Many farmers still do not have access to this quest line yet.
FarmVille is aware of the issue and released the statement below which can be found above the FarmVille Loading Screen in the yellow box area,
“On top of the loading screen, “Howdy Farmers, We are aware of some farmers not seeing their Summer Quests. We are working to address this now. Thanks for your patience! -FarmVille Team”
UPDATE: This evening, the quest became available to many more players.
Do you have access to the FarmVille Summer Harvest Quests on your farm?