Lime trees (Citrus latifolia) are native to central and eastern Asia. Many cultivars have been bred and selected over time for strengths like vigor, productivity, fruit quality and disease resistance. Blossom-end rot syndromes are caused by several potential culprits. Climate variables, nutrient deficiencies, rough handling and harmful fungi can all play a part. Proper cultivation practices and appropriate fertilization can mitigate blossom-end rot concerns. In some cases, fungicidal treatments may be indicated.
Black Rot
Alternia alternata is a fungus that affects citrus trees, including limes. It is commonly known as black rot or navel end rot. Early fruit coloring and fruit drop may indicate infection. After harvest, the fruits’ blossom ends may develop a dark, sunken spot. The fungus is harbored on dead citrus plant tissue and grows in wet weather. Infected fruit should be removed. Proper tree maintenance, including pruning of non-productive or dead stems and balanced irrigation and fertilization, can help keep your lime tree healthier and more resistant to this infection. For severe infections, you can treat lime trees during their dormant season with Bordeaux mixture (copper sulfate, lime, and water) or a chemical orchard fungicide.
Stylar-End Breakdown
Stylar-end rot appears on the stylar (bloom) ends of lime fruits, eventually destroying the entire fruit. It usually occurs during the hot months of summer when fruits have become turgid with water. Mature fruits are more apt to develop this syndrome. Internal juice sacs are ruptured by rough handling during harvest, especially if harvested in the morning. Gentle handling of fruit and harvesting during afternoon hours can diminish the threat. Cooling the fruits to between 50 and 55 degrees Fahrenheit while controlling humidity at 90 to 95 percent is also recommended.
Lime Cultivation
Citrus trees prefer growing in well-drained, slightly acidic loam or sandy loam soil. They may flounder if grown in dense clay or soils that otherwise remain boggy. Balance drainage and moisture concerns by amending problem soils with organic matter like finished compost, aged manure and chopped pine bark prior to planting citrus trees. Alkaline soils (pH greater than 7.0) and those that are too acidic (pH less than 6.0) may require amendment with sulfur or lime, respectively. Weak lime trees grown in poor soil are more prone to diseases and poor health.
Essential Nutrients
Citrus trees are known as heavy feeders. They require consistent and regular amounts of essential nutrients to flourish. Without them, they may be more prone to rot syndromes when stressed. Supplemental fertilization with a balanced citrus food is recommended. Nitrogen supplements can be applied in February, July and September. Use smaller amounts on young trees, increasing them slightly in the third year. A small amount of a phosphate compound can be mixed into the planting hole for lime trees and repeated thereafter every three to four years.
Blossom end rot is the result of a lack of calcium in the fruit tissue. This calcium deficiency can be caused by a lack of calcium in the soil or by the plant’s inability to effectively absorb calcium from the soil. Here are a few simple ways to prevent and/or reduce the impact of blossom end rot in the garden (most of these things you should be doing anyways!):
Check the pH of your soil. Proper pH range for most fruiting vegetables is between 6.3 and 6.9. Maintaining the proper pH will help crops absorb nutrients from the soil.
Maintain even watering cycles through the season. Most often, blossom end rot is a result of water stress which disrupts the plant’s ability to draw calcium up from the soil. Keeping the soil adequately and consistently moist can eliminate this problem.
Add bone meal to your soil. Bone meal, known primarily for its supply of phosphorus, but also supplies calcium. Bone meal feeding supplements are a long-used tool to prevent blossom end rot in long-season fruiting crops.
Add dolomitic lime. Dolomite lime supplies both magnesium and calcium to the soil (in addition to adjusting soil pH). If used in high doses or too frequently, it can lead to nutrient imbalances in the soil, but it can also be highly effective in supplying fruiting crops with adequate calcium to support healthy fruit production.
If you plan to add organic amendments like bone meal and dolomite lime to the soil every season, be sure to take soil samples regularly to guard against nutrient imbalances and over fertilization (which can lead to their own set of crop health issues).
Here are some other links that may help:
https://www.ecoorganicgarden.com.au/problem-solver/blossom-end-rot/
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19326
https://www.pe.com/2016/03/18/master-gardener-fight-blossom-end-rot-with-calcium/
