Taking a harvest sample is simple, but time consuming. Never-the-less, it should be done because damage is hidden by the handling that occurs during sweeping, pickup, and processing. In some cases, we have found 4% more damage in harvest samples than what was indicated in the grower’s processor report. In other words, when we found an estimated 5% damage/reject level in the harvest sample, the processor indicated a 1% rejection level. The 4% discrepency is most likely due to damaged nuts lost during the steps of harvest.
Another reason for performing a harvest sample is to account for the damage that does occur in the field. Often times processors lump all worm damage together, not separating out NOW, PTB, OFM, or other worms. Ant damage often does not show up because the chewed out pellicles are blown out the back of the pick-up machine. Gummy nuts due to deficiencies, feeding, or other conditions are all lumped together.
Collecting a harvest sample is easy. In each block of concern, collect 500 nuts from the ground after shaking but before pickup and place them in a paper bag. Two samples of 250, or 4 samples of 125 nuts from differing areas of the block can also be collected, but try to keep the total number of nuts per block at 500. Store the bags in a freezer until they can be cracked out. Once able to crack out the almonds, check for signs of pests and disease. Pictures of damaged nuts can seen in a previous post or at the UC IPM website. A hand-sheller can be helpful in processing many samples. It can take 60-90 minutes for each sample depending on size. 500 nuts split into 4 125 nut samples should suffice for a 40 acre block.
So, is a harvest sample worth the time and energy? Using the 4% discrepency in the example above, and assuming that pest management practices will be implemented will reduce total damage by 1%, the marketable yields will increase by 30 pounds/acre in a 3000 lb crop year. Take that times 20 acres – a small block- totaling 600 pounds of increased marketable production, which would provide a $900 gain for 90 minutes of work. This doesn’t include any premiums that may occur from the processor for the improvement of quality.
Knowing the damage that occurs provides the ability to develop the most cost-effective way to manage orchard pests. If practices are changed within the orchard for a season, the harvest sample can provide the information to see if the changed practices provided an increase in marketable yields. If not, it may be best to modify or return to the previous year’s program.