
the case of the grapefruit and lime varieties was difficulty 
encountered in the infection of such foliage. 
Control of insects to prevent dissemination of canker.—Along 
the edges of leaves where chewing insects have bitten, cankers 
are very often found (Plate 1). Cankers also often appear in 
definite trails following the work of leaf miners (Plate 2). This 
emphasized the need for thorough control of such insects, and the 
addition of lead arsenate to the spray mixtures was frequently 
made. In canker-control work on all varieties of Citrus species 
at Lamao, then, it has been evident that insect control is also an 
essential factor. ee 
Windbreaks to aid in prevention of canker dissemination.— 
From field evidence it was apparent that another agent which 
contributes to the dissemination of citrus canker is the wind. 
This aid to canker development is due not alone to the spread 
of the canker organism by the wind, although that is of course a 
considerable factor, but also to the fact that a strong wind, whip- 
ping the twigs and foliage, causes spine wounds and surface in- 
juries to the leaves resulting in infection by the canker organisms 
under conditions in which they would not develop on unwounded 
tissue. It has been shown in unpublished experiments on the 
moderately susceptible species that canker will develop at a 
wound on a mature or nearly mature leaf, while infection will 
not take place, or at least will not develop, on uninjured surfaces 
of the same leaf. The prevention of the whipping and stabbing 
of the branches and foliage by the wind is therefore also an 
essential point. The windbreaks at Lamao consisted of dense 
thickets of bamboo, 10 to 15 meters high and almost im- 
penetrable. Such windbreaks were very efficient and very 
materially aided citrus-canker control work. 
At Lamao it has been observed that, by attention to such ap- 
parently minor points as the control of chewing insects, the 
utilization of windbreaks, and the regulation of the growing 
periods, much can be done to minimize the development of canker 
on the moderately susceptible hosts. The comparison of results 
at. Los Bafios with results at Lamao supports this conclusion 
and would point to these indirect methods of control as being 
fully as important, if not more so, as prevention of the disease 
by spraying. 
1807823 
