Trees might bloom, but getting fruit is another matter

Mangoes, lychee and longan usually flower around the beginning of the year.

Pollinators of mango flowers, pictured, include bees, flies and, to some degree, wind and gravity. Mango trees might often bear one year and not the next. Or, a tree might flower on only one side of the tree and then flower on the other side the following year. Factors that influence mango tree flowering include temperature, water, fertility, cultivar and diseases. Mango trees produce better on the dry leeward sides of the islands and tend to have more disease problems in wet areas.

Longan and lychee are native to Southeast Asia and usually require cooler temperatures to initiate flowering — longan more so than lychee, so it was somewhat unusual to see longan trees flower in 2015. Lychee, longan and mango trees produce flowers on panicles usually at the tips of the branches. In the case of mangoes, there may be numerous flowers on the panicles, however, not all will bear fruit. Some of the flowers are males, and the others are hermaphrodites, meaning it has both male and female flower parts. It is the female pistil that contains the ovary, which, if pollinated, matures into a fruit.

Two common fungal diseases of mango flowers are powdery mildew and anthracnose. Powdery mildew is a problem in dry areas. The flowers are covered with a gray-white mold or mildew, and flowers will not bear fruit. Anthracnose often is a problem of mango flowers in wet areas, and the infected flowers are either black or brown. Anthracnose is also common on the fruit, causing black spots.

Pests of mango include the mango blossom midge, the oriental fruit fly and the mango weevil. The mango blossom midge can be a problem if the larva destroys the mango flowers. It is difficult to determine the extent of the damage, as the fungal diseases often are the leading cause of flower damage. The oriental fruit fly is a major pest, as the maggots damage the fruits and prevent export of mango fruits without disinfestation procedures. The mango weevil burrows into the seed, often without detection, and is usually found if one cuts open the seed.

Girdling fruit trees to induce flowering has had some success. A cut is made around the branch into the bark and the underlying phloem cells. The destruction of the phloem cells causes the carbohydrates produced from photosynthesis to accumulate above the girdle and, hopefully, stimulate flowering. Success depends on the type of fruit tree as well as variety.

Developing fruits such as mango, lychee and longan can be protected from fruit flies and bird pests by covering the fruits with fruit-protection bags. These are lightweight bags made of either nonwoven fabric or paper. The bags may be carried by agricultural distributors or found on the internet.

Richard Ebesu is an extension agent with the Kauai Cooperative Extension Service.