156 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



TOBACCO DISEASES. 



Investigations on " tobacco sick " soils in the Connecticut Valley, 

 in Maryland, and elsewhere have fairly well established the fact that, 

 in addition to the well-known Thielavia disease, there is involved in 

 many cases a second parasitic root disease of tobacco which may 

 cause serious injury to the crop under certain conditions. 



As a result of cooperative investigations in Wisconsin a striking 

 relationship has been shown to exist between the prevailing tem- 

 perature during the growing season and the extent of the injury to 

 the tobacco crop by the Thielavia root-rot. It has been shown that 

 temperature is an even more important factor in this connection than 

 rainfall. In relatively hot growing seasons the tobacco plant readily 

 resists the parasite, while in cooler seasons the tobacco is much more 

 susceptible to the disease. 



As a result of further cooperative tests with growers in the Burley 

 district of Kentucky it is expected that limited quantities of seed of 

 Burley tobacco resistant to root-rot will be ready for distribution to 

 growers for the next season. 



It has been found that outbreaks of the leaf-spot of tobacco in 

 Virginia and North Carolina, such as have occurred recently, are 

 most effectively prevented or controlled by the relatively high top- 

 ])ing of the plants, avoiding the use of land or fertilizers containing 

 an excessive supply of nitrogen, especially in the inorganic forms, 

 and using at least a moderate application of potash as a fertilizer. 



In the investigations on the black-rot of leaf tobacco it has been 

 found that the extent of the damage from this decay during the 

 fermentation process usually is proportional to the water content 

 of the leaf when packed, and a patent, dedicated to the public, hag 

 been secured on a process for standardizing the water content by 

 partial drying under controlled conditions. 



SUGAR-BEET NEMATODE. 



The special investigation of the sugar-beet nematode inaugurated 

 during the last fiscal year has received a marked impetus in combat- 

 ing the growing losses by the introduction of a new method for esti- 

 mating nematodes in soil. 



The results of surveys indicate that the losses suffered by growers 

 in the State of California alone have risen from about a quarter of a 

 million dollars in 1916 to more than four times that sum in the 

 calendar year 1917. Examinations of samples of soil from some of 

 the beet-growing areas of Colorado have revealed the nematode pest. 



TOMATO DISEASES. 



The control of the Fusarium wilt of tomatoes through breeding 

 for disease resistance now seems assured. The occurrence of this 

 disease is one of the principal limiting factors in the cultivation 

 of tomatoes, as the fungus which causes it lives for an indefinite 

 time in the soil and the larger part of the tomato-growing area east 

 of the Mississippi is already infected. We now have an excellent 

 commercial variety, a selection from the Stone, which appears to 

 possess a high degree of resistance to Fusarium wilt in tests in a 



