Growing apples is rewarding but it has its challenges. After many years of waiting, our two trees (Grimes golden and Jonathan) finally reached full production last year – the year the brown marmorated stink bug (BMSB) found them. The usual method of controlling disease and pests on apples tree is to use a lengthy list of fungicides and pesticides, but none of that will deter the BMSB’s open buffet. This summer we tried a different strategy: use of physical barriers to stop the culprit.
Using a row cover on an apple tree is not a practical solution. Using liquid or dust copper as a fungicide and a BMSB repellant can be a good idea, except that our Grimes golden can have a bad reaction called russeting. The two other options were to bag the apples on the trees or spray with kaolin clay powder. Fearing the cost of the clay, we gave a shot with the bags (thanks to Washington Post/Times for a daily supply). But we reconsidered the clay and decided to use it starting from mid-July until harvest time.
Now, the post-harvest report.
The stalks on the Grimes golden are longer and weaker than those on Jonathan, and for this reason we lost at least 25% of Grimes’ bagged apples, plus a lot more of the no-bagged apples due to the squirrel’s playing in the branches, thinking the apples were black walnut fruits. On Jonathan, only a handful of bagged apples were lost, and few overall were lost to squirrels. (We can only speculate that the squirrels liked the Grimes because they were yellow (walnut-colored), and Jonathan were red.) In short, despite the up-front time, the result of bagging the apples was excellent on both trees. The fruits looked great (with just the occasional blemish), and they were very sweet.
As for the clay, despite that our trees are “dwarf” trees, they are 18’ tall, making it hard to reach the top with the tank sprayer. Still, the kaolin clay powder did the job by keeping the BMSB out of the fruits. They were spotted on the trees in August but they didn’t damage the fruits covered with clay. The only damage we saw on the fruits on both trees occurred in June before the start of the clay program and/or on the areas of the trees where the sprayer could not reach (the treetops or areas of dense foliage).
On a surprising note, after the base coverage –a minimum of two back-to-back sprays in a short interval – little use of kaolin clay was needed to keep the fruits covered. Even 1” of rain did not wash away all the coverage on the fruit. It was easier to keep the clay on Jonathan’s fruits and leaves than Grimes; however, because of its tendency to have a denser canopy, Jonathan was harder to cover all the fruits, making them more prone to BMSB damage. Note that having not all fruits on a tree covered with clay can be a good thing. Overuse can result in harm to beneficial insects and a surge in red mites. For the backyard gardener, leaving some unsprayed areas of the trees should help keep a natural balance. In the end, the fruits covered with clay were, despite a late start, mostly good looking, and about the same size as their bagged counterparts. Also, brushing off the clay before use was not difficult at all.
Was all this worth the effort? YES!!!!! Less pesticide was used and we have nice, pristine bagged apples to eat fresh as well as quick-to-prepare clay-covered apples for baking.
In short, the wife is happy and we have pie.
 see product label too for warning.