Organic and low-spray apple growers will want to consider a new approach to controlling plum curculio (PC) in their orchards next season. A new product called "Surround," developed by the Engelhard Corporation, shows real promise against this tough pest. Surround is made from specially milled kaolin clay, plus a spreader-sticker that disperses the clay over the foliage and holds it there. The idea is to "turn the trees white" by covering them with a thin layer of clay during the period from pink to four weeks after petal fall. This is when PC is active and damages the fruit by laying eggs in it.

Evidently, the clay coating either irritates the plum curculio adults that land on the trees, making them leave, or disguises the trees so the beetles look elsewhere. In any case, several University, USDA, and grower trials have shown dramatic decreases in PC damage when the Surround product is used, often 90-100% less damage than controls. This is far better than the organic pesticide rotenone.

About 50 pounds of clay is used per acre per spray, at a cost of around $25. It is a bit unwieldy to apply that much clay; a high-volume sprayer is needed. The trees should be kept white with weekly applications. Evidently, the clay covering does not negatively affect the trees by reducing photosynthesis, but more time will be needed to make sure that this is true.

It is fascinating to me that biodynamic growers, following Rudolf Steiner's guidance, have been using BD tree paste for years. This paste is a mix of clay and cow manure, and is usually painted on orchard tree trunks and branches. It has also occasionally been diluted and sprayed on the foliage as well.

I've heard that Surround is approved by OMRI, the national group used by NOFA-NY to approve materials for use in organic production. In my opinion, we owe the Engelhard Corporation a debt of thanks for pioneering this breakthrough approach to pest management, and ought to use their product if possible. Tests are being done to see whether clay sprays can help with other crops including vegetables.

Surround is not effective against many other apple pests. For commercial production, you will still need to have controls ready for codling moth and other worm pests (mating disruption and Bt sprays), apple maggot (red sticky spheres), and other pests you may have like European apple sawfly (though clay may be helpful here too). Also, the clay coating may interfere with the effectiveness of sulfur sprays against apple scab.

There are still a few bugs in the system, but this is really good news for ecological fruit production. I've heard of two IPM apple growers who are converting to full organic production now that there is a reasonable organic approach to plum curculio.