PRESS BULLBTIN 216 September 20, 1913
AGRICULTURAL EXPERIMENT STATION
UNIVERSITY OF FLORIDA
SPRAYING FOR THE VELVET BEAN CATERPILLAR
By J. R. Watson
This caterpillar, Anticarsia gemmatilis, Is by far the worst pest with which
the grower of velvet beans has to contend. It frequently consumes all the
leaves of the plants, ruining them for either forage or seed. Ordinarily, when
troubled by an outbreak of caterpillars, the farmer turns for relief to the
arsenic compounds; but in this case he is confronted by the fact that velvet
beans are easily burned by such compounds. Dry arsenicals in any form, used
as a dust, burn them too severely. We found in our experiments last sum-
mer that 4 ounces of lead arsenate paste to fifty gallons of water was about
as strong a spray as could safely be used, even when lime was added. As this
weak dosage was not very effective, we have been trying various compounds,
and have this summer found a solution that is cheap, effective, and safe. It
Commercial lime sulphur solution.............. 1 quart,
Lead arsenate paste ............................ 8 ounces,
W ater .................................. .....50 gallons.
The amount of lead arsenate that can be safely used .depends somewhat
Son the weather, on the condition of growth of the beans, and on the thorough-
ness of the stirring. A black sediment forms in the tank; and unless the mix-
ture is constantly stirred, or is strained before spraying, the pump will become
clogged, or the plants that receive the settling from the bottom of the tank
will be burned. Eight ounces of the lead paste to fifty gallons of water seems
to be sufficient to kill the worms, if the solution is not too soon washed off by
rain. The caterpillars do not die promptly, twenty-four hours being usually
necessary; but they become sick at once and cease to feed. With this strength
there will be no serious burning. An occasional old leaf may be scorched, but
.this is of no practical consequence. The younger foliage is not burned. With
from threee-fourths to a pound of arsenate to fifty gallons of water there was
considerable burning. This burning was not noticeable until three or four days
The newer insecticide, zinc arsenite, which can often be substituted for
lead arsenate, did not work well for this purpose. The lead arsenate should
be of the neutral or basic form, not acid.
For economical spraying, a good barrel pump mounted in a wagon is neces-
sary, and a power spraying machine is much better. It will take about fifty
gallons to cover an acre.
These caterpillars have many natural enemies, the most efficient of which
are birds, especially rice-birds, blackbirds, mocking birds, and native sparrows.'
If our farms harbored as many of these birds as they should, the farmers would
have no need to spray for caterpillars. We found that the birds congregate on
the unsprayed portions of the fields; so that by spraying the portions most
heavily infested and leaving the remainder to be taken care of by the birds, we
were able to control the pest over the whole Experiment Station Farm. The
birds do not seem to feed on the poisoned caterpillars to any extent, and we
have seen no instances of birds being poisoned by so feeding.
Wasps also feed actively on these caterpillars and render efficient serv-
ice in keeping them down.
A fungus disease kills many, and, in favorable weather, may even control
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