Bloom Time is Blossom Blight Time!

Infected blooms first appear water soaked and later begin to wilt.

As we enter into full bloom this week, we have a major pest to consider, and probably the foremost pest at bloom time, fire blight.   Fire blight is a serious bacterial disease of apples and pears that is twofold in its development. Fire blight differs from other diseases of apple in that it is caused by bacteria, not fungi. The fire blight bacteria attacks all tissues of apple tree including blossoms, leaves, shoots, branches, fruits and even the roots.  The bacteria usually enter the tree through the blooms during bloom time which creates a condition we call blossom blight.  Under rainy conditions, the bacteria then move into the tissues of the flower and on into the rest of the flower cluster. This infection causes the death of the flowering spur, which is often the first visible symptom of the disease.  As the initial fire blight symptom seen in an orchard, blossom blight usually indicates where the pathogen first gains its entry into the tree. The bacteria kill the flower (blossom blight) and sometimes the spur (spur blight). The damage may resemble frost injury to fruit spurs.  

Spur Blight

If fire blight is allowed to become established in the tree, it can rapidly spread from the current season’s growth into spurs or older growth.  Spur blight is the collapse of entire spurs on spur type varieties, after the initial fire blight symptoms on single flowers. The bacteria then begins to move inside the plant, killing nearby tissues. 

Note blackened leaves and fruitlets

So, if the spur on a main branch or the trunk becomes infected, the disease can move from the spur into the trunk or branch eventually developing into a canker which girdles the branch or limb.   Death of infected branches is very rapid and the leaves do not even have time to fall off the tree.  The systemically infected shoot has orange-colored leaves at the tip and is starting to wilt. You can also see wilting leaves around the infection and the woody stem is also starting to ooze, both above and below the initial infection. Young, non-bearing and newly bearing trees can easily be killed by the infection while mature-bearing trees can usually survive if all the new growth that is killed is pruned out.  

Shoot Blight

As we have seen, fire blight produces several different symptoms depending on the host and site of infection. As the pathogen moves from blossoms it can go to  spurs and then shoots.  Shoot blight is probably the most well known of all fire blight symptoms. The most commonly observed of these symptom is the characteristic “shepherd’s crook” that develops on wilting twigs, shoots, and leaders. In fact, the name “fire blight” aptly describes the  characteristic infections on apple, infected branches turning reddish brown to brown. 

Tips of the shoots have that "shepherd's crook" look to them

Cankers can then develop, and the margins become raised and blistered, eventually cracking. When the bark is removed, the cankered area may show red-brown streaking. Dead branches scattered throughout the canopy of the tree are common, and trees can die if infections spread into the main stem. The younger the tree, the more likely it will die following infection.  

In cases of serious infection, when the bacteria have entered the trunk of the tree, it’s best to remove the tree entirely, including the stump. Infected tissue allowed to remain in the planting is a source of bacteria to infect the rest of your trees. Once the main trunk is infected, trees cannot be cured of the disease.

 

Managing Fire Blight

Our first line of defense against this fire blight bacteria is a copper based spray at silver tip, before bud break, which we covered in a previous post. To prevent spread after bud break, and to prevent spread, apply a combination of mancozeb and copper to protect new growth.  Then at full bloom, a streptomycin spray is necessary using Bonide Fire Blight Spray® or Fertilome Fire Blight Spray®, which are acceptable for home use.   Serenade Garden Defense (Bacillus subtillis) is a biological control product containing an antibiotic producing bacteria. This product has been show to reduce infections on apple blossoms if applied to healthy but at risk blossoms.   Any chemical management is not recommended after petal fall. If you are managing fire blight with streptomycin, it is essential to reduce the risk of antibiotic resistance from developing, so do not use streptomycin after any symptoms may have developed or to control any shoot blight that may develop.  Using  streptomycin in those cases is not only ineffective, but it increases the risk that the bacterium will become resistant to streptomycin.  Once shoot blight has appeared during the growing season, when the weather is dry, prune back about 12 inches below visible symptoms.  Remove the prunings from the yard/orchard and burn them.  Between each pruning cut, clean your pruners by dipping them in a 70% ethyl or isopropyl alcohol solution for 30 seconds or spray pruning shears with Lysol spray to avoid spreading the bacterium.

Apple Scab Season!

 Apple scab is the most prevalent and most damaging disease to apples we have in the Midwest. We are now officially emerging into the apple scab season and scab sprays should be applied according to the spray guide protocol.  In the spring, once temperatures rise above the 42 degree or so  mark, apple scab fungal spores can germinate in water on the surface of  apple tree leaves and eventually,  on the fruit itself. The water or moisture that is on the leaves is termed "leaf wetness". The spores will germinate once the leaves are wet for a certain period of time at temperatures above 42 degrees  On the leaves, olive green to brown spots appear on the site of the infection.  If the leaves have not been protected from this "primary" scab infection, the spores will mature and produce more spores during "leaf wetness" periods and move onto the apples where they form a "scab" like lesion, if the fruit is not protected.  We call the lesions on the apples "secondary" scab.  With enough moisture (leaf wetness), the cycle continues throughout the growing season and destroys the crop.  Each leaf wetness event at the proper temperature that occurs during the early growing season is called and infection period.

Managing Apple Scab

 

The apple scab fungus survives in dead leaves on the ground and over winters there on the leaves.  A lack of spring rains can reduce its importance, but as a rule, apple scab requires yearly spray treatments.  And, ornamental crab apples are also hosts. As plant parts mature and the weather gets warmer, susceptibility to this disease decreases, usually in late June, but pinpoint scab can occur during extended periods of moisture during summer.  The main objective in scab management is the reduction or prevention of primary infections in spring. Extensive primary infections result in poor fruit set and make scab control during the season more difficult. If primary infections are successfully controlled, secondary infections will not be serious. The key to success in scab control is exact timing and full spray coverage. Wet periods, temperature, and relative humidity are important factors. Because scab control often is part of a combination treatment aimed at other diseases and insect control, choice of materials and timing are also extremely important.

How Can an Infection Period be Determined?

 

Apple scab infection periods can be predicted based on temperature and moisture (leaf wetness)  conditions. The Mills Table below, derived from research by Mills and La Plante, gives hours needed at various temperatures under constantly wet conditions for primary spores (ascospores) to cause infection in spring. This system for forecasting scab and timing sprays has been validated for apple-growing regions in the Midwest.

How to use the table: Figure the average temperature for the rain period by adding the maximum and the minimum temperatures and dividing by 2. If wet periods are intermittent, total their duration until there is a period of at least 6 hours of continuous dryness. You will need a wetness recorder to do this efficiently. If the dry period is sunny, and drying is quick and thorough, it is assumed that 6 hours after the trees have dried, the danger is passed. If drying is slow, and humidity remains high, then the 6-hour dry period is extended by a safety margin of 3 to 4 hours. 

 

To Spray or Not To Spray

 

Monitoring for apple scab can be quite complicated for the home grower.  But there is an alternative.  Unless wetness periods are being monitored as outlined in the section above, you can simply apply protective or eradicant fungicides at regular intervals beginning with green tip. Spraying should be done every 7 to 10 days, depending on the number of rain events between sprays.  If there are no rain events between sprays, a single protectant spray will last at least 10 days but not more than 14 days, based on the product's label directions.  You will need to make sure that your trees and fruit are protected prior to any rain event if you are going to use only a protectant.  A good protectant is Captan or Mancozeb.  But, a protectant can lose its effectivness after 2" of rain, so you also want to keep and eradicant on hand like a myclobutanil, which is available as Spectracide Immunox. A protectant like Captan has to be applied prior to a rain event.  If no protection is available during the wetting event, then only an eradicant like Immunox can be applied that has a reach back of at least 48 hours.  That means that it can still have an effect on the scab pathogen for up to 48 hours after a wetting event. A good option is to actually use both a protectant and an erdicant at the same time, like Captan mixed with Immunox, which will give you both protection and eradicant action after a wetting event. Be sure to monitor wetness periods throughout the spring to insure that trees are always adequately protected.  

More About Fungicides

 

Fungicides can be contact fungicides or penetrant fungicides and non-systemic, locally systemic or systemic. Mobility describes fungicide movement after it is applied to a plant. To understand differences in mobility, it’s important to know the difference between absorption and adsorption. 

Fungicides that can be taken up by the plant are absorbed. Fungicides that adhere in an extremely thin layer to plant surfaces are adsorbed. Because fungicides are either adsorbed or absorbed, they have two basic forms of mobility: contact and penetrant.  Regardless of the type of mobility that a fungicide possesses, no fungicide is effective after the development of visible disease symptoms. For that reason, timely fungicide application before establishment of the disease is important for optimal disease management.

Contact fungicides are adsorbed and considered non-systemic. They are susceptible to being washed away by rain  or irrigation, and most (but not all) do not protect parts that grow and develop after the product is applied.  Captan is one such contact fungicide.

Penetrant  fungicides are absorbed, so they move into plant tissues, and penetrate beyond the cuticle and into the treated leaf tissue itself.  There are various kinds of penetrants, characterized by their ability to spread when absorbed by the plant.  They can be locally systemic, penetrating leaf tissue only or systemic, moving beyond the leaf tissue. Systemic fungicides can be further subdivided based on the direction and degree of movement once they have been absorbed and translocated inside the plant. Immunox is a penetrant that is xylem mobile, therefor, not totally systemic or amphimobile.

Xylem-mobile fungicides (also called acropetal penetrants ) move upward from the point of entry through the plant’s xylem.

Amphimobile  fungicides (also called true systemic penetrants) move throughout the plant through its xylemand phloem.

Locally systemic fungicides have limited translocation from the application site

Translaminar fungicides are absorbed by leaves and can move through the leaf to the opposite surface they contact,but are not truly systemic and do not move throughout the plant.  

In summary, systemic fungicides work by becoming absorbed into the plant tissues and protecting the plant from fungal diseases as well as ridding the plant of any existing diseases. Some systemic fungicides are locally systemic, meaning that the chemicals aren't transmitted very far from the application site on the plant.  Other systemic fungicides are applied to and absorbed up through the roots, moving throughout the rest of the plant. Eradicant fungicides can have systemic action, depending on which chemistry is chosen. Some are translocated within the host tissue and are able to kill the scab fungus up to a certain length of time after infection occurs. This is called the kickback or reachback period. Because kickback periods may change, always check the label for the most recent information. Kickback is calculated from the beginning of an infection period, as determined by the Mills and La Plante table. 

2017 Growing Season Spray Protocol and Guide

It's time to actively examine a spray protocol  for your fruit 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.  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 and southern Wisconsin. 

 Four Main Pests

 

The four main pests that we face in apple orchards here in our climate zone are apple scab, plum curculio, codling moth and apple maggot, in that order. 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 “Managing Pests in Home Fruit Plantings” from the Purdue University Extensions Publication web site or our web site 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.

Spring Spray Time!

It's just about time to begin thinking about a dormant oil and copper spray for your fruit trees! The apple trees are getting ready to silver tip in the orchard here at Royal Oak Farm Orchard in northern Illinois and that is a sure sign that spring has arrived!! It also indicates that just as soon as the nights stay above freezing, it will be time to do a dormant oil and copper 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.

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

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. As of this afternoon we had accumulated approx. 751 chill hours from October 1 of last fall. 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 chart below to determine the growth stage your trees may be at.

As I mentioned earlier, now is the time to do our fire blight 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.