April 6, 2021

Spring Spraying Protocol Begins!

If you have not done so already, it's time to begin spraying a dormant oil and copper spray for your fruit trees! The apple trees are at green tip in the orchard here at Royal Oak Farm Orchard in northern Illinois. We may green tip fully in the next day or so with the daytime temperatures, but those night projections in the 50's will push the tree growth to full green tip and 1/4" green by the end of the week.  It also indicates that just as soon as the nights stay above freezing, the trees will pop and we will be moving into apple scab season.  So it is not too late to do a dormant oil and copper spray if you have not already.  We complete our spray on tonight, April 6, which is 4 days before last season's spray.  

The oil (mineral oil) is sprayed for mites, scale and aphids because spring is the time to cover those eggs at the base of the buds before they begin to hatch.  The oil smothers the eggs and they suffocate before hatching.  Below you can see aphid eggs that were laid last fall.

Aphid Eggs

Copper is also sprayed at this time for control of fire blight and to aid in the suppression of apple scab pathogens, scab being a severe diseases that can destroy a crop, and fire blight even more severe, which can destroy trees. 

We also have to be aware of the spring critical temperatures as the buds progress in development. Each spring I post the spring critical temperatures chart from Utah State to help you determine at what stage your fruit trees may be at as spring progresses.  For those who may have ,missed my last post, here are the charts again.
Critical Spring Temperature Apple Pear

Critical Spring Temperatures Stone Fruit

Ever wonder how the fruit trees know when it's time to come out of dormancy? Well, the trees won't come out of dormancy until they have endured a certain amount of time with temperatures between 32 and 45 degrees Fahrenheit. Once the number of chill hours they need is achieved and temperatures warm in the spring, the trees come out of dormancy and resume their normal growth. The number of hours required at cooler temperatures is known as the chill requirement or chill hours.  Most apple varieties require 400-1000 chill hours, so most of the trees in our area have met their requirement and will come out of dormancy just as soon as temperatures warm. Growth resumption can be predicted by tracking what we call growth units. Growth units are the number of degree hours above 41 F. For example, if the temperature averages 51 F for and hour, then 10 degree units are accumulated. Bud break initiates after approx 3710 F growth units accumulate, and progresses depending on the temperature. We do our dormant oil and copper spray generally around April 10. The best time to spray is at silver tip....when the buds have that silvery/gray tinted fuzz on them. 

You can use the development chart below to determine the growth stage your trees.

As I mentioned earlier, now is the time to do our fire blight/scab copper spray and our horticultural oil spray.  We want to get the copper on the trees before they reach full 1/4” green and the horticultural oil can be sprayed at the same time in a tank mix or done as a dormant,silver tip,green tip, or 1/4” green spray.  In other words, your oil can be sprayed at any time from silver tip through 1/4” green providing you are using a mineral oil based product such as Superior Oil 70sec or an off the shelf Horticultural Oil such as Bonide’s All Seasons Horticultural Spray Oil.  Your copper spray should be done before the trees reach 1/4” green to avoid any phytotoxicity issues.  For your copper spray you can also use an off the shelf brand such as Bonide Copper Fungicide RTU (Ready to Use).  Both of these products should be available at your local hardware store or garden center of from Amazon.com.

A dormant oil and copper spray should not be done until we get at least a 24 hour period that is above freezing at night. The oil cannot freeze on the trees, but it pretty much dries within about 24 hours. Once dry, there is no chance of it freezing.  We usually get at least one 24 hour period above freezing at night before the trees get to 1/4" green. 

This “window of opportunity” for dormant sprays for fruit trees depends on the bud stage of your target fruit tree. You can follow these guidelines:

Apples: swollen bud to 1/4” green
Pears: swollen bud to cluster bud
Peaches/Nectarines: swollen bud to pre-bloom
Apricot: before bloom

When applying, spray trees just until they are dripping to get good application on all the stems and crevices at the buds. If you are using horticultural oil alone, use a rate of 2% (mixed in water) for best results or follow your chosen product’s label rate.  For situations where aphids have been real problems in the past, consider adding an insecticide (such as acetamiprid, etc.) to 1.5 - 2% oil or use one of the Bonide RTU (ready to use) pre-mixes for insect pests.
For get our Growing Guide on maintaining your trees and Resources for the Home Orchard Grower of the above charts, visit our Nursery Growing Guide web page!


This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these  recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned.  The author assumes no liability resulting from the use of these recommendations.

March 29, 2021

Critical Spring Temperatures for Frost Damage

Early spring is the time of the year when apple trees are beginning to wake up from their winter sleep, and is also the time for colder night temperatures that we are sure to see. It's always a good idea to revisit the critical temperatures that can cause frost or freeze damage to fruit trees, specifically apple trees.  We are currently at silver tip to green tip here in northern Illinois with a forecast of night temperatures in the low 20's later in the week. Fortunately, our trees haven't progressed to far this spring, but we could see green tip next week.   This spring has marked another unprecedented weather pattern that raised our temperatures in late March and and is dropping our temperatures the first few days of April.  The early warm temperatures accelerated bud swell, and the lower temperatures that are anticipated present the threat of frost or freeze damage to new green tip leaf tissue.  It seems that each spring since about 2012, we have been on the verge of critical temperatures for frost or freeze damage with our fruit trees. 

Dark brown centers and signed appearance of the petals
indicate that both king and side blooms were killed in a
freeze the morning this picture was taken.  (Photo credit:
Mark Longstroth, MSU Extension)
As the trees develop in the spring and buds start to swell, they lose the ability to withstand the cold winter temperatures that they could withstand in dormancy during the cold winter months. The young, actively growing tissue can then be damaged or even killed. Swollen fruit buds can better withstand temperatures in the teens without any damage. As the buds open, temperatures in the low 20s can cause harm, but sometimes leave other buds undamaged.  As growth moves from green tip to 1/4” green to 1/2” green to tight cluster to pink in apple trees, temperatures in the upper 20s can cause considerable harm to an early blooming tree. Near bloom, the range between slight and severe damage can be very small. Freezing temperatures of 28 degrees F. will result in about a 10 percent loss and 24 F will result in a 90 percent loss, as indicated by the charts down below.

The dark brown center of this apple flower  indicates it was
killed by a freeze. (Photo credit: Mark Longstroth, MSU Extension)
In a radiation freeze with clear, calm conditions, fruit at higher elevations or in the tops of trees will be less damaged than those at lower elevations, since colder air is more dense than warmer air and sinks to ground level, pushing the warmer air up. The percent of flowers killed in a frost may or may not relate directly to lost yield later in the season. With large-fruited fruits such as apples, peaches, plums and pears, the loss of 50 percent of the flower may not be devastating since we may only want a small percentage of the flowers to become fruit, meaning that fruit thinning may be totally unnecessary.  So the stage of bud and bloom development determines how susceptible any given fruit crop is when freezes occur.  For more information on what those critical temperatures are that can cause freeze damage to trees during development, I have added two charts on the Critical Temperatures For Frost Damage on Fruit Trees from Utah State University below that you can download by clicking on either chart below.

(Click on the photos to download the chart in PDF format.)
Given the weather patterns we have experienced so far this spring a spring frost could still be possible.  Once the fruit has set, then the critical temperatures that can damage the fruit become lower.   We will need to constantly assess the stage of development our trees are at over the next weeks and their susceptibility to possible freeze injury.

If we continue in a spell of colder weather, apple trees will continue to develop more slowly, but once they begin showing tight cluster, pink and bloom, the critical temperature rises from the low 20’s to the high 20s, to levels just below freezing at bloom time, which is the most critical time to get frost damage.   

Reference in this blog to any specific commercial product, process, or service, or the use of any trade, firm, or corporation name is for general informational purposes only and does not constitute an endorsement, recommendation, or certification of any kind by Royal Oak Farm, Inc.   People using such products assume responsibility for their use in accordance with current label directions of the manufacturer.

March 15, 2021

Main Pests, Tree Growth Stages, and Spray Guide

If you have a Home Orchard or just a few apple trees in your back yard, and if you have not thought about how to handle those pest problems you had last season yet, now is the time to actively examine a spray protocol  for your fruit trees!  And start right away, before it is too late and the pests have a chance to establish themselves in your trees!  The question everyone needs to ask before spraying is “Do I want to spray or not?”   Well, unfortunately, in northern Illinois, we have four main pests that we will almost always have to spray for.  This is pretty much true for any area east of the Rocky Mountains.

The decision to spray or not depends on how much fruit loss you are willing to take. That is your threshold.  If you can accept some fruit loss, then the need to spray diminishes greatly.  But if you only have a few trees and some fruit damage may mean losing half your fruit, then spraying becomes more important.  Let’s meet our top four pests in northern Illinois,  southern Wisconsin, and in most of the states east of the Rocky Mountains. 

 The Four Main Pests


The four main pests that we face in apple orchards here in our climate zone of 5/5A are , , and , in that order. What isn't listed here is fire blight, whihc is a devastating disease that must be sprayed for because it can wipe out entire trees in a matter of days.  For more information on these and other potential apple tree pests, visit our web site Growing Guide page.  But how do we know when to spray for them if it is a last resort to protecting our fruit? 
All tree fruit have several distinct growth stages as the fruit matures.  Knowing and identifying those growth stages is  very important for the home grower because recommendations and spray timing for spray applications are linked to these specific growth stages.  The chart below shows the common growth stages for apple trees.  

Tree Growth Stages (Phenology)



Since the average home grower does not have access to their own weather stations or degree day calculators, the fruit tree development stages play an ever greater  role in pest management for the average grower.  Most spray schedules (protocol) follow the tree development stages to aid in the timing of sprays so they are most effective.  It is important to note that many diseases and some insects can only be controlled by spraying before they can be seen like apple scab.  Spraying less frequently or at the wrong time will typically result in poor results.  And, spraying more frequently will not necessarily give greater control.

The tree developmental stages or tree phenology gives us a guide as to when to spray, but what do we spray if we have to spray?  If we consult some of the various spray guides available to the home grower, we will find that most of the spray guides provide us with the tree’s development stages (phenology) and the insects or diseases that frequently  occur during each of theses stages.  So the tree phenology serves as timing guide when the application of a particular spray is recommended in order to control specific insects or diseases at the right time.   The following spray guide for apple trees will give us the time to spray based on tree phenology, the pest to spray for and the product recommendation for that pest(s).

Apple Spray Guide

This particular spray guide is included in “” from the Purdue University Extensions Publication web site or our as a free download.  It goes into detail as to the various products available for spraying that include both conventional and organic alternatives.  The publication includes apples,  pears, peach, cherry, grape, strawberry and raspberry guides as well as the phenology charts for each fruit type.  For recommendations on spray products for the Home Orchard visit our spray product recommendations.

Reference in this publication to any specific commercial product, process, or service, or the use
of any trade, firm, or corporation name is for general informational purposes only and does not
constitute an endorsement or certification of any kind by Royal Oak Farm.

People using spray products assume responsibility for their use
in accordance with current label directions of the manufacturer.

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