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Sample Nuts to Evaluate IPM Effectiveness

An effective pest management program includes the ability for growers to accurately evaluate what’s working – and what’s not – in their orchards. Harvest sampling is can provide those answers.



Integrated Pest Management (IPM) is an important and much discussed topic among growers, who invest a lot of time and money each year trying to prevent pests from damaging their crop.

But how do growers know if what they are doing is efficient or whether they should make any adjustments to their IPM strategy year to year? One increasingly popular method is harvest sampling, also known as windrow sampling for almond operations.

Sampling combines two key elements central to continual IPM improvement – evaluation and adaptation.

“By the time harvest arrives, most pest management programs have been executed, making it the proper time to evaluate how these programs performed,” said Drew Wolter, Pest Management Specialist for the Almond Board of California. “Harvest sampling offers a perfect opportunity for growers and pest control advisors (PCAs) to assess strengths and weaknesses of each program.”

Sampling is different from the grade sheets growers receive from handlers. Though grade sheets may specify damage to nuts, they don’t identify what caused the problems. Sampling, on the other hand, allows growers to pinpoint the specific kind and percentage of pest damage among the nuts tested. This has two distinct advantages:

  • Accuracy: Knowing what caused nut damage during the last growing season allows growers to better assess their management decisions, including the efficacy of the material applied, the timing of those treatments and how well any monitoring programs worked.
  • Record keeping: Through this evaluation process, growers can develop historical records for each block. Overtime, this provides valuable context and information – such as where infestations may be coming from and the location of perennial orchard hot spots. This information allows growers to adapt management programs according to the orchard’s specific patterns and pressure.

How to Conduct Harvest Sampling

UC IPM guidelines for harvest sampling recommend that 500 nuts per block should be taken; however, not every block has the same layout, pressure, size and neighboring conditions and the total number of samples should be adjusted accordingly. Wolter said larger blocks may require additional sampling to provide an accurate representation of that location’s true pressure and damage. The primary is to obtain a representative sample from multiple areas within a block.

If growers know a block has historically shown high pressure, they can partition and denote which rows samples were taken from to gain more precise information. For example, five 100-nut samples can be taken from five evenly spaced rows within a block. Because insect populations build over time and space in orchards, this method should give growers more detailed information regarding where pressure is coming from.

Wolter said that if growers don’t have time to crack out samples at harvest, they can store them in a cold room or freezer until activities wind down and the analysis can be completed. 

Tips to Identify Damage

The main pests to keep an eye out for during damage assessments include navel orangeworm (NOW), ants, leaf-footed bug and brown marmorated stink bug (BMSB). Wolter offered these recommendations for what to look for:

  • NOW: Signs include deep feeding tunnels throughout the kernel. Also, white frass and webbing on the kernel.
  • Ants: Kernels often are shriveled, with sanded or stripped kernel skins and sawdust-like residue, without the presence of webbings and white frass. In severe cases, nut meat will be hollowed out, leaving only the kernel skin.
  • Leaf-footed bug and BMSB: Leaf-footed bug feeding can result in dark spots on the surface of kernels. BMSB can feed later into the season, creating black necrotic tissue on the kernel that appears sunken. Pitting, stippling and dark necrotic tissue often are present. Soft shell varieties such as Fritz, Sonora, Aldrich, Livingston, Monterey and Peerless are the most susceptible to bug damage