Now’s a good time to refresh ourselves on the benefits of horticultural spray oil and the many questions related to its use!
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
3) when it is applied
It’s the trifecta you’ve heard for years……
MATERIAL - COVERAGE – TIMING
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 being killed 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.
Every spring the question is raised regarding, “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,
4) emulsifiable concentrates,
5) oils. Always, always always add oils LAST!
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.
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.
As new rules continue to develop regarding chemical use and safety requirements, here’s a list we found of fruit related chemicals that require the use of a respirator at this time (Do not consider this as an exhaustive list. Always check the product label):
Agree WG Bacillus thuringiensis aizawai
Assail 70WP acetamiprid
Azera azadirachtin + pyrethrins
Carbaryl 4L carbaryl
Chateau SW flumioxazin
Chlorpyrifos 15G chlorpyrifos
Chlorpyrifos 4E AG chlorpyrifos
Diazinon 50W diazinon
Diazinon AG500 diazinon
DiPel DF Bacillus thuringiensis kurstaki
Dithane 75DF Rainshield mancozeb
Double Nickel 55WDG Bacillus amyloloiquefaciens D 747
Echo 720 chlorothalonil
Eptam 7E EPTC
Gramoxone SL paraquat
Grandevo Chromobacterium subtsugae strain PRAA4-1
Imidan 70WP phosmet
Lannate SP methomyl
Lorsban 4E chlorpyrifos
Orthene 97S acephate
Proclaim 5SG emamectin benzoate
Pyganic 1.4EC pyrethrins
Pyganic 5EC pyrethrins
Rely 280 glufosinate
Rovral 4F iprodione
Serenade ASO Bacillus subtilis QST 713
Serenade Max Bacillus subtilis QST 713
Sonata Bacillus pumilis QST 2808
Vangard WG cyprodinil
Vapam HL metam-sodium
Ziram 76DF ziram
Hope this helps as we increase our awareness of the changing compliance requirements related to our industry!
“My reading of History convinces me that most bad government results from too much government.” – Thomas Jefferson