Timing of Hull-split sprays for Navel Orange Worm

Written by Walt Bentley, UC IPM Specialist, San Joaquin Valley.

Hullsplit of Nonpareil almond, the most susceptible cultivar to navel orangeworm (NOW), is almost 2 weeks behind schedule in the central San Joaquin Valley.  Interestingly, the development of the second generation of NOW is not behind schedule with eggs being laid during the first week of July (see figure below).  This presents an interesting situation.  I believe many of these eggs will result in suicidal emerging larvae, not being able to infest the nut meat until hullsplit occurs.  This, however, doesn’t mean we are home free concerning NOW infestation.  It points to the importance of timing sprays to the development of the susceptible stage of the nut (initiation to 5% hullsplit).  Such timing will optimize the effects of any insecticide applied with the residual remaining through the complete second generation egg laying.  I believe a good portion of the early second generation eggs will hatch and be unable to infest the nut.  The remainder of the generation, that can reach the nut meat, will be shorter in time duration than normal.  If sprays are timed correctly, excellent chemical control should be achieved. 
The same scenario that could optimize control of NOW in Nonpareils may result in making later splitting varieties such as Carmel, Sonora and Price more susceptible.  This is a scenario that we see from time to time.  Here the third generation eggs may be timed to Carmel hullspit resulting a greater potential for infestation.  Try to focus on early harvest of any late soft shell variety.  It may still be a good idea to monitor egg traps to see how NOW egg laying coincides with the hullsplit of these later soft shell varieties.  This can give you an idea if additional chemical control may be needed. 
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