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Sunflower issue, Japanese beetle problems arise

posted: September 04. 2018 08:05a CST
by / Bev Carney | Gardening Columnist

With the recent winds and storms, I have noticed a lot of sunflowers toppling over in the garden. When I go to cut them down, I see that they are hollow inside and the inside is quite soft and squishy. What causes this? Is there anything I can do to stop it?

We have the same problem with our sunflowers toppling over and being hollow. At first I thought it was stalk borer, and indeed we do have stalk borer damage on some of them. But our problem was too widespread for it to be just a borer.

The National Gardening Association addressed this issue a few years back and placed the blame on sunflower stem weevils. These insects overwinter in the base and roots of old sunflower stalks and emerge in the spring or early summer to lay their eggs. The larvae hatch and begin eating their way up the core of the sunflower stalk, causing it to rot and fester.

The best control is to remove the entire sunflower plant and its roots from the garden. If possible, plant in a different location next year.

In an earlier column, you mentioned a product that might kill off the Japanese beetles, and in our follow-up conversation, you mentioned that you were going to purchase some. Did you follow through with that and what were the results?

There were two things I was planning to try: milky spore disease powder to kill the grubs and a bacillus thuringiensis (Bt) product which specifically targets mature Japanese beetles. So far, I have purchased only the Bt product, named BeetleJUS. This is a fine powder you mix with water. The instructions called for 3 to 12 tablespoons per quart of water — rather a wide range. I opted to mix about 6 tablespoons in a quart spray bottle and sprayed the product on some of the beetles’ favorite plants. It left a grayish residue. This is not a contact killer but one that works after ingestion so it is important that the beetles eat the leaves.

I am happy to report that I did see several dead beetles the next day. It was hard to tell if this was a direct cause and effect but I remain hopeful. However, the product is expensive and there are a lot of beetles. We decided to wait until the Japanese beetles start arriving next summer and then start the spraying process. That should help us determine whether the product is actually working.

I looked for milky spore powder at a local store and, unable to find it, completely forgot about it. I will add it back to my shopping list. Milky spore is a soil-borne disease that affects all white grubs. In order to infect them with fatal results, the grubs must be actively feeding and the soil temperature must be 65 degrees or higher. On Aug. 26 of this year, my soil temperature was 69 degrees so I had best hurry and get it spread. The more grubs in the soil when you apply it the better, as infected grubs breed more of the disease. If I can get the product on before the weather cools off, I should have a good start for next year.

A friend reported great success with the Japanese beetle traps. Commonly lambasted as attracting more beetles to your garden than it kills, he reported a tremendous reduction in beetle numbers with the use of traps. This certainly sounds like it is worth a try and I will add traps to my arsenal for next season.

Beverly Carney can be reached at cultivatingcountry@gmail.com.

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