Cottonseed Bug In Southern California Nurseries

Cottonseed bug (Oxycarenus hyalinipennis) is an invasive pest that was first detected in Los Angeles County in 2019 and has since spread across most of Southern California. It can now be found in San Diego, Orange, Riverside, Los Angeles, Santa Barbara, and San Bernadino Counties. Cottonseed bug (abbreviated CSB) primarily feeds and reproduces on malvaceous hosts like cotton, hibiscus, and mallows, but can also be found feeding on a wide variety of other plants from wheat to citrus. CSB feeding can cause seeds to abort and will occasionally damage fruit or young shoots. This damage is usually minimal except on a few crops like cotton where CSB is a serious pest. Their feeding can cause direct cotton yield losses and crushed CSB nymphs can stain cotton lint. 

CSB has mostly gone unnoticed in Southern California because it does not damage common landscape plants or food crops in the region. This changed in 2025 when CSB was first detected on hibiscus plants in commercial nurseries in San Diego, Santa Barabara, and Orange Counties. CSB is not present in the major cotton-growing regions of California or the rest of the US and finding it on plants that could be sold and shipped to these regions was a serious export concern. CSB is considered an A-rated pest in California and is subject to state-enforced actions like containment and required eradication if it is found on nursery stock. The infested plants at nurseries were put on hold, but because little research has been conducted on this pest, guidance on what treatments to apply or whether to destroy the infested plants was mostly left up to individual growers while regulatory agencies figured out what to do. 

The USDA, CDFA, and county agencies are currently working to determine what protocols growers need to follow to ensure their plants are free of CSB before shipping. One of my colleagues at USDA and I conducted preliminary insecticide trials to determine what tools growers could use to eradicate CSB on their nursery stock and to help inform the protocols regulatory agencies adopt. We tested drenches of acephate, dinotefuran, and flupyradifurone to see if they killed CSB on hibiscus plants and to see how long they would protect plants from reinfestation by CSB. We found drenches of flupyradifurone were completely ineffective, while drenches of dinotefuran reduced but did not completely eliminate CSB. Acephate was 100% effective at killing all CSB present and continued to fully protect the plant for up to a month after application. Additionally, acephate significantly reduced living CSB on the plant up to 2 months after application. From our results, acephate seems like the best tool to use to eradicate CSB at this time. 

For now, nursery growers in Southern California should check any malvaceous plants they are growing like hibiscus and mallows regularly for CSB to catch any infestations early. CSB adults are small, about 3-4mm long with a dark body, light colored wings, and a long face. Their nymphs are reddish and are smaller and rounder. You’ll most frequently see CSB on reproductive parts of a plant, especially inside of seed pods. CSB are hard to spot, so tapping plants over a clipboard or piece of paper is a good way to check if CSB are present. Check flowers and reproductive parts of plants and crack open any seed pods if they are present to see if CSB are inside. Also keep an eye out for malvaceous landscape plants that may act as hosts either within the nursery or on the borders: there were several cases where mallows infested with CSB were growing right outside nurseries who later found CSB on their plants. 

If you do end up with an infestation of CSB and need to do eradication treatments, acephate is currently the best option. Foliar sprays of flupyradifurone may work to knock CSB numbers back, and spray or drenches of dinotefuran could do the same. Neither will be as effective as acephate, however. Don’t use bifenthrin or other pyrethroids as CSB populations are known to be resistant to these insecticides. 

Keep an eye out for additional guidance from CDFA and USDA as the situation progresses, and also keep an eye out for new research from UC on ways to manage this pest. If CSB makes its way to cotton growing regions of the US it will become a very serious pest for cotton growers, so keeping nursery stock free of CSB is essential. For now, prevention and good scouting are your best tools to avoid a serious infestation in your nursery and to avoid your plants being put on hold.