proportionately smaller factors with respect to their relative market value. The grade
index was reported as the mean for four replications. Crop index was obtained by multiplying
the yield in pounds per acre by the grade index. The crop index was a measure of the total
value of the crop; reported as the mean of four replications. The fire-holding capacity was
determined by measuring the length of time in seconds that the leaf burned after being
ignited by an electric cigarette lighter. Five leaves of the 2nd, 4th, and 6th primings
from each replication were tested by burning the tip and base of each leaf. The mean of 120
readings were reported as the index for four replications. The weight of the crop in off-
color, dark wrapper, light wrapper, light medium, and top three grades was calculated in
percent.

 RESULTS AND DISCUSSION

 Weed growth (Table 2) was reduced most effectively by M-2633 and M-2811. Best plant
 response resulted from treatments with the split application of Bayer 25141, and single
 applications of M-2633, NIA-10242, and NIA-9227. Growth differences between the 300 and 600
 pound rates of NIA-10242 indicated that the higher rate was causing some stunting or root
 phytotoxicity. Both rates of NIA-10242 gave best reduction of Pratylenchus spp. in the
 roots, and the highest rate gave best reduction in the soil. Populations of Rotylenchulus
 spp. were erratic and evaluation of results impossible. Reduction of Helicotylenchus spp.
 was best with NIA-10242, NIA-9227, M-2633, and Diazinon A-1619. The results indicate that
 both Diazinon formulations were relatively ineffective in reducing nematode populations at
 the rates used, except for Helicotylenchus spp. with A-1619. UC-21149 was also ineffective
 and somewhat of a disappointment. NIA-10242 showed considerable promise for control of both
 Pratylenchus spp. and Helicotylenchus spp. Black shank index was lowest in plots treated
 with M-2633. Root knot was not a problem in any plot. Coarse root was best controlled with
 NIA-10242 at the higher rate followed by NIA-9227, and the lower rate of NIA-10242.

 Listed in order of descending yields (Table 2): M-2633, NIA-10242 at both rates, and
Bayer 25141 gave best results. NIA-10242 at the higher rate showed the best grade and crop
indices. The best fire-holding capacity resulted from treatments with the lower rate of
NIA-10242, UC-21149, and the split application of Bayer 25141. None of the treatments were
particularly outstanding with respect to the various grades analyzed. The higher rate of
NIA-10242 was generally the best treatment from the standpoint of improving the quality of
the tobacco as indicated by the grade and crop indices.

 Both rates of NIA-10242 caused considerable foliage phytotoxicity characterized by
chlorotic and necrotic spotting of the lamina, and upward curling of leaf edges and tips.
Some stunting was apparent with both NIA-10242 and Penphene.

 Linear correlations (Table 3) showed that the crop was adversely affected by *'- '
Pratylenchus spp. and Helicotylenchus spp. in the soil. The relationship of Pratylenchus
spp. in the roots and Rotylenchulus spp. in the soil to the crop was not as strongly
correlated. Black shank, being a light infestation, caused some adverse effects in grade,
but not enough to be of much significance. The most interesting correlations were those
between Helicotylenchus spp., yield, crop index and off-color. There is a definite relation-
ship between these nematodes and poor tobacco. So far, no evidence in pathogenicity studies
has confirmed this; that is, on cigar-wrapper tobacco.


 WBT
 100 CC
 11/15/67