DISEASES AND INSECTS 



DISEASES AND INSECTS 1041 



At times hundreds of acres of peas have been ruined 

 by an aphid. Nursery stock often suffers severely and 

 bearing fruit trees are often seriously injured by them. 

 About forty different kinds of aphides live in green- 

 houses where a perpetual warfare has to be waged 



against them. In four 

 years nearly 100 genera- 

 tions of a common aphis 

 have been reared hi 

 greenhouses, and there 

 were no indications of 

 any egg-stage or of male 

 forms during this tune, 

 so that they may thus 

 breed indefinitely in 

 houses, their young be- 

 ing born alive and no 

 males appearing. The 

 standard remedies for 

 plant-lice are whale-oil 

 soap, kerosene emulsion, 

 and tobacco in various 

 ways (as a decoction, dry 

 as a dust, or in the form 

 of similar extracts), and 

 these are successfully 

 used to kill the aphides 

 in all situations. 



Scale insects. Since 

 the advent of San Jos6 

 scale into the eastern 

 United States, scale in- 

 sects of all kinds have 

 attracted world- wide 

 attention. They are all 

 small insects, and derive 

 their name from the fact 

 that their tender bodies 

 are protected by hard, 

 scale-like coverings se- 

 creted by the insects. 

 Thus protected, they are 

 difficult insects to kill, 

 and as they are easily 

 transported on nursery 

 stock, buds or cions, and 

 also multiply rapidly, 



1321. A spreading board for 

 drying soft-winged insects. 



the scale insects are justly to be considered as among 

 the most dangerous and destructive of injurious 

 insects. A single female San Jose scale may rear a 

 brood of from 100 to 600 young, and there may be 

 four or five generations a year; and more than 2,000 

 eggs have been laid by a single Lecanium scale. The 

 scale insects, the dreaded San Jos<3 species included, can 

 be controlled successfully by judicious, intelligent and 

 timely work with sprays of lime-sulfur, crude petro- 

 leum, or hydrocyanic acid gas, which should be used 

 in the case of nursery stock. Since 1889 fumigation 

 with hydrocyanic acid gas has been extensively prac- 

 tised in the citrus orchards of California, and now 

 Florida and South African fruit-growers are also using 

 it in their orchards. Large gas-tight tents or boxes are 

 placed over the trees and the gas then generated within. 

 Much nursery stock is now treated with the gas in 

 tight boxes or houses; this is required by law in many 

 states, and it should be practised in other regions. 

 Recently greenhouses, railway coaches, rooms in private 

 houses, and whole flouring mills have been effectively 

 fumigated with this gas. 



Insects are preserved in collections by securing them 

 in tight cases by means of a pin inserted through the 

 thorax, or through the right wing if the subject is a 

 beetle. Moths and butterflies are pinned in position on 

 a spreading-board until thoroughly dried. See Figs. 

 1318-1322. Every horticulturist should make a col- 

 lection of injurious insects. 



Insect literature for horticulturists. Horticulturists 

 should keep in close touch with the experiment sta- 

 tions and state entomologists of their own and of other 

 states, and also with the Department of Agriculture at 

 Washington; for it is from these sources that the best 

 and latest advice regarding injurious insects is now 

 being disseminated free, either by personal correspon- 

 dence or by means of bulletins. Among the books, one 

 or more of which may well find a place hi a horticul- 

 turist's library are the following: Weed's "Insects and 

 Insecticides," Lodeman's "The Spraying of Plants," 

 Saunders' "Insects Injurious to Fruits," Sanderson's 

 "Insect Pests of Orchard, Farm and Garden," and 

 Slingerland and Crosby's "Fruit Insects." 



M. V. SLINGERLAND. 



C. R. CROSBY! 

 Other invertebrate animals. 



Mites. Mites belong to the class of animals known 

 as Arachnida, which are closely related to insects. 

 Spiders and scorpions also belong in this group. Mites 

 are small creatures, usually possessing four pairs of 

 legs when mature, and the body is not divided into 

 three divisions as in the case of insects. The green- 

 house red-spider (Tetranychus bimaculatus) is one of the 

 most common and injurious species. It occurs on a 

 wide variety of plants grown under glass and also out- 

 of-doors on the foliage of many wild and cultivated 

 plants. It is about s^in. long and varies in color from 

 yellow through orange to brown and dark green, often 

 with a darker spot on each side of the body. It spins 

 a very delicate silken web-like nest over its breeding- 

 ground. It can be killed on the foliage of plants grown 

 in the open with soap solution, dusting with sulfur, 

 and hydrated lime, or by using a flour-paste spray. 

 In greenhouses, it is best controlled by repeated spray- 

 ing with water, using much force and little water to 

 avoid drenching the beds. 



The clover mite (Bryobia pratensis) is a minute, 

 spider-like, oval, reddish brown mite about -riroinch 

 in length with long front legs. It attacks the foliage 

 of many fruit and forest trees as well as clover and 

 grasses. The tiny, round, reddish eggs often occur in 

 great numbers on the bark of trees in winter giving the 

 branches a reddish color. It may be controlled by the 

 same treatment as for red-spider. In addition, the eggs 

 may be killed with a lime-sulfur solution while the 

 trees are dormant. 



The pear-leaf blister-mite (Eriophyes pyri) differs 

 from most other mites in having only two pah's of 

 legs and in its elongate body. The mite is only ji^inch 

 in length; it burrows in the tissue of the leaf, causing 

 blister-like galls. The eggs are laid within the gall, 



1322. A cross-section of spreading board in front of 

 the cleat "d," in Fig. 1321. 



and some of the mites when mature leave through a 

 small opening and migrate to new leaves. The mature 

 mites hibernate under the bud -scales. This pest is 

 controlled by applications of lime-sulfur or miscible 

 oils while the trees are dormant. 



Nematodes. A species of nematode worm (Hetero- 

 dera radicicola) lives parasitically in the roots of a 

 wide variety of wild and cultivated plants producing 

 enlarged knots or swellings. This disease is known as 



