Help! My Tree Is Dripping!
If you notice sticky stuff dripping from your trees, you’re not alone. This is one of the most common issues we receive calls about, so we decided to dedicate our inaugural blog post to it. Here are several common culprits, which can occur individually or together:
Aphids
Aphids are common critters that feed on leaves and stems. They are often found in abundance - they can produce as many as 20 generations per year in their asexual reproductive stage! Aphids are not harmful in normal numbe rs, but large populations can cause damage.
Aphids suck sugars out of plant tissues, and because their digestive systems are very inefficient, much of that sugar comes out the other end as honeydew. Honeydew is edible (and delicious!), and it is sometimes used by ants and bees as a food source.
Unfortunately, honeydew’s sugar content also makes it quite sticky, which can be a nuisance in high-traffic areas. To make matters worse, one of the organisms that eats it is sooty mold, a potentially allergenic fungus.
In most cases, aphid infestations are caused by tree stress, usually from insufficient water. But some plant species are more susceptible to aphids than others, and problems like girdling roots and overfertilization can also contribute.
Increasing irrigation usually reduces or eliminates the problem. Spraying the tree’s canopy with water can also dramatically reduce the aphid population. Honeydew with or without sooty mold can be removed easily from most surfaces with plain water or mild soap.
Insecticides aren’t recommended, as they can trigger a mite population explosion - besides removing competition from insects, some actually stimulate mites’ reproductive systems. And what are the symptoms of a mite infestation? Similar to an aphid infestation, but with tiny, sticky silk webs!
Nitrogen-heavy fertilizers are also best avoided, as they can both contribute to drought stress and increase aphid reproduction (and they usually aren’t needed anyway - more on that in a future post).
Drippy nut
If you’ve ever seen clear or brown dollops of liquid under your coast live oak or interior live oak, it is most likely drippy nut disease (Brenneria quercina, syn. Erwinia quercina). This is a bacterial infection of acorns, spread by insects. It is usually most noticeable from spring to autumn.
Fortunately, although the drip can be a nuisance, the tree’s health is unaffected. The sticky substance is usually fairly easy to wash off. In some situations it may be beneficial to set up a shade cloth to intercept all or part of the drip. To our knowledge, no reliable chemical control exists.
Sap
Most drip from trees is not actually sap! If you notice a thick, yellow substance that’s very hard to remove, it is most likely sap. But if it doesn’t match this description, it’s probably something else.
The most common cause of sap drip we see is pruning. Certain trees, especially conifers, figs, and mulberries, produce huge amounts of sap when pruned in warm weather. This is just because sap flows most freely in warm weather, and it is not a cause for concern. It can certainly be messy, though, so we recommend pruning these trees in cool weather.
Certain pests and diseases can also cause trees to exude sap. The most common ones we see are pitch canker (Fusarium circinatum), red turpentine beetle (Dendroctonus valens), and Cytospora canker (Cytospora spp.).
The treatment and prognosis for these issues depends on many factors, mainly the tree’s overall condition and the extent of the damage. Increased irrigation is usually recommended, and certain insecticides and fungicides can sometimes help.