Whether we are speaking of Adonis, Dionysos or Hyakinthios, Apollon has a certain undisputed relationship with seasonal dying gods. As a migrational god (probably why he is more aligned with herding and migratory birds…both which involve seasonal movement and only slightly with grain cycles in the ripening and safekeeping of the crops) he seems to have little in common with apparent agricultural associated dying gods. Except, that is he is always there. Therefore, while Apollon himself is not a dying god, he is firmly linked to those gods whose vitality is given to the earth in their sacrifice.
In the myth of Adonis we are told that, alternative the common narrative in which Ares is the boar who slew Adonis, that it was Apollon who took the form of a boar. By this act we find Adonis as a dying god whose festivities celebrated the end of spring before the onslaught of summer. Some have suggested in modern worship to rear seedlings and expose them to wither in the blistering heat of the sun in remembrance of this. However, that the blood of Adonis turned the Adonis river in modern Lebanon red in the spring, it can be argued that like Dionysos whose autumnal sacrifice imbued life and vitality within the vineyards and the grape harvested for wine, imbuing the very sacred subsistence of the wine itself in his finest mysteries, Adonis died earlier in the spring (likely in line with modern Adonia worship in Hellas around the time of Easter) to imbue life into the vegetation. His representation by the very tender spring anemone flowers that spring from his yearly sacrifice of blood is a strong testimony to his lifeblood feeding the flowers and vegetation.
For a latter spring festival with similar theme we may look to the myth of Hyakinthios in which the youth was slain by accident by a disc (which most scholars to take for Apollon’s most favored disc…the heavenly disc of the sun). Although his blood yields the hyacinth flower, the correlation of the sun slaying the youth is more in line with what many folks have taken the Adonia to represent…the sun killing the last of the spring flowers even as the altar was piled with them. Despite the myth of the hyacinth flower, it is quite probable that Hyakinthios had a strong grain relationship established in his death cycle and myth given that on the first day of the Hyakinthia to honor the slain youth no bread was eaten. If we are talking about a late spring/on the verge of summer festival it would have been around the time of the grain harvest in the first part of summer. This cultic reference is the only connection to grain that we have though, so it may or may not be reaching to consider this. All the same, if we find Adonis being sacrificed by Apollon at the early parts of spring to renew the vegetation (in partnership with the cult of Aphrodite), it would follow in perfect sense that Hyakinthios (in partnership with the cult of Artemis Hyakinthia) would bear relation to the next stage that we find in which the heat of the warm dry season begins to reach it zenith and the spring vegetation gives its last hurrah as it were. Given that the beauty of Adonis bears much in common with Apollon (as well as Dionysos) and the apotheosis of Hyakinthios and his identification with Apollon we are following along a theme in which the slain god is in a manner identified with Apollon, likely by the subject and purpose of their slaying. That is to say…for the provision of subsistence for the herds/flocks (includes beasts and humans here).
This is very much true as well in Apollon’s relationship with Dionysos, perhaps even more so as the mysteries of Dionysos’ were of such paramount importance in Hellas. In this case the succor being provided by the action of Apollon the great herder is less about satisfying physical hunger and fending off famine and death, but more for helping in providing for the spiritual nourishment (which we find also in the worship of Persephone too but strictly speaking that is a different subject as she is more of a migratory goddess like Apollon is a migratory god than a *dying* goddess…but she provides the double boon of spiritual and physical succor for which it is not unusual that Apollon would play a role in her mysteries as well). In this respect we have the relationship between Dionysos and Apollon acting in very much a parallel fashion to that of Apollon and Adonis, and that of Apollon and Hyakinthios. Likewise in Plutarch we find identification of Dionysos with Apollon in his discussion on Delphi. This is not to say, in my opinion, that they are the same god any more than Adonis and Apollon are the same, or Hyakinthios and Apollon are the same, but establishes the active relationship which *may* have originated in one proto-Indo-European deity that would account for similarities both Apollon and Dionysos enjoy in gods such as Jarilo/Yarilo and Shiva.
However that may be there is a special relationship ongoing between the cycles of the dying gods and Apollon’s own migratory cycle, one that cannot be ignored and contains within it a special meaning and coding within the mysteries of these gods. Apollon is enthroned on the tomb of Hyakinthios, Dionysos and Zagreus are buried at Parnassos where Apollon’s sanctuary is supreme, and Adonis died on the mountain sacred to Apollon (and Artemis) that took its name from his son. The cycles of these gods are part of him, he who is nurturer and slayer…the herder to whom the seasons and the winds of the seasons pay heed as turns the seasons around.