Could it be the manufacture date, or have you had it longer than that? The numbers from the label are obviously a date, model number then the date again. What's the product?

PS. In case it IS azadirachtin, your concern should be the water you use in the sprayer rather than any 'use by' date. Use deionized water if your tap water is quite alkaline.

Thank you so much roseseek and nikthegreek! Your replies are extremely helpful to me.

It is indeed azadirachtin.

Nikthegreek, I've just found out the PH of tap water where I live is 7.8. Is that borderline or OK?

I also discovered an easy DIY on wikiHow:

"The easiest way to make alkaline water is to thoroughly stir 1/8 tbsp of baking soda into 1 cup (240 mL) of water."

Will that work? I not only spray, I also do a soil drench for larger impossible-to-spray trees, so i'll need quite a lot of water

7.8 is borderline IMO. 7 is neutral, more is alkaline, less is acidic. Baking soda will make your water more alkaline, some acid (like vinegar) will make it more acidic. If you decide to do something you should make it more acidic, or use deionized water for spraying, as suggested. Azadirachtin readily decomposes in an alkaline solution. I'm not sure why you would drench with azadirachtin... In any case if you do drench, soil buffering is too great so I would not bother with the quality of water. Azadirachtin will probably rapidly decompose when mixed with soil.. But, is there any sense in drenching? What exactly are you fighting against?

I've had an infestation of spidermites for several years now, especially in Italian cypress Totem Pole variety (worst), syrian hibiscus (pretty bad) and crape myrtles (occasionally). I can't spray the larger plants, so I started looking for a systemic. I tried Movento soil drenches and they didn't do much. Then I came across several Sundaram experiment reports on the Internet. This one for instance:

http://www.tandfonline.com/doi/abs/10.1080/03601239609373068?journalCode=lesb20

And here's another one from Oregon University site:

"Azadirachtin is systemically taken up by plants through roots and weakly systemic in the leaves. It has both systemic and dirct contact action. Only sucking and piercing insects are affected by the systemic form."

http://extension.oregonstate.edu/lane/gardens/profiles_of_natural_pesticides

Azadirachtin soil drenches work better for me, so I'd rather use azadirachtin.

It is apparently weakly systemic, but using large dosages improves the performance. In the Totem it worked when I gave each tree 20 ml of a 3% azadirachtin product' and not the recommended dosage which didn't do much. The 20 ml dosage kept the trees clean for about 6 weeks. Those were young Totems of varying heights 1 to 2.5 meters but only about 15 cm wide. May they rest in peace. I shovel pruned them 10 days ago and planted Duranta Geisha instead.

I wonder if it would work for midge and if it affect bees, etc.