A streaky Adam LaRoche has seen his numbers creep upward this month. (Jonathan Newton/The Washington Post)

Adam LaRoche has a history of starting slow and streaking late. LaRoche’s career OPS rises nearly every month of the season, jumping from .776 in June to .821 in July to .902 in August. Through 24 games this month, LaRoche is hitting .266 with four homers and a .825 OPS. August has been a far kinder month for the first baseman — he has six multi-hit games this month while only eight the previous two months combined. But this season has still been a struggle.

LaRoche is hitting .238 with a .324 on-base percentage and .414 slugging percentage and 18 homers — all below his splendid 2012 season, and below his career averages of .265/.336/.476 and 27 homers per season.

“He’s not alone,” Manager Davey Johnson said. “A lot of veteran guys have not played up to their standard.”

LaRoche, in the first year of his two-year, $24 million extension, has always had the propensity to be streaky. This season has been extreme and his has OPS fluctuated wildly each month. His OPS in April was .473 with three homers, then he caught fire in May with a 1.024 OPS with seven homers. His July OPS of .511 was sandwiched between a June OPS of .807 and August OPS of .825.

LaRoche has hit four homers in August, the same number as the previous two months combined. He has struck out 19 times in 79 at-bats. He has battled a leaner body, playing at 200 pounds, about 10 to 15 pounds less than he would prefer, the byproduct of the Ritalin medicine he takes to combat ADD (attention deficit disorder).

“From the get-go [last season], he came out smoking and pretty much carried it through the year,” Johnson said. “Got a lot of big hits. This year, he’s lost a lot of weight. His weight is down. He’s got some big hits. [Ryan Zimmerman] is kinda the same situation. Zim is not doing the things he’s done in the past. Can’t just pick on Adam.”

Zimmerman, too, another key bat in the heart of the Nationals order, has posted numbers this season below his career averages, most notably his power. The third baseman is hitting .270/.345/.433 with 15 homers in 504 plate appearances — below his career triple slash line of .282/.346/.478 with 25 homers per season.