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New Mexico State University

New Mexico State University

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NMSU finds first-ever leaf spot in New Mexico pistachios, plans workshop for growers

Scientists at New Mexico State University have identified Septoria leaf spot, a fungal disease in plants, in Otero, Hidalgo, Luna and Dona Ana counties' pistachio trees. The disease is common in other states where pistachios are grown but has never before been documented in New Mexico. NMSU will hold a pistachio growers workshop in Alamogordo to help educate those close to the disease about minimizing its effects.

"It's of concern," said Richard Heerema, an NMSU extension specialist. "Fungal disease is very much weather driven. In New Mexico, with our dry climate, we typically don't see these sorts of things."

The Septoria fungus creates small, brown lesions on the leaves of trees. If enough lesions are present, the tree will have difficulty photosynthesizing, or turning sunlight into energy. The fungus does not directly affect the tree's fruit, but continued difficulty photosynthesizing can have a negative effect on yield. Each of the 20 southern New Mexico pistachio orchards tested by NMSU has been positive for Septoria.

Natalie Goldberg, NMSU's extension plant pathologist, believes the fungus has been present in the state for years.

Heerema said the fungus thrives in wet weather. He believes a string of wet summers in southern New Mexico have increased the severity of Septoria in the region, perhaps explaining why it had gone undetected.

"At this point, because of the level of infection, we need to pay attention to it," Goldberg said. "There are some low-risk fungicides available, but that's an added input for growers."

Goldberg wants to ease fears about the disease. She said a relatively dry growing season could significantly reduce the amount of Septoria in the region.

"One of the most important aspects of letting our growers know about Septoria leaf spot is the issue of good sanitation practices in the orchard, such as raking and destroying fallen leaves," said Elizabeth Gordon, Otero County extension agent. "Those leaves contain the fungus and will produce spores that will re-infect the new leaves coming on."

She said many growers incorporate leaves from the previous year into the soil for mulch, which ordinarily is a good practice but not with Septoria present.

If trees are left untreated long enough, they become weakened and more susceptible to other diseases and could eventually die. This strain of Septoria is pistachio-specific and will not affect other types of trees. Previously, Septoria has been found in Texas and Arizona pistachio trees.

Pistachios are a relatively small crop in New Mexico with approximately 1,300 acres of trees. By comparison, there are approximately 40,000 acres of pecans in the state. New Mexico pistachios are predominantly grown in Otero County.

The pistachio growers workshop will be held from 9 a.m. to 3 p.m. Thursday, Feb. 12, at the gymnasium at 1316 Scenic Drive in Alamogordo. There is a $20 registration fee, which includes lunch and notes. Space is limited. The registration deadline is Feb. 1. For more information, contact the Otero County Extension Office at (575) 437-0231 or egordon@nmsu.edu.