Ipll 



BETTER FRUIT 



Page SI 



TWO DESTRUCTIVE PLANT LICE OF THE PEACH 



BY C.P.GILLETTE AND GEORGE P. WELDON, EXPERIMENTAL STATION, FORT COLLING, COLORADO 



GREEN PEACH APHIS is the 

 common green peach louse so 

 prevalent early in the season curl- 

 ing the leaves, and often attacking the 

 blossoms and forming peaches in a most 

 destructive manner. The eggs of this 

 species of plant louse 

 are deposited on peach 

 trees (occasionally on 

 the other stone fruit 

 trees) in the autumn, 

 where they remain 

 unhatched until early 

 spring. Their detec- 

 tion is not as easy as 

 that of the common 

 green apple aphis egg, 

 but is not extremely 

 difficult when one 

 knows where to look 

 for them. Last fall 

 the eggs were depos- 

 ited in such large 

 numbers that they 

 could easily be found 

 in a great many 



feeding they do takes place on the buds 

 or very tender bark into which their 

 beaks are inserted, and from which a 

 portion of the early flow of sap is 

 extracted. Plant lice of the spring 

 brood, which hatch from eggs that have 

 remained on trees over winter, are 

 known to the entomologist as stem- 

 mothers. The full grown stem-mothers 

 of this plant louse are of a pinkish or 

 salmon color, and before there is a sign 

 of a peach blossom in the spring, these 

 stem-mothers have begun reproduction. 

 Their progeny are born alive, eggs never 

 being laid except in the fall, and then by 

 an aphis which, though only a different 

 fiirm of the same species, might be taken 

 by the orchardist for an entirely different 

 kmd of plant louse. The generation 

 from the stem-mothers differ from the 

 latter in that they are light green in 

 color, with darker green, longitudinal 

 markings on the dorsal surface of the 

 abdomen, but are never pink like the 

 stem-mothers. Just as soon as the buds 

 on infested trees begin to unfold, the 



orchards. In some EGGS DEPOSITED ON gtej-,.,.,.,.iothers, with their progeny, are 



BUD 



cases the buds of the 

 peach twigs were dotted black with them. 

 In most instances these eggs are found 

 deposited on, or very close to a bud, 

 and very often just as deep in wrinkles 

 iir depressions as possible, and unless 

 ihey are plentiful it may require sharp 

 eyes to detect them. When first depos- 

 ited the eggs are light green in color, 

 turning black after exposure to the air. 

 They are much smaller than the eggs 

 of the common green apple aphis, which 

 nearly every orchardist has seen, but are 

 quite similar in shape, color and general 

 appearance. This pest may live over 

 winter on vegetation that remains green 

 throughout the winter season, so there 

 would be a possibility of trees becoming 

 infested at least late in the season from 

 other sources, even though the eggs were 

 all killed by an insecticide, or failed to 

 hatch because of unfavorable weather 

 conditions or other causes. 



The eggs of this aphis hatch very early 

 in the spring. E. P. Taylor reports hav- 

 ing found them hatching at Grand Junc- 

 tion, Colorado, on the 16th day of Feb- 

 ruary, 1907. The month of February 

 that winter was unusually warm, and the 

 extremely early hatching of the eggs 

 was due to that fact. However, hatch- 

 ing takes place when the buds have 

 scarcely begun to swell, a fact which is 

 not generally understood by the fruit 

 grower, and one which is of very great 

 importance in its relation to the control 

 of the pest by means of a spray. The 

 past spring eggs were found hatching on 

 the 7th of March at Clifton, Colorado, 

 at which time the buds seemed perfectly 

 dormant. 



When first hatched from the eggs 

 these aphids are dark green in color, and 

 may be seen as tiny, dark specks crawl- 

 ing along the twigs, or more often cling- 

 ing to the buds. It is probable that they 

 can exist for a number of days after 

 hatching with little or no friod. What 



ready to enter within. At first they seem 

 to prefer feeding in the blossoms, but 

 after these fall quite serious injury is 

 often done by their feeding on the leaves. 

 Probably the greatest injury to peaches 

 resulting from their attack consists in 

 the dropping of the small fruit which 

 has become devitalized from the loss of 

 sap until it can make no growth, hence 

 shrivels and falls to the ground. The 

 injury to the peach is practically all done 

 while it is yet in the husk or calyx tube. 

 After the peach has cast off this calyx 

 tube it is not likely to be molested fur- 

 ther by the aphids, and unless it has 

 been too much weakened before this 

 tiine the probabilities are that it will 

 not drop as the result of aphis attack. 



Fortunately this pest cannot, or does 

 not, spend its entire existence upon the 

 peach or other trees, but leaves them for 

 more succulent vegetation. Shortly after 

 the peaches are formed, winged lice 

 begin to appear in the colonies; these 

 fly away to other food plants, and by 

 the last of June very few can be found 

 on peach trees. This is indeed a bless- 

 ing to the peach grower, for should this 

 pest continue its ravages throughout the 

 summer on the peach it would require 

 great effort and expense to control it. 

 As it is trees often suffer a great loss 

 of foliage, and if it were not for the 

 wonderful power of the peach tree to 

 recover after this injury the result of the 

 aphis attack would be more disastrous. 



Gillette and Taylor, in bulletin 

 of the Colorado Experiment Station, 

 gave a list of fifty-three plants growing 

 in the greenhouse which were found to 

 be infested with this aphi<=. and twenty- 

 five plants growing out of doors, the out- 

 of-door plants comprising most of the 

 common garden vegetables and weeds. 

 The variety of plants upon which this 

 louse feeds during the summer time is 

 so great that it is probable that it will 

 seldom be plentiful enough on any one 



kind to do serious injury. While on the 

 summer food plants this aphis is usually 

 light yellow in color, and without the 

 green stripes so characteristic of it while 

 feeding on the peach. 



The last winged generation of lice 

 appearing in the fall are known as fall 

 migrants because of the fact that they 

 leave the vegetation upon which the 

 summer has been spent and migrate to 

 peach trees. These fall migrants do not 

 deposit eggs, but give birth to the true 

 sexual forms, males and females. The 

 females are pink in col'or, somewhat 

 similar to the stem-mothers which were 

 on the trees in the spring, but smaller. 

 After feeding for a time and becoming 

 mature they deposit the eggs previously 

 described. 



Because of the abundance of green 

 peach aphis eggs last winter a number 

 of different spray tests were made in the 

 spring with various insecticides in order 

 to determine their value as egg destroy- 

 ers. The spraying was delayed a little 

 too long, however, and ,on the 7th of 

 March, when the first applications were 

 made in the W. C. Strain orchard at 

 Clifton many of the eggs were found 

 to be hatching, and there was no trouble 

 in finding the little green lice here and 

 there on the twigs. A great many of the 

 eggs were not hatched at that time, 

 hence the various sprays were tested as 

 destroyers of both the eggs and the 

 young lice. The block of trees sprayed 

 in the Strain orchard, was only three 

 years old, but contained both the eggs 

 of green peach aphis and the hibernat- 

 ing larvae of the twig-borer in abun- 

 dance. The small size of the trees made 

 very thorough spraying possible. The 

 work was done with a barrel pump, so 

 it was not possible to make the appli- 

 cations with a high pressure. Thor- 

 oughness was depended upon to com- 

 pensate for the deficiency in pressure. 

 Tests were made in this orchard with 

 Rex lime and sulphur, two strengths, 

 namely: One gallon of the "Rex" to 

 ten, and one to eleven gallons of 

 water; Black Leaf tobacco extract, four 

 strengths, namely, one gallon to thirty, 

 one gallon to forty, one gallon to fifty 

 and one gallon to seventy gallons of 

 water; Black Leaf "40," three strengths, 

 namely, one gallon to six hundred, one 

 gallon to eight hundred and one gallon 

 to one thousand gallons of water; sol- 

 uble oil, one strength, namely, one gal- 

 lon to twenty gallons of water. Thirty- 

 eight trees in all were sprayed in this 

 test, and five were left without treatment 

 for checks. 



On the 8th of March twenty-one trees 

 were sprayed in Mr. M. Paxson's orchard 

 at Clifton. These trees were five years 

 of age, and fully as many eggs of the 

 aphis and larvae of the twig-borer were 

 found on them as in the Strain orchard. 

 The following insecticides were used on 

 this date: Nico-fume at two strengths, 

 namely, one gallon of Nico-fume to six 

 hundred and one gallon to eight hun- 

 dred gallons of water. Kerosene emul- 



