http://www.usada.org/can-poppyseeds-cause-a-positive-drug-test
How well the poppy seeds are cleaned and processed will determine how much morphine residue is on the seeds, and this varies depending on which country the seeds are from as well as how and when they were harvested. However, it is known that morphine and codeine can sometimes be detected in the urine up to 48 hours after ingestion of poppy seed from some pastries such as bagels, muffins, and cakes (Reference 1 is a very interesting FREE article on this topic).
According to the WADA Prohibited List, morphine is a threshold substance and WADA-accredited laboratories determine a test is positive for morphine when the level of morphine in the urine is greater than 1.3[1] micrograms/mL. In most cases, consumption of poppy seeds in foods will not cause a positive doping test, but it may be possible to exceed the morphine threshold by eating foods with poppy seeds.
USADA cannot predict the amount of poppy seeds you can eat and still be below the testing threshold set by WADA, nor can USADA predict how long morphine or morphine metabolites from poppy seeds will stay in your system. The most conservative approach would be to avoid poppy seeds in the lead up to, and during, competitions [2].