About 15 years ago, the AgCenter used to publish a newsletter entitled, “Bugs, Bugs, Bugs” by several staff entomologists. In the same spirit, this RSFF will look at the insects our readers have encountered this past growing season.
Thomas sent in some very clear images and asked, “These [insects] are in crepe myrtles and oak trees. What are they and what harm do they do?”
Tom has “tree cattle”. According to Howard Russell, plant specialist at Michigan State University, “Tree cattle…are large barklice and get their common name from their habit of forming large colonies that move about in unison (much like a herd of cattle, I guess). Tree cattle are harmless and no cause for concern…. As scavengers, tree cattle perform a valuable function in consuming excess accumulations of fungi, algae, dead bark, and other materials that occur on tree trunks and large limbs. Tree cattle do not eat leaves or the bark of the tree, nor do they damage the tree by boring into the bark and control measures are not recommended for these insects.”
Ms. Judy called the AgCenter concerned about their small blood orange tree. She and her husband, Merle, found 16 “orange dog caterpillars” on their tree.
This caterpillar is an orange dog caterpillar (ODC), and it resembles bird droppings. This caterpillar becomes a beautiful giant swallowtail butterfly. Once gardeners understand that this caterpillar becomes an attractive butterfly, they tend to tolerate the slight damage it causes to citrus foliage.
In the case of Judy and Merle, they wanted to protect their small tree from damage and to enable it to establish. Instead of killing these caterpillars with insecticides, we discussed moving the OCDs to their mature satsuma trees, and they were pleased with this solution.
Mara asked, “WHAT is eating my canna leaves? The yellow ones seem to be more delicious than the red. They're nice, not eating the bloom. I never see the culprit, but I have seen a grasshopper in the area in the past.”
Mara seems to have a canna leafroller. Dan Gill, retired AgCenter horticulturist, made a video entitled, “Canna Leafrollers” in which he discussed this pest. A caterpillar grows in a rolled canna leaf and is very hard to treat. An insecticidal soil drench may be the best way to attack this pest. An organic gardener would have to try to spray a Bt treatment, but, again, reaching this pest is difficult.
Rodney, a manger of the LA Ecological Forestry Center, sent an image of confirmed infestation of the red bay ambrosia beetle (RBAB) in the sassafras and bay trees at this property.
Dr. Laura Sims, a forestry professor at Louisiana Tech, confirmed this infestation. The woodpecker damage is a secondary symptom. All these symptoms point to laurel wilt (LW), a fungal disease spread by the RBAB. Native trees like sassafras and bay are susceptible to LW. If any gardeners are trying to grow avocados, their plants are also at risk of infection. Currently, there is no treatment for either the disease or for the insect.
Jimmy sent an image of a worm attacking his grape leaves. This image was taken earlier this year.
Dr. Sebe Brown, an AgCenter entomologist identified this insect as the juvenile form of the grape flea beetle (GFB). GFB is a native insect, and in early spring, it attacks the buds of grapevines while the larvae feed on the leaves. GFB will overwinter in nearby woodlands. A website of Virginia Tech recommends, “Sprays and fall vineyard cleanup for grape berry moth aid in controlling flea beetles, but sprays may need to be directed against this pest early in the season.” The sprays need to be broad spectrum insecticides.
One gardening website listed diatomaceous earth, neem oil, and horticultural oils as possible organic treatments, but failed to cite the source of this information. These suggested treatments should be used as a botanical trial to see how effective they are.
If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 318.264.2448 or firstname.lastname@example.org. Also, you can be on the “green thumbs” email list by emailing your request to the address above.
“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute endorsement by Louisiana State University AgCenter.”
“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”
Figure 1: Tree Cattle.
Figure 2: Orange Dog Caterpillar.
Figure 3: Damage on a Yellow Canna.
Figure 4: Red bay ambrosia beetle.
Figure 5: Grape flea beetle larvae.