Effects of simulated rat damage on yields of macadamia trees

• Published in: Crop protection 1997-05, Vol.16 (3), p.203-208
• Main Authors: Tobin, M.E., Koehler, A.E., Sugihara, R.T.
• Format: Article
• Language: English
• Subjects: compensatory growth; integrated pest management; Macadamia integrifolia; mammal damage control; Rattus rattus
• ISSN: 0261-2194; 1873-6904
• DOI: 10.1016/S0261-2194(96)00105-6

Rattus rattus damages 5–10% of the developing macadamia ( Macadamia integrifolia) nut crop each year, but the impact on yields of mature nuts has not been well documented. We evaluated the effects of simulated damage on yields of mature nuts at two locations on the island of Hawaii during the 1995 crop season. We removed 10 or 30% of the developing nut clusters from 5-year-old trees at 90, 120, or 150 days post-anthesis (dpa) and evaluated yields of mature nuts at 210–215 dpa. Removal of 10% of the crop load had no measurable effect on yields of mature nuts regardless of when damage was inflicted. Yields of trees with 30% of nut clusters removed differed from the control (no nut clusters removed) only when damage was inflicted at 150 dpa. These results raise questions about the cost-effectiveness of current rodent control programs, especially during early nut development. Growers may be able to tolerate damage to 10% of their developing nuts without suffering economic losses, and may be able to sustain losses as high as 30% provided that damage is incurred before 120 dpa. Damage control efforts should focus on reducing damage after 150 dpa. However, high rat populations and damage prior to 150 dpa might indicate the need to apply measures to reduce damage later in the crop cycle.