Japanese Beetles in Apples
Rami Aburomia, Mt. Horeb, WI
If you’ve had a large population of Japanese Beetle (JB) in your orchard, you might have wondered if there are any insects that don’t love apples or apple trees. I wanted to write up my experience managing JB organically this year, with the hope it may help other growers.
The beetle emerges from grassy areas around late June in southern Wisconsin. The beetles mate almost immediately after emerging from the soil. In grassy areas, females dig a couple of inches into the soil to lay their eggs. The eggs hatch, the grubs eat plant roots, then dig deeper to overwinter. While the beetles are adults, they search out a desirable food source, and when they find food, they release an aggregation pheromone that tells other beetles, “Good food here!” It is this aggregation pheromone that is used for the commonly available JB traps. JB traps are used to monitor for the arrival of the first beetles. Once the first beetles are caught, the trap is removed to avoid pulling in more beetles. Without traps, it is simple enough to just watch the crop for those first beetles.
My orchard in southern Wisconsin is around three acres of high density apples. We have about 700 Honeycrisp trees - which are a preferred apple variety for JB. In 2017, I was taken by surprise by a large population of JB that skeletonized the top 25% of all the Honeycrisp trees. By the time I realized JB was going to be a problem, there was such a large population already in the orchard that there was not much that could deter them. I tried using diatomaceous earth spray on the the top of the trees, but it had minimal impact on the beetles. Finally, midway through August, out of desperation, I did the unthinkable and put up five JB traps along the Honeycrisp rows. The traps filled fast, and it felt good to collect five gallon buckets of fermenting JB carcasses, but this was not a sustainable solution to my JB problem. The damage had already been done.
For 2018, I took a number of actions to control JB. I monitored the orchard carefully for the first sign of beetle arrival. When I spotted the first beetle on July 3rd, I used an airblast sprayer to build up Surround (3#), diatomaceous earth (8-10#) and raw Neem 40oz (in 50 gallons of water per acre) in the upper portion of Honeycrisp trees and their neighbors. After that first combination application, I switched to spraying diatomaceous earth alone, reapplying coverage after rain or new leaf growth in order to keep coverage throughout the month of July. Neem was also applied 2 times. The goal was to deter JB from establishing themselves happily in my orchard and calling in more beetles. Through most of July, the beetle population stayed at low levels, but I began to see more beetles and more activity by the end of the month.
On July 27th, before a warm, dry spell when I thought the beetles would be very active, I used the product Beetlegone from Phyllom Bioproducts. This insecticide is a subspecies of Bt that has activity on beetles. A Bt such as Dipel is not effective on beetles. As with any Bt product, it has a limited time of activity once applied. I used 5#/acre with most of the spray going into the top two-thirds of the tree. After two days I saw fewer beetles and much less activity. Ten days after the first application, I began to see an increase of activity and applied Beetlegone again at 2.5#/acre. At that point I was happy with control. After this application, beetles could be seen in raspberries on my farm but not in the apples.
Chris McGuire, of Two Onion Farm, grows apples and vegetables about 30 miles west of my farm. He has dealt with JB using a slightly different strategy. He considers his JB pressure moderate, but last year had 5-10% damage to fruit on early ripening apples. In 2018, Chris saw his first beetles on June 23rd, and began to apply Bettlegone on July 17th at the 2.5#/acre rate. This year, he did not have the damage he had last year on Pristine apples. Hoping that this Bt also effects weevils (in the beetle family), Chris continued to apply Beetlegone throughout July and August. His hope was that it would have some effect on Plum Curculio and Apple Curculio survival.
Beetlegone is expensive - at $23-28/lb, you can do the math. However, if JB becomes a perennial problem on your farm, it may limit the health of the trees and the quality of fruit. By repelling the beetle as long as possible before using this Bt product and focusing on those favored varieties, you may be able to stretch your dollar. It will take more growers’ experiences to fine tune the rate of Bettlegone that is
effective. The manufacturer recommended rate is 1-17#/ acre. They suggested to me that their price should go down in the future. An important cultural control, which costs nothing, is to allow grass around your trees to grow longer than three inches to deter the females from laying their eggs successfully.
The population of Japanese Beetle seems to vary quite a bit from year to year, but in the last ten years I have always seen some beetles in the orchard. Knowing how large a population will be in your orchard may be difficult to predict, but with scouting and a plan in place you can be prepared if the population grows.
About the Author
Rami Aburomia, of Atoms to Apples in Mount Horeb, WI, has been growing apples for 15 years. At first, managing an IPM pick-your-own operation and for the last four years, running his own certified organic farm. His high density orchard of apples, pears and stone fruit is 3.5 acres. Rami’s key goal of running an orchard business is growing delicious fruit efficiently. He has served two terms on the board of OFGA.
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