Whenever there is a brood of cicadas preparing to emerge, a question that often comes up is “Can cicadas cause problems for my farm?” The short answer? No, generally cicadas will not hurt row crops. However, they do cause damage to trees and bushes depending on the number of cicadas and the age of the plant, so tree nurseries may be at risk. Today we will learn a bit more about these insects, and what effect they can potentially have on your farm.

Additional reading and resources including tables of some of the most at risk plant types available at the end of the article!

According to the National Wildlife Federation, Cicadas are a type of insect from the Hemiptera family that can be found all over the world.  There are two main types of cicadas, the Periodical Cicada, and the Annual Cicada. While there are some physical differences, the easiest clarifying difference between the two types is related to their life-cycle. Annual cicadas tend to emerge every year, and live as nymphs for 2-5 years. Meanwhile, periodical cicadas emerge in large groups called broods, and have a 13 or 17 year period that they live as nymphs before emerging depending on the specific brood of cicadas. The news as of late has been discussing the 2024 cicada “Invasion.” This will be where two different broods of cicada’s overlap, a 13 year and a 17 year brood, and emerge at roughly the same time, causing there to be a mass number of cicadas all at once in some locations.

When cicadas emerge from the ground, they only live for a short time before dying. This short period of 2-4 weeks is mainly used for reproduction, and egg laying. Once the eggs hatch 1 1/2 to 2 1/2 months later, the new cicada nymphs fall to the ground where they burrow under the soil to start the cycle again. The cicada nymphs feed on tree and shrub roots during their underground lifecycle, but there tends to be little damage unless there is an extreme population of the nymphs. Once the nymph emerges from the ground during its brood’s emergence cycle, they will crawl up nearby objects to molt. The shedded outer exoskeletons are quite commonly found attached to trees and twigs shortly after the emergence.

While cicadas are similar to locusts, and also typically appear in incredible numbers like them, cicadas tend to have vastly different behaviors to the ravaging locusts. While locusts will eat most vegetative matter in their path,  cicadas tend to only drink juice from trees and bushes, and even then the damage is typically minimal to most trees.  With cicadas, row crops should be mostly un-affected. In fact, as they die, the bodies of the cicadas can actually be useful in adding nutrients to the soil as they decompose. They also help aerate lawns and improve water filtration in the ground according to the United States Environmental Protection Agency.

However, while they may be beneficial to the soil for row crops, they can be damaging to young trees and shrubs in large enough numbers. The female cicada will typically cut tiny slits in tree branches and small twigs to lay their eggs into. Mass numbers of these cuts while negligible to large trees, can weaken, or in extreme cases kill young trees. According to the Purdue Landscape Report,  There is also a possibility of the small cuts being used by other pathogens to get into the affected plant. Once the eggs hatch, the cicada nymphs may also be damaging to the roots of young trees if there is a very high population of them in the ground around the tree.

To answer the question of what plants are at risk, and how to protect them we connected with an expert on plant-insect interactions from Purdue University’s Entomology Department, Dr. Elizabeth Long.

Question: We have heard that young trees and shrubs are most at risk during large brood emergences, but that older trees and other plants are generally safe. Is this correct?  What are the biggest risk factors for orchards and tree nurseries to watch out for during the upcoming periodical cicada emergence?

Dr. Long: Yes, this is correct! Younger trees are smaller and may have fewer resources to recover from the injury caused by cicada egg laying into stems and branches, especially if you are in an area where there will be a really big emergence. Orchards and tree nurseries should prioritize protection of young woody shrubs and trees, with stems between 3/16 and 7/16 of an inch in diameter, and know that damaged stems/branches can be pruned after egg-laying activity has ended to remove damaged tissues with eggs inside.

Question: For farmers and nurseries who have planted young trees recently, what strategies do you suggest for protecting their young trees? I have heard pesticides are generally not recommended except for with large operations. Do you have a take on whether or not farmers should use pesticides during the brood emergences this year?

Dr. Long: The most cost-effective and environmentally friendly option is to use netting to exclude female periodical cicadas from accessing stems/branches that are preferred for egg laying. I realize this is labor intensive, but it is more reliable than insecticides, which would have to be sprayed repeatedly to reduce injury by the cicadas. This is because a large number of cicadas will be emerging in waves for about one month (if you’re in a high activity area), and it’s just not feasible to spray them all. There are other beneficial insects in orchards/nurseries that may also be harmed by repeated spraying for the cicadas.

This resource provided to us by Dr. Long from the Purdue University Extension includes a pair of tables that indicate some of the most at risk plants during cicada emergences.

This map from the University of Connecticut article shows the locations that different periodical cicada broods can occur in. When compared with the chart further down the article, you can also see what year the next brood will emerge.

A periodical cicada brood map for brood emergence in North America by the USDA Forest Service Northern Research Station, and Northeastern Area State and Private Forestry. This map was created in 2013, and shows the next brood emergences and where they will be for the different periodical cicada broods.