710 IOWA DEPARTMENT OF AGRICULTURE 



very rapidly, its dense masses of yellow stems choking the alfalfa com- 

 pletely. As the original host plant dies the dodder spreads to adjoining 

 plants and so on until a single season may show an area more than a 

 rod square killed as a result of a single dodder seed. About the only 

 method of controlling the dodder is to cut the plants upon which it 

 lives and then burn them on the ground. Where dodder is scattered 

 throughout a field, the field had probably best be plowed up at once in 

 order to prevent its spreading to adjoining plants and fields. 



Russian Thistle. — While this weed is often found with alfalfa, it is 

 not looked upon with much concern in this state, though it has proven 

 very troublesome in many portions of the Northwest. Our common prac- 

 tice of cutting alfalfa three or four times during the season almost 

 always kills this annual before it produces seed. 



PLANT DISEASES. 



Leaf Spot. — Leaf spot is probably the most common fungus disease to 

 which alfalfa is subject in Iowa. It is found practically wherever alfalfa 

 is grown and can easily be distinguished by the numerous brown spots 

 which first appear on the upper surface of the leaves and soon there- 

 after may be seen on the under surface as well. Leaves so affected soon 

 turn yellow and fall off thus greatly reducing the yield and quality of 

 the hay under seasonal conditions favorable to the development of the 

 fungus. This disease has reduced the yield of alfalfa fields in Iowa 

 probably as much as one half. The lower leaves are the first ones to 

 be attacked. The diseased spots soon produce spores which are blown 

 by the wind and carried to other plants. The only practical method of 

 eradication is to mow the field, removing the affected hay as soon as 

 cured. The quick vigorous growth of the new shoots will often out- 

 grow the disease, though if seasonal conditions are favorable to its 

 development, the next cutting may also be seriously affected. Leaf spot 

 is often wrongly called "rust" or "blight." 



Root Rot. — This disease is most common in the southern states though 

 it is now spreading northward and has caused some damage in Kansas. 

 As yet it has not reached Iowa. It seems to attack a plant here and 

 there, throughout the field, and from these centers of infection the fungus 

 spreads to other plants. 



INSECTS AND ANIMAL PESTS. 



Grasshoppers. — In semi-arid portions of the country the grasshopper 

 is the worst enemy of the alfalfa crop. Even in Iowa, in seasons such 

 as those of 1910 and 1911 alfalfa is liable to severe injury from this 

 insect since it offers the best source of food supply. Therefore when 

 grasshoppers are particularly abundant it is well to use preventive 

 measures for their control. The grasshopper is best attacked while in 

 the egg stage. The eggs are laid by the female in the ground during 

 the last half of summer. Before the eggs hatch in the spring, a spring- 

 Looth harrow or a disk should be run over the alfalfa field, in this way 

 breaking up and exposing a large number of eggs to the weather and 

 other natural enemies. 



