March 2011. The Falkland Islands Meat Company imported some wood and sawdust from Chile to use for exporting lamb skins to China. The wood, which is to be used as packaging, was heat treated as per EU regulations for packaging material. The sawdust has not been treated as the regulations do not require it. However, on starting to unpack the container some live insects were found, and we believe them to be cockroaches. Everything was put back in, and the container was closed whilst advice was souight on what to do.

A number of suggestions were made:

• Fumigate with methyl bromide.
• Fumigate with aluminium phosphide (Phostoxin), and cover the contaner for 5 days (but note that phosphine is toxic to human beings, and care is required when it is used).
• Spray with Fipronil (0.05%); Imidacloprid (2.15%); Cyphenothrin (5EC); Cyfluthrin (20EC).
• Cold treatment; see www.coresta.org/Guides/Guide-No9-Freezing%20parameters_Nov09.pdf (below).
  • CO₂ treatment using Cryonite.
  • Freeziing at -18⁰C for up to 7 days.
• Just leave the container until Spring!

Note, that neither methyl bromide nor phosphine work well at low temperatures; 15⁰C is the minimum temperature for phosphine use, and temperatures >15⁰C are needed for methyl bromide when used to fumigate grains (and 4⁰C for buildings); so it’s likely that temperatures above 15C would be needed for the fumigation of sawdust.

Section 5: Decay and insect control

Chemical controls
Controlled/modified atmosphere treatments
Heat treatments

The first line of defense against insects and disease is good management during production. The second is careful harvesting and preparation for market in the field. Thirdly, sorting out damaged or decaying produce will limit contamination of the remaining, healthy produce. Yet, even when the greatest care is taken, sometimes produce must be treated to control insects or decay-causing organisms.

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. Rhizopus stolonifer and Aspergillus niger (black mold) can be killed when germinating by 2 or more days at 0??C (32 F) (Sommer, in Kader, 1992). On the other hand, brief hot water dips or forced-air heating can also be effective, especially for reducing the microbial load for crops such as plums, peaches, papaya, cantaloupe and stone fruits (Shewfelt, 1986), sweetpotatoes and tomatoes.

While high humidity in the storage environment is important for maintenance of high quality produce, free water on the surface of commodities can enhance germination and penetration by pathogens. When cold commodities are removed from storage and left at higher ambient temperatures, moisture from the surrounding warm air condenses on the colder product’s surfaces (Sommer, in Kader, 1992). A temporary increase in ventilation rate (using a fan) or increasing exposure of the commodity to drier air can help to evaporate the condensed moisture and to reduce the chances of infection.

Cold treatments can also serve to control some insect pests, and are currently used for the control of fruit flies. Treatment 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 (Mitchell & Kader in Kader, 1992). For produce packed before cold storage treatment, package vents should be screened to prevent the spread of insects during handling.

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 size (Sommer & Arpaia in Kader, 1992). 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.

Control of storage insects in nuts and dried fruits and vegetables can be achieved by freezing, cold storage (less than 5 C or 41 F)), heat treatments, or the exclusion of oxygen (0.5% or lower) using nitrogen. Packaging in insect-proof containers is needed to prevent subsequent insect infestation.

Some plant materials are useful as natural pesticides. Cassava leaves are known to protect harvested cassava roots from pests when used as packing material in boxes or bags during transport and short-term storage. It is thought that the leaves release cyanogens, which are toxic to insects (Aiyer, 1978). The ashes of the leaves of Lantana spp. and Ochroma logopur have been found to be very effective when used as a dust against aphids attacking stored potatoes (CIP, 1982). The pesticidal properties of the seeds of the neem tree (as an oil or aqueous extract) are becoming more widely known and used throughout the world. Native to India, neem acts as a powerful pesticide on food crops but appears to be completely non-toxic to humans, mammals and beneficial insects (NRC, 1992). Any “natural pesticide” must be shown to be safe for humans before its approval by regulatory authorities.

Chemical controls

Washing produce with chlorinated water can prevent decay caused by bacteria, mold and yeasts on the surface of produce. Calcium hypochlorite (powder) and sodium hypochlorite (liquid) are inexpensive and widely available. The effectiveness of the treatment will be decreased if organic matter is allowed to build up in the wash water. The effectiveness of chlorine increases as pH is reduced from pH 11 to pH 8, but at lower pH chlorine becomes unstable.

Fruits and vegetables can be washed with hypochlorite solution (25 ppm available chlorine for two minutes) then rinsed to control bacterial decay. Alternatively, these commodities can be dipped in hypochlorite solution (50 to 70 ppm available chlorine) then rinsed with tap water for control of bacteria, yeasts and molds.

Source: Ogawa, J.M. and Manji, B.T. 1984. in: Moline, H.E. (Ed). Postharvest Pathology of Fruits and Vegetables. University of California, Division of Agriculture and Natural Resources, UC Bulletin 1914.

There are some chemicals that are generally recognized safe (GRAS) which are used to control a variety of molds and fungi on fruit crops.

Sulfur:

Sulfur is used on bananas as a paste (0.1 % active ingredient) to control crown rot fungi.

Sulfur dioxide (SO₂) is used as a fumigant or a water spray (0.5% for 20 minutes for the initial treatment, then 0.2% for 20 minutes at 7 day intervals) on grapes to control Botrytis, Rhizopus andAspergillus fungi.

Careful calculation of the amount of sulfur dioxide required to treat grapes can greatly reduce the need to vent or scrub the storage air after fumigation to remove excess S02. For information on the “total utilization” fumigation technique that has been developed for treating grapes with sulfur dioxide, see Luvisi (1992).

Sodium or potassium bisulfite:

Bisulfites are used in a sawdust mixture (usually contained within a pad that can be placed inside a carton) to release SO₂ for control of molds on grapes (5 grams for a 24 to 28 lb box).

Sources: Luvisi, D.A. et al. 1992. Sulfur Dioxide Fumigation of Table Grapes. University of California, Division of Agriculture and Natural Resources, Bulletin 1932.

Ogawa, J.M. and Manji, B.T. 1984. in: Moline, H.E. (Ed). Postharvest Pathology of Fruits and Vegetables. University of California, Division of Agriculture and Natural Resources, UC Bulletin 1914.

Bacterial soft rot (Erwinia) of cabbage can be controlled by using lime powder or a 15% solution of alum (aluminum potassium sulfate) in water. After treatment of the butt-end of the cabbage heads, the produce should be allowed to dry for 20 to 30 minutes before packing.

Applying alum solution (spray or brush on):

Applying lime powder (press butt-end into powder):

Source: Borromeo, E.S. and Ilag, L.L. 1984. Alum and Lime Applications: Potential Postharvest Control of Cabbage Soft Rot. Appropriate Postharvest Technology 1(1):10-12.

On occasions when fungicides must be applied to produce, a simple tray with holes punched in the bottom can be used hold the commodity while it is sprayed. In the illustration below, a hand-operated knapsack sprayer is used to spray fungicides on bananas to the stage of run-off. The bananas can then dry in the perforated tray before further handling.

Source: FAO. 1989. Prevention of Postharvest Food Losses: Fruits. Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 pp.

When fruit is packed for export, fungicides are often applied to meet the requirements of international quality standards and to reduce deterioration during transport. The “cascade applicator” illustrated below was developed to apply fungicide uniformly and effectively by using a liquid curtain to drench the fruit.

Fruit in a perforated plastic tray is introduced on a roller conveyor belt (not shown) into the applicator. Inside a simple fan shaped deflector creates a curtain of liquid fungicide. The fruit passes under the curtain where it is drenched, then out of the applicator to drain on a tilted return tray. The tank holds up to 50 liters of fungicide solution, and a pump is mounted at the level of the tank outlet. A filter is fitted on the top of the tank to remove foreign matter from the return flow of fungicide from the applicator box and the return tray.

Fungicide Applicator:

Source: Overseas Div., AFRC. Nat’l Institute of Agricultural Engineering. 1974. Bulletin No. 6. Silsoe, Bedfordshire, England.

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 Botrytis cinerea on strawberry, blueberry, blackberry, fresh fig and table grapes during transport. See page 77 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. Following are some examples:

1) 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.

Source: Delate, K. et al. 1990. Controlled atmosphere treatments for control of sweetpotato weevil in stored tropical sweetpotatoes. Journal of Economic Entomology83:461-465.

2) 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.

Source: 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.

Heat treatments

Postharvest heating using hot water or hot forced-air to kill or weaken pathogens can be used as a method for decay control in fresh fruits and vegetables.

HOT WATER trEATMENTS:

HOT FORCED-AIR trEATMENTS:

Source: Barkai-Golan, R. and Phillips, D.J. 1991. Postharvest heat treatments of fresh fruits and vegetables for decay control. Plant Disease (Nov): 1085-1089.