How to Manage Pests

UC Pest Management Guidelines

PREHARVEST FRUIT SAMPLES

Preharvest fruit sampling will alert you to the need to treat before harvest. (Be sure to check the preharvest interval of the pesticide if treatment is necessary.) Monitor weekly beginning at color break (when nectarines start to turn reddish).

How to Sample (View preharvest damage photos for identification)
Examine 100 to 200 randomly selected fresh fruit on the tree (10-20 fruit on 10 trees) by looking at it on the tree and rotating it slightly to detect damage caused by:

• peach twig borer, oriental fruit moth, obliquebanded leafroller, or other larvae
• live San Jose scale, or parasitized San Jose scale
• stink bugs and plant bugs
• katydids
• western flower thrips
• fruit rot
• rust

FRUIT EVALUATION AT HARVEST

Take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program; be sure to keep a record for each block.

How to Sample (View harvest damage photos for identification)
Before the sorting process begins, examine 500 to 1,000 randomly selected fruit from harvest containers. Plan to sample 500 fruit for each variety unless unexpected damage is discovered, in which case increase the sample size up to a maximum of 1,000 fruit in order to thoroughly assess the damage. Distinguish damage caused by peach twig borer, oriental fruit moth, and leafrollers, San Jose scale, stink bugs, plant bugs, and katydids as well as brown rot, rust, and scab.

Look for the presence of:

• Larvae or larval feeding from peach twig borer, oriental fruit moth, or other caterpillars.
  • Peach twig borer: shallow feeding holes. Over time these may appear as scabs.
  • Oriental fruit moth: often small entry holes that may be difficult to see, especially if brown rot has invaded the site.
  • Leafrollers: tunneling into fruit; shallow holes or grooves in the fruit surface; this can sometimes be difficult to distinguish from severe thrips feeding that was done just after bloom.
• Live or parasitized San Jose scale and halos or spots on the fruit surface.
• Scabs, pits caused by stink bugs, plant bugs, and katydids.
• Silver discoloration on fruit surface caused by late season thrips feeding.
• Fruit rot. In many cases, this damage may occur in conjunction with peach twig borer or oriental fruit moth damage or other physical injury.
• Scab lesions on fruit are dark spots and may have green or yellow halos. They are most commonly on the upper surface and may merge to form large blotches.
• Rust lesions, which can resemble stink bug damage but can be distinguished by the presence of spore masses in the lesions, and lesions are often surrounded by halos.
• Powdery mildew scars are raised, scabby patches of corky tissue.

Record on a harvest monitoring form (PDF) the number of fruit infested by larvae, type of larvae present or, if there are no larvae present, whether damage is surface feeding only or if the larvae penetrated the fruit. Record the number of fruit with live San Jose scale, or parasitized San Jose scale. Record the number of fruit with damage caused by stink bugs, plant bugs, katydids, and thrips, and note any indication of rust, brown rot, scab, and powdery mildew.

IMPORTANT LINKS

• Fruit sampling for pest damage at harvest form (PDF)
• Photos of damage to fruit in harvest sample
• Photos of damage to fruit in preharvest sample

PUBLICATION

UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
General Information
W. J. Bentley (Crop Team Leader), UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension Tulare County
R. A. Duncan, UC Cooperative Extension Stanislaus County
J. K. Hasey, UC Cooperative Extension Sutter/Yuba counties
S. Johnson, Pomology, Kearney Agricultural Center, Parlier
J. A. Roncoroni, UC Cooperative Extension Napa County

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