work precisely in ail locations
the concept can be applied ina

jury level was applied on a larger scale;

ilex) were monitored in San Jose. Due to the scale

ted time for decision-making the oakmoth larval

fied into high, medium and low. High and medium

exceeded the injury level and were consequently
sprayed with Bacillus thuringiensis. A fotal of 2,300 or 55% of the trees
were treated. i
concept,

Under non~
deations at

*

considerable cost to the city.

Pp
City of Palo Alto,
pounds over the years,
the material being used
we started detailed studies that documen
trees. Through weekly monitoring,
ed specimens, aphid populations w
tree. Four branches from the nor
four times with a stick a
counted and recorded.

Situation in subsequent
served to be susceptible
over a series of seasons

Spot Treatments

Some horticultural personnel have observed the wide variation in pest

rs on adjacent trees of the same species. Those trees which repeatedly
each season show excessive pest populations are called "host trees". We
have observed this "host tree” phenomena for a series of species (9) and
pest herbivore populations, but the actual mechanisms that produce the
phenomena are still unknown. However, the fact that a

has been observed with the plant pathogen (G1 and
"Modesto') which are all
Propagated from a slugle
tree from Modesto, variations in the environ~
mental conditions or casual agent, and not genetic variaticens, May account

for the differences observed. Even without knowing the mechanism of the