November marks the start of the white grub peak on sugarcane, with beetles already appearing quite prolifically across certain areas of the industry. This peak usually spans from November until end-December each year. Areas where most observations and trap captures have taken place include the Midlands North and South regions, Umfolozi, Zululand North and Umfolozi.

There are at least seven species of white grub associated with cane: Pegylis (syn. Hypopholis) sommeri, Schizonycha affinis, Adoretus fusculus, Asthenopholis spp., Anomola spp., Heteronychus licas, and Maladera spp. The Schizonycha, Pegylis and Heteronychus species (Figure 1) are most frequently captured in cane field over the grub peak season.

Figure 1. Common beetle species that occur on sugarcane in South Africa; (a) Heteronychus spp., (b) Schizonycha spp., (c) Pegylis spp

All species follow a similar general life cycle. Eggs are laid in the first few centimeters of the soil at the base of cane plants from December to February. These hatch and the grubs develop from February to September. Typically, most grubs can be found within the first 30 cm of soil under or close to the cane stool. The grubs that do the most damage tend to be more prevalent from June onwards. The grubs pupate around September, descending below 30 cm in the soil to do so. Adults emerge from about October to December, with only one generation per year.

In all species, the grubs feed on the roots of the sugarcane plant and at the base of young shoots, reducing growth and crop yield. However, in the species Heteronychus licas, damage is caused by both the grub and the adult (the beetles bore into the shoot just below the soil surface but seldom penetrate more than 5-6 mm). Typical symptoms of white grub infestation include the presence of dead hearts and patches of stunted cane in an otherwise healthy field (Figure 2).

Figure 2. Typical symptoms associated with white grub infestations; (a, b) stunted growth, and patchy distribution, (c) dead hearts (white spindles).

In terms of chemical recourse, there are currently no insecticides that are registered for use against white grub on sugarcane in South Africa. Control by natural enemies is not sufficient to prevent serious crop loss in parts of the industry. Deep ploughing when a crop is affected can expose the grubs to predation and desiccation. If conducted around mid-winter, many of the large grubs would be killed, so reducing the subsequent adult population that would appear from November to December. In the northern irrigated areas, where H. licas may be a problem, it is suggested that cane not be planted from August to January (over the period of adult activity). Slow germinating varieties should be cut early in the season, as ratoons are also susceptible to H. licas damage.