It should be apparent from these facts that it is not enough to say an
aphid can carry virus for a mile. The whole point is -- what are the chances
for this to occur. It could be summed up this way -- there is very little like-
lihood of an aphid carrying virus more than a few hundred feet during the fall
and winter months; there is very little likelihood of an aphid carrying virus
for over a quarter-mile during late spring when aphid populations are at a peak
and the area is well covered with diseased plants. Always keep in mind that
99.9 plus percent of the aphids that come into a field are not caxbying a virus.
Most virus transmission is the result of aphid flights it-iZb~ th field. That
is why you see circular patches of disease and gradientT wofnfection that
lessen as you get into the field.


 Control of Virus Y /

 There are many possibilities for virus control that can be suggested. The
most obvious are listed below and the reason (s) why they do or do not work are
stated.

 1. Kill the aphids after they have some into the field -- This does not
work because the aphids can acquire and transmit virus before the insecticide
takes effect.

 2. Kill the aphids before they get into the field -- There is evidence
that spraying around a field (ditch banks, etc.) with an aphicide will reduce
the chance of aphids bringing in virus from ditchbanks. By next fall we will
probably be able to report how useful this may be. One of the biggest draw-
bakes is that insecticides like parathion cannot be sprayed indiscriminately on
neighboring pastures, crops and homes without endangering other peoples' pro-
perty. Also, and just as important, the use of an insecticide like parathion
can upset the natural balance between aphids and their predators and parasites
and result in heavy aphid buildup after.the spray program is discontinued.

 3. Treat the crop with a chemical that protects the plant from infection.
There are no such chemicals as yet.

 4. Rogue out the diseased plants -- This may be worth doing the first time
you see a diseased plant but fails to give control in the long run. This is
because an infected plant can be used as a source of virus by an aphid before
symptoms appear. Thus, a roguing operation is never 100 percent thorough.

 5. Use resistant varieties There are no varieties of pepper or tomato
that are resistant to virus Y. The mosaic resistant pepper varieties are re-
sistant only to tobacco mosaic virus.

 *6. Eliminate the weed hosts of the virus -- Since we know that all of
our virus infections originally come from diseased weeds the eradication of
these weeds is the most direct approach possible in eliminating the virus. Because
of this directness it follows that this should be a very effective control method.


2/ These procedures also apply to viruses affecting squash, cucumber and
 watermelon.


* Indicates recommended treatments.