While there have been no reports of insect damage to Ontario tobacco so far this spring, growers should be keeping an eye out for damage from cutworms, seedcorn maggot and grubs, which can appear at this time of year.
Cutworms can cut transplants off at or below the soil surface, and/or cut off the “hearts” or chew holes in the leaves. If cutworm control is necessary after transplanting, this can be achieved with an over-the-top spray application of insecticide. Consult the 2012 version of OMAFRA Publication 298, Appendix A for recommended products.
Seed corn maggot
Seed corn maggot will sometimes damage recently transplanted crops. Under fairly moist conditions seed corn maggot damage can be difficult to detect. Under warmer and drier conditions it can be more obvious. Generally, plants that have been damaged by maggot feeding will be slightly droopy. Sometimes the maggot can be found inside the stem of the plant.
Seed corn maggots are about 4mm (.25 in.) in length and are a yellowish white in colour with a darker coloured head. Because of their small size and colour, they can often be difficult to find. Feeding normally occurs during mid to late May and then the larva will pupate, therefore tobacco planted in early June is usually relatively free from maggot damage.
Injury symptoms caused by seed corn maggot are small pin holes in the stem of the tobacco transplant and burrowing or hollowing of the stem. In some instances the seed corn maggot can be found inside the stem of the transplant. A good strong transplant will usually recover from this injury and may do better than a replant although it may look a bit droopy for a few days. Plants that are injured more severely will probably need to be replaced.
Some growers may have observed European chafer white grubs when transplanting tobacco. Grubs will chew the tobacco plants off just below the soil surface. The European chafer is white in colour with an orange-brown head and dark posterior. At this time of year, the European chafer turns more yellowish in colour and develops large folds in its body as it nears pupating. When the chafer pupates it will no longer be feeding.
There are no chemicals registered for the control of grubs in tobacco crops, and the effectiveness of the registered planting water treatments for other insects on grubs is unknown. No research has been conducted in tobacco for the control of grubs, however, when the grubs are brought up to the soil surface during transplanting they may be eaten by predators, or die from exposure to the elements. Replanting is about the best method of dealing with any grub damage that occurs.