CHAPTER 5: DECAY AND INSECT CONTROL - 2

Cold treatments

Certain fungi and bacteria in their germination phase are susceptible to cold, and infections can be reduced by treating produce with a few days of storage at the coldest temperature the commodity can withstand without incurring damage (0 ° C for apple, pear, grape, kiwifruit, persimmon and stone fruits). Rhizopus stolonifer and Aspergillus niger (black mold) can be killed when germinating by 2 or more days at 0 ° C (32 ° F) (Adaskaveg et al, in Kader, 2002), and pathogen growth can be nearly stopped by storage at temperatures below 5 ° C (41 ° F).

Cold treatments can also serve to control some insect pests, and are currently allowed for the control of fruit flies, the false codling moth, melon fly, pecan weevil and lychee fruit borer. Treatment for control of fruit flies requires 10 days at 0 ° C (32 ° F) or below, or 14 days at 1.7 ° C (35 ° F) or below, so treatment is only suited to commodities capable of withstanding long-term low-temperature storage such as apples, pears, grapes, kiwifruit and persimmons. Since requirements are subject to change, always refer to the latest edition of the APHIS treatment manual.

For produce packed before cold storage treatment, package vents should be screened to prevent the reinfestation by insects during handling.

Cold Treatment Protocol for Mediterranean Fruit Fly (Ceratitis capitata)

Sources: USDA APHIS PPQ Treatment Manual - http://www.aphis.usda.gov/ppq/manuals/online_manuals.html

Controlled/modified atmosphere treatments

For commodities that tolerate high CO₂ levels, 15 to 20% CO₂ -enriched air can be used as a fungistat to control decay-causing pathogens, such as Botrytiscinerea on strawberry, blueberry, blackberry, fresh fig and table grapes during transport. See page 88 for a description of the method for atmospheric modification within a pallet cover.

Insecticidal atmospheres (0.5% or lower O₂ and/or 40% or higher CO₂) have been shown to be an effective substitute for methyl bromide fumigation to disinfest dried fruits, nuts and vegetables The effectiveness of insecticidal atmospheres depends upon the temperature, relative humidity, duration of exposure and life stage of the insect.

Low O₂ and/or high CO₂ have been used to kill certain insects in commodities that can tolerate these conditions. The effectiveness of insecticidal atmospheres depends upon the temperature, relative humidity, duration of exposure and life stage of the insect. The first five of eight examples are from Mitcham et al (1997):

1) The first and third instars of the greenheaded leafroller (Planotortrix excessana) and the first and fifth instars of the brownheaded leafroller (Ctenopseustis obliquana) and the light brown apple moth (Epiphyas postvittana) are completely killed in 2 months when apples are stored at 0.5 ºC in 3% O₂ and 3% CO₂.

2) The eggs of the apple rust mite (Aculus schlechtendali) and the European red mite (Panonychus ulmi) are killed in 5.3 months when apples are stored at 2.8 ºC in an atmosphere of 1% O₂ and 1% CO₂.

3) Codling moth larvae (Cydia pomonella) are killed in 3 months when apples are stored at 0 ºC, 1.5-2% O₂ and less than 1% CO₂.

4) In kiwifruit, the adult two-spotted spider mite (Tetranychus urticae) is killed by 40ºC, 0.4% O₂ and 20% CO₂ in only 7 hours.

5) When persimmons are stored at 20 ºC, 0.5% O₂ and 5% CO₂, the third instar of leafrollers (Planotortrix excessana) is killed in 4 days and the larvae and adult mealy bug (Pseudococcus longispinus) is killed in 7 days.

Sources: Mitcham, E.J., S. Zhou and A.A. Kader. 1997. Potential for CA for postharvest insect control in fresh horticultural perishables: an update of summary tables compiled by Ke and Kader, 1992. pp. 78-90 In: Thompson, J.F. and Mitcham, E.J. (eds) CA'97 Proceedings Volume 1: CA Technology and Disinfestation Studies. Department of Pomology Postharvest Hort Series No. 15.

6) Sweetpotato weevil (Cylas formicarius elegantulus) has been controlled at ambient temperature in stored tropical sweetpotatoes by treatment with low oxygen and high carbon dioxide atmospheres. At 25 °C (76 °F), storage in 2 to 4% oxygen and 40 to 60% carbon dioxide results in mortality of adult weevils in 2 to 7 days.

Sources: Delate, K. et al. 1990. Controlled atmosphere treatments for control of sweetpotato weevil in stored tropical sweetpotatoes. Journal of Economic Entomology 83:461-465.

7) Codling moth (Cydia pomonella) in stone fruits can be controlled at 25 °C (76 °F) by using atmospheres of 0.5% oxygen and 10% carbon dioxide for 2 to 3 days (adult or egg) or 6 to 12 days (pupa). Normal color and firmness changes during ripening are not affected by treatment.

Sources: Soderstrom, E.L. et al. 1990. Responses of codling moth life stages to high carbon dioxide or low oxygen atmospheres. Journal of Economic Entomology 83:472-475.

8) Treatments with 45% CO₂ at 0 ° C (32 ° F) are being developed for several surface pests, including omnivorous leafroller ( Platynota sultana), western flower thrips ( Frankliniella occidentalis), and Pacific spider mite ( Tetranychus pacificus) on harvested table grapes. This treatment requires 13 days at 0 ° tO₂ ° C (32 ° to 36 ° F) and could be conducted in a marine container during transport. However, neither this nor other insecticidal CA treatments are approved yet as quarantine treatments.

Sources: Mitcham, E.J., F.G. Mitchell, M.L. Arpaia, and A.A. Kader. 2002. Postharvest Treatments for insect control. p. 251-257, in: A.A. Kader (ed). Postharvest Technology of Horticultural Crops, third edition. University of California , ANR Publication 3311.

Heat treatments

Hot water dips or heated air can be used for direct control of postharvest insects. In mangoes, an effective treatment is 46.4 °C for 65 to 90 minutes, depending on fruit size, variety and country of origin (Mitcham et al in Kader, 2002). Fruit should not be handled immediately after heat treatment. Whenever heat is used with fresh produce, cool water showers or forced cold air should be provided to help return the fruits to their optimum temperature as soon as possible after completion of the treatment.

Some pathogens are susceptible to heat treatments. Brief hot water dips or forced-air heating can be effective for disease control, especially for reducing the microbial load for crops such as plums, peaches, papaya, cantaloupe and stone fruits (Shewfelt, 1986), sweetpotatoes and tomatoes.

Hot water treatments

* papaya anthracnose control requires both treatments, 30 min at 42 C followed by 20 min at 49 C.

Hot forced-air treatments

Sources: Barkai-Golan, R. and Phillips, D.J. 1991. Postharvest treatments of fresh fruits and vegetables for decay control. Plant Disease 75:1085-1089.

Biological control and plant growth regulators

Two biological control products (antagonistic organisms) are currently used as complementary tools (to chemical and/or heat treatments) for the management of postharvest decays together with other strategies as part of an integrated pest management program for a few fruits and vegetables (see table below).

Two plant growth regulators can be used to delay senescence of citrus fruits and consequently delay their susceptibility to decay (see table below).

Commercially available biological control materials and plant growth regulators (PGR) registered as postharvest treatments:

Sources: Adaskaveg, J.E., H. Forster, and N.F. Sommer. 2002. Principles of postharvest pathology and management of decays of edible horticultural crops. p. 196-195, in: A.A. Kader (ed). Postharvest technology of horticultural crops, third edition. University of California , ANR Publication 3311.