750 THE MONTHLY BULLETIN. 



Caution must be taken not to .apply too much ])otash. In 1907, in fact, Icainit 

 ■ at 1,000 pounds per acre was harmful in thni u)an.v of the young seedlings were 

 killed, necessitating replanting several times, iu order lo get a r'air stand. This 

 tjuantity was not harmful in 3900 on another plat, showing that the danger 

 limit is probably not far below that amount. Muriate of potash at the same 

 rate was very harmful iu 1907, as was also the same amount of ammonium 

 sulphate. Potassium sulphate, 007 pounds to the acre, and potassium mag- 

 nesium carbonate, 007 and 1,338 pounds to the acre, were absolutely harmless, 

 while the latter amount of potassium sulphate ^^■as only slightly harmful. 



In spite of the high fertilization a field conlinually planted to nematode- 

 susceptible crops will, if the nematode is present, eventually become so infested 

 with that parasite that it will be impossible to make paying crops. However, it 

 can not be denied that for special occasions it is of value to reduce part of the 

 evil effects of the nematode infestation by high fertilization." 



Starvation.— Probably the most effective method of ridding soil 

 of Heterodera is attained by keeping the land free from vegetation for 

 a period of two years. Where this is not practicable, nonsusceptible 

 crops should be planted for two or three years. Care should always 

 be taken in keeping out weeds that might serve as a host for this worm. 

 By referring to the list of susceptible plants it will be noted that most 

 of the ordinary farm crops can not be considered and those that are 

 known to be resistant are few. 1 he following list can be recommended : 

 Cowpea (iron variety), all species of the Stizolobium (the velvet bean) 

 and close relations, most varieties of winter oats {Avena sativa), pea- 

 nut {Arachis hypogcta), Florida beggarweed, rye (Secale cereale) , 

 Cr^bgrass {Syntherisma sanguina), sorghum, milo, kaffir, timothy and 

 red top. This list includes both summer and winter crops and in 

 favorable localities the use of both is recommended. 



For the most part these are crops that will barely pay expenses on 

 valuable land, yet if the soil may be rid of the pest and expenses met it 

 is well worth the necessarj^ time and money losses incurred. Corn and 

 sorghum have been especially recommended because they permit clear 

 tillage and all weeds upon which the nematodes may live can be easily 

 kept out. 



Flooding. — Other methods, such as flooding, excessive drying and 

 trap crops have been used with varying success. Flooding can not be 

 applied with safety to fields bearing perennial crops, but under favor- 

 able conditions, where the soil maj' be kept under water and where all 

 roots that might protect the worms have been removed, success has 

 been attained by submerging the soil for a period of fifteen or twenty 

 days. This method is impracticable in many instances, owing to the 

 lack of sufficient water and unevenness of the infested area. 



Drought. — Heterodera is pai-ticularly susceptible to drought and 

 in regions of little rainfall, thorough drying of the soil has greatly 

 reduced the injury from the pest. Ploughing deeply after the last 

 rains in the spring will loosen the soil, and if kept unharrowed during 

 the hot dry months of the summer, the numbers of worms will be 

 greatly reduced. Of course, this method can only be applied in a 

 region of very little or no summer rainfall, and in regions with no 

 underground seepage. 



Trap crops have been used but results that have been obtained do 

 not warrant their use. 



