Carolina Buckthorn Recovery

The Carolina Buckthorn seems to be recovering from its earlier infestation of Asian Soybean Aphids.  Those plants that hosted just a few aphids appear almost normal.

Plants that were hardest hit still show the curled leaves that afforded shelter to the aphid colonies. 

Despite their odd appearance, the damaged leaves remain alive and green.  I assume they are still performing their photosynthetic duties, but at a much less efficient level.

New leaves are developing in a normal manner.  It’s encouraging to see that they aren’t yet showing any signs of drought stress.  These plants are growing on an extremely dry site and most of the other plant species in the area are looking distinctly wilted.

Presence of the Asian Soybean Aphids on the Carolina Buckthorns is a fairly recent phenomenon.  I imagine now that they are here, the aphids will continue to be an annual event.  Being at the extreme northern edge of their range already puts the buckthorns under a certain amount of stress.  Dealing with annual aphid damage will certainly add to that stress.  I’m wondering how long it will be before I begin seeing a dieoff of Carolina Buckthorn.

I took this as a bit of positive news.  A few of the plants are producing a bit of fruit.  Of course I’m also aware of the fact that stress can act as a stimulus to produce more fruit before death occurs.  I guess I’ll just have to wait a few years to see how things are trending.

Asian Soybean Aphid

The Carolina Buckthorns are once again under attack by Asian Soybean Aphids, Aphis glycines.  I first encountered the aphids last year when they were found on a few Carolina Buckthorns.  This plant that I found yesterday is typical of the worst condition I found in July of 2011.  There are some yellowed leaves and a few tightly curled leaves.

The aphid damage is much more severe and widespread this year.  Entire branches are showing curled leaves.  Carolina Buckthorn is an uncommon plant in Ohio with a range that just catches the southern edge of the state.  Its primary threat has always been extreme low winter temperatures.  I frequently monitor the plants to see how they are growing, so I am certain that the aphids were not a problem before last year.

This is what’s inside the curled leaf.  Aphids busily feed and reproduce within the protective folds of leaf.  Ants visiting the aphids to collect honeydew, provide another measure of security.  Asian Soybean Aphids are a non native species that was first discovered in the United States about 12 years ago.  They became a species of concern because of their use of Soybeans as a summer host plant.  Large populations of these aphids can cause severe damage to soybean plants and devastate yields. 

Soybeans are annual plants that only exist for a limited time each year.  In order to sustain themselves during the non soybean season, the aphids utilize a second host for the winter.  Non-native Buckthorns, Rhamnus species, were the original preferred winter host.  It became a case of one invasive species damaging another.  Now it’s obvious that at least one native Buckthorn is a suitable host for the Asian Soybean Aphid.

Aphids feeding on the buckthorn cause the distorted, curled leaf formation.  Judging by what I found, it appears that the leaves curl prior to being invaded by the aphids.  The leaves remain green even after intensive feeding has taken place, so the leaf functions may continue to provide nutrients to the plant.

Aphids on the buckthorn come from eggs laid the previous fall.  These aphids are all females that reproduce by giving live birth.  The youngsters begin producing their own young when about a week old, so it doesn’t take long for a population explosion to occur.  Eventually, winged females are produced and these fly off to find soybean plants on which to start a summer colony.

The aphid spends most of its time attached to leaf veins by way of its tubular mouth.  Consuming sap and producing babies is the life of the aphid.  After producing many generations of aphids on soybean plants, male and female winged adults search out buckthorns where mating occurs and eggs are laid.  Aphids in the wind may travel hundreds of miles, so the proximity of soybean fields is not an indicator of whether or not the buckthorns will be found by aphids.  The eggs overwinter and the whole cycle begins anew.

The winged individuals apparently don’t all develop on the same schedule.  This population looks to have everything from winged adult to newborn infant.  I’ll have to wait to see what level of survival threat the aphid poses to the Carolina Buckthorn.  Since the aphids will leave the buckthorn in early summer, the buckthorn may have time to regrow with minimal ill effects.  What I’m expecting next is to find the aphids on local native legumes.  I’m afraid that won’t be a fun discovery.

Curled Leaf

I hate to see plants suffering from afflictions that result in abnormal growth or deformities of the leaves. It’s especially disturbing when the plant in question is generally uncommon. From a distance I noticed the pale yellow coloring of the new growth on a patch of Carolina Buckthorn, a southern species that just barely makes its way into Southern Ohio.

Then I found a few older leaves that were tightly curled and displaying a mottled coloration. Most of the leaves still looked perfectly healthy, but I know how quickly that can change. Besides being curled, the leaves contained holes and various sized spots of dead leaf. The leaf petiole and portions of the branch contained similar discolorations. It’s not normal for Carolina Buckthorn to be showing this type of damage.

Ants are always foraging on the plants of Blue Jay Barrens, so it’s not odd to find them on the buckthorn. Their behavior can often give clues as to the reason they are present. As you might imagine, ants displaying a defensive posture usually have something to defend. That means there must be something here that is of interest to them. There doesn’t appear to be anything of significance on the outside of the leaf, so maybe it’s hidden in the curl.

The ants would have been hovering over these aphids if they had not all exited stage right to attack my hand as it held the leaf open enough to take a picture. Aphids produce honeydew which is collected by the ants for food. There are several aphid species that cause curling of the leaf as a result of their feeding activities. These aphids worry me because they look like the Asian Soybean Aphid, which is one of the new invasive species rapidly infesting the Midwest. They have become quite a pest in Soybean fields. So what are they doing on buckthorn?

The Asian Soybean Aphid is one of those species that uses multiple hosts during the year. During the summer it feeds on Soybean plants. In the fall, it lays its eggs on the invasive European Buckthorn. The eggs hatch in the spring and feed on the buckthorn. When winged adults are produced, they fly off to develop colonies on Soybeans. Carolina Buckthorn is in the same genus Rhamnus as the European Buckthorn. Having invasive insects attacking invasive plants doesn’t bother me. When the invasive insect begins to utilize native plants, I become concerned. Will the aphids next find a native legume to use in place of the Soybean? This situation deserves a little more study.