BETTER FRUIT 



AX ILLUSTRATED ^L^GAZINE PUBLISPIED MOXTHLY IX THE IXTEREST OF MODERX, PROGRESSIVE FRUIT GROWIXG AXD MARKETIXG 



Relation of Height of Fruit to Apple Scab Infection 



By Leroy Childs, Entomologist and Pathologist, Hood River Branch, Experiment Station 



IN the past, while checking up scab 

 experiments under investigation, 

 an interesting observation was 

 made relative to the distribution of 

 scab-infected fruit on the trees ex- 

 amined. Early in the summer it was 

 observed that the fruits in the tops of 

 the trees were much more scabby than 

 those nearer the ground. It seemed 

 probable, then, that since this condi- 

 tion existed in carefully sprayed ex- 

 perimental plots the condition would 

 be found to be present in a more pro- 

 nounced form where especially careful 

 oversight had not been given each 

 application of spray. Several orchards 

 were examined to determine the cor- 

 rectness of this supposition. In nearly 

 every case this variation in the amount 

 of scab relative to distance from the 

 ground was found to be present, and 

 often very conspicuous indeed. 



In view of the important bearing of 

 this discovery upon the whole subject 

 of spraying practice, it was decided to 

 undertake a careful investigation of 

 actual conditions existing at harvest 

 time in certain trees that had been (as 

 was thought) w-ell and carefully 

 sprayed according to schedules that 

 had been arranged by the Experiment 

 Station. 



At picking time twelve large trees 

 were chosen in one of the orchards in 

 which scab control experiments were 

 being conducted. These trees were 

 sprayed at the proper time, though not 

 under the personal observation of the 

 writer, and as thoroughly as the equip- 

 ment of the owner permitted. Seven of 

 these trees received four scab applica- 

 tions (Block 1), the 30-day lime- 

 sulphur application being omitted, and 

 five (Block 2) were given five applica- 

 tions of lime-sulphur. 



The apples from Block 1 were picked 

 and separated into three divisions 

 (Figure 1), viz., (1) from the ground 

 to a height of ten feet; (2) from ten 

 feet to fifteen feet; and (3) from fifteen 

 feet to the tops of the trees. After the 

 fruit was picked the percentages of 

 scab were determined for each division 

 in each tree. Only two divisions were 

 made in the case of Block 2 (Figure 2), 

 the fruit being separated from the 

 ground to ten feet, and from ten feet 

 to the tops of the trees. 



In choosing the trees from which the 

 counts were made it was necessary to 

 select those which were bearing a rela- 

 tively light crop and which stoofi erect. 

 In the case of trees heavily loaded it 

 was impossible to accurately segregate 

 the fruits in their respective normal 

 positions, owing to the sagging of the 

 healiy-laden branches. 



The average height of the twelve 

 trees chosen was 26 feet. (Figures 1 

 and 2.) The largest reached a height 

 of 28 feet. The average greatest diam- 

 eter of these trees was 22 feet, the 

 widest being 24 feet. Fruit was found 

 present to an average height of 21 feet; 

 on one tree apples were taken 24 feet 

 above the ground. 



Although considerable variation was 

 found to exist on the different trees 

 studied, the increase in every case from 

 the ground to the top was found to be 

 constant, the difference in degree of in- 

 fection in each section of each tree 

 being very pronounced. (See Figures 

 1 and 2.) 



From Block 1, w^hich received four 

 applications of lime-sulphur, the fol- 

 lowing average percentages of scabby 

 fruits occurred in the respective sec- 

 tions; from the ground to ten feet, 6.52 

 per cent; from ten to fifteen feet, 22.31 

 per cent; fifteen feet to the top, 45.72 

 per cent. The following ratio was 

 observed in the most seriously infected 

 tree: ground to ten feet, 13.72 per cent; 

 ten to fifteen feet, 40.30 per cent; fifteen 

 feet to the top, 60.01 per cent. The 

 fruit in the least infected tree was 

 found to be as follows: ground to ten 

 feet, 2.46 per cent; ten to fifteen feet, 

 8.23 per cent; fifteen feet to top, 21.47 

 per cent. The average total scab in- 

 fection from Block 1 amounted to 

 22.52 per cent. At first glance an in- 

 fection of this extent does not appear 

 serious. However, it is so distributed, 

 with nearly 50 per cent of the fruit in 

 the tops of the trees infected, that it 

 cannot be thinned out without heavy 

 losses. 



Much less scab was found in Block 2. 

 In this group of trees two divisions 

 only were made in separating the fruit 

 as mentioned previously. (See Figure 

 2.) A decided variation in the relative 

 amounts of scab according to height 

 was found to occur here, standing out 

 even more distinctly than that in I51ock 

 1. An average of but 1.62 per cent in- 

 fection was found on the fruit between 

 the ground and ten feet, while the in- 

 fection from ten feet to the tops was 

 18.08 per cent. The average percentage 

 of scab on these five trees was 12.41 

 per cent, or nearly half that which 

 occurred on the trees sprayed only four 

 times. The importance of the fifth 

 spray in this case is easily seen. 



Unfortunately no segregation of fruit 

 according to height was made from 

 apples on the check trees, so that the 

 natural distribution of scab on un- 

 sprayed trees was not determined. 

 However, the total infection present on 

 some of the control trees kept under 

 observation during the past year 



amounted to 97 per cent. This very 

 high percentage of scabby fruits indi- 

 cates that infection must have been 

 general over the entire tree. 



It is interesting to compare the result 

 from two other experiments conducted 

 in the orchard in which the observa- 

 tions just discussed were obtained. In 

 these experiments, lime-sulphur was 

 used in the same strength and in the 

 same number of applications; i. e., in 

 one (Block 3) five applications were 

 given; in the other (Block 4) four 

 applications were used. Equipment, 

 rodmen and method of application 

 were identical in all four blocks. 

 Though Blocks 3 and 4 were sprayed 

 earlier in all applications the interval 

 existing between these was about the 

 same throughout the orchard, as the 

 trees were sprayed in their regular 

 turn throughout the season. Two ma- 

 terial differences, however, appear to 

 be responsible of the differences in the 

 percentages of scab present. In com- 

 paring the average heights of the trees 

 in Blocks 1 and 3, a difference of five 

 and a half feet occurs; in Blocks 2 and 

 4 but three feet difi'erence in the heights 

 exists. Xot only this difference in 

 height occurs but in the case of Blocks 



3 and 4 personal inspection of the 

 spraying was given by the writer dur- 

 ing each ajjplication and parts of the 

 trees missed by the rodmen were 

 pointed out and resprayed. No in- 

 spection was given in Blocks 1 and 2; 

 both men working with the spray rig 

 operated rods; in the case of very large 

 trees a man spraying cannot tell the 

 parts of the trees that are not hit with 

 the spray. 



The trees in both Blocks 3 and 4 were 

 heavily laden with fruit. On this ac- 

 count the figures given in Figures 3 and 



4 are not entirely accurate, as it was 

 impossible to segregate the fruit in all 

 cases owing to the confusion brought 

 on by the severe bending of the higher 

 limbs. An accurate percentage of in- 

 fection was obtained, however, from 

 fruits which were actually above ten 

 feet at the lime of picking. It was 

 found in Block 3 that top infection 

 amounted to 3.86 per cent, while the 

 infection from the ground to the top, 

 which included a good many fruits 

 from the upper division, was .95 per 

 cent. An infection of 62.5 per cent 

 was present on adjoining check trees. 



Figure 4 illustrates the results ob- 

 tained in Block 4, where the "30-day" 

 spray was omitted. The trees in this 

 plot averaged larger than in Block 3, 

 but not as large as those in Blocks 1 

 and 2. Though many top fruits are in- 

 cluded in the figures given in the lower 

 division, the differences occurring in 



