16 THE TOBACCO THRIPS. 



should be made to check other insects. This will apply to the seed 

 bed wherever it be located. 



Since it is evident that the thrips pass the period between crops 

 in the tobacco field feeding upon catch crops that follow, as rye, 

 wheat, etc., or upon weeds which have been allowed to grow, it seems 

 advisable that thorough and clean cultivation be practiced. While 

 it is possible that the employment of the kerosene emulsion treat- 

 ment, as recommended, may prove so effective as to permit the grow- 

 ing of catch crops (PI. I, fig. 1) without injurious effect, yet a thor- 

 ough cultivation of the soil after the crop is harvested is strongly 

 advised, for besides its effect on the thrips it will result in the destruc- 

 tion of budworm and hornworm pupae and grasshopper eggs. 



As soon as priming is finished the stalks should be plowed under, 

 together with all other vegetation in the field. Although cockleburs 

 were observed repeatedly during the summer of 1905, coining up the 

 day following cultivation, and although the seed may lie in the soil 

 two and three years before germinating, yet if the weeds are prevented 

 from fruiting in the fall by keeping the soil well plowed the effect 

 will soon become apparent. 



The practice followed by some planters of keeping a space of 10 

 feet bordering the shade field free from all vegetation is quite desira- 

 ble as affecting the thrips. 



It is the general practice to grow oats in fields bordering the shade 

 tobacco, but as the tobacco thrips is found breeding in vast numbers 

 in oats it would seem advisable to replace oats with corn in these 

 border fields. 



The part that irrigation may take in controlling the thrips seems 

 to be of importance. Somewhat less than one-fourth of the shade 

 tobacco in Florida is irrigated. This is carried out by one of two 

 methods, namely, surface or overhead delivery. Surface irrigation, 

 which is largely practiced, does not seem to affect the pest. In the 

 overhead method piping is employed, provided at intervals with 

 laterals that extend 1 or 5 feet above the cover and to which are 

 attached nozzles that give a fountain spray. In this way an artificial 

 rain is produced. This overhead irrigation seems to have quite a 

 noticeable effect in decreasing the numbers of thrips. Three irriga- 

 tions weekly seem to be much more effective than two. One firm 

 estimates a decrease in injury of 10 per cent in a field thus irrigated 

 in 1901. The great expense of piping and damage from freezing has 

 kept the method from being installed to any great extent as yet. 



In growing wrapper tobacco, shade is produced by the use of either 

 slats (PL I, fig. 1; PL II, fig. 1) or cheese cloth. (PL II, fig. 2.) 

 The temperature in the shade produced by the former is reduced 

 about 10° from the normal, while by the latter it is increased 10°. 

 From information received it is found that the thrips have, up 



