Where are Leaffooted Bug Overwintering?

Written by Kris Tollerup, University of California Cooperative Extension Area-wide IPM Advisor, Kearney Agricultural Research and Extension Center, Parlier, CA For a few seasons now, I have been interested in understanding more and ultimately finding better monitoring tools for Leaffooted bug, Leptoglossus spp.  Most growers and PCAs have a  good working knowledge of this bug and likely have attended one or more of my talks covering the subject.  We know that leaffooted bug overwinters in aggregations consisting of just a few to several hundred individuals.  The aggregations tend to occur on citrus, palm frowns, Cyprus trees, pomegranate, walnut (Fig. 1), olive, and on/in non-plant substrates like pump houses, farm equipment, and wood piles.  The list is extensive.  The reason why aggregations can occur on such a diversity of substrates is that they are not necessary interested in feeding but more so in seeking a protected area to survive winter.  An  interesting behavior that I have made is that aggregations typically occur where the group can best collect heat from the sun during peak solar radiation periods.  In spring or as early as late winter, individuals begin leaving aggregations.  I, as well as other researchers, found that dispersion is closely associated with temperature and not necessarily dependent on other environmental factors such as day length.  I observed some moderately large aggregations on pomegranate in Tulare Co. and after warm mid-February temperatures of about 80 F, nearly all the LFB dispersed.  To particularly where, at that early time in the season, we did not determine.  The site had neighboring plantings of citrus and olive, which we surveyed but did not observe LFB in those crops.  Typically at mid-March, LFB starts moving into almond and history shows that they can cause substantial economic damage.  Because of work conducted by a host of researchers

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Almond Set and Nut Drop

Annually, I receive several questions on nut set. Many are aware that not all of the flowers on the tree will set a nut, but how many do? This, of course, can range  between 15-40%.  Most orchards, however, set between the 20-30% range, with average orchards around 25%. This percentage varies year-to-year, and is dependent on flower density, temperature at bloom and post-bloom, and tree health. Spur dynamics play a key role in fruit bud density and the ability for a flower to set. Research by Tombesi and colleagues found that a fruiting spur, if maintained in a position with ample light for photosynthesis, tends to alternate bear. These spurs may flower the year after cropping, but rarely set a nut. This is believed to be due to carbohydrate and nutrient depletion within the spur. Surprisingly, tagged spurs that double or triple crop die, regardless of light position. Therefore, orchards that have a high set percentage deplete the spur pool, leading to a reduced set in the following year (i.e. alternate bearing). Generally, however, most orchards are able to re-develop spur positions which lead to sustained yields. Farmer practices come into play in developing and maintaining spurs- they include PROPER irrigation and nutrition, as well as adequate potassium levels to reduce spur mortality. Tagging studies have also found that set percentage is generally inversely related to flower density. This means that trees that have fewer fruit buds/flowers will set at a higher percentage than trees with a high fruit bud/flower count. This most likely is due to a greater amount of resources able to be allocated to a fewer number of buds. This compensation for the lower bud count, however, does not typically lead to a higher yield. Temperature can impact set as well. Almond pollination and fertilization can occur over

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