Figure 1: Identifying an issue through gumming on fruit.
There are no studies to confirm but it may be possible that a pathogen can enter the clear gum and cause an infection making the gum darker.
IN THE ORCHARD
COLOURED/ CLOUDY GUM
COLOURED/ CLOUDY GUM Amber or cloudy/ murky gumming is common when a disease pathogen has entered the fruit. Less commonly, a nutritional toxicity may also cause this effect.
CLEAR GUM There are four scenarios for clear gum. It is either physiological, an insect, nutritional or physical. Have a closer look at the symptom 1.
PATHOGEN When a pathogen attacks the fruit it is likely to be either anthracnose (fungus) or bacterial spot (bacteria). For observational differences view link 2 . When observing, look for trends to determine how widespread the disease is and what treatment is required.
NUTRITIONAL It is uncommon but nutritional toxicities can cause a dark gum formation. Toxicities will be generally be displayed in the leaf. For confirmation check your nutrition levels through leaf and hull analysis lab tests.
NUTRITIONAL A nutritional deficiency of Boron can be like that of a pinhole. As it develops, a browning embryo can be observed.
PHYSICAL Physical damage can also cause gumming. Check for rub marks and dents with surrounding twigs to note possible source.
PHYSIOLOGICAL A slit may arise as a physiological disorder, resulting from rapid fruit growth. Upon cutting open you will see no sign of kernel damage.
If you see a pinhole, it is likely an insect has pierced the fruit. Cut a slither under the gum and see if a darkened circle is present to confirm .
PICKING THE DIFFERENCE If unsure, look further in to the orchard and try to find trends. Specifically, in different soil types, topography, valves, varieties and location on trees.
SYMPTOMS ARE RANDOM OR ISOLATED Random or isolated incidences lead to a belief of insect damage. Monitor the symptoms to see any further development.
I FOUND A TREND! If you have found a trend, it is likely there is a nutritional deficiency. Boron is the common element that causes this. To confirm, do a hull sample test post-harvest. In season, leaf sample tests are not representative of boron levels.
Figure 2: Observations made January 17, 2020. A strong indicator of boron deficiency.