Kawika asks: The limes on my tree are ripening but they have a kind of scaly growth on the skin. What is this? Is there a treatment for it? Will the limes be edible when ripe?
Kawika asks: The limes on my tree are ripening but they have a kind of scaly growth on the skin. What is this? Is there a treatment for it? Will the limes be edible when ripe?
Tropical Gardener Answer: It sounds like you have citrus scab on your limes. This disease is caused by the fungus Elsinoe fawcetti. Though this fungal disease causes ugly warty scabs to appear on the skin of the fruit, it will not affect the edibility of your limes.
If it is any comfort, know that this disease is a common issue for citrus in Hawaii. Only a few species, mostly oranges and grapefruits have shown natural fungal immunity. Several other citrus cultivars show some resistance, but most citrus are susceptible.
Once the disease is widespread on a single tree or on several on your land, low-toxic or organically approved fungicides can help curb its spread. The best remedy, however, is prevention of the problem in next year’s crop. Wet weather encourages this pathogen’s growth. During our wet summer season, the scabby pustules may appear on a plant’s leaves and twigs and can move to the fruit as it develops.
The fruit is most susceptible to infection in the first three months of development. The pustules on a diseased plant produce spores that can spread through overhead irrigation water or splashing rain. Infection usually occurs when plant tissue is exposed to the pathogen and remains wet for at least three hours.
The disease can be prevented in the future or treated in its early stages in several ways. Reducing the humidity in and around citrus trees is helpful. If possible, grow the trees in dry, sunny locations. Intercropping the trees with plants that are not hosts to this fungal disease can also help reduce the likelihood of infection. Managing tall weeds that hold moisture near the trees is also helpful. Keeping young citrus plants under cover to protect them from splashing rain and watering them at the soil level rather than overhead can also lessen the likelihood of spreading the fungus. Pruning the trees periodically to promote air circulation also helps lower the humidity in the canopy and can make complete coverage of fungicidal sprays possible.
Several fungicides can help control this disease. Many of them as well as more information on the disease can be found in the UH publication at https://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-60.pdf. Quite a few of the products on the list are approved for use in organic systems. In some cases three fungicide applications during fruit development may be needed. To prevent infection of the fruit you need to begin spraying just as the tree starts to flower, when it puts out its annual flush of leaves. A second application should be done when the flowers fade and the petals fall. The third spraying should be done several weeks later, when fruit formation begins.
Though your fruit may be unattractive this year, preventing the spread of the scab to next year’s crop can provide you with some lovely looking limes in 2017. Removing all of the infected fruit in this year’s crop and juicing or otherwise using it will definitely reduce the spore count in the area and lessen the probability of future infection. Be sure to dispose of the infected rinds off site.
Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook. Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.
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. Water and snacks provided. Call Peter at 323-3318 for more information.
Sunday: “2nd Annual Going Nuts for the Holidays Festival” from 10 a.m. to 7 p.m. at the Old Airport Pavilion. Celebrating local coco and mac nuts. A zero waste event. Free to the public.
Farmer Direct Markets
Wednesday: “Sunset Farmers Market” 2 p.m. to sunset at the north makai corner of the Kmart parking lot.
Wednesday & Friday: “Ho’oulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort & Spa at Keauhou Bay
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. – 2 p.m. at Amy Greenwell Garden in Captain Cook
Tuesday–Saturday: “U-Pick greens and produce” 10 a.m. to 4 p.m. Tropical Edibles Nursery, Captain Cook.
Plant Advice Lines
Anytime: konamg@ctahr.hawaii.edu
Tuesdays & Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892
Mon., Tues. & Fri: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu
Photos:
(Picture courtesy www.ctahr.hawaii.edu – The warty bumps on the skin of citrus fruit is often evidence of a fungus disease called citrus scab.
2. Citrus scab on limes & leaves from www.ctahr.hawaii.edu – “Citrus scab is a fungal disease that is identified by the warty scales that appear on the leaves as well as the fruit of many citrus varieties.”