54 BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



the Laguna when preparing the land for the new crop. While this is 

 done for purely agricultural reasons to make plowing easier, large 

 numbers of live hibernating larvae are killed. On the experimental 

 plot at Lerdo the stalks were cut on the last day of February and 

 examined during March. At this examination live larvae at the rate 

 of over 5,000 per acre were found in the bolls attached to the stalks. 

 So many bolls had fallen or were knocked off during the cutting and 

 piling that over half were left on the ground. A little extra effort in 

 collecting and destroying these is well worth while. No boll or piece 

 of Cotton is so small or negligible that it should not be picked up and 



burned. 



Cutting Stalks and Fall Plowing. 



Experiments have shown conclusively that the mortality is greater 

 in hibernating larvae buried in the soil than in those left on top of the 

 soil and greater in those buried in irrigated soil than in those buried 

 in dry soil. It has also been found that the most favorable of all 

 places for larvae to hibernate under field conditions are the old bolls 

 left undisturbed on standing stalks. During the winter of 1919-20 

 100 larvae per 100 bolls successfully passed the winter on old stalks 

 left standing in the fields and were alive on July 12, whereas only 4 

 larvae per 100 bolls were found alive on this date in bolls lying on top 

 of the soil. These facts suggest certain agricultural practices that 

 can be used to good advantage in reducing the number of surviving 

 larvae. 



Ordinarily the old stalks are not left standing in the fields, but on 

 some plantations large acreages which are not to be cultivated the 

 following year are left, and on others where °zoca" is produced the 

 stalks are not cut till late spring or summer. All fields should be 

 gone over with a stalk-cutter as early as possible, and in many cases 

 the small amounts of cotton which are picked during the winter 

 and spring could profitably be sacrificed in order to do this earlier in 

 the season. Fall and winter plowing to cover the bolls is recom- 

 mended whenever it is possible, and water should be applied in years 

 when there is an excess. 



Pasturing. 



If it is not possible to cut and burn the stalks or plow the field in 

 the above manner, owing to labor shortage, weather conditions, or 

 other causes, it is a very good idea to graze the fields. Cattle, goats, 

 and burros will eat the majority of the bolls on the stalks. One 

 important drawback to the grazing plan is that there is a certain 

 amount of infested material tramped into the ground. In one field 

 near the town of Tlahualilo where the animals had been concentrated, 

 only about one boll per square yard was found on the ground. In 

 other fields that had been grazed, but not so thoroughly, an average 

 of 5 or 6 bolls per square yard was found. 



