UNIVERSITY OF CALIFORNIA 
 COLLEGE OF AGRICULTURE 
 AGRICULTURAL EXPERIMENT STATION 
 
 June/ 1922 
 
 APRICOT BROWN ROT CONTROL 
 
 By B. A. BTJDOLPH 
 
 Since Circular No. 238 was prepared, extensive spraying experi- 
 ments have yielded new information upon the subject of controlling 
 Brown Rot. The present leaflet therefore supersedes much of that 
 which is said upon this subject in the circular and should be followed 
 wherever the statements seem to conflict. Emphasis should be placed 
 upon the importance of spraying in the early blooming period, the 
 necessity of spraying badly diseased orchards more than once during 
 this period, the use of strong Bordeaux mixture, the value of cutting 
 out the old, diseased twigs and spurs which form the principal source 
 of infection during the following spring, and the inadvisability of 
 spraying apricots with lime-sulphur on account of the danger of injury. 
 
 The critical or strategic period of spraying for this disease lies in 
 the spring, just before and during the bloom. Infection usually takes 
 place at any time after the buds commence to crack, showing the white, 
 folded petals beneath the red sepals, continuing until the petals have 
 fallen and the jackets are shed. Because of this relatively long period 
 during which infection may take place, it has repeatedly been found 
 that a single application of spray is insufficient to protect the blossoms 
 against infection. This is particularly true in badly diseased orchards 
 and in damp localities. One spraying applied when the red buds are 
 cracking often gives good control in orchards which are not severely 
 attacked. For full protection in badly diseased orchards, two or more 
 sprayings are necessary, starting with the red bud and following in 
 quick succession up to the full bloom or even later, in order to protect 
 the blossoms as they continue to open. Where the trees are badly 
 diseased the control obtained has ordinarily been found to be directly 
 proportional to the number of sprays applied. 
 
 Bordeaux mixture has proved the best spray for the control of 
 Brown Eot, and while at this time the data are incomplete, the figures 
 obtained indicate that a spray of stronger strength, say 7-8-50, is 
 more effective than one of the standard 4-4-50 strength. 
 
Because of the frequent damage resulting from the use of lime- 
 sulphur on apricots, it is considered inadvisable to use this spray at 
 any time when a satisfactory control of Brown Rot might be expected. 
 In addition to a tendency to burn the buds, lime-sulphur frequently 
 produces on apricots an injurious effect known as "sulphur sickness." 
 In such cases the foliage is stunted and yellow and the fruit is late in 
 ripening, undersized, and of poor quality. Badly affected trees fail 
 to bloom the following year. 
 
 Too much stress cannot be placed upon the necessity of pruning out 
 all old twigs killed by Brown Eot. Experiments both last year and 
 this showed that Brown Rot infections in very carefully pruned trees 
 were about one-third as many as in trees receiving conventional prun- 
 ing, the spray treatment being identical. This pruning should be 
 commenced in the fall as soon as the crop is off, or even sooner. 
 
 Information is still lacking as to a satisfactory method of prevent- 
 ing Brown Rot in the ripe fruit of prunes and apricots. The best that 
 can be recommended at present is to spray susceptible orchards with 
 Bordeaux (4-4-50) as late as possible, without running the danger 
 of leaving the fruit disfigured with spray residue at harvest time. 
 With apricots such spraying may possibly be done up to a month bef ore 
 the fruit is mature. Prunes, since they are washed, may be sprayed 
 even later with no bad results. This subject of controlling the ripe 
 fruit rot is still receiving attention.