CANBERRA, May 14 (Reuters) - Chicago wheat futures extended gains on Tuesday and were within a whisker of a 10-month high touched in the previous session after frosts damaged crops in Russia and threatened to reduce supply from the world's biggest wheat exporter.

Soybean and corn futures also rose as excessive moisture in the Midwest hampered U.S. corn planting and floods in southern Brazil shrank the soybean harvest there.


* The most-active wheat contract on the Chicago Board of Trade (CBOT) was up 0.8% at $6.92-1/2 a bushel, as of 0012 GMT, after rising to $6.94 on Monday, its highest since last July.

* CBOT soybeans rose 0.2% to $12.22 a bushel and corn climbed 0.6% to $4.75-1/2 a bushel. Corn was at its highest level since December 2023.

* All three contracts fell to their lowest levels since 2020 earlier this year due to plentiful supply and speculators amassing bearish short positions.

* But prices have risen as adverse weather and a leafhopper insect plague in Argentina hit crops and speculators were forced to buy back some of those shorts.

* Wheat has climbed around 30% so far from the lows earlier this year, corn is up around 17% and soybeans have risen 8%.

* Unseasonal frosts struck Russia's southern cropping regions again over the weekend, following dry weather that had already begun curtailing yields.

* Russia's IKAR agricultural consultancy cut its forecast for the country's wheat crop by 5 million metric tons to 86 million tons, and said exports would be 3.5 million tons lower at 47 million tons.

* "A crop below 85 million tons would likely start to impact global trade patterns, shifting market focus toward tighter stocks among other major exporters," StoneX analyst Arlan Suderman wrote in a note.

* Suderman also said CBOT prices were benefiting from a move by fund managers away from the 'commodity deflation' mantra of recent years, which fed bearish bets across commodity markets.

* Russian wheat export prices rose last week.

* In the United States, meanwhile, the Department of Agriculture (USDA) said half of the nation's winter wheat crop was in good-to-excellent condition, the highest for this time of year since 2020, but that corn planting progress was behind average.

* Wheat stocks in Indian government warehouses have fallen to their lowest since 2008 after two years of poor production.

* In soybeans, flooding in Brazil's Rio Grande do Sul state has destroyed 2.4 million tons of the crop, consultants Pátria Agronegócios said, downgrading their overall 2023/24 harvest projection to 142.82 million tons.


* Global stock indexes were little changed on Monday while the U.S. dollar index eased as investors awaited this week's U.S. inflation data that could influence U.S interest rates.

(Reporting by Peter Hobson; Editing by Sherry Jacob-Phillips)