Julie asks: My mango tree put out tons of fruit last year. This year’s flowers are fewer, and they look terrible. The fruit that does start forming is dropping off. What’s going on and what can I do about it?
Tropical Gardener answer: You may simply have an alternate year production issue. However, if your flowers match photos of mango anthracnose, you may have a disease problem that you should address right away.
Many fruit trees fall into a pattern of heavy production one year and little or none the following year. This pattern is often repeated year after year. As long as weather conditions, as well as pruning, fertilizing and watering practices, are annually consistent, not much can be done to alter the tree’s bearing pattern.
If, on the other hand, mango anthracnose has infected your flowers or fruit, swift action is required to mitigate its negative effect on this year’s crop. The University of Hawaii College of Tropical Agriculture and Human Resources has a publication “Mango Anthracnose (Colletotrichum gloeosporioides)” by Scot Nelson. Check it out at www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-48.pdf to see photos and learn more about the disease.
The disease thrives in warm, moist, humid conditions. The recent rains during mango flowering have set up ideal conditions for the anthracnose fungus to flourish. Spores of this fungus are usually dispersed by splashing rain or irrigation water and can attack leaves, twigs, flowers and fruit. Evidence of anthracnose can start with black specks on twigs or flowers that eventually cause the flower panicles to blacken and disintegrate. The flowers that do survive may produce infected fruit that drops. In some cases, the infection only appears on the fruit as it starts to mature. You may see black spots that enlarge as the fruit ripens or a kind of “tear stain” of dry, dead skin down the length of the fruit.
Preventing anthracnose is obviously the best practice. Growing mangoes in a sunny spot at lower, dryer elevations with less than 15 inches of rain per year can help. Planting the trees far apart, or intercropping with other species, can prevent the fungus spores from spreading. Planting resistant cultivars like Carrie, Earlygold, Julie (dwarf) or Keitt can also help prevent infection. Annual pruning to open up the canopy and remove low branches can help. Also, keeping the area around the trees clear of tall weeds, fallen debris, old fruit or any plant parts that may have the fungus is helpful.
Low toxic fungicides can also be used to control anthracnose. Those containing clarified neem oil or wettable sulfur have shown good results. Spraying once when flowers appear, and at periodic intervals while the fruit is ripening, should allow you to get some harvest this year. Whatever you use, be sure it is registered for use on mango anthracnose and follow the directions carefully.
Some questions that appear here were originally directed to Kona’s Certified Master Gardeners. You may contact them with questions at konamg@ctahr.hawaii.edu.
Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.
Gardening Events
Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Call Peter at 323-3318 for more information.
“Living Laboratory: Forest Restoration and Growing Edibles” from 11 a.m. to noon at Kailua-Kona Public Library at 75-138 Hualalai Road with Calley O’Neill, landscape designer. Presentation on living lab at Palamanui campus. Free.
“K’au Coffee Festival Hoolaulea” from 9 a.m.to 5 p.m. at Pahala Community Center. Entertainment, food, crafts, coffee tasting. Free. Farm and mill tours available. More information at kaucoffeefestival.com/events.
Sunday: “Ka’u Coffee College” from 9 a.m. to noon at Pahala Community Center. Free. Talks by renowned coffee experts. Final event of Ka’u Coffee Festival.
Farmer Direct Markets
Wednesday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at the Sheraton Kona Resort and Spa at Keauhou Bay
Wednesday: “Sunset Farmers Market” 2 p.m. to sunset at the north makai corner of the Kmart parking lot.
Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center
“Kamuela Farmer’s Market” from 7 a.m. to noon at Pukalani Stables
Sunday: “South Kona Green Market” 9 a.m. to 2 p.m. at Amy Greenwell Garden in Captain Cook
Tuesday to Saturday: “U-Pick greens and produce” 10 a.m. to 4p.m. Tropical Edibles Nursery, Captain Cook.
Plant Advice Lines
Anytime: konamg@ctahr.hawaii.edu
Tuesdays and Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892
Mondays, Tuesdays and Fridays: 9 a.m. to noon at UH-CES at Komohana in Hilo 981-5199 or himga@hawaii.edu