Cryptolaemus

Some History

I don’t know the score over the years, but this year’s victory is mine. The battles have been with scale insects, both armored scales and their cousins, mealybugs (but rarely both in the same year), on my greenhouse fig plants.

Those fig plants are planted in the ground in a minimally heated greenhouse, where winter temperatures can sink to about 35°F. The oldest of these plants have trunks 8 inches in diameter. They thrived for years without any pest problems, scale of otherwise. A few years ago, the insects made their appearance, sometimes ruining almost the whole crop.

Over the years I fought them in various ways. One year it was spraying the dormant plants with alcohol. Another year it was, more aggressively, scrubbing trunks and stems of dormant plants with a toothbrush dipped in alcohol. Ants herd and protect scale insects, so another year I fenced the ants off the plants with a band of masking tape coated with forever (almost) sticky Tangletrap around the trunk of each plant.

An expensive but short-lived success was the two releases of the predatory ladybird beetle Cryptolaemus montrouzieri and the parasitoid wasp Anagyrus pseudococci.

Mealybug destroyer

These biocontrol helpers ended up valuing each fig at about a dollar, still worth it. I screened all openings in the greenhouse, hoping to perennialize them inside. (It was not effective.)

Battle Plan, Done

So this year I tried a multipronged approach.

The biggest change was, rather than growing the figs as bushy trees, training them as espaliers. Espalier is the training of plants to an orderly, usually two-dimensional form both for beauty and, in the case of fruit plants, for good production of high quality fruit. For my figs, an additional benefit would be that each plant would only have one point of contact — its trunk — with the ground. IA band of masking tape coated with Tangletrap would be a roadblock on the ant highway. (Plus the look of the plants always elicits a “Wow” from visitors.)

The fig plant growing near the greenhouse endwall has a short trunk that, after rising to about 18 inches from ground level, bifurcates into two, self-supporting horizontal arms extending parallel to the wall in opposite directions. At the head of each of the south beds, a fig tree is planted each of whose trunk is terminated by just a single, self-supporting, horizontal arm reaching down the bed to the sidewall. With just a trunk and one or two arms, thoroughly scrubbing down the dormant plant with alcohol is a relatively quick job. Quick enough to prevent 2 or 3 scrubbing before plants resume growth in early spring from becoming tedious.

Another nice feature of this training system is that pruning the plants at the end of the season is a no-brainer. Vertical shoots that rise up from the horizontal arms are thinned to keep neighboring shoots 8 inches apart and helped along in their vertical growth by being trained to pieces of bamboo attached to the greenhouse roof. (Yes, an ant could walk up the wall and across the roof of the greenhouse and then down the bamboo to get at the plants but they are either not that smart or energetic; it hasn’t happened.)

A little later in the early part of the greenhouse growing season I gave the plants some dowsings with neem oil. I’m not sure how effective the neem component is but “horticultural oil” itself is effective in fighting off scale insects.

A ring of cinnamon around the base of each plant provided further disincentive to the ants, who will not cross a cinnamon line. The cinnamon and the Tangletrap did need renewal once per season.

As new fig shoots soared skyward near the greenhouse roof, I used a pole pruner to prune out the top of the growing shoot. Side branches, of course, then grew, and I periodically had to to hack them back also.

Uh Oh, But All Still Good

Everything was copacetic and we were harvesting figs, which formed along the vertical stems at the juncture of almost every leaf. Then, in late August I noticed some mealybugs on one plant. Time for Cryptolaemus montrouzieri again. I released them in early September and we were back in business, harvesting large handfuls of three different varieties of delciously sweet figs — San Piero, Brown Turkey, and Rabbi Samuel — daily.

And then, just today, I noticed armored scales on the plants, and a few ants! I’m not sure how the ants are getting onto the plants, but one possible “benefit” of the armored scales is hardly any mealybugs. Perhaps they can’t coexist.

All the measures I took against mealybugs should also be effective against the armored scales, except for the Cryptolaemus montrouzieri. Their predator Aphytis melinus, also known as the Golden Chalcid, has been effective against armored scales.

I’m not taking action. With less sunlight and cooler temperatures the figs trees have slowed down, running out of new stems on which to hang fruit. No matter; it’s been a good season of fresh figs.