it 
CONTROL OF BACTERIAL WILT 
TABLE 3.—Percentage of wilt on tobacco grown in rotation with weed-free and weedy 
corn 
ake | 
Wilt on tobacco Wilt on tobacco 
Preced: ii cues after— Preceds (crow after— 
: A ING Ase eS re. 2 ing = ae 
Year grown years | eed. | Year grown years | waeg. 
grown rye Weedy grown ees Weedy 
free free 
corn oe corn Boat 
Perceni| Percent Percent| Percent 
MG By fpsiecpateraaite se Pe hie Sik Pa Ne ea 1 128 2) TOA ree eit ee Tee UE scape i 2 53 48 
TOYS Seto ei a GA A ee 2 19 30 | . 
HIG) 3 O pears ete aS as er oS 3 4] 46 | IASMOT AGE Se ees ceil st Nace 36. 2 32. 4 
TES Se ie Zi ce crn lara 1 AQ) 17 
1 Approximately 800 tobacco plants per plot. 
The results show that in some cases tobacco grown after weedy corn had the 
higher percentage of wilted plants and that in other cases tobacco grown after 
weed-free corn had the higher percentage. The average wilt percentages for ail 
five comparisons show that susceptible weeds had no effect on the extent of wilt. 
Extensive survey work was carried out on farmers’ fields to continue this phase 
of the investigation. During the summer of 19386, the weed floras were carefully 
studied on 25 infected fields being rotated for wilt control. The weed species were 
listed, and their respective populations were counted on 50 quadrat samples each 
of 1 square meter an acre. Of the 103 species observed, the following were known 
to be susceptible to natural infection (6) and hence potential host plants for 
Bacterium solanacearum: Jimsonweed, horsenettle (Solanum carolinense L.), croton 
(Croton glandulosus L.), horseweed, black nightshade (Solanum nigrum L.), 
cocklebur (Xanthium sp.), ragweed, and Aster sp. Nineteen of the surveyed fields 
were planted to tobacco in 1937, and there was no relation between total weed 
populations in 19386 and wilt severity in 1937. Ten of the fields had been rotated 
to corn alone and hence comprised a group within which comparisons could be 
more closely made. ‘The data in table 4 show the estimated population of suscep- 
tible weeds in 1936 and the extent of wilt on tobacco in 1937. The number of 
susceptible weeds ranged from 0 to 20 individual plants to each 100 square feet 
in 1936, but showed no consistent relation to the extent of wilt on tobacco in 1937. 
TaBLe 4.—Relation of the population of susceptible weeds to severity of bacterial 
wilt on subsequent tobacco crops 
Period Period 
Tobacco | during Tobacco | during 
Number of susceptible weeds | plants which Number of susceptible weeds | plants which 
per 100 square feet in 1936 | wilted in| corn pre- per 100 square feet in 1936 | wilted in } corn pre- 
1937 ceded . 1937 ceded 
tobacco | tobacco 
Percent Years | Percent Years 
(tees eons oy Se icky Mo ie yn ak tine 1 27 DO ral RS ucneaon Casalsel aes aa eRe el NUE GS | 5 il 
Rees Meee rn eer tice en nN: 27 3 DiS saa OA aia ea ene eee 35 3 
FS Ae PC AOA MORSE ks RE iy eM 12 3 ReneS UNE HR a ICON ea Dea a eat | 6 1 
RA pe Nici aS) aN ic tsise at Menu NnMernpsia Sera AN 36 | TIES A el G7 Au aa ied 2 tae ie Yo ee Ra 28 1 
Til Se SS ieee a 27 SON Ota ae ere ayy bude 28 2 
! Estimated from counts made on every fifth row about August 1. 
In some fields there was a more or less definite pattern of wilt distribution, as 
shown in figure 4. 
this distribution, survey work was conducted on a second group of fields. 
To determine whether susceptible weeds were associated with 
Counts 
of weeds known to be susceptible were made in August 1937 on permanently lo- 
cated plots 50 by 50 feet each. In 1988 the fields were planted to tobacco, the 
plots relocated, and wilt counts made about August 1 on 59 plots in 10 fields. 
There was no relation between the susceptible weed population in 1937 and the 
extent of wilted tobacco on plots within the same field in 1938. For all 59 plots 
the correlation coefficient between the population of known susceptible weeds and 
the percentage of wilt on tobacco was negative and not statistically significant. 
Thus, the data from 3 different lines of work showed that weeds known to be 
