﻿46 BULLETTlSr 1374, U. S. DEPARTMENT OF AGEICULTURE 



These data show particularly the effect of pasturing after the stalks 

 were cut. Between December 20 and 27, a herd of cattle was 

 pastured in this field for a number of days. These cattle ate a 

 considerable part of the bolls left on the surface of the soil. They 

 picked up practically all the larger bolls, the sudden decrease in the 

 number of larvae found per boll on December 27 being due to the 

 removal of the larger bolls, which contained the greater number of 

 larvae. Apparently there was no increase, or very little, in the 

 number of larvse in the soil to offset the decrease in living larvae 

 in bolls on the surface. The figures in the last column, giving the 

 average number of the larvse in the soil that are found within locks 

 or open bolls, before and after pasturing, show that there can not 

 have been much tramplmg of bolls into the soil by the cattle. 



Early cleaning of fields in the fall, before a great part of the late 

 unpick able bolls open, is recommended. In this way the number 

 of bolls shed would be reduced. Grazing after cutting the stalks 

 should be practiced, if possible, and it is possible that grazing before 

 the stalks are cut is even more beneficial. If the stalks are not cut 

 until all bolls are dry and open, it may even be advantageous to 

 delay cutting until after cold weather has set in and the larvse have 

 spun up more completely. Then possibly there might not be any 

 appreciable issuance of larvae from shed bolls and entrance into the 

 soil, and consequent pasturing would destroy a great part of the 

 larvae in the shed bolls. 



TREATMENT OF SEED BY HEAT 



Machines for killing the pink bollworm in seed by heat have been 

 in use in Egypt for some years. The Egyptian seed is practically 

 lintless, whereas that produced in Mexico and the United States is 

 covered with lint. For this and other reasons it was necessary to 

 devote considerable attention to methods of treating seed. 



Laboratory tests were made to determine the amount of heat 

 required to kiU the pink bollworm in cottonseed, and the amount 

 of heat to which seed may be exposed without injury. The latter 

 point was determined by tests conducted by the Federal Horti- 

 cultural Board at College Station, Tex., where laboratory facilities 

 for this work were furnished by the college. These tests were 

 conducted ic February. 1921, with Texas seed. A Freas electric 

 oven was used. 



THERMAL DEATH POINT 



The tests on the thermal death point were conducted at Tlahualilo, 

 using a Freas oven also. At first several series of tests were conducted 

 in which larvae in double cottonseed were used. The procedure 

 followed was to bring the oven to the desired temperature, which 

 was maintained by thermostatic control. The seed, arranged in a 

 single layer on a sheet of perforated cardboard, was then introduced. 

 All larvse upon removal from the seed were placed in pill boxes and 

 kept under observation for several days. One hundred double seed 

 were used in each test. 



In one series of tests the seed was heated in dry air, that is, the 

 normal air in the oven. In another series dishes containing water 

 were placed in the oven. Evaporation from this water brought 

 about a moist condition of the air. 



