Californians are souring on a ballot measure to legalize adult recreational use and cultivation of marijuana, according to a new poll conducted by the Public Policy Institute of California.

The poll found that 44 percent of likely voters support Proposition 19, the marijuana ballot measure, while 49 percent are opposed. The results are a significant decline from last month, when the same survey found Prop. 19 leading 52 to 41 percent.

Prop. 23, which would suspend the state's greenhouse gas law, lost support in the latest poll as did Prop. 24, which would overturn corporate tax breaks. Prop. 25, which would allow the Legislature to pass a budget with a simple majority vote, gained slightly, and is the only measure of those polled that is winning. Five other measures on the ballot were not polled.

"In an initiative campaign, the burden of proof is always on the 'yes' side," said Mark Baldassare, president and CEO of the Public Policy Institute of California. "The yes side has to do a very convincing job of explaining not just why, in concept, something is good, but why it is a good law."

For Prop. 19, he noted the array of high-profile figures who have come out against the proposition, including every candidate running for statewide office, while the proponents have yet to gain such high-profile endorsements.

The biggest drop in support is among independent voters. Last month, 65 percent of independent voters supported the initiative and that number has shrunk to just 40 percent. The poll also found a significant decline among Latino voters, whose support dropped from 63 percent in September to 42 percent today.

"This was in concept something that Californians were evenly divided on and I guess they are just not hearing reinforcing messages that would put them in the position of support," Baldassare said.

For Prop. 23, the measure to suspend the state's climate-change law known as AB32, 37 percent of likely voters are in support while 48 percent are opposed. Last month, voters were almost evenly split on the initiative, which would suspend the greenhouse gas regulation law until unemployment falls to 5.5 percent for an entire year.

The voters polled knew the least about Prop. 24, a measure that would repeal three corporate tax breaks that have been included in budget negotiations the past few years. The measure is losing, with 31 percent in support and 38 percent opposed, but a large number of people - 31 percent - said they did not know how they would vote.

"I think voters can't figure out what this one is all about," Baldassare said.

The only ballot measure of the four polled that is leading is Prop. 25, which would allow the Legislature to pass the state budget by a simple majority. Current law requires a two-thirds majority vote, which forces it to be bipartisan, and earlier this month lawmakers finally approved a spending plan 100 days after the start of the fiscal year.

Forty-nine percent of likely voters support the measure, while 34 percent are opposed. The findings are nearly identical to the survey taken a month ago.

The survey polled 2,002 Californians who said they are registered and active voters. The poll was conducted between Oct. 10 and Oct. 17 and has an error rate of plus or minus 3.1 percentage points.