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<pre>We have been thinking more about this.
Earlier in April/May we started to get black scale on the leaves, as this was
getting more widespread we decided to spray with oil.
We were encouraged to use ordinary blended vegetable oil (10% v/v) emulsified in
warm water and with household detergent as surfactant.
We sprayed this (attempting with limited success to target the underside of the
leaves) on May 27th.
We are now wondering whether, during each spraying cycle (from a 20litre tank),
the solution may have separated resulting in a stronger concentration of oil at
the end of the tank... this may explain the "oily" appearance along the trunks
of the worst affected trees.
Looking in UC "Olive Production Manual" the leaves look now a bit like the
illustration of black scale...but we sprayed the oil to get rid of the black
scale and we can't see any sign of actual insects on leaves elsewhere in the
grove. Leaves on the badly affected trees are turning black and falling off.
We are concerned that the vegetable oil may have been a bad move...but could it
have CAUSED the problem we see now? Most importantly we want to arrest/reverse
the damage ASAP!
HELP!
Judith Leslie


[Non-text portions of this message have been removed]
</pre>
</td></tr></table>

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<pre>> We have been thinking more about this.
> Earlier in April/May we started to get black scale on the leaves, as this
was getting more widespread we decided to spray with oil.
> We were encouraged to use ordinary blended vegetable oil (10% v/v)
emulsified in warm water and with household detergent as surfactant.
> We sprayed this (attempting with limited success to target the underside
of the leaves) on May 27th.
> We are now wondering whether, during each spraying cycle (from a 20litre
tank), the solution may have separated resulting in a stronger concentration
of oil at the end of the tank... this may explain the "oily" appearance
along the trunks of the worst affected trees.
> Looking in UC "Olive Production Manual" the leaves look now a bit like
the illustration of black scale...but we sprayed the oil to get rid of the
black scale and we can't see any sign of actual insects on leaves elsewhere
in the grove. Leaves on the badly affected trees are turning black and
falling off.
> We are concerned that the vegetable oil may have been a bad move...but
could it have CAUSED the problem we see now? Most importantly we want to
arrest/reverse the damage ASAP!
> HELP!
> Judith Leslie


I also had black scale & sooty mould on my trees. Although I sprayed and
cleaned up most of them (white oil / malathon) I was quite surprised to find
that the scale was not only still evident on some trees, but in some cases
still active is spite of the cold weather.

My experience has shown that 3 to 4 sprays, about 10 days apart, are needed
to break the cycle.

Mike Wilson.
Twin Trees Cottages.
Pokolbin.
</pre>
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<pre>From what you describe I think the oily appearance and the damage is most likely
caused by the oil you sprayed on the trees.

I do not have recommendations or label information on the rates of application
for vegetable oil sprays, but, in the case of petroleum spray oils, the maximum
recommended cumulative dose in citrus is 2.5%. In other words 2 sprays of 1%
solution and one spray of 0.5% solution or equivalent during the whole season.
The NSW Agriculture Agfact, Citrus Petroleum Spray Oils (Agfact H2.AE.5)
recommends that spray concentration is kept below 1% after April and before
October due to great plant injury risk in this period.

A 10% solution of Petroleum spray oil applied in late May would be highly
phytotoxic. Vegetable oil sprays can be as phytotoxic as petroleum spray oils
but I do not have more detailed information on this as yet.

It is worth noting, that with good application method, giving thorough coverage,
a 0.5% spray can achieve very good control of susceptible scale. An important
component of correct method is thorough agitation of the spray solution to
achieve a water/oil emulsion. This results in a white solution, hence the name
"white oil".

Another issue here is the timing of application and the condition of plants
before spraying.

Even at very low concentrations petroleum spray oils can cause damage if
temperatures are too high (>33C) or in prolonged cool weather. If spraying in
warm weather (usually spring/early summer) the spray should be applied early in
the morning, so that it has time to dry on the foliage before temperatures rise
above the safety threshold. Once it is dry the risk of damage is much less.
Spraying should be avoided under humid conditions where the spray does not dry
for a prelonged period.

Other considerations: Do not use oil sprays on stessed plants. Water stress,
nutrient imbalance or other causes of stress will increase the risk of damage
significantly.

I hope this information is useful. If you want to be sure of what has cause the
problem, the Plant Health Diagnostic Service at Elizabeth Macarthur Agricultural
Institute, near Camden should be able to help.

Regards

Damian








____________________Reply Separator____________________
Subject: [OliveOil] More on our? dying trees
Author: <OliveOil@egroups.com>
Date: 13/07/2000 13:59

We have been thinking more about this.
Earlier in April/May we started to get black scale on the leaves, as this was
getting more widespread we decided to spray with oil.
We were encouraged to use ordinary blended vegetable oil (10% v/v) emulsified in
warm water and with household detergent as surfactant.
We sprayed this (attempting with limited success to target the underside of the
leaves) on May 27th.
We are now wondering whether, during each spraying cycle (from a 20litre tank),
the solution may have separated resulting in a stronger concentration of oil at
the end of the tank... this may explain the "oily" appearance along the trunks
of the worst affected trees.
Looking in UC "Olive Production Manual" the leaves look now a bit like the
illustration of black scale...but we sprayed the oil to get rid of the black
scale and we can't see any sign of actual insects on leaves elsewhere in the
grove. Leaves on the badly affected trees are turning black and falling off.
We are concerned that the vegetable oil may have been a bad move...but could it
have CAUSED the problem we see now? Most importantly we want to arrest/reverse
the damage ASAP!
HELP!
Judith Leslie


[Non-text portions of this message have been removed]


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