In Venezuela, while they have many large, mature mango trees, no fruit is borne. There are heavy crops at other stations within a hundred miles or less. What is needed in order to produce fruit?" Dr. Carl Campbell, was familiar with the problem. The most common cause is a location where the trees bloom during periods of high humidity and temperature. This leads to anthracnose infection of the flowers and no fruit set. It can be controlled by spraying with fungicides, such as those containing copper, carbamate (e.g. Maneb), or Benylate. It is so humid in southern Florida that Florida growers are wiped out most years unless they spray. There are varieties from Southeast Asia that will do better under such conditions. He mentioned varieties Saigon, Florigon, Pico and Carabao. The good news is that all of these varieties are polyembryonic and consequently most trees will be just like their parents. The bad news is that mango seeds are viable for only a couple of weeks after removed from the seed and dried. I asked whether you could extend the life of the seed by wrapping it in wet paper towels. Carl explained that mould is a terrible problem with seeds stored this way. The best approach is to surface sterilize the seed by dipping it in 10% chlorox, then pack it in barely moist (no free moisture should be visible) activated charcoal and ship in a plastic bag.
There are locations where the trees do not even bloom. (Carl said you need to be alert because sometimes people have insisted their trees do not bloom, but more careful observers contradict them.) Fungicides will be no help there. For example, he has seen large areas in the Philippines where mangoes do not bloom. This appears to be due to the uniformity of high rainfall and temperature which does not permit the trees to have their normal dormancy. In 1972 scientists in the Philippines found that if they spray the leaves with as little as 10 g/litre of potassium nitrate (no longer available because of the security issue) the buds will start elongating within 2-3 weeks and will bloom within a month. Spraying is done only once, but the trees are drenched completely. They time the spray to have bloom and fruit growth during the least stressful season possible. Apparently it is effective only when the tree has attained a "ripeness to flower." Signs of this stage include: leaves become dull green or greenish brown and brittle when crushed with the hand and the tree has an appearance of suspended growth. Another use of this technique is to induce earlier flowering to beat the market and get higher prices for the mangoes. The fruiting season can be advanced several months in the Philippines.
Pestnet website says: The answer may be fungus, insects or both. In Australia, Johnson and Muirhead (1988) recommended a spray of Mancozeb (800g/kg) at the rate of 2 g/ltr weekly during blossoming and then monthly until harvest. In countries with high rainfall, flowers are commonly infected by the anthracnose fungus, Colletotrichum gloeosporioides (sexual stage, Glomerella cingulata). It causes a blossom blight. Symptoms begin as small black spots on flower buds, peduncles, pedicels and the rachis of the inflorescence. Necrotic flowers abscise leaving the persistent peduncles. Lesions may enlarge and coalesce to form large patches of necrotic, brown tissue.
As for non-chemical methods: prune out diseased twigs and clean up fallen infected trash. Also, make sure there are no mangoes sitting in the trees as they are likely to be a source of inoculum. Sounds good, but almost impossible to do on large trees! Therefore, prune trees to no more than 4 m tall, starting from an early age. The other cause of the problem is blossom moth, the larvae of which eat the flowers. The easiest way to recognise blossom moth damage is to look for clumps of flower debris held together by webbing. If the remains of the flowers are pulled apart, it is possible to find the small caterpillars hiding inside. Other insects are a possibility: beetles, large grasshoppers or chafer beetles, which would only be obvious at night time. Put a sheet or umbrella beneath the trees to catch any insects that may be present when the flowers are gently tapped.
Powdery Mildew in Mangoes Signs to look for are when they completely lose their first flowering but put out a second flowering. You’ll usually see a white residue and the panicle flowers are brown and brittle. Some people spray neutral copper and a wetting agent when the panicles are almost ready to open and others swear by wettable sulphur and a wetting agent. Sulphur will give a good set.
Sheryl: Here are Bob’s notes on how to extract the embryo before planting:
The husk must be taken off to expose the embryo. Watch out for the mango weevil borer which must be removed then plant the seed on its edge concave edge down and the top just above ground level.
Required tools: Dry rag to hold the slippery husk and tin snips that have a mechanical advantage. Hold the husk at one end with the rag and snip off about 5mm on the other end. The gap between the two sides of the husk is wide enough to let the blade of the tin snips in. Cut along between the two halves on the bottom concave section being careful not to cut the embryo. Lever the husk halves apart with your thumbs and gently pull the embryo out. Plant out as soon as possible.