Fig tree brown leaves

Prevent Fig Rust: Stopping Rust On Fig Leaves And Fruit

Fig trees have been part of the North American landscape since the 1500s when Spanish missionaries brought the fruit to Florida. Later, missionaries brought the fruit to what is now California, but initial attempts at cultivation were failures. The fig wasp, so necessary to fertilization, was not indigenous to the area. Self-fertilizing cultivars fixed the problem. Today, fig trees can be found throughout the Southern United States and beyond.

The fig’s natural habitat is a warm, dry, Mediterranean type climate and under those conditions, the fig is relatively pest free. However, under more humid conditions and heavier rainfall, figs are more prone to infestation by insects and disease. The most common fig disease, rust, occurs under these conditions.

Identifying Fig Rust on Fruit Trees

Humid air or excessive rain will encourage this fig’s disease. Rust is a fungal growth that is rarely found in dry climates.

The first sign of fig rust on fruit trees are tiny yellow spots on the underside of leaves. The rust on fig leave’s underside then spreads to the upper portion and the spots become reddish brown. Home gardeners often miss early signs of the fig’s disease. Rust spots are only .5 to 1 centimeter across and are easily missed until the infection is severe.

As the fig rust progresses, fig leaves will yellow and fall to the ground. Since rust on fig leaves is usually found in late summer or early fall, the new and tender replacement growth will be at risk for frost damage, which may, in turn, foster winter die back of branches. Though fruit is unaffected by the fungus, rust on fig leaves can encourage premature ripening of the fruit.

How to Prevent Fig Rust

The simplest way to prevent fig rust is to water only the ground under your figs. Rust fungus seeks free moisture on the leaves. Water in the morning so the sun has a chance to dry the foliage.

Careful pruning of fig trees can also help by improving air circulation through the branches, allowing the evaporation of excess water from the leaves of the figs. Rust will over winter in fallen leaves and debris, so fall cleanup is essential to prevent fig rust.

Once you find rust on figs, treatment is difficult as there are very few fungicides that are registered for use on figs. Rust seems to respond best to fungicides containing copper sulfate and lime. Bare trees should be sprayed during the dormant season followed by repeated treatments every two to three weeks. By the time you detect rust on figs, treatment is usually unsuccessful for the current season, but beginning a spray regimen can help prevent recurrence.

While rust on fig leaves and fruit can be a disappointment to home gardeners, it isn’t fatal. Proper cleanup and good air circulation will go a long way to keep the disease at bay and a spray treatment for previously infected trees can stop its recurrence.

What Causes Brown Spots on Fiddle Leaf Fig Leaves? (And How to Treat Them Quickly)

Brown spots on fiddle leaf fig leaves can be frustrating and confusing. It’s disheartening to see brown spots spoiling the beautiful large green leaves of your ficus lyrata. What’s worse, brown spots on fiddle leaf fig leaves can be difficult to treat if you don’t know what is causing them. There are actually four main causes of brown spots.

First, you’ll need to diagnose the cause of your particular type of brown spots. Then you’ll need to figure out how to save your plant before the damage is too great. Here’s how to determine what is causing the brown spots on your fiddle leaf fig plant and how to treat them, including our Fiddle Leaf Fig Root Rot Treatment here.

But before you get started troubleshooting brown spots on fiddle leaf fig leaves, the best way to keep your plant green and gorgeous is to take a deep dive and learn what they need in order to thrive. The Fiddle Leaf Fig Expert, available on Amazon now, is the ultimate top-rated guide to fiddle leaf fig care. Another great resource is The Ultimate Fiddle Leaf Fig Care Webinar, which you can watch for free here. For more advanced fiddle leaf fig care, we even offer a Fiddle Leaf Fig Course. Happy growing!

What Causes Brown Spots on Fiddle Leaf Fig Leaves?

There are four common causes of brown spots on a fiddle leaf fig plant. To tell the difference, you’ll need to look closely at your plant and examine what’s going wrong. Examine your fiddle leaf fig to determine the following:

  • Are the brown spots starting at the edge of the leaf or in the center of the leaf?
  • Are they very dark brown (almost black) or lighter brown (more tan in color)?
  • Are there many spots on each leaf or just one large brown area?
  • Do the brown spots result in the leaves eventually falling off?
  • Are they affecting older leaves near the bottom of your plant or younger new leaves near the top of your plant?

Once you’ve taken a good look at your brown spots and reviewed the characteristics, it’s time to figure out what the cause is. Here are the most common causes of brown spots on a fiddle leaf fig, in order of prevalence:

1. Brown Spots on Fiddle Leaf Fig Leaves Caused by Root Rot

The most common cause of brown leaves on a fiddle leaf fig is due to a fungal infection from the roots sitting in too much moisture. Over-watering and poor drainage causes root rot, which spreads from the roots to the leaves of your plant. The roots of a fiddle leaf fig need to slightly dry out between waterings to function properly. Once the leaves are affected by the fungal infection, they will slowly turn brown and then eventually fall off. Our Root Rot Treatment is formulated to treat this type of infection.

The only way to be certain that your plant has root rot is to remove the pot and inspect the roots. If the roots are brown and mushy, root rot is the culprit. You’ll need to remove the damaged roots and the leaves with brown spots and then repot your plant, taking care not to over-water in the future. However, you can make a diagnosis of root rot and treat your plant without repotting it.

One interesting feature of root rot is that it tends to affect older leaves first, as your plant attempts to save the newer growth that is closer to valuable sunlight. If you notice more brown spots on your older growth near the bottom of the plant, root rot could be to blame.

Another key symptom of root rot is leaves that are dropping. The brown spots may start as small black spots, then will get larger, until the entire leaf drops. If you think your plant has root rot, you can use a moisture meter like this one to take a moisture reading near the bottom of the roots. If your reading is very wet, root rot is likely the cause.

Here you can see classic dark brown (almost black) spots from root rot that caused this leaf to drop.

The classic dark brown spots on this dropped fiddle leaf fig leaf are due to root rot.

Bottom Line:

If you suspect you’ve been over-watering your plant or it has poor drainage, root rot is probably the cause of your brown spots on fiddle leaf fig leaves. Not enough sunlight can make this problem worse. Too large of a pot can also cause your plant’s roots to remain too wet between waterings.

How to Treat Brown Spots Caused by Root Rot

Generally, root rot is very treatable, especially if you catch it early. Since root rot is generally a problem of poor drainage, you’ll want to address your drainage immediately. Make sure you have a well-draining container, fast-draining potting soil, and that you aren’t watering too frequently.

The next thing you’ll want to do is assess the damage. If there are just a few brown spots on the leaves, you do not need to repot your plant. Let your plant dry out for two weeks or more until the roots have adequate time to recover. Remove the affected leaves and make sure your plant has enough sunlight.

If you’re not sure whether your plant has wet roots, you can use a moisture meter to make sure the roots are drying out between waterings. Then, your plant should recover with proper drainage and watering. Take a look at our Ultimate Guide to Watering Your Fiddle Leaf Fig here to learn more about proper watering.

However, if the damage is severe or spreading rapidly, you’ll want to perform root surgery and repot your fiddle leaf fig. Remove your plant from its pot and hose down the root ball. Cut away any brown, mushy roots. Make sure you have proper drainage and repot with fast-draining house plant soil like this. Follow good watering practices in the future to make sure the problem doesn’t recur.

If your fiddle leaf fig still needs help or you would like to protect it in the future, we’ve spent over a year creating a treatment to protect your plant from root rot infections. Our Root Rot Treatment is a natural plant bio-stimulator, enhancing your plant’s existing immune response and promoting growth.

This treatement was designed with input from microbiologists, fiddle leaf fig growers, and botanists. It provides protection against the common Pythium, Pphytophthora, and pseudo-fungi that cause root rot in fiddle leaf figs. It’s gentle and safe for your plant, designed to be used every time you water, along with fiddle leaf fig plant food. Get your Root Rot Treatment today on Amazon.

2. Brown Spots on Fiddle Leaf Fig Leaves From a Bacterial Infection

Bacterial infections can be some of the most stubborn and frustrating problems to fight. If your plant has some of the symptoms of root rot but doesn’t respond to treatments, a bacterial infection may be to blame. This is unfortunately very common in plants purchased from big-box stores. One key characteristic of bacterial brown spots is they are less black and more brown in color. Our Root Rot Treatment treats most bacterial infections in fiddle leaf figs.

Bacterial leaf spot will attack all areas of a plant, including older, larger leaves, but especially young, new leaves. If you see small leaves with stunted growth, yellowing, and brown spots, consider a bacterial problem. Bacteria can also cause many brown spots per leaf, not just one large brown area.

The bacterial spots have irregular margins and can occur anywhere on the leaf, including near the edge of the leaf or where the leaf meets the stem. Bacterial leaf spot actually prefers feeding on new growth, so if your newer leaves are worse off than your older leaves, bacterial leaf spot is likely to blame.

Another telltale sign of bacterial leaf spot in your fiddle leaf fig is a yellowing of the leaves in addition to the brown spots. With root rot, the leaves will typically remain dark green with dark brown spots, but with bacterial leaf spot, the leaf will turn yellow as the brown spot spreads. Both root rot and bacterial leaf spot will cause your leaves to eventually fall off.

Here we see classic bacterial leaf spot on a fiddle leaf fig, with multiple spots throughout each leaf.

Here you can see the bacterial infection is attacking new growth and causing smaller leaves to stop growing.

If you are a pretty experienced plant owner and are confident you’re not over-watering, a bacterial infection may be your problem. They’re very tricky to overcome, even with proper care. If you’ve tried everything and your fiddle leaf fig still has brown spots throughout the plant and is dropping leaves, this is likely the cause. Bacterial infections are more common if you purchase your plants at a big-box store.

How to Treat Brown Spots From a Bacterial Infection

Unfortunately, this is one of the hardest conditions to treat in a fiddle leaf fig. The key is to treat the spots as early as you can before the damage spreads too far. The treatment is similar to treating root rot: you’ll want to make sure your plant’s roots dry out between waterings and that it’s getting plenty of sun.

If the damage is not severe, cut off all of the leaves with brown spots and repot your plant with fresh, sterile soil in a container with good drainage. Give it plenty of light and go easy on watering until it recovers.

One good way to treat bacterial infections is to put your fiddle leaf fig outside in the shade to recover, depending on your climate. Fresh air, plenty of sunlight, and warm conditions can help your plant recover. Just be sure that your plant is protected from direct sunlight and doesn’t get too cold (less than 50 degrees) or too hot (greater than 95 degrees).

However, if your plant has more than 50% of the leaves affected by brown spots and the condition is spreading, you may be better off starting over. Discard the plant and start fresh with a healthy specimen. You may want to contact the store where you purchased your plant to see if they’ll replace it.

Compare these two classic examples of fungal vs. bacterial root rot. The fungal is the black circular dots, and the bacterial is the brown that do not have as much of a circular pattern but more of a spreading pattern.

3. Brown Spots on Fiddle Leaf Fig Leaves Due to Dryness

Dry plant brown spots are somewhat easier to diagnose, as they will have dry tan or lighter brown areas that start at the edge of the leaf and cause the leaf to curl. Your plant will overall look wilted or dry at times and the soil may have receded from the pot (shrinkage). This can cause the water to run between the pot and the soil and never reach the root ball.

If you’ve forgotten to water your plant on a regular basis or if it’s in a very dry environment, brown spots may occur. The relative humidity for your plant should be between 30-65%, so if your home humidity is much lower or your plant is near a heater, you may need to create more humidity for your fiddle leaf fig by misting or changing locations.

Symptoms of dryness on a fiddle leaf fig tree

This leaf completely dried out while outside on a 110-degree day.

Bottom Line:

If you know you’ve missed a few waterings or your plant was in very hot conditions and your plant looks dried out, lack of water is probably the cause of your brown spots. Soil shrinkage is a dead giveaway of dryness.

How to Treat Brown Areas on a Dry Plant

If you notice soil shrinkage, you’ll want to repot your plant to make sure your root ball is getting adequate water. If your fiddle leaf fig is in a very dry environment or near a heater, consider moving it to another location. Water regularly (try once a week) and monitor your plant to make sure it’s getting enough moisture. You can try misting every one to three days or using a humidifier (we recommend this one) near your plant if your home is very dry, though this is not typically necessary unless a heater is running near your plant.

4. Brown Spots on Fiddle Leaf Fig Leaves From Insect Damage

Insect damage in a fiddle leaf fig plant is thankfully less common. The giveaway to diagnose insect damage is small dark spots that damage the plant leaves that turn into holes in the leaves. This happens more commonly in the new, tender growth. You can also look out for any insects on your plant (use a magnifying glass) or any white or gray insect webs. If you find any evidence of insects living on your plant, you’ll know this is the cause of your brown spots.

Insect damage can start as very small black or reddish spots that turn to holes.

Here’s evidence of mealy bug infestation on fiddle leaf fig plant.

Insect infections are rare but leave obvious clues. Use a magnifying glass to look for webs or insects on your plant.

How to Treat Brown Spots from Insect Damage

Insect infestations are easy to treat. Use a neem oil product designed for houseplants. Take your plant outside if possible, as the neem oil has an unpleasant smell that lingers. Spray all the leaves of your fiddle leaf fig thoroughly. Turn each leaf to spray the underside and don’t forget where the leaf meets the stem. Wait two weeks, inspect again, then repeat the spraying process if needed.

Keeping Your Fiddle Leaf Fig Healthy in the Future

Now that you’ve diagnosed the cause of your fiddle leaf fig plant’s brown spots and you have a Root Rot Treatment, you’ll want to make sure you keep your plant healthy in the future. Make sure your plant has proper drainage, follow watering best practices, and make sure to fertilize with Fiddle Leaf Fig Plant Food each time you water to keep your plant strong.

How to Learn More About Brown Spots on Fiddle Leaf Fig Leaves

Are you still confused? Check out our ultimate photo identification guide for brown spots on a fiddle leaf fig here! Another great resource is The Ultimate Fiddle Leaf Fig Care Webinar, which you can watch for free here.

Check out the post about How to Treat and Prevent Root Rot in Fiddle Leaf Fig Trees. This post also includes a helpful video.

For more information, join the Fiddle Leaf Fig Club, download the Ultimate Guide to Watering Your Fiddle Leaf Fig, and ask the Fiddle Leaf Fig Doctor a question!

Read The Fiddle Leaf Fig Expert, your complete guide to growing healthy fiddle leaf fig plants. The book is available in full-color paperback or Kindle edition on Amazon now!

To ask questions about your brown spots on fiddle leaf fig leaves and share your plant’s story, click to join our community on Facebook: Fiddle Leaf Fig Plant Resource Group.

Rust spots on your leaves

Rust beginning to form on leaf

There are fungi that can attack your fig tree leaves. If you find large brown areas, or with a mold growing – immediately cut off the affected leaves and discard them so that the fungus will not spread throughout. Take note that there is a very dangerous common leaf mold pathogen called Rust. It mainly affects potted plants and can spread to your house plants. It will begin with small brown spots and gradually spread through the leaf. When you discover this type of infection, cut the leaf off and burn it.

This fungus generally appears following long rainy days without a chance for the leaves to dry under the sunshine. If you touch an infected leaf, be sure to wash your hands thoroughly before handling other plants. Sometimes if you see sporadic brown spots, on a few leaves don’t be alarmed. Rust will not kill your tree and you don’t have to remove all of the leaves. It’s best to monitor the brown spots carefully to assess the situation before of jumping to conclusions. Sometimes small brown spots can indicate that the plant suffered from lack of water following a yellowing of the leaves.

Solution

There are anti-fungal products available, though the most effective means of stopping the spread of this infection is by burning the leaf. I use a small propane torch with the leaf on a non-flammable surface while the leaf is still green.

Common Name

Pacific Pests and Pathogens – Fact Sheets
Fig rust (307)

Fig rust

Scientific Name

Cerotelium fici; previously known as Kuehneola fici, and Uredo fici.

Distribution

Widespread. In warm humid tropics and sub-tropics. Cerotelium fici is recorded from Australia, Fiji, Guam, New Caledonia, New Zealand, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, Vanuatu, Wallis & Futuna.

Hosts

Figs (Ficus species), breadfruit (Artocarpus species), and paper mulberry (Broussonetia papyrifera).

Symptoms & Life Cycle

A fungal disease, known as a “rust”, causing early leaf fall. At first a yellow spot on the top surface of the leaves, then small raised spots, or pustules, on the lower surface. They are scattered over the leaves, grouped around the edges, or follow lines taken by dew as it runs across the leaf blade. The pustules also occur on the fruit. When mature, they are pale reddish-brown, circular, 0.5 mm diameter. The spots on the top surface, above the pustules, turn dark, angular, and merge. The leaves yellow and fall.
Spread occurs when spores are splashed short distances from one leaf to another, or between plants; spread over long distances occurs as spores in wind. The spores require water on the leaf surface for germination and infection.

Impact

On edible figs, defoliation and yield loss can be significant, and immature fruit fails to ripen.

Detection & Inspection

Look for yellow spots on top surfaces of leaves, later merging and becoming dark and angular. Look for large numbers of tiny (0.5 mm diameter) pustules on the undersides.

Management

CULTURAL CONTROL
A difficult disease to control by cultural techniques once trees become infected. There are different varieties and they should be tested, although none appear to have good tolerance and acceptable market fruit qualities.

  • It is importance to reduce the time that leaves are wet to stop spore germination and infection. Do the following:
    • Increase air movement in the canopy by regular pruning of branches.
    • Avoid overhead irrigation, instead use trickle tape to apply water at soil level.
    • Do not plant beneath shade, especially in high rainfall areas.
    • Weed to reduce the humidity around the trees.
    • Do not plant in areas that flood or where there is free-standing water after rains.
  • Ensure trees have adequate nutrition with the application of fertilizer or manures so that new healthy leaves will be produced as quickly as possible after defoliation by the rust disease.

CHEMICAL CONTROL
If fungicides are required use mancozeb or copper. The frequency of application needed to obtain control is not reported, nor are the economics of treatment.

AUTHORS Grahame Jackson & Eric McKenzie
Information from Verga A, Nelson S (2014) Fig rust in Hawai’i. College of Tropical Agriculture and Human Resources. University of Hawai’i at Manoa. Honolulu. Photos 1-4 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Cerotelium fici PaDIL – http://www.padil.gov.au.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

This fact sheet is a part of the app Pacific Pests and Pathogens

The mobile application is available from the Google Play Store and Apple iTunes.

Android Edition Apple iOS Edition

By Kerry Stober

Q: The leaves on my fig tree are covered in brown spots and some are falling off. What can I do?

A: The most likely culprit of these symptoms is a common fungal disease called Fig Rust, caused by the fungus Cerotelium fici. The good news is this disease only occurs on the leaves and should not damage the fruit. Rust usually attacks younger leaves first. You may start to see yellowish spots, which then get bigger and turn into a brownish color all over the leaves. There also can be raised brown spots or lesions on the underside of the leaves. Over time, these leaves will turn completely yellow, followed by becoming brown and curled, and then falling off of the plant. Rust usually begins appearing in the late summer and, when severe, it can cause the tree to lose leaves very rapidly. This disease and loss of leaves will not kill the tree, but when it occurs many seasons in a row, you may see a reduction in yield of fruit. Rainy weather can cause this disease to be more prevalent, and unfortunately we had a particularly rainy summer followed by a series of wet tropical storms. Figs produce their best fruit in a climate with warm dry summers and cool wet winters.

Spraying to control this disease presents a bit of a problem, as there are no fungicides currently labeled for figs in Alabama. As a result, your best methods of control are going to be using cultural methods of sanitation and pruning. Prune out infected areas and rake up older dropped leaves, disposing of them by bagging or burning. You can also prune the tree to open up areas to more airflow throughout, as moist enclosed areas are more likely to become diseased.

Fig rust.

These methods will not completely defeat this disease, but can reduce its effect on your plant’s overall health. If you water your fig plants regularly, try to avoid spraying the leaves, as we learned earlier water plays a large factor in fig rust appearance. You can also add mulch around the tree and fertilize in the spring to help keep it healthy.

The fig is a hardy tree with relatively few pest and disease issues. Keeping the area around your tree clean plays a huge role in keeping their most common pests at bay. Hopefully by following the methods, you will see less spots on your tree next year!

“Garden Talk is written by Kerry Stober of the Alabama Cooperative Extension System (ACES). She is housed at the C. Beaty Hanna Horticultural and Environmental Center, which is based at the Birmingham Botanical Gardens. This column includes research based information from land-grant universities around the country, including Alabama A&M and Auburn Universities. Email questions to Kerry at [email protected] or call 205-879-6964 x19. Like us on Facebook. Follow us on Twitter. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University), is an equal opportunity educator and employer. Everyone is welcome!

Fig Fact Sheet

  • Family: Moraceae (mulberry)
  • Genus: Ficus
  • Commercially important species:
    Ficus carica subgenus Eusyce (only member of genus cultivated for fruit)
  • Description: deciduous tree; subtropical; soft, pithy wood; bark is generally smooth and free of fissures, however ‘burrknots’ often occur on lower trunk and roots, nodal swellings form under and on both sides of leaf scars; leaves are large, petiolate, 3-7 lobed to almost entire (leaves aid in cultivar identification); bears morphologically unusual fruit called ‘syconium’ which is almost entirely vegetative peduncular tissue (true fruits are tiny pedicellate druplets within); Gynodioecious with two distinct forms: monoecious nonedible capri fig which serves as a pollenizer, and a pistillate edible fig; pollination achieved by fig wasp (Blastophaga psenes L.), which colonizes the syconium of the capri fig in a symbiotic relation; lateral bearing; 5-year generation time.
  • Origin: Southern Arabia (native to semi-desert regions.
  • History of cultivation: Millennia
  • Current major production area: California ranks second after Turkey, and ahead of Spain, Greece and Portugal. Production from 1996 was 14,000 tons.
  • Site requirements: Semi-desert. Cultivation limited by winter cold more than summer heat; low relative humidity (<25%); intense light; high summer temps. (32-37 C); moderate winters (temps. <-1 C are limiting); avoid late fall rains (damages fruit); spring winds interfere with wasp pollination and produce scarred fruit.

Cultivation in California

  • History: Spread with Franciscan Missionaries. First figs planted in California in 1769 in the gardens on the mission at San Diego. In the 1850s, American settlers imported a wide variety of figs from the east coast and Europe which led to the first established orchards. By 1867 there were over 1000 acres (400 ha.) in the Sacramento Valley.
  • Yield: varies with cultivar from 1.25-3.7 t/ha (industry average)
  • Cultivars: Smyrna (Calimyrna, only prominent Smyrna type);Common: Kadota, Mission, Conadria, White Adriatic.
  • Rootstocks: None in use; all varieties own-rooted.
  • Propagation: Young figs are gown from rooted cuttings.
  • Spacing: 30-40 ft. on the square (old spacing: Mission orchards). 20-22 ft. square for newer varieties. 15-30 ft. hedgerows.
  • Irrigation: On level ground: flooding and furrow are used; on level areas, sprinklers and drippers are used.
  • Training System: modified open-center system.
  • Nutrition: Nitrogen is the only nutrient applied regularly (2.2-2.5% of the dry leaf weight); 20-40 lbs/acre nitrogen is an average application rate. Other nutritional deficiencies are rare. Figs are more likely to suffer toxicities from sodium, boron, or chloride.
  • Harvesting: Edible fig cultivation may produce 1 to 2 crops per year. A small amount of figs are marketed fresh, these are hand picked. Most figs are harvested as a dried crop. These are allowed to dry on the tree and fall to the ground. Dried figs are mechanically swept into windrows and collected. Harvests are repeated at 2-3 week intervals, fumigated, and sun dried or dehydrated to 17% moisture or less.
  • Marketing: The California Fig Marketing Order determines grade and quality. Marketing depends on the variety: Calimyrna are used for dried fruit or paste: Kadota and Adriatic are used primarily for paste; Mission figs are used for dried fruit, paste or juice of concentrate. California produces 100% of domestic dried figs.

Prepared by Steven Soby 1995, updated 1997

The story of the fig and its wasp

Posted By Katie Kline on May 20, 2011 |

Inside the rounded fruit of a fig tree is a maze of flowers. That is, a fig is not actually a fruit; it is an inflorescence—a cluster of many flowers and seeds contained inside a bulbous stem. Because of this unusual arrangement, the seeds—technically the ovaries of the fig—require a specialized pollinator that is adapted to navigate within these confined quarters. Here begins the story of the relationship between figs and fig wasps.

The queen of the fig wasp is almost the perfect size for the job—except, despite her tiny body, she often times will lose her wings and antennae as she enters through a tight opening in the fig. “The only link the fig cavity has to the outside world is through a tiny bract-lined opening at the apex of the fig, called the ostiole, and it is by means of this passage that the pollinating fig wasp gains access to the florets,” as described in Figweb, a site by Iziko Museums of Cape Town.

Once inside, the queen travels within the chamber, depositing her eggs and simultaneously shedding the pollen she carried with her from another fig. This last task, while not the queen’s primary goal, is an important one: She is fertilizing the fig’s ovaries. After the queen has laid her eggs, she dies and is digested by the fig, providing nourishment. Once the queen’s eggs hatch, male and female wasps assume very different roles. They first mate with each other (yes, brothers and sisters), and then the females collect pollen—in some species, actively gathering it in a specialized pouch and in others, accumulating it inadvertently—while the wingless males begin carving a path to the fig’s exterior. This activity is not for their own escape but rather to create an opening for the females to exit. The females will pollinate another fig as queens. The males will spend their entire lifecycle within a single fruit.

While this tree-wasp relationship may not be common knowledge to all fig-eaters, it is well-known to biologists as one of the most solid examples of coevolution. “One of the best activities to do with an introductory biology class is to pass around Fig Newtons, let them take a bite and then tell them the story of the fig wasp life cycle,” said tropical plant ecologist Greg Goldsmith as we recently hiked through a cloud forest in Monteverde, Costa Rica. “It’s a fascinating story.”

After learning the story of the fig and its wasp, the most common question is, “Do we eat wasps when we eat figs?” The short answer is that it depends—that is, some figs are parthenocarpic, meaning they are seedless. According to a 2006 Science study, these domesticated sterile figs could be evidence of the first use of horticulture in human history. The researchers discovered carbonized fig fruits in “an early Neolithic village, located in the Lower Jordan Valley, which dates to 11,400 to 11,200 years ago”—nearly one thousand years before cereal domestication. The commercially cultivated fig tree is usually a female parthenocarpic variety of the ancient common fig (Ficus carica) and does not need pollination to produce fruit.

On the other hand, those species of fig trees that rely on wasps for pollination will likely contain bits of wasps in the fruit. In general, frugivores, like monkeys, birds and humans, are most attracted to the fruit once it ripens; at this stage, the wasps have already mated and escaped to find another fig. However, the wingless male wasps stay behind and die once they have mated and completed their tunneling duty. Therefore, animals, including humans, who eat figs that have not been commercially cultivated likely consume dead wasps.

Each species of Ficus has a corresponding specialized species of wasp that fertilizes it. Wasps that actively collect pollen in pouches have a responsibility to uphold in the mutualistic relationship. That is, scientists have found that there are consequences for the queen if she does not uphold her part in the relationship. “n passively pollinated pairings, the tree almost never aborted its fruit, and the wasp always carried pollen,” according to a Cornell University press release of a recent study. “However…in actively pollinated pairings, where the wasp needs to expend energy to collect pollen, the tree dumped the fruit and killed the offspring when the wasps did not carry pollen.” In other words, if the pouched wasps did not deliver the pollen they are adapted to carry, the fig tree dropped those fruits—essentially killing the wasp eggs inside. If the fig did not get pollinated, the queen did not get the protection for her eggs inside the ripening fruit.

Greg Goldsmith was leading us—that is my boyfriend and I—to a massive strangler fig that had enveloped another tree at one point in its lifecycle. The host tree had since died and decomposed completely. In its place, the strangler fig—likely over hundreds of years old—had woven itself into a hollow, rooted cave.

The image that came to mind was paper-mache—laying gooey slabs of paper over a balloon to create a laced pattern and then popping the balloon, leaving behind a dried paper basket. The craft project takes only a couple hours, but the strangler fig’s handiwork took decades as the host tree rotted away. Standing at the impressive roots, the full size of this Ficus was hard to distinguish as it was masked within the canopy. It jutted out from the side of a large, steep hill that had been continually carved by the stream and waterfall below—the tree seemed suspended at a 45 degree angle over this sizeable ravine. The reason this particular tree’s canopy was difficult to spot is likely because it started its growth in the canopy of another tree.

While wasps are required to pollinate fig trees, seed dispersal is another matter altogether. Birds, monkeys and other animals eat the tree’s figs and then move along to perch on other trees. When the animals defecate, the seeds stay behind in the branches and germinate. The roots of the fig tree grow slowly to the ground, and once they are anchored, the tree rapidly grows in size. The fig tree competes with the host tree for soil nutrients and strangles its canopy.

This particular fig tree was just big enough to allow one person to climb to the top. There, the roots split in a way that allowed the climber to look straight down the ravine. Starting its growth in the canopy of another tree enabled this strangler fig to reach incredible heights.

Thanks to Greg Goldsmith who shared the ecology of Monteverde, Costa Rica.
Photo Credit: Rainer Zenz (fig) and Greg Goldsmith (strangler fig)

Kislev, M. (2006). Early Domesticated Fig in the Jordan Valley Science, 312 (5778), 1372-1374 DOI: 10.1126/science.1125910

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