How to tackle Mealybug infestations in rose greenhouses – and why early intervention is a must

Figure 1: Mealybugs on a plant in a glasshouse (Image source: CSIRO, CC BY 3.0 <>, via Wikimedia Commons)

Unfortunately for growers around the world, the increase in more sustainable pest management strategies has seen an unintentional rise in unwanted pests such as Mealybugs on greenhouse crops. This destructive pest, once contained by strong miticides to treat spider mites, is now able to thrive in greenhouse conditions as growers increase their reliance on biological controls. In Kenya, the recent arrival and rapid spread of the Papaya mealybug, Paracoccus marginatus is a development that rose growers around the world need to monitor closely. Just like the Coffee mealybug, Planococcus kenyae, the Papaya mealybug species is a quarantine pest that can spread viruses along fresh cut flower pathways and significantly affect crop productivity, quality and quantity.

But it doesn’t have to be a losing battle – with early integrated pest management strategies, you can contain Mealybug infestations before they become too widespread and costly to resolve. Here’s five essential control methods that rose growers can use to manage Mealybugs.

1. Act fast with early detection

One of the main challenges in the management of Mealybugs is the pest’s ability to hide in crevices between branches and the underside of plant leaves. Out of sight, these Mealybugs can reach damaging population levels quickly as adult females lay up to 600 eggs. But that’s only half the problem – once the eggs hatch, immature scale crawlers can spread to new plant parts and new hosts and at this stage, your situation becomes uncontrollable.

This is where a deep understanding of the insect’s biology can make a significant difference. Scouts can learn to check for early Mealybug signs such as the appearance of sticky honeydews on plant material and take immediate action to alert management before it’s too late. If steps like this are missed however, Mealybug’s toxic saliva can go on to support the growth of black sooty mould, which interferes with plant respiration and transpiration.

2. Keep your greenhouse clean and tidy

Practicing good hygiene is important and should start on the greenhouse floor. To limit Mealybug development, you can regularly sweep debris away as these tend to be egg sac hotspots. Unwanted material such as weeds, dead foliage, and hanging leaves should also be cut to allow the crop to open up during the early stages of plant development. This increases the level of coverage and can improve the effectiveness of intervention methods, such as spraying, that might be used in later stages.

If you want to minimize Mealybug build-up and reduce the chances of reinfection, you may also need to use cultural and mechanical controls. Any affected crops and plant material will need to be immediately removed to protect clean areas of the greenhouse. If agrobacterium tumefaciens sets in, you should regularly monitor the rose crop for any fresh crown galls that might attract Mealybugs, and follow this step with a disinfection of the contaminated area. But don’t forget to keep physical contact with infested plants to a minimum as Mealybugs easily attach to clothing and implements.

3. Target intervention on a granular level – with the help of digital mapping

More often than not, Mealybugs can prove to be very resistant and require further intervention. A good tip is to start when Mealybugs are in the crawler stage and have yet to develop their white wax.

For small infestations, a small paint brush coated in undiluted alcohol should do the trick. If the infestation is more widespread, high volume spraying can achieve good coverage of the infected area. While the volume can vary, it is important to disturb Mealybugs from their colonies.

But knowing where to target your intervention can sometimes be a challenge in itself, especially when you have to cover extensive ground. This is where Scarab’s accurate mealybug mapping can help guide your scouts to hotspots that require immediate attention.

4. Follow up with a rinse and repeat

At this stage, your situation may require a reliable spraying routine. To start, apply soapy water or detergent to crack the waxy layer of the pest – but focus on the hard leaves to avoid scorching the younger and less developed leaves. Then it’s time for a rinse. To be more precise, you will need a high-water volume and a suggested size 16 or 18 nozzle to achieve effective coverage.

As an extra precautionary measure, you can follow up with a chemical spray with a pH between 5.0 and 6.0. In cases where the Mealybug infestation is well-established, weekly or semi-weekly intervals between sprays is suggested for effective management. To achieve widespread coverage, you should apply the chemical spray, two or three hours after the crop has been washed with soapy water or detergent.

5. Rethink long-term plans with sustainable practices

With demand for sustainable practices continuing to increase, now is the time to include biological controls in your long-term strategies. As the production of parasitoids starts to increase, natural enemies of the Mealybug such as the predatory ladybird beetle, Cryptolaemus montrouzieri can play a crucial role. These beetles can feed on Mealybug eggs from the beginning of their larvae stage and help growers reduce the population density of the pest.

A relatively new option, which is showing great promise, is the use of insecticides such as Neem Oil. This biological control can prevent Mealybug resurgences and has the potential to significantly alter future control strategies. Already many Integrated Pest Management companies are developing biopesticides that minimize the development of resistance in key insect pests and protect non-target biodiversity.

Investment in the right tools and training will pay off

While early intervention methods such as the use of undiluted alcohol, soapy water, and chemical sprays can be critical in reducing the size of the infestation, most sprays do not give industrial growers the contact needed to eradicate the Mealybugs entirely. This is why investing in a knowledgeable team and an accurate scouting system to detect infestations early on is key to immediate intervention and will help you win the battle against the insatiable pest!

Dr Geoffrey M. Macharia, Managing Director for East Africa, Scarab Solutions