Managing mullein bug in apple orchards

This year mullein bug numbers are extremely high in some apple orchards in the province. Mullein bugs (Campylomma verbasci) overwinter as an egg inserted into the bark of the tree. Egg hatch begins at the pink to king bloom stage of Red Delicious and continues until petal fall. During warm weather, egg hatch usually occurs simultaneously, making management much easier.

Mullein bug (MB) nymphs (Fig 1) feed on developing flowers and young fruitlets, causing reddish pimples on the fruit. This damage eventually turns brown and becomes corky (Fig 2). Severe blemishes and malformation of the fruit caused by MB may decrease the marketability of the fruit. Mullein bug is only considered a pest from two weeks before and after the bloom stage of tree development, after which it becomes an important predator feeding on mite and aphid pests found in apple orchards throughout the summer.

Figure 1 Mullein bug nymph

Figure 2 Mullein bug damage

Monitoring MB populations is very important at this time of year. Mullein bugs are monitored by tapping (Fig 3) the limbs of 25 trees, and recording the number of nymphs present. Nymphs can be easily identified from other common orchard pests (aphids, and leafhoppers) by carefully examining the insect using a hand lens. Aphids, always have the 2 cornicles or tail pipes, located on their rear (Figure 4), and leafhoppers (Figure 5) have more longer, narrow bodies.

Figure 3 Apple scout tapping a tree for mullein bugs

Fig 4 Aphid-note 2 tail pipes on rear

Fig 5 White apple leafhopper. Body is long and narrow.

Insecticides for mullein bug are recommended if 7-9 nymphs are found in 25 traps. There are several good options for managing mullein bugs neonicotinoids such as Admire/Alias, Calypso and Actara are registered and research shows that Assail applied to control other pests in the orchard will provide subsequent control of mullein bugs. Generally Calypso, Assail and Actara are considered to have a longer residual then Admire/Alias, thus they may provide better control in years with cool wet springs when emergence is extended. These products may take slightly longer to kill the insects as compared to Diazinon. However, soon after application the insects begin to act woozy. Some reports from Michigan indicate that Calypso's activity against mullein bug may not be as strong as Assail. While Diazinon is very efficacious against mullein bug, it is not considered to be IPM friendly and is harsh on parasitoids that help suppress tentiform leafminer populations.