Page 10 



BETTER FRUIT 



A Thrips Injury to Apples 



By E. J. Newcomer, U. S. Bureau of Entomology, Yakima, Washington 



IN 1914, when I was first stationed in the 

 Pacific Northwest, my attention was 

 called to certain irregular whitish spots that 

 were quite prevalent on apples. Since then 

 I have seen these spots on almost all varieties 

 of apples wherever they are grown in the 

 Northwest. The spots are frequently very 

 common, sometimes as many as twenty-five 

 or thirty occurring on a single apple. These 

 "pansy spots," as they are sometimes c.illed, 

 invariably show a darit center, or puncture, 



In 1920, Mr. B. B. Fulton, of the Ore- 

 gon Experiment Station found what he took 

 to be a thrips egg shell in one of the punc- 

 tures, and in May, 1921, I began examin- 

 ing apples shortly after the blooming 

 period. 1 found newly-hatched thrips 

 larvae very common in the calyx cups. One 

 lot of 100 apples harbored 89 of these 

 thrips larvae. By rubbing off the pube- 

 scence of these small apples, I was able to 

 find the whitish spots already present, and 



Effect of Thrips on Half-Grown York Imperial 



and are quite obviously caused by an insect. 

 While in most cases the spots practically dis- 

 appear before the fruit is mature, in cer- 

 tain varieties they persist, and cause the 

 fruit affected to be lowered in grade. In 

 any event, they are the cause of much in- 

 quiry on the part of apple growers as to 

 their origin and economic importance. 



The spots are present on the apples very 

 soon after blooming, and during June and 

 July are usually rather conspicuous. (Fig. 

 1). As the fruit grows, the white area 

 spreads out somewhat, and on most varieties 

 gradually assumes practically the color of 

 the rest of the surface, until at picking 

 time it has very largely disappeared, only 

 the small and inconspicuous puncture re- 

 maining. This looks very much like a len- 

 ticel and in no way affects the grade. On 

 some varieties, notably the Mcintosh (Fig. 

 2), the York Imperial and the Northern 

 Spy, the spot shows very conspicuously at 

 maturity and sometimes as much as 25 per 

 cent of the crop is injured in this manner, 

 with a consequent reduction in grade. 



For the last seven years I have attempted 

 to find the cause of this spot, but with no 

 success until this year. The spots were evi- 

 dently produced at about the blossoming 

 time of the apple, but did not become no- 

 ticeable until after the calyx cups had 

 closed, by which time the insect that caused 

 them had apparently disappeared. I have 

 been able to prove that these spots are not 

 produced by any of our apple-,feeding 

 aphides, nor by the tarnished plant bug, and 

 Mr. Childs, of the Hood River Experiment 

 Station, has shown that they are not the 

 work of the leaf hoppers, though the idea 

 it ttill quite prevalent that leaf hoppers are 

 the caute of these apoti. 



after a careful examination of a consider- 

 able number with a binocular microscope, 1 

 was able to find some which contained a 

 thrips egg in the center of each spot. The 

 egg is very small, less than a half millimeter 

 in length, white, and very delicate. After 

 being exposed to the air a few moments, it 

 begins to shrivel. The egg is deposited at 

 nearly right angles with the surface of the 

 apple, and just beneath it, one end of the 

 egg closing the hole made by the thrips 

 ovipositor. The larva, upon hatching, 

 emerges through this outer end, and leaves 

 a small hole in the skin of the apple. The 

 irregular, whitish area is the result of irri- 

 tation produced by the presence of the egg 

 in the apple. This settles the question of 

 what causes these white spots or areas. The 

 matter of preventing them is yet to be con- 

 sidered. 



In most of our commercial varieties this 

 thrips injury is of no consequence. It is in- 

 conspicuous at picking time on such varie- 



October, 1921 



ties as Winesap, Newtown, Rome and usu- 

 ally Jonathan. In such cases, control meas- 

 ures are unnecessary. Where the Mcintosh, 

 Senator, York or Northern Spy is grown, 

 however, it might sometimes be advisable 

 to use preventive measures. The species of 

 thrips causing this injury has not been de- 

 termined. However, the damage is done 

 during a comparatively short period, and 

 the application of a standard thrips spray 

 of miscible or distillate oil and nicotine 

 sulphate at the time of the "pink" spray 

 should materially reduce the injury. 



Thripi Injur/ to Mature Mclntoah Red 



Collar Rot 



By Luke Powell, Horticulturist, Yakima, 

 Wsishington 



THE fruit grower little realizes the 

 heavy loss he is sustaining year after 

 year from the so-called collar rot. ■ If the 

 owner of the average ten-acre orchard was 

 to lose three cows or horses per year, valued 

 at $100 each, he would soon realize that he 

 must find the causes and remedies for the 

 losses or quit raising cows and horses. 



The average fruit grower does not realize 

 that every time a good fruit tree dies it 

 means a loss of at least $100 to him. This 

 is due to the fact that it takes the tree 

 about a year or two to die and usually be- 

 fore one is dead several more have started 

 and so the grower gets calloused to his 

 losses. Nor does he further know that as 

 the trees get older they are more susceptible 

 to the disease, although they are increasing 

 in valu. 



In reality there is no such diseases known 

 as collar rot. But due to the fact that 

 the trees are most usually affected below 

 the surface first and die when the infection 

 has about spread to all the roots and girdled 

 the tree at the surface of the soil, it is com- 

 monly called collar rot. 



We have here in the Yakima valley sev- 

 eral different types of this root injury 

 which, if not promptly checked, soon kills 

 the tree. 



On some slopes with good soil and splen- 

 did drainage we are losing trees during the 

 summer or irrigation season. 



In other localities the injury is done 

 later on as the fall and early winter sets 

 in, or it may be delayed until spring, de- 

 pending on the factors that cause the 

 trouble. 



We have some few cases of real pear or 

 fire blight attacking the roots and trunks of 

 the trees. This is easy to control compared 

 to the other cases. 



There are three factors that enter into 

 the control of this so-called collar rot. 



First: The grower must fully realize the 

 economical loss he is sustaining from year 

 to year. 



Second: That he is going to find out the 

 factors that causes it in his orchard and how 

 to prevent its further occurrence. 



Third: That in the future he will plant 

 only such nursery stock as is as near im- 

 mune to these troubles as it is possible to 

 |TOW. 



