I would assume that its ordinary seasonal leaf drop. However, you say its not
happening to all individiauls in a species, so that seems puzzling--unless
within species needles are dropped not every season, but every other, or every
third season. Chlorosis is certainly not seasonal, and you likely would have
discovered that with your nutrient assays and pH testing.
In article <nGKW3.4525$7m.262305 at newshog.newsread.com>, "Mike the Tree Doctor" <mlamana at bestweb.net> writes:
>>I have to pose a general question to any with experience in the matter of
>seasonal chloroses in conifers - principally hard pines.
>>I have a situation in southern New England (Zone 4) where for multiple years
>now I have observed gradual yellowing of pitch pines (Pinus rigida), table
>mtn. pine (Pinus pungens), and to a lesser degree 'Waxman' eastern white
>pines as each winter approached.
>>The trees in question are from multiple provenances, in multiple soils,
>obtained in multiple years. Not each individual of a species for lot is
>affected. I have done the usual battery of soil and paired soil/foliage
>nutrient assays - all are inconclusive. Soil pH, iron, manganese, copper,
>Ca:Mg ratios are all in the ball park, but micronutrient concentrations in
>foliage are off in some tests. All trees have been treated with NPK,
>sea-kelp extracts, humates, etc. at various times.
>>Generally speaking, the condition goes away or attenuates greatly with the
>onset of Spring - any ideas or similar experiences.
>Mike the Tree Doctor