A recent agricultural research project with pistachios paid more attention to the nuts that fell to the ground during harvest than to those that were collected and sent to market. The reason for the odd focus is the navel orangeworm (NOW), a persistent pest of several California tree crops, but especially nuts. The insect likes to lay its eggs in the winter or early spring in pistachios and almonds that remain in orchards after harvest.

The number of nuts, particularly pistachios, that spill over or otherwise escape harvesting equipment is significant. The researchers estimated it to be 30,000 pistachios per acre.

The orchard sanitation research team included four entomologists and biological science technicians from the Agricultural Research Service, U. S. Department of Agriculture, three from University of California Extension who are specialists, research associates or laboratory assistants and a research entomologist with Paramount Farming, the state's largest nut producer.

They found that the wasted nuts, called mummies, are an important source of NOW, and that mowing the groundcover or disking in row middles reduced the number of the harmful insects that emerged.

So far, so good. But because the harvested nuts that spill out of the harvesting equipment tend to cluster near the tree trunks an extra step is required to scatter them into the drive rows between the tree rows, where the disking or mowing can disperse them.

One of the methods evaluated by the research team for that task is a blower, easily attached to a small tractor which can get the job done by traveling through an orchard at relatively high speeds.

The clustering of nuts around the tree trunks is peculiar to pistachios. They are harvested by shaking the trees mechanically. The falling nuts bounce off of tough fabric stretched over inclined frames that roughly form a V, with a conveyor belt at the bottom. It moves and lifts the nuts into a bin, which is moved aside when full to allow its replacement by an empty. Only a complete seal around the tree trunks can prevent the clustering.

Almonds are harvested by mechanical shakers as well, but the nuts are allowed to fall to the orchard floor, where they are later swept into a windrow and then picked up mechanically. Clustering is not as big a factor with almonds.

In both crops most trees are planted on berms that extend the full length of each tree row. The berms tend to cause the harvested nuts to roll or bounce toward the middles between the tree rows.

Until this research project was undertaken the prevailing control efforts focused on nuts that remained on the trees after harvest. Now both sources have to be considered and dealt with. It appears that mummy nuts left on the trees as a breeding ground for NOW egg layers are more of a factor in almonds than pistachios.

The 152,000 acres of pistachios grown in California account for more than 95 percent of the country's production. The acreage has almost doubled in the past 10 years to make pistachios the second most valuable nut crop in the state behind almonds.

With 30,000 individual pistachios per acre left in orchards, the waste represents a lost market potential as well as an unwanted breeding ground for a troublesome insect pest.

The research report said nothing about it, but maybe it's time to send in the gleaners

(July 17, 2008)