Wednesday, January 31, 2018

Scale Insects

Almost 20 years ago now we were heavily into growing lilium of every variety we could find. We  were gardening in Shelburne on the shores of Lake Champlain and we had found a gardener in Cabot who had started growing Asiatic lilies. We knew nothing about lilium and went to the man's home. I'll never forgot driving to the house and spotting him sitting outside in a chair enjoying the day. We walked over, introduced ourselves and chatted for a while. "Lilies are in the garden, shovel and boxes in the shed. Dig what you want and put the shovel back." We bought a box full at some absurdly inexpensive price and away we went. We didn't know at the time that within ten years we would be selling the most potted lilium in New England and that by 2006 we would have made a giant decision not to grow them any more. The reason for the change:  because of the arrival of the lily leaf beetle that entered Montreal in 1945 and into Cambridge/Boston in 1992.  It took that many years from two directions for the beetles to reach Vermont.

 Adult lily leaf beetle

Larvae exit the soil and eat their way to the top of the lily stem in about 2-3 weeks.

If you  are familiar with the lily leaf beetle you know it's an insidious beetle, 3/8" long, bright red in color, and it squeaks if you try to squish it. It has great eyesight and if it sees a hand coming its way, it rolls off the plant and onto the ground to hide. In the springtime the beetles appear consistent with the ground-breaking approach of the lily stems and in short order the lilies grow taller but the beetles grow more prolific.
Hungry beetles defoliate the entire plant and over a couple years the bulbs decrease in size and die

Lily growers began writing about various chemicals that they used with success while others mentioned hand picking the insects every day. Neither approach was feasible when you're growing thousands of pots. Chemicals made no sense to us because our son faces each day with autism and environmental involvement with chemicals prior to birth is still researched as a possible cause of a diagnosis that never goes away. As such we sought other solutions.

One day a devoted gardener from Burlington stopped by to purchase his annual collection of new lilium. He mentioned using dormant oil spray by accident on his lilies while spraying some fruit trees for scale. He said the organic character of the spray pleased him because he raised honey bees too, and although the spray required fairly regular repeat spraying, it suffocated the insects at various points in their life cycles. Once we tried the horticultural oil (mixed it with Dawn dish detergent as a sticker) we never looked back. It worked. Not 100% but it was inexpensive and environmentally it was a good choice. The key was repeat spraying and the time involved was what made it clear that we should not sell lilium at the flower farm when we moved. We knew that at our new, more visible Route 2 location we would be selling bazillions of lilies and the time element of keeping them insect free just didn't fit with a 5 acre, two person business. 

So in 2018, lilium are history with us although we miss them dearly. They are a very important part of the American floral industry and as such introductions hit the market with new colors and new names all the much so that I don't even know the names any more. But the key to me mentioning this floral journey is the use of hort oils and insecticidal soaps which worked so well on the lilies and are used regularly by orchardists growing almost any fruit that grows on a tree. And one of the big issues with trees and shrubs is scale, another insidious insect that does not receive enough attention. So-o-o if you have a chance to learn about scale and have found any on your property, read this little article on treating scale. It appeared in a recent issue of the GrowerTalks Newsletter by Ball Publishing. If you have any questions, write or call. Read on!

"Oil or soap for scales?
Scale insects are my specialty. These’re tough little buggers to kill. Systemic insecticides work great for some species, but not for those that feed on woody tissues. Sprays work best when hatchlings (or crawlers) are coming out from their mamas’ shells.
For years I recommended horticultural oil and insecticidal soap for sprays, and thought they worked equally well against all species. A recent article by Cliff Sadof of Purdue University and his graduate student, Carlos Quesada, in HortTechnology (October 2017, volume 27, page 618-624) shows me that I need to update my recommendation.
Carlos and Cliff did a series of lab and field studies on two armored scales (pine needle scale and oleander scale) and two soft scales (calico scale and striped pine scale). Oil and soap, both applied one time at 2%, killed 67-93% of crawlers of all four species; that’s a pretty good level of control. But both oil and soap became less effective as the scale insects settled comfortably and grew. Spraying oil or soap against adult scales was as good as spraying water. No surprises so far. The basic recommendation still applies: You need to spray against crawlers to achieve the best control.
Here’s the good part: In the field studies, oil was more effective against settled armored scales, whereas soap was more effective against settled soft scales. Who knew there are differences between oil and soap on which group of scale insects they are most effective against? I didn’t!
Carlos and Cliff speculated that the difference arises from the chemical properties of the chemicals and the scale insects. Both oil and soap kill mainly by suffocation, but, chemically speaking, soap is polar (so it likes to stick to another polar object) and oil is non-polar (it is repelled by a polar object). As armored scale crawlers settle, they produce a waxy cover over their bodies within three days. Most soft scales, on the other hand, do not usually produce a thick wax layer until adulthood. Wax, being non-polar, reduces penetration of polar soap but allows penetration of non-polar oil. Skin of soft scales is polar, so soap sticks and penetrates the layer more effectively, thus doing a better job of killing soft scales.
Fascinating, isn't it?!
What about those soft scales that produce plenty of wax when they are babies, such as the wax scale? Perhaps oil works better in this case? I don't know; I will need to find out. More research!

Big, fat adult female oak lecanium scale is a common sight on oak trees in the spring. Good luck trying to kill these ladies! Kill their babies instead."

Writing this morning from the mountain above Peacham Pond where the moon is bright and the temperature just above zero.

George Africa
The Vermont Gardener
Vermont Flower Farm
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At the nursery from Mothers Day until Columbus Day, 7 days weekly.

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