MODESTO  (AP) — A nursery near Modesto sold pistachio trees with a disorder that officials say could affect as many as 20,000 acres of San Joaquin Valley orchards.

Duarte Nursery sold a type of pistachio tree that had bushy top syndrome, which causes stunted growth and other problems. It’s unclear whether the cause is a mutation or a bacteria.

The president of the family-owned farm, John Duarte, says it’s reached legal settlements with most growers and has halted pistachio tree sales.

The California Pistachio Research Board says the problem involves trees planted in 2011 or later, and since orchards typically need six years before producing a crop, current nut supplies won’t be affected.

As of 2013, pistachios were a $1 billion crop in California.