CONTROL OF RED MITE AND WOOLLY APHIS IN NURSERY STOCK.

New Zealand Journal of Agriculture, Volume XIX, Issue 2, 20 August 1919, Page 94

CONTROL OF RED MITE AND WOOLLY APHIS IN NURSERY STOCK.

G. ESAM,

Acting Assistant Director of the Horticulture Division.

Not only is the fruitgrower concerned with the control of red mite, but the nurseryman is most anxious to keep his stock clean. All are only too familiar with the serious and harmful work of this pest on the foliage of fruit-trees. Nurserymen have been accustomed to relying on red oil at a strength of i-io to control the insect, but of late it has been noted that this could not altogether be depended upon to prevent red-mite eggs hatching. Mr. Thomas Horton, of Hastings, on behalf of the Association of Nurserymen, requested the Department to undertake an experiment on nursery stock with a view, if possible, of finding a cheaper and at the same time a more effective control than oil, i-io, applied in the early spring. Such work being one of the chief functions of the Horticulture Division, the request was readily acceded to, and Mr. Horton placed a block of two-year-old Jonathan trees planted out in nursery rows, comprising ten thousand to twelve thousand trees, at the Department's disposal. It was an ideal block for the purpose, and by request the trees were not lifted last winter. The block had been sprayed in the spring of 1917, after it was planted, with red oil, i-io. By the end of May, 1918, an examination showed that it was generally infected with red-mite eggs throughout.

The block, which consisted of eighteen rows, was divided into three equal plots of about I chain in length by removing the trees for about 20 ft. between each plot. These plots are referred to hereafter as plots A, B, and C. In the spring and early summer the corresponding row in each plot received the same treatment, as follows : —

The trees were quite dormant on 13th August, when oil, 1-10, was applied. It was originally intended to spray with oil, 1-15 and 1-20, in September, but owing to the pruning of the block being delayed the trees got further advanced than the stage at which it was considered safe to apply these sprays. On 4th October the trees were showing pronounced leaf, but. young wood shoots had not started. No damage was done by any of the sprays. The block was examined on 29th October. A few live mites were found on rows 1 and 2, and quite a number on rows 11 to 18, while there were none on rows 3 to 10. This examination indicated that the

delayed oil-application is an advantage, while lime-sulphur when used at the strengths tabulated and applied close on the time when the eggs normally hatch does not prevent them hatching.

The summer treatment of each plot was varied as follows : Plot B was sprayed on 27th November with Blackleaf 40, 1-800. An examination made a fortnight later showed that the spray had killed all the mites that were on the move at the time the spray was applied, but a number of mites had subsequently hatched and were then on the move. Plot C was sprayed, on the same date with lime-sulphur, 1-100. The result a fortnight later was the same as in plot B.

By this time rows 3 to 10 appeared to be assuming almost as much infection as the other rows. One could not say whether the oil on these rows was not as effective as it appeared to be in an earlier examination, or whether the mites , had spread from the other rows in the block. Plot A, which had not had the additional summer spray, had if anything slightly more infection at this time than the other two plots.

The partial failure of all treatments up to this time left the field open for further experiments. It was then decided to endeavour to completely eradicate the pest in summer before it commenced laying what are known as winter eggs on the wood of the tree. These are the eggs that carry the infection through the winter and hatch out the following spring. In this the experiment was successful. Early in January all the plots appeared to be similarly infected. At this time plot A had received no summer treatment.

Plot B was sprayed on 18th and 26th January and 3rd February with Blackleaf 40, 1-800, combined with lime-sulphur, 1-100. Plot C was sprayed on the same days with lime-sulphur only, at 1-100.

The reader’s attention is now drawn to the matter of woolly aphis. On 1st April, 1919, this pest was very bad on plot A, with a moderate infection on plot C, while plot B was as free from it as one could wish. Something had to be done at this season for woolly aphis on plots A and C. Each plot was therefore divided into two sections, one sprayed with Blackleaf 40, 1-800, combined with lime-sulphur, 1-100, and the other with Blackleaf 40, 1-800, with 3 lb. soap to every 100 gallons. The spraying was done on 2nd April. On 5th May the plots were examined, and no marked difference between the effect of the sprays could be detected.« It was at the best only a partial control, and on plot A where the wood had been deformed fresh colonies of aphis were showing. Plot B; which had not been treated since January, stood out as an object-lesson.

Returning to the control of red mite, readers are reminded that plots B and C had received three sprayings within sixteen days. This was considered necessary in order to catch all the mites as they hatched out from the summer eggs, as it was recognized that no spray could be put on in the summer sufficiently strong to kill the summer eggs without injuring the foliage.

A careful examination of all trees was made after they were lifted on 4th May last, with the following results : —

Plot A. — 63 per cent, of the trees in the plot were infected with red-mite eggs.

Plot B. —-12 per cent, of the trees were infected with red-mite eggs ; but if the first twenty trees in each row at the end next to plot A were

not counted there would have been under i per cent, of the trees infected.

Plot C. — This plot was practically clean, only about j per cent, of the trees showing red-mite-egg infection.

It will be observed that plots A and C were sprayed once in April for woolly aphis, but in my opinion this would have little or no beneficial result in preventing the laying of winter eggs, as the majority of them were on the trees before this spray was applied.

CONCLUSIONS

The experiment clearly demonstrated that summer spraying for red mite is essential in addition to the spring sprays used. Although three sprayings towards the end of January, at an interval of six .to eight days, controlled the mite and prevented the laying of what are known as winter eggs, I am of the opinion that three similar applications in October before the mite has a chance to lay its summer eggs on the foliage would prove efficient and eradicate the mite. If these earlier sprayings are given it is highly essential that the first should be commenced soon after the first mites hatch from the winter eggs, and certainly before they are fully grown and commence laying their summer eggs. However, this phase of the question is being thoroughly tested at the Department’s horticultural stations this spring. Lime-sulphur is as effective as Blackleaf 40 as a summer spray for red mite, but where the dual control of red mite and woolly aphis is required Blackleaf 40 should be used. Although the three sprayings on block B with this nicotine preparation in January were expensive, they were highly effective against woolly aphis as well as red mite, whereas it was necessary to treat woolly aphis separately in plot C. While this experiment was primarily carried out on nursery stock for the benefit of nurserymen, the result obtained is equally applicable to fruit-trees in established orchards. . -

The cultivation of the land is the basis of national strength and prosperity. — David Lloyd George.

Horse Bot-flies. —A Wanganui correspondent states that he finds he can keep bots off his horses by dabbing a little sheep-dip and oil —half-and-half—on the fore legs every day or two ; also that if any eggs are on the horse this application kills them.

Calculi from Animals. — Several interesting specimens of calculi (stone-like concretions) from domestic animals have been recently examined at the Chemical Laboratory. A spherical brassy calculus from the urethra of a ram in the Wairarapa district was found to be merely calcium carbonate. A specimen of renal calculus from sheep at Berwick, Otago, was entirely organic, and consisted largely of uric acid and urates. As calculus is stated to be a somewhat frequent affection of the sheep on this farm, a dietetic origin of the trouble may be presumed.— B. C. Aston.

Spray. Date. Rows I, 2 . . Red oil, 1-10 I-IO 13 Aug., 1918. 13 Aug., 1918. Rows 3, 4, 5, 6 , . . Red oil, . 1-25 1-25 4 Octi, 1918. 4 Oct., 1918. Rows 7 , 8, 9, io Red oil, 1-30 1-30 4 Oct., 1918. 4 Oct., 1918. Rows ii, 12, 13, 14 . . Lime-sulphur, 1-20 1-20 4 Oct., 1918. 4 Oct., 1918. Rows 15, 16, 17, 18 . . Lime-sulphur, 1-25 1-25 4 Oct., 1918. 4 Oct., 1918.