COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
STATE OF FLORIDA
COLLEGE OF AGRICULTURE, AGRICULTURAL EXTENSION SERVICE
UNIVERSITY OF FLORIDA, AND I Cr COUNTY AGENT AND
UNITED STATES DEPARTMENT Vegetable p peilit HOME DEMONSTRATION WORK
OF AGRICULTURE, COOPERATING GAINESVILLE, FLORIDA
April 5, 1955
MR. COUNTY AGENT:
You have been exposed to several summaries of the VIRUS situation on vegetables
in Florida. However, since it involves new terminology we felt you may appreciate
some further assistance in the form of a newsletter.
We will not attempt to present a complete picture of every possible virus-like
condition; however, we do feel this will add to your knowledge and be of use as ammu-
nition in answer to the many vegetable grower inquiries on this subject. Confusion
can result from trying to identify viruses in the field, even by people supposedly
familiar with them.
We've relied heavily on Dr. C. W. Anderson, virologist here at the Main Station,
and Dr. J. N. Simons at the Everglades Station, Belle Glade. Dr. M. K. Corbett rec-
ently joined the Main Station staff in this field. Huch, but not all, of the follow-
ing information has been based on Florida work. Note further details in 1954 Florida
State Horticultural Society Proceedings.
RECENT PROiIIrEIHCE....but here for a long time.
Evidence suggests some known viruses (and probably man7 still undescribed) pres-
ent before development of agriculture in state; some probably endemic (look it up)
in Florida; others introduced by man or arose in very recent times. Disorders attri-
buted to viruses known in Florida at least as early as late teens and early 20's.
However, other records and studies had to await development of science of virology
and recognition of importance of virus diseases. Causal viruses in many cases still
WHAT'S KOWJN ABOUT THOSE WE DEFINITELY HAVE IN FLORIDA?....briefly.
Cucumber mosaic virus: at least two strains; apparently numerous substrains;
spread by aphids; does not occur in soil; rarely or never seed-borne in commercial
crops; causes important losses in cucumber, pepper, celery, Easter lily, and prob-
ably tomato and melon; important sources include Commelina, Easter lily and gladiolus.
Watermelon mosaic virus spread by aphids; attacks cucumber, squash, melon,
watermelon, citron, wild cucumber and angora gourd; infected none outside cucumber
family; did not infect wild mock cucumber; sole known source wild cucumber; probably
occurs throughout Florida; symptoms in watermelon sometimes mild and overlooked.
Muskmelon mosaic virus: seed-borne; attacks melon and wild cucumber in Florida,
cucumber elsewhere; indicated not spread by aphids and not now economic problem here;
not known to infect plants outside cucurbit family.
Aster ringspot virus: attacks pepper, china aster, pansy and nightshade;
sources and insect vectors unknown; not nor considered important but infects wide
range plants; might be damaging in future.
Tobacco mosaic virus: attacks tobacco, tomato and pepper mostly; certain
strains common on plantains and occasionally reported various solanaceous plants
and others; man spreads; tobacco products important sources; various insects pos-
sible but doubtful vectors; tobacco refuse, volunteer or old tobacco plants, weeds,
and possibly tomato and pepper seed may occasionally be sources; may persist in
plant refuse for several months.
Tobacco etch virus: attacks tobacco, tomato and pepper mostly, also certain
solanaceous weeds (including Jimson weed), and legume Cassia tora; spread by aphids;
living plants considered source; Cassia does not overwinter virus in North Central
Potato virus Y: aphid-borne; resembles tobacco etch; attacks potato, tobacco,
tomato, pepper, henbane and various solanaceous weeds; potato considered important
source but weeds additional danger; importance in state not well-known but severe
disease of tomato in some cases and some trouble on tobacco; may prove less im-
portant to Central Florida pepper than etch and tobacco mosaic.
Tobacco ringspot virus: common in gladiolus; insect vectors only known experi-
mentally; seed-borne in several hosts including tobacco, petunia and soybean; attacks
tobacco, eggplant, bean, soybean, cucumber, melon, watermelon, sweet clover, and
others; infected seed, wild plants and vegetatively propagated plants are sources.
Lettuce mosaic virus: common and can be damaging; seed-borne; spread by aphids;
causes systemic diseases in Composite and Legume families; lettuce seed main source
but reported from few other plants.
iAilY OTHER VIRUSES ARE RECOGHIZED.... there will be more.
For example, common bean mosaic, cowpea mosaic, sweet potato internal cork,
and potato X occur in Florida; infected seed common sources of first two, sweet
potato and potato tubers sources of last two; cowpea virus attacks some Crotalaria
and Desmodium sp. but their importance as weed sources is unclear. Many others
could be listed as having been reported or studied.
YES, SEVERAL MAY ATTACK SAME CROP....double trouble.
For example melon is attacked by cucumber mosaic, watermelon mosaic and musk-
melon mosaic in Florida; cowrea is attacked by a cucumber mosaic virus strain and
by a cowpea mosaic. A given weed host may harbor several viruses....
CONTROL....a big question.
You can see why from the above and we hope this short presentation will assist
you in helping the grower and others to understand. A great deal of research
needed, as in other phases of virus work...however,
1. Resistant varieties may offer some control as others are developed; used
as a means to control common bean mosaic on bean (nearly all varieties) and tobacco
mosaic in pepper (Yolo Wonder).
Yet, must remember a variety resistant to one virus may be susceptible
to another, and resistant varieties must be adapted to Florida.
2. Weed control may be promising for some viruses but must learn more about
many weed hosts; determine whether practical and economical control can be achieved
in this way, chemical possibilities, etc.
3. Other methods that may prove useful in certain cases are maintenance of
healthy seed stock, insect vector control, and sanitation.
No one method will control all viruses. Remember that methods to control
virus primarily spread by man, such as tobacco mosaic, will not necessarily control
aphid-borne virus of same crops. Healthy seed stock will not control if weeds are
infected, or if neighbor uses diseased materialT y-hid control may be particularly
ineffective if large migrant flights are responsible for spread of the virus.
The main point to remember is that a single method is not necessarily the
answer -and that an apparent failure may result from an attack by a different-
virus from the one considered, or from other factors which do not indicate that
the method actually failed to control or is useless against the virus in question.
Several things are necessary to get virus spread in a crop:
1. Virus must be present, whether in crop or weeds.
2. Vector must be around and moving from infected source to new host.
3. Susceptible crop must be available.
Breaking this down at any point will stop the cycle.
NO, IT'S NOT A ONE-HAN SHOW.... many concerned.
Although we've used words of workers mentioned herein, you should realize
about every plant pathologist in the State is or has been closely concerned with
virus diseases in the various vegetable areas.
Very truly yours,
F. S. JAMISON
Vegetable Crop Specialist