Ecology and Management of Plum Curculio, Conotrachelus nenuphar (Coleoptera: Curculionidae) in Alabama Peaches

Abstract

Peach production is a major industry in Alabama and many other southeastern states of the United States. Over 40,000 acres of fresh and processed peaches worth $65 million are produced annually in Alabama, Georgia, and South Carolina. In Alabama alone, approximately 22 million pounds of peaches were produced in 2001 with a market value of about $12 million. The plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) is the most serious economic pest of peaches in Alabama and other parts of the southeastern U.S. This study was conducted to develop and implement cost-effective and environmentally friendly pest management practices for plum curculio. Specific objectives are: (1) Field evaluation of traps and lures for monitoring plum curculio in Alabama peaches, (2) Laboratory evaluation of behavioral response of plum curculio to synthetic host plant volatiles and male-produced aggregation pheromone (grandisoic acid); (3) Seasonal occurrence and development of a degree-day model for forecasting spring emergence of plum curculio in Alabama peaches; (4) Field evaluation of targeted insecticide sprays against plum curculio in Alabama peaches and (5) Evaluation of the effects of soil and weed management practices on plum curculio pupal development and adult emergence in Alabama peaches. In chapter II, the effectiveness of two widely used trap types (pyramid versus Circle traps) and commercially available synthetic lures for monitoring plum curculio was evaluated in two peach orchards in Alabama during 2008 and 2009. The lures evaluated alone or in combinations included benzaldehyde or BZ (a component of fruit odor), plum essence or PE (mixture of fruit odor extracted from food grade plum), and grandisoic acid or GA (male-produced aggregation pheromone of plum curculio). The results showed that pyramid traps captured more plum curculio adults than Circle traps, particularly, during the first generation. Trap performance was improved numerically by the addition of BZ, PE or GA alone (single lures), and was significantly enhanced by the addition of the combined BZ + PE lure. A follow-up study was conducted in the laboratory (Chapter III) to determine the influence of physiological factors (sex, age, diet and mating) on the response of plum curculio to the commercial lures (BZ, PE and GA) in four-choice olfactometer bioassays. The results showed that the physiological state of the weevils did not affect their response to the lures. In Chapter IV a degree-day model was developed for forecasting spring migration of plum curculio in peaches using historical temperature and trap capture data. The degree-day model predicted well the first and peak trap captures of plum curculio adults occurred in peach orchard. January 1 at a lower temperature threshold (LTT) of 10°C were found to be a better combination for accumulation of degree-days in peach orchards in Alabama. A six-order polynomial function fitted best to seasonal trap captures and cumulative degree-days, and revealed three overall seasonal peaks with the first (spring generation), second (summer generation), and third (summer generation) peaks occurring at cumulative degree-days of ca 220, 1122 and 1932 (base 10°C, biofix of January 1), respectively. The three-parameter Weibull model predicted the first trap and first peak (spring generation) trap captures to occur at mean cumulative degree-days of 108.02 ± 9 and 220.07 ± 16, respectively. In chapter V, studies were conducted in a peach orchard in Alabama during 2007 to 2009 to compare the conventional calendar-based insecticide spray program involving weekly applications of phosmet (Imidan®) to three different reduced spray programs using three targeted (well-timed) insecticide sprays (TIS) of phosmet, permethrin (Arctic®), or thiamethoxam (Actara® ) applied in an alternated fashion. All the three TIS programs significantly reduced plum curculio damage at harvest compared to the untreated control in two of the three years (2008 and 2009). Fruit damage due to stink bugs, which are emerging pests of peaches in the region, was also significantly reduced in the TIS programs in both years. In chapter VI the effects of soil and weed management practices on development and emergence of plum curculio was investigated in both field and greenhouse studies. Significantly fewer plum curculio adults emerged from centipede grass understory treatment than from other soil and weed management treatments. The results have identified promising tactics for the development of an IPM program for plum curculio in the southeastern United States.