Learning by Observing Nature at Work

Barb Mgrich
Adams County Master Gardener

(2/10) As Penn State master gardeners, we learn to follow the guidelines of IPM (Integrated Pest Management) when fighting insect damage and disease in plants in our home gardens. IPM teaches us to always use the least invasive methods first. We learn that the use of chemicals is not always necessary and should be used as a last resort. We know that healthy soil is the key to healthy plants. When plants are healthy and not under stress, they can usually fight off disease and insect attacks using both their own chemical defenses and the help of beneficial insects. Last summer, we decided to put that knowledge to the test at the expense of some Oxeye Daisies.

In our trial gardens at the Penn State Extension building in Gettysburg, we have a bed devoted to Native Plants of Adams County. One of those plants is Heliopsis helianthoides, a perennial false sunflower, commonly called Oxeye Daisy*. This past summer, near the middle of June, the plant became entirely covered with aphids. Aphids are tiny insect pests that suck the juices out of plants.

Since this is a trial garden, we elected to let nature take its course, wait to see what would happen, and learn by observation. If this problem were in my garden at home, I would take my garden hose, and direct a firm spray of water at the aphids to wash them off the plant, drowning most of them in the process.

A couple weeks after first seeing the aphids, we closely examined the leaves of our sunflower and were able to spot some juvenile Lady Bug larva. We knew that ladybugs, especially their larva, which look quite different from a mature lady bug, are champion aphid eaters. But by now, those funny-looking little guys were hugely outnumbered!

It took them a while, but by the end of July, the aphids appeared to be gone, but now the plant leaves were black. They weren't dead, just covered with a thick black substance. This presented a new problem for the plant called Sooty Mold. When the aphids suck the liquid out of the leaves, they secrete honeydew, a sticky substance that coats the leaves. Sooty mold spores find this substance and begin to grow. (Some other destructive insects that suck the juices from a plant and then produce honeydew are mealybugs, leafhoppers, and scale).

Unlike other molds, Sooty Mold does not actually infect the plant, it just covers the surface of its leaves. If you felt inclined to do so, you could scrape it off with your fingernail. However, by covering the entire surface, it eventually affects the plantís ability to photosynthesize. Prohibiting the plantís ability to convert sunlight to energy weakens the plant. In this case, the leaves were very small, the flowers were few, and the plant was obviously not happy or healthy.

At this point, we could have used a weak dish soap solution and scrubbed off the leaves. Had we washed the aphids off with the strong spray of water when we first saw them, we could have avoided the whole sooty mold problem from the beginning.

But, we stuck to our plan of observing nature at work, and by September most of the mold had been washed off the leaves by some heavy summer rains. The plant was looking healthier and had popped out a few new flowers. It continued to improve throughout the fall. Of course, being a herbaceous plant, it dropped its leaves sometime in October. We carefully cleaned up the soil and dead leaves around the plant where the leaves fell and cut the stems down to the ground. We feel very sure that the plant will return happy and healthy in the spring. We will be on the lookout and, this time, remove any aphids who may appear next summer!

So, what is there to be learned from this experience? That the Balance of Nature is a wonderful thing. For every villain out there, Mother Nature has provided an opponent. It is not always necessary for you as the home gardener to jump in and "spray something". Free, mechanical methods (hosing down, scraping, scrubbing) in this case could have taken care of the problem early on.

AND, that, in the world of insects, the good guys usually take care of the bad guys. And most important to me, there is fascination, entertainment, and education to be found in simply observing nature at work which is much healthier for you, the gardener, than spraying a potentially toxic chemical.

*Heliopsis helianthoides, commonly called Oxeye Sunflower, grows close to six feet tall in average garden soil in full sun and produces yellow flowers. It actually prefers lean soils and tends to flop if the soil is too rich. To be safe, it is best to put a support in place at the beginning of the growing season. It pairs nicely with Purple Coneflower, Bee Balm, and Joe Pye Weed. Heliopsis plants are closely related to the species, Helianthus, which is the true sunflower. The genus, Heliopsis is often referred to as false sunflower. This plant attracts pollinators and butterflies. Song birds eat the seed heads during the winter.

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