Geranium Pests

While both perennial and annual Geraniums are fairly deer-resistant plants, there are smaller pests that are common problems for gardeners in just about all gardening zones. Whiteflies and Aphids are sap-sucking insects that most commonly strike plants growing in crowded or protected conditions like in a greenhouse. Geranium Budworms are a type of caterpillar that can do extensive damage during its short life. Root Knot Nematodes are microscopic worm-like creatures that cause damage to the roots and can build up in garden soil when not treated. 

Whitefly

This sap-sucking insect is most often found in greenhouses where the adults can continuously lay eggs producing many generations a year. Outdoors, in climates with winters that rarely have freezing temperatures, whitefly can also be a pest. The small white adults have small wings that allow them to fly only short distances. Adults and larvae feed on the foliage sucking out the plant's nutrients causing plants to grow less vigorously and eventually fail as they are not able to photosynthesize properly.

Adults produce honeydew that is sticky and can cover parts of the plant and drip onto surrounding surfaces. Eggs are laid on the underside of the leaf in clusters along the veins.

Treating Whitefly on Geraniums

Monitor greenhouse plants with yellow sticky cards that attract and trap any flying adults. Horticultural soap sprays are effective on minor infestations. Coat both the upper and lower parts of all the leaves to ensure all pests are treated. Washing plants with a strong stream from a hose will also wash the adults of your Geraniums. Releasing parasitic wasps into the greenhouse can be effective and must be done while the populations of Whiteflies are still low. 

Prune out the most damaged parts of the plant to remove pests and prevent infection from bacterial or fungal diseases. 

Preventing Whitefly on Geraniums

Regular monitoring is needed when growing plants in controlled conditions like a greenhouse. Wetting down of floors and walls helps to raise the humidity around plants when temperatures are high. Inspect new plants and cuttings thoroughly for signs of infestation before placing them in the greenhouse or garden. Remove weeds that may act as a host or overwinter Whitefly. Clear dead plant material from under and around benches and shelving in the greenhouse and dispose of badly infested plants in the trash, not the home compost pile. 

Aphids

Aphids are common pests for many plants and typically strike those that are weakened or already stressed. Aphids can be green, black, or white and feed primarily on the sap in the leaves and flowers of Geraniums. The small bugs mostly feed on the undersides of leaves where they are protected from beneficial predators. The eggs of future generations can be found in masses in leaf and stem joins.

Multiple generations are produced during the warm summer months, while eggs laid late in the summer can overwinter in leaf litter and plant parts.  Secondary infections from sooty mold and ant infestations occur when populations are allowed to grow, depositing copious amounts of honeydew on the plants. Other signs of Aphids are distorted and twisted leaves, rolled leaves where eggs may be deposited, yellowing and brown leaves, and damaged flower buds.

Treating Aphids on Geraniums

A sharp jet of water from the hose will dislodge adult Aphids and their eggs. Complete coverage of both the top and bottom of leaves is required and may need to be repeated for a few days. Horticultural soap sprays are also effective at controlling and reducing outbreaks. Ensure that that spray is specifically listed for use on your plant before using. Prune out and dispose of any affected foliage or flowers. Cutting back the plant severely may be needed but will not damage the overall health of most Geranium types. 

Preventing Aphids on Geraniums

Plant Geraniums of all types in a location with at least 6-8 hours of full sun. Geraniums planted in too much shade result in a plant that is weakened and stressed and much more likely to succumb to an Aphid attack.  Over-watering and over-fertilizing also stress Geraniums. High nitrogen fertilizers encourage large amounts of foliage growth that is not well supported by the roots resulting in weaker-than-normal growth.

Provide excellent drainage for container-grown plants to develop a robust root system that can sustain damage from Aphids. Encourage natural predators like Lady Beetles, Lacewings, and predatory wasps to your garden by providing a habitat for them to overwinter and not using broad-spectrum insecticides which harm both pests and beneficial insects. 

Geranium Budworm

Heliothis virescens is the Latin name of the Geranium Budworm. This pest is a smallish caterpillar that primarily feeds on the flowers and flower buds of not only annual Geraniums but nightshades like tomatoes, peppers, eggplants, and Nicotiana. The adult form of this pest is a brownish-colored moth that lays eggs in the target plants which hatch into green, brown, black, or cream-colored caterpillars that feed for weeks at a time.

Typically there are two periods of caterpillar hatching. Early spring from any overwintered pupae and August through September from eggs laid in early summer. Damage ranges from tunneled and hollowed-out stems from the emerging caterpillars to the loss of entire flowerheads by the mature caterpillars as they prepare to pupate. 

Treating Geranium Budworm

Using insecticides on Geraniums is generally not recommended. The densely petaled flowers make direct application on the burrowing larva near impossible. Instead, start monitoring plants as soon as they are planted outdoors in late spring. Remove any stems that appear to be damaged with tunneling or ragged edges on leaves. Handpick and dispose of larger caterpillars to prevent them from growing to the adult stage and laying eggs for later generations. 

Preventing Geranium Budworm

The pupae of Geranium Budworms easily overwinter in protected locations near greenhouses, decks, patios, and house foundations. Make sure to clean up spent plant material at the end of the growing season and do not reuse potting soil if you have had trouble with these caterpillars. Repot any Geraniums in fresh potting mix if they are being brought indoors to overwinter. Any cuttings of stems need a thorough examination to ensure there are no pupae or larvae present.

Ivy-leaf Geranium tends to be more resistant to Budworms and may be a good alternative to zonal or Regal varieties.

Root Knot Nematode

Root Knot Nematodes are microscopic pests that affect the roots of many perennial plants in garden borders. Over time these small parasitic worms cause knots, or galls, to form on the roots which can restrict the flow of nutrients and water to other parts of the plant.The nematodes multiply year after year in the soil and are easily transplanted to other parts of the garden (or other gardens) by root divisions.

Perennial Geraniums are much more susceptible to this pest, although annual Pelargoniums planted in the same location year after year can also be affected. The first signs of damage are yellowing foliage, drooping of stems and leaves or overall reduced health despite them being well tended to. Digging up plants will reveal roots with small globular growths that are the root knots.  

Treating Root Knot Nematode on Geranium

There are no pesticides registered for home use on Root Knot Nematodes. Removing plants that are failing as soon as possible and practicing good garden hygiene are the best ways to prevent large outbreaks. Do not compost any plant that has visible root knots. Home composting rarely reaches high enough temperatures to kill off pests or diseases on plants.  

Preventing Root Knot Nematode on Geranium

Rotation of annual plants in the garden helps to lower populations of Root Knot Nematodes. In areas of the garden that have large outbreaks, solarization is a good method of sterilizing the soil so it can be replanted later. Clear all plants before laying down sheets of clear plastic on well-watered soil. Keeping the plastic in place for at least 8 weeks can help to kill off eggs as far down as 12 inches in the soil, allowing replanting of shallow-rooted annuals and perennials. Keeping plants and garden beds adequately watered reduces the multiplying of nematodes. Using other moisture-holding materials like mulches and organic compost is also helpful in keeping the soil healthy. 

Geranium Pest Chart

Sources:

“Geranium: Pests in Gardens and Landscapes”, the University of California Statewide Integrated Pest Management Program. www.ipm.ucanr.edu