Dispersal of NOW and Prediction and Prevention of NOW Damage in Almonds

Authors: Burks, Charles - Chuck; HIGBEE, BRADLEY - PARAMOUNT FARMING; Sisterson, Mark; Brandl, David

Submitted to: Almond Industry Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/29/2007
Publication Date: 12/5/2007
Citation: Burks, C.S., Higbee, B., Sisterson, M.S., Brandl, D.G. 2007. Dispersal of NOW and Prediction and Prevention of NOW Damage in Almonds. Proceedings of the 35th Almond Industry Conference, Modesto, California. p. 1-6.

Interpretive Summary: The navel orangeworm is the principal insect pest of almonds, a crop worth over $2 billion (unprocessed) in California. In 2007 we found that: 1) the number of eggs in traps and navel orangeworm damage in harvest samples decreased compared to the previous year, whereas males in pheromone-baited traps did not during the first part of 2007; 2) transects along gradients of high to low navel orangeworm damage in almonds treated with either mating disruption or a residual insecticide showed the greatest decrease within the first 400 feet; and 3) there was a significant decrease in males in pheromone traps following a treatment in July with the growth regulator methoxyfenozide, but not with the organophosphate phosmet. We conclude that: 1) the data to date suggest that egg traps hold greater promise than pheromone traps for prediction of navel orangeworm damage; 2) even though navel orangeworm is known to disperse over large distances, most oviposition and damage in almond orchards occurs relatively near the site of female emergence from the pupa, and 3) our field observations are consistent with laboratory studies in other species suggesting that methoxyfenozide has sub-lethal effects reducing the ability of males to locate females. If this is the case, then methoxyfenozide may work synergistically with mating disruption. These data show the potential for prediction of navel orangeworm damage while mating disruption is in use, offer guidance on block size for effective use of mating disruption, and suggest a mechanism for increased effectiveness observed in other studies comparing a combined mating disruption/methoxyfenozide to either treatment alone.

Technical Abstract: The current proceedings reports the results of experiments in 2007 examining: 1) use of pheromone and egg traps for in-season prediction of navel orangeworm damage to almonds; 2) movement of navel orangeworm females in and between adjacent blocks under mating disruption and conventional control, and 3) the effect of methoxyfenozide treatments on males captured in pheromone traps. In the second year of a study comparing counts of males in pheromone traps (using unmated females as a pheromone source) and eggs in egg traps to subsequent damage, we found that damage and the count of eggs in egg traps were significantly lower compared to the previous year whereas males in pheromone traps were not. Augmentation of egg traps with 10% crude almond oil increased the number of eggs present on traps where oviposition occurred, but not the number of traps on which oviposition occurred. Bootstrap analysis of 2006 egg trap data indicated that the use of 16 or 32 traps provided =90% probability of detecting second flight oviposition that year, whereas use of 4 or 8 traps did not. Navel orangeworm damage from harvest samples taken from 6 adjacent trees at 200 foot intervals along 1000 foot transects from the edge to the center of an almond block had a high goodness of fit when regressed on the inverse of the distance. The damage reached a lower plateau within in the first 400 feet of these transects. Replicated blocks comprising adjacent 160 acre plots were treated with methoxyfenozide or phosmet, while monitoring male activity with pheromone traps. In May there was no treatment effect with either insecticide, but in July there was a significant decrease in males in pheromone-baited traps after treatment with methoxyfenozide, but not with phosmet. We conclude: 1) Egg traps currently seem more promising than pheromone traps for prediction of navel orangeworm damage, but the number of egg traps used for prediction is at least as important as the use of crude almond to increase their attractiveness. 2) Even though navel orangeworm is known to disperse over large distances, most oviposition and damage in almond orchards occurs relatively near the site of female emergence from the pupa. 3) The field observations reported here are consistent with laboratory studies in other species suggesting that methoxyfenozide has sub-lethal effects reducing the ability of males to locate females. If this is the case, then methoxyfenozide may work synergistically with mating disruption.