Insect and Disease Control 253 



present for an indefinite period as a minor and unimportant 

 pest suddenly becomes a serious menace. Therefore the 

 peach-grower should be ever on his guard for new insects, 

 and on discovery he should take steps without delay, 

 to ascertain definitely their significance. It is only by so 

 doing that he can fully safeguard his interests. 



The nematode {Heterodera radicicola) 



This pest has a large economic relation to successful 

 peach-growing in the warmer parts of the country where 

 there is but little freezing of the ground during the winter. 

 Where the ground habitually freezes in winter to a consider- 

 able depth, nematodes do not occur in suflBcient numbers 

 to be of economic importance. 



This organism is a very minute, practically microscopic, 

 worm-like object which infests the roots of a great number 

 of plants, causing knots to develop on them sometimes in 

 great numbers if the nematodes are abundant. These 

 knots are often confused with the nodules formed on the 

 roots of legumes by the nitrogen-gathering bacteria. If 

 peach trees infested in the nursery with nematodes are 

 planted, they are likely to prove disappointing. They 

 may make a lingering, sickly growth for a year or two, but 

 early failure is probable. Trees that are free when planted, 

 if set where the soil is infested, are not likely to succeed. 

 The knots that develop on the roots interfere with their 

 normal functions, hence the tree becomes weakened and the 

 roots die where badly infested. 



Methods of control. 



Control measures are largely preventive in their nature. 

 Trees free from nematodes, planted in uninfested land, are 



