296 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



remarkable outbreak of the pea-aphis in 1899 and 1900 seems to be 

 that, due to two exceptionally dry springs, the fungus was unable 

 to develop, as it propagates best in damp weather, and the aphids 

 increased unchecked. Though occasional individual aphids were 

 found killed by the fungus early in the season, not until June 11, 

 1900, were diseased aphids found in any quantity, but after that 

 so swiftly did the disease destroy them that a week later but few 

 aphids were to be found and almost all were diseased. Probably 

 this fungus usually destroys the aphids on clover before they have 

 become excessively numerous or have migrated to peas. 



Control. Inasmuch as the aphids spread from peas to clover, 

 the latter crop should not be planted near peas when avoidable. 

 In the spring the aphids should be carefully observed on the 

 clover and if they become excessively abundant, the only way to 

 prevent their migration to peas is to plow under the clover deeply 

 and roll the field. 



Highly fertilized land in which the moisture is retained by fre- 

 quent cultivation very often enables a crop to mature in spite of 

 moderate injury. Peas sown broadcast or planted in 8-inch 

 drills have been much more seriously injured than those planted 

 in rows 18 to 30 inches apart and cultivated, and those planted 

 close together afford no opportunity for brushing or cultivating 

 as described below. 



Early varieties of peas have practically escaped injury where 

 late varieties have been wholly destroyed, so that it is obvious that 

 only the earliest varieties should be grown where injury is 

 anticipated. 



Early in 1900 Professor W. G. Johnson found that when peas 

 were planted in rows that the aphids could be readily knocked from 

 the vines by means of brushing with a branch, and that by follow- 

 ing the brushes with cultivators, the aphids would be covered with 

 earth and destroyed, either by suffocation or by the heat of the 

 soil. Where the air temperature is 95 F. the soil will be nearly 

 120, and aphids brushed onto it will be actually roasted to death 

 in a few minutes. The cultivation should not be repeated for 

 about three days, as it requires about that time for the destruction 

 of the insects covered with earth, if it is not hot enough to kill 

 them at once. By this method large areas of peas have been saved 

 fiom destruction. 



