Imperial Valley press., 1930-04-11
CONTROL OF POWDERY MILDEW
IN VALLEY is SUCCESSFUL

Iected patc>cs should not be allowed
lie threaten the crop grown on more
than $4,000 acres and worth more
than $11,00o,000.
Volunteer melon plants and the
winter grown squash are the two
principal hosts upon which the dis
case lives through the winter months.
They are likewise the chief source
rom which the mildew found in
early cantaloupe fields originates.
The wild gourd (Cucurbita palmata
Nats.) exhibits Il high degree of
resistance to the disease and the mil
Gcw which attacks the wild sunfiow-
er appears TO be distinct physiolo-
gieal race of the species incapable
OF injecting cucurbits.
Field experiments have S h o W IL
that very small quantities of sui
phur applied as dusts or sprays
caused too severe Injury to the
plants to be recommended fer use
after April i under Imperial Val
ley conditions. During very hot
weather, sulphur particles in direct
contact with the more mature leaves
cause the so-called "sulphur burn. -
Earlier applications of such dusts or
SPRAYS may leave residue which
later becomes injurious when the
temperatures are high. This prac-
tically prccludes the use of either
sulphur dusts or sprays in the I'M
.,,1 No1lar- Tho r,rnSpnt
ties of cantaloupes now grown there.
Selections from them which arc now
under test may yield commercial
trains resistant to sulphur injury.
Squash varieties are highly resist
;:nt to sulphur burn and may be
busted or sprayed without danger
Of severe injury resulting.
Dry copper dusts in the absence
of free moisture on the plant foli-
age as dew, fog or rain proved fun
gicidally inactive and hence of no
value in controlling powdery mil
dew. Bordeaux sprays gave only
partial control. Other liquid sprays
proved to be either injurious or in
effective.
Field trials in which sulphur was
applied to the soil in piles or spread
in semi circles around the hills have
shown that the plants may be in
iured by heavy applications espcci-
ally during the periods of strong
prevailing winds. These are of COM
mon occurance during the mid-sea-
son months of March, April and
May. The sulphur is lifted from
the soil and carried to the front
foliage. Spreading exposes more of
it to the action of the wind than
if the same quantity is concentrated
in piles. Therefore, if the sulphur
is to be scattered over the canta
lOupe beds more than 80 pounds per
acre should not be used. If it is to
be distributed in piles on the soil,
more than go pounds per acre should
not be used. Although this method
of controlling the disease has been
tried extensively during several
seasons, positive evidence that it is
effective is lacking. Sulphur or in
organic fertilizers drilled into the
soil have shown no effect on the
susceptibility Of resistance of can
taloupe plants to mildew.
Prompt destruction of all host
plants that may carry the fungus
through the winter will remove po-
tcntial sources of primary infec-
tions in the spring. As soon as the
crops are harvested from fields of
cantaloupcs, squash, cucumbcrs and
other susceptible plants the vines
should be plowcd under. These
fields as well as ditch banks, waste
areas and land near field packing
sheds should thereafter be kept
clear of volunteer vines The ef-
fectiveness of this method of com
batting the disease will depend upon
how generally and how thoroughly
this sanitary measure is practiced.
Thorough dusting of squash fields
will keep them free of mildew. Dust
ing should begin before the disease
appears and should be repeated
several times before the crop is
harvested, after which the plants
should be promptly plowed under
and destroyed. The most effective
dustings will likely be those
made during March and April as
the mean maximum temperature is
usually then above 80 degrees +.
Applieations Of to 10 pounds of
finely ground or Of sublimed sui
phur should be made at two-week
intervals. A small quantity of hy-
drafted lime or GYPSUM NAV be
added to prevent the sulphur from