War on cocoa dieback

is now hotting up

By DON BARRETT, in Rabaul

Dieback is not yet beaten. Dieback is still killing New Guinea cocoa trees, particularly in Gazelle Peninsula. But re search continues in an effort to find a way of combating the disease—there are new developments in this field. Research also continues in an effort to find a strain of cocoa that will resist dieback.

That is the present situation in re lation to the most serious threat New Guinea’s cocoa industry has ever faced.

The biology and chemistry depart ments of the University of Papua and New Guinea, operating on funds con tributed by cocoa growers and cocoa buyers and users, are making a new approach to research into possible control measures.

While it is too early to make any forecasts regarding this new research it can be said that new minds on the matter are welcomed by producers who have become disenchanted with the Department of Agriculture’s “we are doing all we can.”

Is it weather?

The practical observations by planters of weather factors are being sought by the university researchers.

It has long been thought that weather conditions affect the incidence of die back, and the virulence of an out break; several observers now hold the opinion that dry conditions over an extended period are usually followed by an upsurge of the disease. No con crete conclusions have been arrived at.

A recent visiting scientist put forward the view that pruning tech niques might have some bearing on the disease incidence. He based his view on certain factors of similarity to a fungus disease which affects apple trees in New Zealand, where pruning had been discovered to be an influencing factor.

Shade important

Both pruned and unpruned trees die in the Gazelle. The Department of Agriculture has foresaken its stand regarding drastic pruning. Best advice on control now seems to be light and regular pruning of extremities—where dieback first strikes; collection and burning of excised material.

Shade control is important. Over

shading generally brings disease and insect pests, but too drastic thinning all at once can also lower the trees’ resistance. Care is needed in this.

Replacement of trees killed by die back is not now recommended. It is unlikely to be a very successful operation until proven disease resist ant strains are available to the com mercial grower.

A good deal of experimentation to find such strains is taking place at the Lowlands Agricultural Experiment Station at Keravat, near Rabaul.

Those engaged on this work do not forecast any early result. Many trials and years of patient work are needed.

Dieback is gravely affecting produc tion in New Britain. Because new plantings come into bearing and gen eral season conditions affect any one year’s crop it is difficult to accurately assess the overall conse quence.

But one has only to see dead trees and gaps in planted and bearing areas to realise that dieback must mean reduced output. It would not be an exaggeration to say that in in fected areas a drop in production of 25-30 per cent, is common.

Young trees

New plantings, that is plantings in areas not previously under cocoa, are coming into bearing. Some of these have not been infected and are bear ing well; others show dieback at an early age. Usually where dieback appears in very young trees these plantings are adjacent to old infected trees.

It is virtually impossible to save a tree under two years old which becomes infected—there is not suf ficient strength and resistance.

Some growers in Gazelle are looking to alternative crops while carrying out recommended control measures, and hoping—which is all they can do at present—their trees will develop a natural immunity, as some trees do.