Potato spraying and dusting in New Jersey, U.S.A.
Authors: Cameron Alfred E. 
Published: July 2009

In employing the most up-to-date methods in the prosecution of his business, the American farmer endeavours to get the best return for his labours. The adoption of the latest prophylactic measures for combating the fungus and insect enemies of his crops, is but a single instance of that progressiveness which is characteristic of the man.

The State Agricultural Experiment Stations encourage the farmer in many ways and are of genuine practical value in dealing with local problems. The establishment of similar institutions in this country would be quite justifiable.

The experiments with various fungicides and insecticides were carried out in the State of New Jersey. They were intended to demonstrate how a larger yield of potato tubers per acre might be procured by the employment of scientific methods of spraying and dusting.

The principal fungus diseases attacking the potato are early blight (Macrosporium solani), late blight (Phytophthora infestans), and dry rot (Fusarium oxysporum). Late blight, which levies a heavy toll on the potato crop in America, is injurious in New Jersey only in exceptionally wet seasons. A pathological condition of the leaves known as “ tip-burn ” is in some years responsible for a reduced yield.

Of the various treatments applied, Bordeaux mixture vindicated itself in each case. It is not only a most excellent fungicide, but also an effective insecticide when arsenate of lead is added. Both the Colorado and flea-beetles were better controlled by the Bordeaux-lead arsenate mixture than by any of the other insecticides used in the field experiments.

Bordeaux mixture acts as a plant stimulant by maintaining the green colour of the leaves for a longer period. This naturally means larger tubers.

Thoroughness of application of the Bordeaux mixture and frequent repetition of the treatment, at least once every ten days, are necessary for effectiveness. Care in its preparation is strongly advised. Sufficient lime must be used to ensure that all the copper sulphate is changed to the hydrate form, otherwise burning of the leaves may ensue.

The use of Bordeaux mixture may increase the value of the yield of tubers anything from £3-£5 per acre. The increase, however, varies considerably in different localities and in different years.

Sulphur did not quite realise expectations as a crop stimulant. Various proprietary Bordeaux mixtures proved less economical and less efficient than the home-made article.

The cost of spraying or dusting varies according to the locality, but of all the treatments applied, home-made Bordeaux mixture always proved cheapest.

Concurrent experiments carried out in the laboratory and field with many insecticides additional to those used in the large field tests, were the means of discovery of an insecticide which seemed to fulfil all requirements in controlling the flea-beetle. It is composed of a combination of pyrethrum infusion, gelatin or soap, and lead arsenate. Extended trial will, however, have to be made to establish its efficacy.

The fenestration of the leaves by the flea-beetle, besides materially reducing the assimilating surface of the leaves, also renders the injured tissue more susceptible to the attack of various cryptogamic diseases. This is notoriously true of early blight.

Counts made of the fenestrations of the leaves on a large number of shoots, gave an idea of the intensity of the damage caused by the flea-beetle at any one period. A comparison of the counts made on plants treated with different substances, supplied a rough estimate of their value in controlling the pest.

For a true interpretation of the results of the field experiments various factors must be considered, amongst which not least are the physical and chemical conditions of the soil, previous cultivation and the vagaries of the weather.

A Braconid parasite (Perilitus epitricis) of the flea-beetle was reared from adult captured specimens. Its behaviour in relation to its host was closely observed in the field, especially the manner of its oviposition. No figures were obtained of the percentage of parasitism, but it is considered that the Hymenopteron is practically a negligible factor of control.