Boone County Purdue Extension, 1300 East 100 South, Lebanon, IN 46052 cemanuel@purdue.edu 765-482-0750

Sunflower Head-Clipping Weevil

At a recent Master Gardener meeting, Susan Kovach asked if anyone had the problem of purple coneflowers having their flower heads almost cut off and left hanging toward the ground. Four summers ago I noticed this problem in my garden. 

This is the work of the sunflower head-clipping weevil (Haplorhynchites aeneus) a well-documented pest of cultivated and wild sunflowers in the Great Plains. Sunflowers are the preferred plant but the weevil also attacks purple coneflowers and other plants in the aster family. 

The shiny black to brownish-black weevil is a little over 1/4″ long with the measurement including an exceptionally long, curved snout.  As with all weevils, the mouthparts are located at the end of their snout.  The females insert their snouts and chew a ring of holes around the stem one to two inches below the flower head. The flower stem is not completely cut; this weakens the stem to the point where it eventually breaks over, leaving the flower hanging by a thin strand of tissue.

There is only one generation per year. Only females are thought to perform the clipping behavior. “The female enters the flower to feed on the pollen and lay eggs.  The flower eventually falls to the ground, eggs hatch and the immature weevil, a worm-like larvae, moves into the ground for winter.  Next spring the larvae pupates, then transforms into a weevil and starts feeding on the flower stems in mid-summer.” (Melinda Myers website) It is speculated that the weevil’s odd head-clipping behavior reduces larval exposure to plant defense chemicals and also prevents other insects from competing for the seed head prize.

Removing the flower heads that are still hanging as well as those that have dropped to the ground can help to reduce populations next year. I have found that if the flower head has turned brown before it drops off, it is often difficult to find it on the ground. When removing the flowers from the stem, hold a bucket of soapy water under the flower and clip the rest of the stem, dropping the flower into the bucket. This may help to kill any adults that are feeding in the flowers, reducing the populations and further damage to other plants. It also kills the larvae and prevents them from further developing.

In past summers I have removed the damaged coneflowers and stems well below the weevil cut, put them in a plastic bag, sealed the bag, and put the bag in the garbage. Initially I cut the damaged part of the stalk just below the weevil cut leaving several inches of stem. When checking a few days later for further damage, I was not sure if I had removed the damaged stem and flower or the flower had dropped to the ground leaving a flowerless stalk. To solve this issue, I now cut back to the leaves below the weevil cut and I know that the flower head has not dropped to the ground. I tour my garden about every three days and carry a bag and clippers with me to remove any new damage. This minimizes damage and reduces future infestations.  

Cutting off the damaged part of the plant and disposing of it is the best garden control method for the sunflower head-clipping weevil. Pesticides are not a good option. Pesticides should not be used on a plant in full bloom because of the risk of killing pollinators.

This weevil has been at work in Indiana for several years. The first mention I found of the weevil causing damage in Indiana is in an August 2011 Hoosier Gardener article by Jo Ellen Meyers Sharp. Other websites report the weevil in Illinois (2007) and Ohio (2009)

Jane Savage

Note. This article is a compilation of information the websites listed below.

https://55krc.iheart.com/featured/ron-wilson/content/2018-07-02-coneflower-weevil/

https://www.daytondailynews.com/lifestyles/these-weevils-are-new-pest/gYKSZyql0iKcwNMvTitd4M/(Ohio)

https://entomology.k-state.edu/extension/insect-information/crop-pests/sunflowers/sunflower-headclipping-weevil.html (Kansas State University website)

https://bygl.osu.edu/node/1087 (good pictures – Ohio State University)

https://www.melindamyers.com/audio-video/melindas-garden-moment-audio-tips/problems-pests-weeds/coneflower-damage-from-sunflower-head-clipping-weevil?ccm_paging_p=2

Tomato Leaf Spots

Tomato Septoria Leaf Spot Disease
Tomato Leaf Spot Disease

I’ve been surprised – and gratified – at how few calls I’ve received about tomatoes this year. Let’s face it, this has been as lousy a year for growing them as it has been for most other crops. In a year like this I often am not able to offer much help. But since they are the vegetable most commonly grown in Central Indiana home gardens I want to mention two diseases they are particularly susceptible to.

About this time of year two common fungal leaf-spot diseases often appear. Septoria leaf spot and early blight are both characterized by brown spots on the leaves. Septoria usually appears earlier in the season than early blight and produces small dark spots. Spots caused by early blight are larger and often have a distorted “target” pattern of concentric circles. For each disease, heavily infected leaves eventually turn yellow and drop. Older leaves are more susceptible than younger ones, so symptoms generally first appear at the bottom of the plant and progress higher.

These diseases can spread rapidly so it’s important to scout for symptoms. Plants usually become susceptible when fruit is about the size of a walnut. If you see symptoms, fungicides can help prevent their spread. Be sure to apply fungicide to both upper and lower leaf surfaces, and reapply if rainfall removes it. Chlorothalonil is a good choice for fruiting plants because most products have no harvest waiting period, meaning that fruit can be harvested once the spray is dry.

Chlorothalonil is an ingredient in several products. Be sure to start protecting plants when the disease is first seen. It is virtually impossible to stop it on heavily infected plants. As with all pesticides, always read and follow all label directions.

Several practices can help with disease prevention. Mulching, caging, or staking keeps plants off the ground. Better air circulation allows foliage to dry quicker than in plants allowed to sprawl. Mulching also helps prevent water and soil from splashing and carrying disease spores to the plant.

You can reduce many diseases by following proper sanitation at the end of each growing season. This includes removing and disposing of any plant material. Composting, if done properly, will also destroy disease organisms.

If you experience either disease and you are able to, consider rotating tomatoes out of that area of your garden. Other plants such as peppers, eggplant and potatoes are also susceptible so avoid replacing tomatoes with these crops.

Frequent rainfall and high humidity are conditions which favor the development of these diseases. We’ve had an abundance of both this year. For additional information on these and other tomato diseases, see Purdue Extension Publication “Five Steps for Healthy Garden Tomatoes,” by Purdue Extension Specialist Daniel S. Egel. It is available online at: https://www.extension.purdue.edu/extmedia/bp/bp-184-w.pdf.

Black Walnut Fruit

Black Walnut Harvesting Video

Do you have Black Walnut trees? Would you like to put the nuts to good use? If so, there are techniques for getting the ground around your trees ready for easier harvest.

In the imbedded video, one of our Boone County Master Gardeners walks you thru the steps that you can take in preparing the ground around your trees. Following these steps will enable an easier harvest of the green Black Walnuts this fall.

By shortening the grass under the trees and removing any dry limbs and other debris makes it much easier to see and collect the green Black Walnuts. It also shows techniques for removing standing water and improving the drainage of the soil around your trees.