4^ ANM AL lii:rni; rs ()!• I >i:i'AlI l .MliN T n]' A( MiK L I/U KI:. lICiT 
TKl CK CROP AM) (iAKDKN INSECT INVESTIGATIONS 
WIKKWORMS 
Invcstijjatioiis on the biolojcy and control of wircwornis {Lim'ni'tiot ctiUfornicun 
Mann, and L. cnniis Loc. ) which infest tho irrii;at«'d lands f>f tlw Wost ha vo been 
continued in California, \\asliiiiuf<»n. and Idah(t, enijihasis beiiii; i»laeed on 
testiii<r soil fumigations with naphthalene and dichloroethyl ether, soil-siirface 
applications of sulphur in an attenipt to prevent or n'duce e;:i,' dejfosition by 
wireworni adults, jind the effect of crop rotations on wireworni infestations. 
It was found that the daniajre caused by wireworms to onions coidd be de- 
creased jjreatly by the incorporation into the soil of H(H> iKiunds of crude 
naphthalene per acre, while the land was beinj? plowed, and during a time 
when soil teiiiiM-ratures were 70° V. or hij;her. Although best results have 
been f>l)tained with nai)hthalene funiiiration of the soil wlien the teini>eratures 
reach 70° or hitrher, experiments perl'<jrmed in the State of Washini^ton indi- 
cated that worth-while results may be obtained with naphthalene even when 
the soil temperature to a dei)lh of 12 inches rauires from (i.")- to <»7 . Compara- 
tive tests with several other funiij^ants showed that crude naphthalene at the 
rate of S()() pounds to the acre was more effective and cheaper than either 
calcium cyanide at the rate of 400 pounds to the acre or a commercially pre- 
pared fumigant consisting principally of crude naphthalene* and silica at the 
rate of 22 parts of the former to 78 parts of the latter. In these tests crude 
naphthalene killed approximately 92 percent of the wireworms, calcium cyanide 
killed approximately 78 percent, and the commercially prepared soil fumigant 
killed (is percent. 
In California dilute .solutions of dichloroethyl ether at a concentration of 
5 cc of this material in 1 gallon of water were found to be highly toxic to 
wireworms when drilled into rows of beans used to attract and concentrate 
the pests. Tests on plant growth demonstrated that at concentrations of 1, 3, 
and 6 cc respectively, per gallon of water, this material caiised no apparent 
injury to growing lima beans. Higher concentrations caused plant injury. 
Evidence was also obtained that applications of dilute solutions of this material 
of .sufficient strength to be effective against wireworms will not injure tomatoes, 
potatoes, cabbages, and corn. Before such treatn)ent is advocated as a general 
practice, however, further experimentation is necessary. 
Field-plot tests in the State of Washinirton indicated that the .soil-surface 
application of sulphur at rates of 4(M.) and 8(K) pounds \)vr acre, respectively, did 
not have any appreciable effectiveness in preventing egu' deposition by the 
adults of either tlie sugar-beet wireworni or the Pacific coast wireworm. 
The late planting of potatoes iu the irrigated section of the Pacific Northwest 
where wireworms are abundant offers a means of escaping maxinnim injury 
by these pests. In Washington during the season of IIK^G. an average of 57 
percent of the potatoes planted on April 7 and harvested during the ix»riod 
from August 10 to 17 were injured by wireworms. whereas in comparable plant- 
ings made on June 2.S and harvested early in November -an average of approxi- 
mately 44 percent of the tubers showed wireworm injury. Actually the differ- 
ence in relative wireworm injury suffered by early planted and late i)lanted 
potatoes was less in l!t.'>(> than durini; i)revious years ln'e:nise eouditions during 
that year were such that the wirewoims did not bc^in their seasonal migration 
downward until a later date than normal. 
Crop-rotation studies continue to bear out the information previously gained 
that wireworm abundance increa.ses rapidly in fields planted to red clover and 
sweetclover. that tho rate of increase is retarded in fields i>lanted to truck 
crops, and that practically no increase of these pests occurs when .ilfalfa or 
pasture grasses are grown. 
Field studies on the (inlf wireworm in Alabama sIiowimI deJinitely that tlu're 
w.'is a difference in the number of wir(>worms f»)und in land pl.anted year after 
year in potatoes as compared with tlu' number occurring in new groinid and 
in old field sod. The wireworms were less Mhundant in ticlds wheri* suitable 
crop rotation was practiced an<l in cotton fields than in fields wliere i>otatoes 
were phinted year after year. It has be(>n demonstrates! tlnit whih^ tlu^ trapping 
of ;idnlls )Muler crop renniants inked into \\iii(l:o\\s fnIlo\\e<l by the burning of 
such windr{)ws destroyed n high lUMcentage of adults, this method was not 
eff<'ctive unh-ss the soil so treated was cleaned thoroughly of i)lant renniants 
and the soil surf;ice leveled off. Soil fumigation with < ru<le nai)litlial«Mi(\ follow- 
ing the nietluMls .'ind dosages used successfully again(*t wirt'worms in tin* P;iciflc 
Northwest. w;is not successful in combating mixed pojiulations of the (lulf 
wireworm ami the sand wireworm in experimental field tests jM^rformed at 
