The Biggest Pest Problems of 2019

The Kemper Center for Home Gardening is the largest non-profit gardening information center of its kind in the nation. That means they get a lot of gardening questions every week. Many of those questions are about pests wreaking havoc on home gardeners. The type of pests doing the most damage varies from year to year, depending on weather and other factors. The following are the most common issues Kemper staff has been asked about this summer, and some advice on identifying and dealing with these problem pests.

Rose slugs or rose sawflies 

These pests are by far the most common rose problem this year, and possibly even the most common garden problem overall. Rose slug larvae leave two distinct kinds of foraging marks in rose leaves, making them relatively easy to identify. When they are young, they will only eat the upper surface of the leaf, creating light brown areas. When they get older, they will eat through the entire leaf, leaving holes. 

Learn more about dealing with these pests here

Powdery mildew 

From cucumbers to clematis, it seems like powdery mildew has been reported on almost everything this year. Most of these incidences are likely due to weather. The above average rainfall and high levels of humidity have created the perfect conditions for this type of fungal infection. Removing infected foliage, watering at the base of the plants instead of overhead, giving plants more room to breathe, and a bit of good weather luck should help reduce powdery mildew infection next year. Remember, don’t add the infected foliage to your compost pile! 

Boxelder bugs and milkweed bugs 

Both orange and black insects, boxelder bugs and milkweed bugs look similar and can often be mistaken for one another. Milkweed bugs are only found on milkweed plants and have slightly different markings. Boxelder bugs are found on a number of host plants including plums, cherries, apples, ashes, and maples. In both cases, these insects do not cause significant harm and do not warrant the use of chemical insecticides to control. 

“My tree has spots on the leaves, help!” 

The Kemper Center has received this question, usually accompanied by a photo of offending leaf spots, quite a bit this season. There are many kinds of fungal and bacterial leaf spots. The solution to those problems is similar to that of powdery mildew: rake up and remove leaves in the fall, keep sprinklers from hitting the foliage, and hope for better weather next year. Most mature trees are usually not affected in the long term by leaf spot diseases. You can read more about fungal spots here.

Catherine Martin
Public Information Officer

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