Wheat headed for a weekly gain of more than 10% on fears that growing threats to the Black Sea grain trade would curb supplies.

Futures edged higher on Friday at the end of a volatile week that saw Russia terminate a deal allowing Ukraine to export grain via some Black Sea ports, and then attack Ukrainian agricultural facilities. Both countries have warned that ships headed to each other’s ports could be considered military targets.

The flaring of Black Sea tensions adds to risks in global grain markets. Extreme weather is already wreaking havoc on crops across Asia, southern Europe and the US. India added to the food supply shocks on Thursday, saying it will ban some rice exports.

Corn and soy trimmed this week’s gains, but their declines are capped by the outlook for hot weather in key US growing regions. Drier conditions across the Midwest and Delta next week would reduce moisture and increase stress on corn and soybeans, Maxar said in its latest report.