DOWNY MILDEW OF TOBACCO 5 
odspores, however, are rarely if ever produced by the tobacco downy- 
mildew fungus, and the ordinary spores are thin-walled and _ rel- 
atively short-lived. It is possible that the mycelium remains dor- 
mant in some of the plants attacked and is carried over in the oc- 
casional plants that survive. The fungus, actively growing and 
producing spores, was actually observed during the winter of 1931-32 
in Georgia on volunteer plants in old tobacco beds. Overwintering in 
this manner in the extreme South, it may possibly spread north as 
the season advances. 
FIGURE 3.—A conidiophore bearing conidia. (> about 300.) The 
oval spores are very light and are easily carried through the 
air from leaf to leaf 
CONTROL 
NUMBER AND LOCATION OF BEDS 
Until more certain methods of control can be developed than are 
now available, it will be advisable for growers in affected districts 
to sow an increased number of beds, as mildew, like most diseases, 
does not attack all plant beds with equal severity and some escape 
entirely. The beds should be separated and sown at different times. 
In districts warm enough for tobacco plants to survive the winter, 
every effort should be made to destroy all hold-over plants. There 
appears to be little use of attempting to find a place the mildew 
can not reach, since beds located in new woods clearings, remotely 
situated, seem as likely to be attacked as beds located in open fields. 
