Page 30 - Simply Veg 3.21

temperature, at a lower temperature the air will hold less water but can still be very humid.
As leafy vegetables have a large surface area they will lose water faster than root vegetables or fruit; a reason to keep salad leaves and lettuce in poly bags. Also small fruit lose water faster than large fruit. Managing water loss to keep the produce fresher can be done by keeping the humidity high or wrapping the produce in polythene. If using polythene the produce needs regular inspection as if rots start they can soon spread in these conditions.
Mechanical Injury / Physical Damage
This can lead to rots in the produce and also water loss even if it only surface damage
to the skin. Some produce can seal the wounds by corky layers but its storage life
is often reduced. Damage can also lead to attacks by pests and diseases.
Air Movement
When first harvested crops may be cooled by fans to remove the field heat or this can be done by dipping in cold water, but this depends on the crop. Once cooled it is best to reduce air movement as this can reduce the humidity by moving the humid air away from the produce. Storing in crates that are wrapped in polythene or cling film helps to reduce air movement and maintain humidity.
Storage Atmosphere
There is usually little that amateur gardeners can do to control the atmosphere in the storage area but commercially the cold stores have reduced oxygen levels and remove the ethylene gas. Fruits like apples, pears and sometimes cherries are stored
in controlled atmosphere stores with low oxygen and increased CO2 which slows down respiration.
Diseases
There are a number of diseases that can cause rots in store to many fruits and vegetables, these include fungal, bacterial and physiological (like scald of apples). Most physiological disorders are caused by a nutrient deficiency like shortage of calcium and this should be rectified whilst the crop is still growing. Calcium deficiency is possible the most common and this can be overcome by spraying with calcium nitrate during
the summer and improving the irrigation if possible. If boron deficiency occurs spray with boron sprays.
There are a number of other diseases that affect fruit and vegetables whilst they are still growing but may not show until the produce is in store. Also most rotting produce will give off ethylene which will reduce the storage life of the remaining produce and can lead to further rots. Fungal diseases that can cause
rots in storage especially if infected when harvested includes Alternaria, Aspergillus, Botrytis, Fusarium, Geotrichum, Monilinia, Penicillium, Rhizopus and Sclerotinia;
the bacteria include Pseudomonas and Pectobacterium (used to be called Erwinia). Fortunately these disease are not that common apart from Botrytis and Brown rot. Many diseases are specific to certain crops so are to some extent limited in what they infect.
Control of Diseases
This starts with the pre-harvest measures in the field or orchard to prevent any infection. Any sources of infection (i.e. Brown rot infected fruit in the tree) should be removed as these can spread spores onto healthy fruits. It can also pay to spray with a fungicide if problems have occurred in the past to prevent any spores germinating and infecting produce in store. As an alternative to pre-harvest spraying the produce can be dipped, washed or sprayed with fungicide solution when harvested and put into store.
Handle all produce carefully when harvesting and storing to prevent any damage which soon results in rots in store. If possible harvest on dry cool days so produce is not put into store wet. Keeping produce cool helps to reduce rots and regular inspection to remove any produce that is developing rots promptly before it spreads. The saying “one bad apple....” Is very true and can soon produce thousands of spores. If some produce does produce spores remove them and clean the rest in chlorinated water, allow to dry before putting back into store should reduce infection spread.
Research is being carried out into using biological control methods to control diseases in store but at present these are not available.
Other physiological disorders of fruit and vegetables includes:
Produce
Disorder
Symptom
Celery Onion Potato
Turnip
Pithiness Watery scales Black heart Gangrene Brown heart
The internal pith of the petiole starts to breakdown.
The skins become thick, leathery with watery glassy internal scales.
Dark grey to black tissue in the tuber centre.
Tubers rot and smell vile, the infection is often on / in the tuber when lifted but can spread in store. A brown internal tissue.
Garlic
Waxy breakdown
The clove become translucent, sticky and waxy; the outer dry skins are not affected.
Plums
Gel breakdown
The skins and flesh have brown gelatinous areas and start to breakdown (rot).
Spraining
Similar to the above but affects the tubers when lifted.
Sweet potato
Pithiness
The internal tissue goes spongy.
Fungal and Bacterial Diseases
Apples, pears, grapes, strawberry and leafy vegetables
Potato and leafy vegetables
Grey mould a fungal disease
Bacterial soft rot or dry rot a fungal disease
Botrytis cinerea – a common disease of many crops that continues in store
Pectobacterium carotovara, Fusarium species
Produce
Problem
Pathogen
Apples pears peach, cherry, plums
Brown rot a fungal disease
Monilinia fruticola
Carrots and leafy vegetables
Watery soft rot a fungal
Sclerotinia sclerotiorum
30 Simply Vegetables