Buyers of US soft red winter wheat were urged to "pay close attention" to their quality requirements after tests showed a "variable" quality crop, including the highest levels of vomitoxin in at least nine years.
US Wheat Associates, which promotes demand for US supplies, said that "excessive moisture" either during wheat flowering or on ripe grain had resulted in a harvest of soft red winter wheat - the type traded in Chicago - with "variable quality".
"If there is a defining factor for soft red winter wheat quality this year, it is the timing of rainfall," the group said.
"Moisture was ample, or even excessive, for most of the soft red winter wheat area throughout the growing season."
The impact had been reflected in a protein level of 9.8%, below the average of 10.1%, and a Hagberg falling number, in essence a measure of sprouting, of 311 seconds, below the mean of 322 seconds.
However, the main concern was a test weight of 58.0 bushels per pound (76.3 kilogrammes per hectolitre), below the average of 58.6 and a figure which "just barely meets the requirement" to meet a Number 2 grading.
For vomitoxin, a toxic fungal residue which can leave grain unfit even for feed, the level of 2.2 parts per million was the highest on records going back to 2006, and well above the average of 1.3 parts per million.
The contamination was worst in Corn Belt states such as Indiana, where the reading reached 2.9 parts per million, and Illinois, where it hit 5.2 parts per million, with the precipitation supporting large corn yield expectations less favourable for wheat crops.
"There is evidence that soft red winter wheat grown from Arkansas south avoided moisture at flowering but had rain at harvest, which affected soundness," US Wheat Associates said.
"In contrast, wheat farmers in Illinois, Indiana and Kentucky experienced more rain at flowering than they did at harvest so DON [vomitoxin] levels in that wheat are higher."
The group added that, according to industry sources, "buyers should be able to source soft red winter wheat with less than 2.0 parts per million DON", with levels coming in low in eastern growing states such as North Carolina and Virginia.
And laboratory analysis suggested that the crop had "typical soft red winter wheat milling characteristics".
Nonetheless, it advised that importers "should pay close attention to their specifications to receive the wheat they need".
The comments come at a time when the quality of many foreign crops has been compromised too by late rains, with US Wheat Associates noting "high" concerns over French supplies, and a ProAgro estimate that 35% of Ukraine wheat will not meet milling specifications, compared with a typical 25-30%.