Bananas are fun to grow, with tips from a pro
Bananas can grow quite vigorously and productively in many landscapes and gardens on the Big Island. The many varieties of this large, perennial herb yield the world’s most important fruit. The ripening, homegrown bunches hang in garages around the state, ready to nourish our families.
Most banana plants can produce large and high-quality fruit yields if they receive sufficient plant nutrition and well-timed horticultural care. Here we describe simple practices that growers can use to cultivate better bananas and to harvest bunches heavy with delectable fruit.
Growing a great banana starts with supplying each plant with enough water and available nutrients. The precipitation patterns in East Hawaii are ideal for banana crops. Copious rain falls throughout the year; supplying supplemental irrigation for banana is usually unwarranted. However, in drier regions of the island growers must regularly irrigate banana to prevent drought from impinging upon plant growth and reducing bunch size.
Professional banana farmers in East Hawaii apply specially formulated banana fertilizers. The "banana special" is a 13-3-38 formulation consisting of 13 percent nitrogen (N), 3 percent phosphorous (P), and 38 percent potassium (K) by weight. This complete fertilizer also contains the minor elements such as magnesium (Mg) that are required by these tall, quickly growing plants. In the high-rainfall Hilo area, farmers apply it monthly. They also periodically amend soils with agricultural lime or dolomite to provide calcium. They apply boron to avoid yield-limiting deficiencies.
Organic farmers fertilize banana with large amounts of mulch, composts, chicken manure, and natural materials such as potash (for K) and green sand (for Mg).
Successful farmers periodically thin out (prune) unwanted plants in their banana clusters (mats) so that only select plants remain for production. Banana plants, when heavily congested within a large clump, tend to not yield well and have stunted or spindly growth. Periodically prune unwanted keikis by digging them out with a pruning shovel. A well-maintained and productive banana mat has about three plants — a mother plant bearing a bunch, a mid-sized plant that is attached to the mother plant but is not yet flowering, and a young keiki that sprouts from the base of the mother. Pruning of unwanted plants ensures efficient use of fertilizer and water. Pruning also reduces high relative humidity in the leaf canopy, which improves control of fungal diseases of the foliage and fruits.
Where banana plants are well-fertilized and grow in small mats as described, they are well enabled to combat banana black leaf streak disease (BLS). This fungal disease causes necrotic streaks on leaves that eventually coalesce, causing leaves to turn brown and die. The best growers have a great number of healthy green banana leaves on the plant at flowering. Having more healthy leaves produces larger bunches. De-trashing, or the removal of severely diseased leaves from plants, is done weekly by using a serrated knife with a curved blade attached to a bamboo pole. Many growers apply fungicide sprays such as mancozeb to leaves for management of BLS. Without adequate plant nutrition and management of this disease, it is very difficult to realize acceptable yields in high-rainfall regions.
Growers should scout plant regularly for expression of distinctive disease symptoms caused by the banana bunchy top virus, which now occurs in Hilo. This disease can stunt plants and completely prevent the development of normal bunches. Destroy symptomatic plants manually or by treating with glyphosate herbicide after applying an insecticide to kill viruliferous (winged) aphids on the plant.
Banana corm weevils cause severe damage to pseudostems and the toppling of bunch-bearing plants. Left uncontrolled, these insect pests can prevent the successful cultivation of some banana varieties. Trap the weevils by placing severed sections of banana pseudostems on the ground with the severed side face down. The weevils move to the wounded tissue overnight, and can be exposed and killed after turning the stem section over in the morning. Also, cover stem pruning wounds with soil to hide wounded tissues, or apply a registered insecticide to control weevils.
Plant-parasitic nematodes such as root-knot nematodes and burrowing nematodes can cause unthrifty growth and premature toppling of infected banana plants. They infect and undermine banana root systems. Prop up the stems of leaning, diseased plants with poles so that plants do not topple and thereby destroy bunches. Fallow infested fields every five years, or practice crop rotation by growing other plants with resistance to the nematodes.
There is more free, useful information available online about banana nutrition, bunch management practices, and important banana pests and diseases at the UH-CTAHR Banana Pest & Disease Image Gallery http://www.ctahr.hawaii.edu/nelsons/banana/. You may also contact Dr. Scot Nelson with banana questions by e-mail or telephone at firstname.lastname@example.org or 969-8265. You may also request free DVD copies of the videos "Banana Bunchy Top in Hawaii" or "Growing Bananas."