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March 2011


Here we go again!  Is your sprayer ready?  It better be if you farm pears in Mesa County.


I’ll start up the “Pest Alert” emails once the season gets underway and pest control timing becomes critical.



Horticultural spray oils have been in use for over a hundred years.  They are a unique tool in our arsenal from the perspective that no pest species have ever developed resistance to them.  Brought down to simplest terms, the results one will obtain with oil sprays are governed by three basic factors:

1)The oil used, 2) how well it is applied and  3)when it is applied. 


The same three legged stool I’ve preached on over and over and over…...




Oil covers insects with a suffocating film that kills both larva and eggs by a physical interference with the normal gaseous exchange.  Coverage is essential!

As eggs get closer to  hatching they become more susceptible to killing with oil.  Research shows that oil sprays applied at the beginning of hatch using a lower percentage of oil concentration are as effective as earlier applications at a higher rate.  Timing is essential!


So what’s the point?  We need to know what our target is and when it’s most vulnerable. Whether it’s green peach aphid, European red mite, or Pear Psylla, missing the optimum timing by a week can make a significant difference in control. 


OK, so what’s the optimum timing?

  • Two Spotted Spider mite:  This critter overwinters as an adult female that emerges about the same time as leaf emergence.  Delayed dormant on peach and tight cluster on apple are the best timing.
  • European Red Mite:  Red Mite overwinters as an egg.  Time sprays just prior to tight cluster on apple.
  • Pear Psylla:  Pear psylla overwinters as an adult.  A large portion of the population exit the orchard to overwinter on surrounding vegetation.  They return to the orchard in the spring to mate and lay eggs.  The purpose of oil in this program is TO PREVENT EGG LAYING.  Research shows that proper timing can suppress egg deposition by as much as 50% and delay it for three to five weeks.  Time sprays at the beginning of egg laying.  Give me a call,  I can help you with timing for your area.
  • Green Peach Aphid:  Overwinters as an egg and an adult.  Hatch occurs before bloom.  Time sprays for delayed dormant period.
  • Green Apple Aphid:  Overwinters as and egg.  Delayed dormant to tight cluster timing.


“One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors”

  • Plato


Every spring I get asked “How cold is too cold to spray dormant oil?”  The text book answer is 45ºF.  A bit of common sense also figures in.  Is the temperature on the rise, or decline?  Is it windy, damp, cloudy, etc.  Pay attention to freezing temps during the 48 hour period before application and for 24 – 48 hours after.  If present or predicted, hold off. 


It's common to make an application with a tank mix of several different pesticides and formulations.  There's a specific mixing order that will help keep you out of compatibility problems.  In other words, spending the rest of your day cleaning out your sprayer!  1) soluble packets,  2) wettable powders, or water dispersible granules,  3) flowables,   4) emulsifiable concentrates,  5) oils.   Always, always always add oils LAST!



GMD owns and reuses the barrels that we deliver your dormant oil in.  To ensure you receive a clean product, we steam clean them inside and out before each use.  This requires a bit of handling (expense) on our part, but is far less expensive than buying product in new drums each year.  To help us keep your cost down, please make sure your drums are completely empty.   THANKS!



Green peach aphid (GPA) has a host range of over 875 species of plants, including all stone fruits and many ornamental shrubs and vegetables.  GPA has a complex life cycle with five distinct morphological forms (eggs, nymphs, winged females, winged males and wingless females) and two behavioral forms (flight and flightless). Eggs hatch in the spring, producing wingless females that reproduce parthenogenetically. (OK time to get the dictionary out!) It means without fertilization from males. These eggs develop so quickly that they hatch before they exit the female and living 1st instar females are born.  After several generations of wingless females are produced, winged females are produced which migrate to secondary herbaceous host plants where they produce more wingless females by asexual reproduction.  This event in the life cycle is part of what causes us to believe that the population has “crashed”, when in fact it has simply moved.   Other factors leading to a mid-season population crash are decline in plant nutritional quality, increased natural enemy pressure and extreme weather events such as severe rainstorms.


Toward the end of summer, winged males and females are produced.  They migrate back to their primary host plant (peach), mating occurs and over-wintering eggs are laid at the base of buds.  These eggs are oblong 0.6mm x 0.3mm (smaller than the head of a pin) and shiny black.  Temperature plays a principal role in GPA biology.  The longevity of adults is 3 months at 41F to  10 days at 77F.  Longevity of nymphs is 21 days at 50F to 7 days at 77F.  Females are capable of producing as few as 36 offspring at 50F or as many as 76 offspring at 86F.  Fertility drops rapidly at temperatures over 86F. GPA adults can withstand 32F and larvae will survive to the 4th instar at 37F. 


There are two main reasons that aphids become a problem, nutritional status of the plant and their relationship with predators and parasites.  Aphids feed on the sap of plants.  Excessively vigorous trees with high levels of soluble nitrogen allow GPA to reproduce at faster cycles.  When aphids disperse from crowded conditions they exhibit an orientation to lighter green, fast growing terminals with high N levels.  Mature leaves with less nitrogen cause a decline in reproduction by at least 50%.  Once terminal buds set, aphids will usually cease reproduction and leave within the week.


All general predators plus many specialized predators and parasites attack aphids.  Many years these biological controls will keep populations in check.  Weather is a primary factor in biological control.  Aphids sit attached to their food source.  It only takes a brief period of warmth to allow them to feed.  On the other hand, predators need longer periods of warmth to search for their food and find it before they become too cold to function.  The other key to predator population levels is the choice and timing of insecticides you use.  I’ve witnessed the explosion of aphid populations when a broad- spectrum material was used at an improper timing.  


With stone fruits on the imadicloprid label, bailing yourself out of a GPA problem is easy if you’re a conventional grower.  If GPA is running rampant in your organic peach block, you’re in trouble!  As with any pest, the best control timing is the over-wintering stage, as it emerges in the spring.  A major factor in controlling GPA is proper timing and coverage of a dormant oil application.   Keep an eye on eggs prior to bud swell in the spring.  They’re most vulnerable to oil applications just before they hatch.



Do not argue with an idiot.  He will drag you down to his level and beat you with experience!!!


Here’s to a kind and gentle Spring!

PLEASE call with any questions.

Larry 234-3424

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