- Author: Karen Metz
I planted a crab apple tree many years ago, probably in the 1990s. I wanted a small tree for my backyard. I thought a crab apple tree would give me a bit of shade and beautiful blossoms in the spring. I don't know what variety it is, but the fruit is a beautiful light green.
I mainly used it as an ornamental tree. I didn't know what to do with the fruit. I would collect the small green crab apples and display them in a deep blue bowl. I used it as a decoration to span the late fall to winter transition time.
One year I made crab apple bread and then I got interested in making apple sauce, well crab apple sauce. About that time, I started getting annoyed by how many of the crab apples were damaged. It looked like a worm had eaten through it, leaving a rusty trail.
I went straight to my University of California Agricultural resources and found that the problem was Cydia pomonella or codling moth. Small gray moths lay eggs that become larvae which munch away into apples, crab apples, pears, walnuts, and sometimes plums. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7412.html will take you to a wonderful Pest Note that has pictures of the life cycle of the moth and discusses management techniques. It's a difficult creature to manage as much of its life is spent inside the fruit. There were multiple options, but many seemed to be more pertinent to farmers rather than a backyard gardener with a single tree. I also wanted to avoid using pesticides as I am trying to attract pollinators to my yard.
Sanitation was stressed as a major management technique. Picking up dropped fruit which is frequently infested and raking up fallen leaves can help decrease the population. It will also limit the over wintering sites and interrupt the creature's life cycle. I could do that.
The Pest Note also discussed a bagging technique which tries to protect young fruit before the moth lays its eggs. You use brown paper lunch bags, cut a small X in the bottom of the bag and slip it over the fruit when it is small, ½ to 1 inch. Next you fold over the bag and staple it. Our tree was small and mostly reachable from the ground, we would just need a step ladder for the tallest parts. This seemed doable.
On May 30th I bought a 100-pack of brown lunch bags and my husband, and I worked for about 3 hours slipping bags over fruit. When we ran out of bags, I decided that the remaining fruit would be the control specimens in our experiment. It would be great!
The next day my husband and I were very sore. I found 3 bags that had come off and were on the ground. Two days later after a windy day, I found 3 more on the ground. The bags on the lower branches would get wet from the sprinkler, but they dried out. We lost more bags over time. Sometimes the bags on the ground would have the fruit still in them but other times the bags would be empty. That meant that some of the fruit which had been bagged initially was remaining on the tree “naked”. I had no way of distinguishing those from the original unbagged crab apple controls. So much for my clear-cut experiment. Also, we had to explain to the new neighbor who had just moved in next door what we were doing and why. The tree did look odd!
In mid-October, we started seeing that some crab apples were ready to come down when we wiggled the bag. Some needed a bit longer. Since we had green-skinned crab apples, we were able to leave the bags on until the harvest. Red-skinned varieties need to have the bags removed about 1 to 2 weeks before harvest to allow them to color up.
Because we couldn't do a control versus experimental comparison anymore, I can just make general observations. I think the total harvest was about the same amount as in previous years, even with all the bags that came off along the way. I do think the overall size of the crab apples was larger. From outward appearances, there seem to be fewer infected crab apples. The picture of the harvested crab apples was after they had been in my refrigerator for about 2-3 weeks. We have been traveling and I haven't gotten around to making my crab apple sauce yet.
I think I will try this again next year with a few modifications. Since I am working with crab apples rather than apples, I will try to find smaller paper bags. Even with folding and stapling shut, the larger bags seemed to act almost like a sail in our winds. It will be interesting to see if I have fewer blowing off, if I use a smaller bag and if that will lead to a bigger harvest. Hopefully combining this with the sanitation/clean up techniques, we can decrease the level of codling moths even more in the future.
