Mid summer is a busy time for insects in gardens and landscapes. Gardeners here in Central Kansas are noticing everything from blister beetles to squash bugs.
In some cases these insects can cause quite an alarm, especially if they show up in large numbers. So far this year our office has received reports of elm leaf beetle, walnut caterpillar, grasshopper, chinch bug, bagworm, burrowing bug, and blister beetle ‘outbreaks’ in the area.
No two years are alike when it comes to insects and their potential to explode in number. Weather patterns, availability of food sources, and destruction of natural enemies are often key contributors to whether an insect outbreak can occur.
What do we recommend or what is the best response in these kinds of situations? The answer is…it depends. There is not one black and white answer to give when an insect outbreak is happening in a landscape. Many factors must be considered in order to determine if any action is needed at all.
When an insect ‘outbreak’ occurs there are two important steps to take in order to determine what, if any, action might be needed.
First, identify the insect. This is of course the first critical step in any decision making. K-State Research and Extension can help local gardeners identify the insect if needed to be sure that any further action taken is based on the right information.
Second, learn the biology of the insect. Every insect is different and understanding the life cycle of the insect aids in determining if the insect in question might cause a long term problem or if the nuisance is only temporary.
For example, elm leaf beetle usually has two generations each year here in Kansas. By the time the second generation is occurring on elm trees in mid to late summer, the majority of the leaves on the tree may be damaged, skeletonized, or dropped. Even though the tree looks bad, at this point spraying is ineffective and unnecessary since the beetles are nearing or at the end of their life cycle. The damage from elm leaf beetle feeding is rarely damaging in the long term to an otherwise healthy tree. The elm tree will leaf out again the following spring. If an elm tree is an important source of shade in the landscape, there are options to treat for elm leaf beetle to prevent the excessive loss of foliage. Check out our publication here: Elm Leaf Beetle
Walnut caterpillar which has also been seen in many landscapes this summer follows a similar pattern. This insect also has two generations a year here in Kansas. The first generation feeds during June and early July and skeletonizes and damages large numbers of leaves on walnut, pecan, oak, willow, honeylocust, and apple trees. The larvae feed for about a month before reaching maturity and then a second generation can follow in late summer and early fall. This insect has an interesting habit of coming down lower on the tree trunk to molt (shed old skin) which means that a hard stream of water can dislodge many caterpillars or they can be handpicked/removed from the tree as they molt. Click here for more info: Walnut Caterpillars
Again, healthy trees are not damaged in the long term by an occasional walnut caterpillar outbreak, so control is rarely needed unless the tree’s shade needs to be preserved in the landscape or the tree is young and vulnerable to the stress.
Mobile insects such as grasshoppers can present some real challenges for gardeners, especially in rural settings. The ability to control grasshoppers declines quickly as grasshoppers develop and migrate. This fact sheet from Colorado State University is a nice read.
Monitor trees and shrubs regularly
By learning about each insect and it’s lifecycle homeowners can learn when to monitor trees and shrubs for insect outbreaks. Taking time to regularly examine trees and shrubs especially in the late spring and early summer can identify problems well before they get out of hand and provide time to make educated decisions.
Check out our K-State Research and Extension common plant problems page for many more fact sheets on common problems in the garden and landscape.
Get to know beneficials
It is also very important for gardeners to get to know beneficial insects in the garden and landscape. There are many beneficial insects to get to know. Insects such as these large cicada killer wasps can show up in large numbers in a landscape like they did here in Kansas in 2022. While they look intimidating, they are not a threat at all and are very beneficial in regulating cicada populations.
Soldier beetles often show up in large numbers but are also beneficial. They feed on grasshopper eggs, soft-bodied insects, and can serve as pollinators.
This publication from the Xerces Society is a great resource to use for getting to know beneficial insects. Habitat Planning for Beneficial Insects.
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