IN YOUR ORCHARD
THE BEE BOX Cover Crops and Navel Orangeworm Management in Almond Orchards Navel orangeworm (NOW) is a primary pest affecting almond orchards, causing substantial economic losses through nut damage and the spread of aflatoxin. With depressed nut prices and a changing climate, NOW damage has been exacerbated over the years. Current management practices rely heavily on winter sanitation, well timed insecticide sprays, timely harvests, and mating disruption to reduce NOW populations. This article discusses how cover crops can augment navel orangeworm control.
Historically there were three flights of NOW per year, now four flights have become industry standard.⁴ Early management of this pest is vital in reducing crop damage. Each female NOW moth can lay between 80 to 200 eggs and multiple larvae can develop in each nut. It is well documented that NOW overwinters as larvae in mummy nuts in the trees and on the ground. In addition to NOW, a new pest is emerging in almonds: the carpophilus beetle ( Carpophilus truncatus ). This beetle was first noted in the San Joaquin Valley in 2023 and is known to overwinter in mummy nuts. Little is known about which pesticides may control this beetle, prompting UC researchers and extension officers to
strongly promote winter sanitation efforts for both NOW and the carpophilus beetle.⁵ The numerous detrimental effects of mummy nuts highlight the importance of winter sanitation efforts.¹ Removing and destroying mummy nuts has additional effects on yield quality. Integrating cover crops presents a promising approach to supplement pest control efforts by enhancing mummy nut decomposition, promoting predation, and reducing female NOW moth oviposition.³ Cover crops influence mummy nut decomposition dynamics by fostering favorable conditions for microbial activity and nutrient cycling in orchard soils. Studies have shown that the presence of cover crops accelerates the breakdown of mummy nuts compared to bare orchard floors. Earlier planted winter cover crops, when established by November to December, provided better mummy nut decomposition than later planted cover crops. Also, the height and density of the cover crop affected NOW survival with taller, denser
plantings. This detrimentally affected overwintering NOW populations. Establishing cover crops enhances the habitat complexity of almond orchards, providing refuge and food sources for natural predators of NOW larvae. These predators actively prey upon overwintering NOW larvae in exposed mummy nuts, thereby reducing the population of NOW before they can infest the following summer crop. However, due to the extremely low treatment threshold for NOW, less than 2% nut infestation, natural predators are rarely relied upon for NOW control.³ Cover crops also contribute to NOW management by concealing mummy nuts from female moths during their oviposition period. The vegetation acts as visual and olfactory camouflage, making mummy nuts less detectable to female moths seeking suitable egg laying sites. The reduced visibility and accessibility disrupt the moth’s reproductive cycle, thereby lowering the likelihood of infestation in mummy nuts on the ground.³ While cover crops offer significant benefits in NOW management, they
NOW in Independence. Photo credit Mel Machado
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ALMOND FACTS
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