CONTROL OF BACTERIAL WILT 
TaBLE 1.—Wilt on tobacco grown with crop rotations on small enclosed plots 
Plants wilted August 1 
Year Besser : ; = 
grown Preceding crop or fallow 
Plot 1 Plot 2 Plot 3 Average 
Percent | Percent | Percent | Percent 
QB peette wee Tobacco continwuouslysc 22. wee he 197 91 100 96. 0 
NOB Se ene Keer re CGO) Sai Sip ate NR IL gt RIA pt Pe 96 98 92 95. 3 
N93 OS sees lea caren (GUO sey a aa ee ei ice Co re SE 100 100 100 100. 0 
NGA () eee Os eae CON Oye Relais es SS read (otras EO acacia ee es eer 100 94 100 98. 0 
1 year of— 
OS ieee ASAT UL Oye aaa greeee gel Orn aN 81 TAU eel ener Cte tbe 75.5 
NGS (pee cases SLOMN/ OV EYE aS Setaciets Rice ee meshed CRN apa aie ac 50 Ss ear iees 44.0 
LOB Meats (YO BL) Sea i pt ae ONE Sy a) A a ghee 6 (eset a 6.5 
NOS ipepaieg @ rea BASS a SG a apne as Tin nl ROE Pa Uda ic cal Baan eer ae ee eee cneind 
IBY (ey cee ISON yo OTe 0a 0 ese Sp er dec Wyatt ca Ne shee Dre sees Nia (FRET EG ner lb a Oteree peace an 
NO Bete eee sas Ta(XS) OVEXG (SY AG IS er eles OE ee SOU ECS i eh ace ce aa LS at es ae ee ASS se ea 
ICR eae (OXON OLSEN IT ees ce Scie eas DEN rete [ee Se een | ac ges ele 
MOB Fees eGo Crotalariaispectabilis 22 es SH Eee UI TNS ONE GPO Vicia eee 
QAO Rese K EXO EL HON GE sree Po a gaye dre igs ere emeee 42 AR | eae teers 45. 0 
2 years of— 
GR Shou aioe IBA ee tally Oyster ae eink Nace a sya Nato = cel 43 PGis| eee eens 29. 5 
19882 Soe ss DSKOVANZ) OLEKE WSR Se ee St It RS IE NUE teh 6 DAN essen Uaioe 4.0 
NOSSiae es =e CONG) PLOY eee es asta pn te a ee de 2 Dia | eee 2.0 
GSS Se ieee GAD SASS esse eae aie aes a eG ep OTe, Sis | Stara tesa aor edie aes a ieee: Boa jactricoe 
NOS Siesta RS OER Ov Ba eB oe ech ees a ON ca ae gore a meee (Mies soe ara | Marcas pen aes (RAEN ge PIA 
NGOS See ass BMC STOR CLC Zain oem rae wh I MSR Neen eS Pine Si as ae ea sat te ce ee Pau Ma ra He 
OB Se etar so: (COG OER NSI  e ie a ee ni oA pe nce ee ee his ceactnis eat puso (cele Nc elata | nines ats 
TOSS ite ees Grotalaniaispectabiliss ey kok ON ok oe TS ig Pee een eoee TTA a Reeaeee Oe (feet 
NQAQ Sees: WOGDOMEI Steal Bese Monee Sea Gulny Mit teen ZAM OY icssaensc np Rs cs rae NU a cae 
LOSS ne eae: Soybeans, 1 year, followed by corn, 1 year____ 12 Gir | eae ce: 9.0 
G39 eine a (| Ope rene a PN Ma GPa Mires Orne tel ai cote rt 65 UO rR aR Ral Cen 2 72.0 
1QAQS ets: ENGNG) i ag an NS SR eT rt a ag 33 A\() lee iat 36. 
3 years of— 
G39 eee ee Banegtallow ces 2 Sree eae CA aia aie fen 100 Sis ees Ane 68. 5 
19392 oe: Onl Cam Sneeeseesa sta ee a Ree Ni PASE Oy eae 10 Dre | Wate: eae 17.5 
193 9 ieee 2h © ON Ei RE EUS RGE Satoe Toe mn MORN Baas Zanes 38 Dy | elie Aches 31.5 
198922 22 SAO SASS eis te a es Rh a et eg ec tO Oiler se mae Nic tee pelle cage pei br te ease eae 
4 years of— 
1940_______| SC ey PO were ee Res eae aa ae a ahey ah 44 MQ) as see 27.0 
1940 Eerie ISKO NA OYEXEN ASH cae as ars fae A eee eat 2 TD. Se epee es 7.0 
1940 CO ORME Sateen aes Mee OO ee ERED ANG Au ae NL Seay OM 6 QO othe Bates 3.0 
QAO sess Grab epaSSments ayo eiae eco ers eiiine ce eerie 5 GRR is oN Rh pores ea Ulett ee cee Sa 
1 Approximately 48 tobacco plants per plot. 
31.5, and 3.0 percent wilted plants. Another illustration of seasonal variation 
was obtained on tobacco grown in a rotation of 1 year of soybeans plus | year of 
corn, in which the tobacco had 9.0, 72.0, and 36.5 percent wilted plants in 1938, 
1939, and 1940. A period of at least 3 years of other crops appears to be necessary 
during seasons of exceptional wilt severity, as in 1939, and for this reason the 
longer rotations are preferable. Periods of 1 or 2 years of other crops, however, 
gave striking reductions in extent of wilt during seasons of moderate wilt severity, 
as in 1937 or 1938. 
EXPERIMENT ON LARGE PLorts 
The experiment on small plots tested crop rotations under conditions of mini- 
mum opportunity for reinfestation by the wilt parasite. In the experiment on 
large plots crop rotation was tested under field conditions similar to those of 
practical tobacco culture, where cultivation is carried out by horse-drawn as well 
as by hand implements. The plots, one-fifth of an acre each, were established on 
soil shown by a test planting of tobacco in 1935 to be badly and uniformly infested. 
Flat-bottom drainage ‘ditches 12 or 16 feet wide, seeded to grass, separated the 
plots on all sides to give protection from reinfestation by surface water. One 
plot was planted to tobacco each vear as a control. Sweetpotato, redtop, crab- 
grass, corn, and native weeds were compared in rotations, providing 1-, 2-, and 
3-year periods between tobacco crops. 
The results were similar to those from the small-plot rotation experiment, and 
the data on tobacco grown in 1937 and 1988, after periods of 1 and 2 years of other 
crops, are not reported in detail. The data on tobacco grown in 1939, after 3 
vears of the various crops, however, are of interest because of the exceptional 
severity of wilt that vear. The extent of wilt and the yield and value of the crops 
are shown in table 2. 
