Insect Pests and Plant Dise.\ses. 



189 



bags of cyanide over the jars by cords running through screw eyes and all leading 

 to a place near the door. By cutting all the cords at once the cyanide will be 

 lowered into the jars and the operator may escape without injury. Let the fumiga- 

 tion continue all night, locking all outside doors and placing danger signs on the 

 house. 



No general formula can be given for fumigating the different 



_ . . c kinds of plants grown in greenhouses, as the species and varieties 



Fumisfation of ,.^^ ^, . \, . , -f.^ , . , \ ,.. ^ , r .u 



greenhouses 



differ greatly in their ability to withstand the effects of the gas. 



Ferns and roses are very susceptible to injury, and fumigation 



if attempted at all should be performed with great caution. 



Fumigation will not kill insect eggs and thus must be repeated when the new brood 



appears. Fumigate only at night when there is no wind. Have the house as dry 



as possible a:nd the temperature as near 60° as practicable. 



IV. THE CONTROL OF PLANT DISEASES. 



H. H. WHETZEL AND F. C. STEWART. 



ALFALFA. 



This disease causes 



Dodder. small areas of alfalfa 



to die. Around the 



of these areas the ground is 



covered with a tangled mat of yellow 



threads that twine closely about the 



plants and kill them (Fig. 161). 



Infested spots should be closely 



mowed; the stubble sprinkled with 



kerosene, covered with dry hay and 



burned. Only seed free from dodder 



should be used. Samples of seed may 



b.^ sent the Geneva Experiment Sta- 

 tion to be examined for dodder. Al- 

 falfa seed can be cleaned by sifting 



through 20 X 20 mesh sieve made of No. 



34 wire. See Geneva Circular No. 8. 

 This is the most 

 Leaf-spot. serious fungous dis- 

 ease of the crop in 



the State. It causes the leaves to be- 



cO!ne spotted and yellow and to fall pre- 

 maturely. New seeding when badly 



diseased, should be topped, but never 



mowed. closely. When older fields are 



attacked, the hay should be cut a few 



days early to avoid loss of leaves and 



to permit a new growth that will usually outgrow the trouble 



Fig. 161. Dodder on alfalfa, shoivmg the 

 slender cord-like stems and the bunches 

 of small zvhitc UoziJers. 



(Fig. 162.) 



