^Hfe MONTI 1 1. V BULLETIN. 225 



COUNTY HORTICULTURAL COMMISSIONERS' DEPARTMENT. 



WIREWORM CONTROL.* 



By J. N. French, County Horticultural Inspector, Oxnard, California. 



INTRODUCTORY REMARKS. 



Wireworm injury in the Oxnard district from a commercial stand- 

 point is confined almost entirely to the beet and bean crops. Of these 

 two the bean crop injury is the one that is causing any great anxiety 

 among the farmers. The fact that nearly all the beets are planted 

 early, thereby allowing them to get started before the worms commence 

 working in the spring, accounts for this. Wireworm injury to beans, 

 however, is a very serious matter. It is very hard to give any definite 

 figures on injury, owing to the fact that most of this wireworm injury 

 consists in the stunting of vines with the corresponding decrease in 

 yield, rather than in taking the stand or in killing the young vines 

 outright. One hundred thousand dollars is thought to be a conserva- 

 tive estimate on the damage done during the season of 1914. During 

 the season of 1915, due to the warm weather which prevailed during 

 the growing season and to the control work which was done, the injury 

 was cut down 50 per cent, or about $50,000.00. 



This wireworm injury was done for the most part by one species, 

 Limonius calif ornicus, although at least three other species were found 

 associated with this one in some instances. The percentage of these 

 other species, however, was very small. 



Nothing can be more erratic, apparently, than the actions of the wire- 

 worm larvae. In some cases they clean out the same place year after 

 year ; in other cases the infested area may move from one side of a field 

 to the other or into another field, and in some instances the infestation 

 seems to be bad in a certain field every other year. According to 

 J. E. Graf (see Bureau of Entomology Bulletin 123), the worms stay 

 in the ground approximately three years before changing to beetles. 

 The first year they are so small they do practically no commercial 

 damage ; the second year they cause considerable trouble, and the third 

 year they are at their worst. In the first case there are constantly 

 recurring generations in the same place, in the second the worms hatch 

 out in one place and the beetles, in search of the most suitable places to 

 lay their eggs, go elsewhere. This explanation does not cover the third 

 case, however. It is possible that this damage is done by some other 

 species of wireworm with a shorter life cycle. 



That old bean settings and fields which have been covered with manure 

 are more subject to wireworm infestations is explained by the fact 

 that they provide more suitable places for the beetles to hibernate and 

 lay their eggs. The food scent of bean settings also has a tendency to 

 attract worms from a considerable distance. The resulting concen- 



♦The following is a report on wireworm control work carried on in the Oxnard 

 district during the past two years. It is lioped tliat tlie report may prove of value to 

 tlie beet and bean farmers, as well as to tlie members of the commission. 



The writer wishes to express appreciation for the many privileges extended to him 

 and the encouragement given to tliis experimental work by Mr. A. A. Brock, Ventura 

 County Horticultural Commissioner. 



Mr. James Leonard, Donlon Bros, and Johnson Bros, are named as colaborers with 

 the writer in this work, and the results as stated may properly be termed the results 

 of their collective labors. — J. N. F. 



