The removal of nuts remaining on almond trees from the prior year's crop is an important winter sanitation practice for the management of navel orangeworm (NOW), Amyelois transitella. Residual nuts are called ‘mummies' and the process of removing the mummies is referred to as a ‘mummy shake' because they are mechanically shaken from trees. This practice is conducted during the dormant and delayed dormant season, a time when orchard access may be thwarted by the winter rains.

Most growers strive to have the mummy shake complete by mid-January when buds are dormant and less likely to abscise from the vibration caused by a mechanical shaker. As the flower buds progress toward bloom, they become more sensitive to the shaker vibration and more likely to abscise. Studies conducted in the 1980s (Sibbett et al.) established that the shaking of mummies by January 31 (approximately 8 days prior to bloom) at a Kern County site did not adversely affect yield; however, the authors cautioned growers of the risk of delaying mummy shakes further, particularly on early blooming varieties and in locations in the southern San Joaquin Valley¹. Because bud development and bloom date advance with increasing latitude, the potential risk of early and mid-February mummy shakes was investigated by W. Asai (Pomology Consulting, Turlock, CA) in the northern San Joaquin Valley. This work, conducted at a more northern latitude, suggested shakes conducted in early February may not compromise yield².

The lack of yield detriment attributed to a mummy shake-mediated bud loss may seem counterintuitive; however, simple concepts of tree physiology may help explain this phenomenon. Consider that only approximately 30% of the flowers on a tree set a crop. A given tree does not have the carbohydrate stores needed to set every flower. As a result, the loss of a subset of flower buds may have little effect on overall yield. Naturally, the risk of crop loss increases the closer the shake approaches bloom, and both research groups suggested that mummy shakes be complete prior to the pink bud stage of development.

Although rainy years make it difficult for growers to access orchards and complete orchard sanitation tasks, the heightened soil moisture adversely affects NOW survival in comparison to dry winters. Mummy nuts on the ground support enhanced NOW survival on a dry orchard floor than on moist soil with winter vegetation in the row middles. The next step in managing overwintering populations of NOW is destruction of mummies by flailing or mowing. Flailing and mowing should be completed by March 1, prior to the emergence of NOW. The emergence profile of NOW varies by location, but the first flight generally starts in late March.

Growers who have not completed their winter sanitation practices by the end of January should walk their orchards to assess bud development in consideration of a delayed mummy shake. Winter sanitation can reduce now damage by up to 80%, so an early February shake may be worth the effort if orchard access is possible and bud development has not advanced into pink tip. For more information on NOW management, visit www.ipm.ucdavis.edu.

The first step in assessing the cause of canopy chlorosis and decline in an orchard is mapping the distribution of the symptoms. If a pattern of chlorosis is similar across irrigation lines, then the cause of the problem may be related to over- or under-watering. Two scenarios present themselves regularly during summer farm calls: a) terminal tree chlorosis, and b) within row tree chlorosis (Figures 1 and2). 

Terminal Tree Chlorosis.  In some orchards, the terminal tree along the irrigation line may become chlorotic and decline in advance of mortality. If terminal tree chlorosis is a trend throughout the orchard, it is worth assessing the sprinkler distribution at the end of the irrigation lines. In some orchards, the terminal tree is outfitted with a sprinkler that is not shared with a neighboring tree (Figure 2A). This terminal tree receives 1.5 x the amount of water as the other ‘healthy' trees down the irrigation line. In an otherwise adequately-irrigated orchard, these terminal trees are over-irrigated and develop chlorosis and decline. Sometimes the terminal sprinkler is positioned adjacent to the trunk (Figure 3), resulting in direct wetting of the trunk, a condition that predisposes the tree to Phytophthora infection, particularly when surface water is utilized.

Correcting terminal tree chlorosis:  To correct the over-irrigation of the terminal tree, the microsprinkler head can be changed to a lower flow rate.  Sprinklers should be placed away from the base of trees to prevent direct contact of the trunk with the stream of water. Additionally, when replanting dead or declining trees at the end of rows, consider that the irrigation needs of the replant are considerably lower than that of the neighboring older tree in the row.

Within-row chlorosis. If canopy chlorosis is consistent throughout the orchard, but terminal trees appear healthy, assess the distribution of sprinklers around the terminal tree in comparison to the trees along the irrigation line. If the terminal tree receives less water (Figures 1B and 2B) than adjacent chlorotic trees, consider the potential that the orchard, as a whole, is over-irrigated. To test this hypothesis, growers and orchard managers can use a pressure chamber to assess the midday stem water potential of the trees. Almond trees maintained from ^-6-^-10 bar are under low water stress, but may be more susceptible to disease. Maintenance of almonds at ^-10-^-14 bar (mild stress) from mid-June through hull split, minimizes risk of disease (ie. hull rot) and supports shoot growth. For information on use of a pressure chamber for enhanced irrigation management of almond, walnut and prune, download UC ANR Publication #8503 (http://ucanr.edu/datastoreFiles/391-761.pdf).

Correcting within-row chlorosis:  If the orchard at large is over-irrigated, a change in the overall irrigation strategy is warranted. A combination of pressure chamber use to measure tree water stress, and consideration of weekly crop transpiration may enhance irrigation scheduling. The California Department of Water Resources and UCCE have teamed up to provide Weekly ET Reports to agricultural water users to assist with irrigation scheduling. The reports include water use information for a variety of crops including almonds, pistachios, walnuts, grapevines, citrus, and stone-fruit of mature bearing age. Adjusted on a weekly basis, water use estimates account for the changing growth stage and weather conditions at the Madera, Parlier, Lindcove, Stratford, Panoche, and Five-Points CIMIS weather stations. Each report gives crop-specific evapotranspiration (ETc, total crop water use including soil evaporation) estimates for the previous and coming week. To learn how to use these reports, please refer to the following article:  http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=26858.  Crop ET reports can be found online (ie:  http://cetulare.ucanr.edu/Agriculture782/Custom_Program911/). 

Cold winter temperatures can reduce populations of leaffooted bug, Leptoglossus zonatus (Dallas), by ~50 to 80%.  But unfortunately, it takes a cold year much like occurred in January of 2007 where daytime temperatures remained low and nighttime temperatures reached about 20° F for several hours.  In other words, ouch for the citrus crop.  Fall and winter temperatures of 2016 / 2017 were ideal for leaffooted bug and the growing season started out with large populations.  I need to add that we do not fully understand if the wet winter positively affected populations - it certainly did not have a negative impact.

Monitoring and managing leaffooted bug presents an IPM challenge.  In the fall between September and mid-November, the species produces a full generation; certainly, on pomegranate and although I have not observed it, also on desert willow.  In most years, adults have moved from those host plants by late December to protected overwintering sites such as Mediterranean fan palm and Italian cypress trees.  In early March leaffooted bug leave overwintering sites to feed on what happens to be available at the time i.e. almonds and subsequently pistachio.

The IPM challenge is that we do not have an effective monitoring tool to detect the bug when they make their initial entrance into almond in spring and pistachio in early summer.  And moreover, once leaffooted bug is detected, pyrethroids offer the best management option – not necessarily the best IPM option. 

Given the importance of pomegranate in the life cycle of leaffooted bug, PCAs and growers need to concentrate monitoring efforts on that crop during September through October, especially focusing on unmanaged orchards and hedgerows near almond and pistachio orchards.  If populations are found they will consist mainly of immature stages and there are two management options, clothianidin and pyrethrins.  The caveat is that those compounds have only contact activity; coverage must be good and the insecticides will likely not have a great impact on adults because they will spook and fly away before being sprayed. 

At this time, pistachios have passed the most vulnerable stage for leaffooted bug damage but can still suffer some damage and should be monitored and treated if bugs are found.  The UC Statewide IPM Program provides a few monitoring recommendations focusing on damaged nuts and nymphs.  Adults can be monitored for by visually searching tree canopies for about 15 – 20 seconds each.  Concentrate searches to the sunny side of the canopy and focus attention on the nut clusters.

              Unfortunately, the treatment options with any residual activity are limited to pyrethroids.  Producers have begun gearing up for “hull split” navel orangeworm sprays.  Note however, that non-pyrethroid compounds such as methoxyfenozide, chlorantraniliprole, spinetoram do not have any activity against leaffooted bug or other large bugs.     

Insecticide use should occur only if monitoring indicates the presence of leaffooted bug and/or its feeding damage.  Apply insecticides only after considering the potential risks of the compound to beneficial organisms, including bees and biological control agents, and to air or water quality.  For more information on these topics please consult the UC IPM Pest Management Guidelines for Almonds at http://ucipm.ucanr.edu > Agricultural pests > Almond

Photo Caption:  

Fig. 1.  Aggregation of leaffooted on pomegranate in early October of 2016.  The aggregation is comprised mostly of fifth instar.