THE MONTHLY BULLETIN. 



4:.H 



SPRAYING AS A MEANS OF CONTROLLING BLACK 

 SCALE ON CITRUS TREES. 



By John P. Cot. County Horticultural Commissioner. San Bernardino, Cal. 



Since fumigation was put on a commercial basis, spraying, as used for the control 

 of scale insects on citrus trees, has been practically discontinued. True, there have 

 been several times when spraying has had a new lease of life for a short time and 



in some districts quite a number of growers would 

 spray, but these spray spasms have always been 

 followed by a return to fumigation. At times a 

 batch of spray men appear on the scene with new 

 sprays or the same old sprays under new names, one 

 of their stock arguments being something like this: 

 "Much cheaper than fumigation: much more effective 

 and no damage." It is reported on good authority 

 that there is a "sucker" born every minute. I don't 

 know that the count is exactly accurate, but I 

 do know that last year many growers "bit," and I also 

 know that there are very few of those who tried 

 spraying last year that are going to try it again this 

 year. 



There are certain reasons why spraying is not a 

 satisfactory method to employ when trying to rid 

 cirtus trees of scale insects. The foliage of citrus 

 trees is usually dense and remains on the trees 

 throughout the year, while the scale scatters over 

 the twigs and leaves. If it is a bad infestation of 

 black scale there may be hardly a leaf on the tren 

 that has not some young scale on one or both sides of it. Under such conditions in 

 order to do satisfactory work with a contact spray it is necessary that every leaf 

 on the tree be thoroughly wet on both sides. This seems to be an impossibility when 

 doing work on a commercial scale. Be the spray ever so good, there are always 

 patches on the trees where live scale can be found due to those places being missed. 

 Then again citrus trees not becoming dormant to the same extent as deciduous trees 

 there is no time when a dormant strength spray can be used on them. 



During the fall of 1916, owing to the shortage of cyanide, about 5,000 acres of 

 citrus trees were sprayed in San Bernardino County. About a dozen different sprays 

 were used and it gave us a .splendid opportunity to compare the results. One of 

 the striking features of the investigation was that none of the sprays gave uniform 

 results. Perhaps there would be a 90 per cent killing in one grove and another grove 

 treated with the same material would show only a 40 per cent killing. This differ- 

 ence may have been due to the denser foliage in one grove or to less careful work : 

 perhaps temperature and moisture conditions had something to do with it also. It 

 seems to be almost impossible to keep the man who holds the nozzle keyed up to a 

 pitch where he will do careful work all the time. 



Another feature of some of these sprays was the very severe damage they would 

 frequently cause. This damage consisted in dropping leaves, burning fruit, dropping 

 fruit, and sometimes killing the twigs and smaller branches until the trees would 

 look as though a tire had gone through them. One of the sprays did little apparent 

 damage at the time of spraying except to leave slight discolored spots on the fruiti 

 We called the growers' attention to these spots, but the spray agent said they 

 would wash off with the rain and do no damage. When this fruit was packed it was 

 culled heavily on account of these spots. 



In one grove that I visited about three weeks after it had been treated with a 

 certain spray, I found that two-thirds of the leaves were on tile ground and all the way 

 from a few up to 350 oranges under each tree. Of course this was a very extreme 

 case, but it shows what may happen with some sprays. This happened to be one of 

 the sprays that the agent claimed could be used for half the cost of fumigation, with 

 50 per cent more efficiency and no injury. In another case which shows the treachery 

 of some sprays, a company recommended that a man use a spray that had been used 

 on another grove a short time before with no apparent damage. The man used the 

 spray and received such severe injury that he brought suit and got judgment for 

 $1,000 damages. 



