February, 1 9 1 S 



THE GARDEN MAGAZINE 



29 



region. In the case of the White Pine blister 

 rust, just recently imported, currant and 

 gooseberry bushes are necessary for the com- 

 pletion of the life-history of the fungus. The 

 affected Pines show tapering swellings of 

 the branches from two to twenty years old. 

 From these swollen branches, white or yel- 

 lowish bladdery structures are pushed out 

 early in the spring. These blisters are rup- 

 tured and the yellow spores within are blown 

 away by the wind as a fine powder. They 

 are innocuous to the Pine and if they do not 

 lodge on the leaves of currant or gooseberry 

 bushes they cause no further harm. On finding 

 lodgment on those plants, however, the leaf 

 tissue is invaded and soon spores are formed 

 in small yellowish spots on the under sides 

 of the leaves. These spores can infect other 

 gooseberry and currant bushes. This process 

 may be continued until several generations 

 of these spores have caused the infection of 

 large numbers of bushes for miles away from 

 the affected Pine. In the late summer another 

 kind of spores is formed on brown hairs on the 

 under sides of the affected gooseberry and cur- 

 rant leaves. These are carried in all direc- 

 tions by the wind and if they lodge on the 

 young twigs of five-needled Pines a new 

 infection is started. By separating the two 

 kinds of plants by a half mile or more, as in the 

 case with the Red Cedar rusts but little 

 chance is afforded for the successful inter- 

 change of spores. Many species of two- and 

 three-needled Pines are subject to similar 

 diseases caused by native rust fungi. These 

 diseases do relatively little damage except 

 to young trees and then only when the re- 

 quired alternate plant is present in abund- 

 ance. 



'""PHE extent to which the White Pine blister 

 -*■ rust will affect the White and other five- 

 needled Pines in this country cannot at the 

 present time be predicted. The fungus has 

 been in this country for more than ten years 

 and has recently been found to have spread 

 over a large territory. The required alternate 

 hosts, the gooseberry and currant, are com- 

 mon weeds throughout the range of the five- 

 needled Pines. This group of Pines includes 

 some of the most important forest trees both 

 in eastern and western United States. The 

 accompanying map shows the distribution 

 of the fungus as last reported. Eventually, 

 no doubt, it will spread to all sections of the 

 country where five-needled Pines and goose- 

 berries or currants are associated. The tem- 

 perature and moisture relations which will 

 effect its destructiveness are not known at 

 present. Likewise, no data are available 

 as yet on the percentage of the younger trees 

 which will be killed by it under different con- 

 ditions. In such regions as Long Island and 

 the lower Hudson River valley where these 

 trees are important as ornamentals the dis- 

 ease may be easily avoided by eradicating the 

 door-yard and garden currants and goose- 

 berries since the wild species are rare. 



'"PHE majority of the destructive para- 

 -*■ sites as mentioned above are limited to 

 certain regions by temperature and moisture 

 relations. The severity with which they 

 affect their host plants as a rule is further lim- 

 ited by the relative susceptibility of different 

 varieties or even the individual plants of the 

 same variety. Many commercially important 

 resistant strains have been developed by se- 

 lecting and propagating the individual plants 

 which fail to develop the disease in question 

 when the majority of the crop is killed around 



them. By starting with a single resistant 

 individual, a desirable resistant strain may 

 be developed if its other qualities are satis- 

 factory. Strains of melons resistant to wilt, 

 cabbage to yellows, asparagus to rust and 

 beans to anthracnose are a few examples of 

 those that have been developed and are prov- 

 ing successful. The grower can often de- 

 velop such strains in his own field by carefully 

 selecting seed from plants of normal size and 

 desirable quality which are at the same time 

 free from disease. Even if this practice does 

 not yield resistant strains those fungi which 

 winter over in the seeds will be eliminated 

 from the new crop the next season. One of 

 the best methods of controlling bean anthrac- 

 nose or "rust" is to select the pods which 

 show no reddish brown or black cankered 

 spots and the seed in such pods will be dis- 

 ease-free. 



' I ''HERE are several other methods of avoid- 

 ■*■ ing losses from diseases which are simple 

 and easily carried out. Several species of 

 fungi attack ornamental shrubs and her- 

 baceous plants in the garden causing diseases 

 known as powdery mildews. The mycelium of 

 these fungi grows externally on the upper or 

 under sides of the leaves producing a white 

 powdery coating. Often these mildews cause 

 the stunting of the leaves and twigs and de- 

 foliation may occur. By dusting the af- 

 fected leaves with flowers of sulphur or finely 

 ground sulphur flour, the mycelium of these 

 fungi is killed. Sulphur dust is most effective 

 during warm, clear weather, if applied early in 

 the morning while the plants are still moist. 

 The club-root of cabbage, a disease which 

 causes swollen and deformed roots, may be 

 controlled by applying good stone lime to the 

 soil at the rate of 2 or 3 tons to the acre. 

 The application should be made the autumn 

 before planting; eighteen months before 

 planting is better. 



The subject of the importance and de- 

 structiveness of some newly imported parasite 

 is frequently brought to the attention of the 

 grower. Popular articles concerning these 

 new troubles and predictions of great depre- 

 dations to follow often cause the layman 

 to overestimate the relative importance of 

 such diseases. Taking the United States as a 

 whole there are many common and destruc- 

 tive diseases of ordinary crops which cause 

 losses of millions of dollars annually and there 

 is little attention given to the fact. Newly 

 imported parasites sometimes cause unusual 

 destruction to particular crops. The appar- 

 ent greater powers of destructiveness of 

 introduced parasites as evidenced by the 

 powdery mildews of grapes and gooseberries 

 in Europe and asparagus rust and Chestnut 

 blight in this country are due to the larger 

 percentage of susceptible individuals in the 

 new territory. In the regions where the para- 

 site has existed for centuries the more suscep- 

 tible individuals have been eliminated by a 

 slow process of natural selection leading to a 

 resistant race of plants. But when the same 

 fungus is transported to another continent 

 it finds an unselected race, the majority of 

 which, in some cases, will be very susceptible. 

 Such great destructive potentialities, how- 

 ever, are fortunately the exception and not the 

 rule. With our present knowledge of these facts 

 and the progress that may be made in the 

 future, it is reasonable to expect that much of 

 the losses now sustained may be avoided. 

 Already certain investigators are obtaining 

 hopeful results in breeding a desirable Chest- 

 nut tree which is resistant to blight. Selec- 



tion and breeding methods to obtain resistant 

 races may be augmented later by scientific 

 methods of artificially immunizing plants to 

 disease. 



With this hopeful outlook for the future 

 and the easily applied protection measures 

 now available for most of the common diseases, 

 growers should do their best to incorporate 

 disease-control methods into the more routine 

 cultural practices. The grower must accept 

 as final the fact that some attention to plant 

 diseases on his part is necessary in order to 

 grow clean crops and it is largely up to him to 

 acquaint himself with the control methods to 

 be used. 



The Leaf Blister Mite on Pear and 

 Apple Foliage 



NEARLY everywhere one can find dur- 

 ing the summer small corky areas on 

 pear leaves. These are the homes of 

 the blister mite, which only compara- 

 tively recently has become a very serious pest. 

 But I have found it in almost every orchard 

 visited in two years infecting the pear, and in 

 New York state, in addition, it has found 

 the foliage of the apple trees. 



It is hardly necessary to describe the blister- 

 mites because they are so small that to be 

 seen a microscope must be used, but their 

 work is very plain. Early in the summer 

 minute greenish pimples appear on the 

 leaves of the pear trees. They enlarge and 

 on the under side of the leaf they have a 

 sort of green velvety appearance; but this 

 does not last long, for they soon change, 

 becoming reddish, sometimes very brilliant, 

 and later the tissue dries up, and becomes 

 dark brown or black and corky. The pim- 

 ples house the leaf mites. In here they breed 

 and rear the young, the injured areas becoming 

 sometimes as much as an eighth of an inch 

 in diameter and somewhat irregular in shape. 

 When these pests infest apple leaves, the 

 spots are usually less brilliant. 



On badly infested trees the foliage drops 

 prematurely. In the fall the mites desert 

 their homes on the leaves and hunt winter 

 quarters under the scales of the buds. The 

 mites do not again make their appearance 

 until the early spring when the buds are 

 swelling preparatory to opening, then they 

 come out and are ready to attack the leaves 

 as soon as they emerge from the buds. 



The eradication of this pest is not difficult 

 if the trees are sprayed in the fall when most 

 of the leaves have fallen. Use either kero- 

 sene emulsion, diluting the stock solution 

 with five parts of water, or lime-sulphur wash, 

 at the same strength as used for San Jose 

 scale. If commercial lime-sulphur wash is 

 used this will mean diluting one part in 

 eight or nine parts water. 



By making a spraying in the fall when the 

 majority of the leaves have fallen, the mites 

 can be reached while still in the pubescence 

 of the buds; if done late the mites will have 

 tucked themselves away under the bud 

 scales where they are much harder to reach. 

 On badly infested trees this spraying should 

 be repeated in the spring just as the buds are 

 swelling and at this time it will be better to 

 use the lime-sulphur wash, as in addition to 

 killing the mites, it will kill any San Jose scale 

 which may be upon the trees and it will also 

 catch most of the plant lice, for their eggs 

 are hatching at this time. 



Penna. Harold C. Clarke. 



