Monitoring for Apple Maggot Begins

Fig. 1

In 2019 we trapped the first apple maggot fly on around the end of June at about 1150 Degree Days from January 1.  We are at 1016 DD as of today at 5:53 PM, so it is time to get out the  apple maggot traps  and get them set.  I set our orchard's traps a few days ago and , as of yet, have no flies trapped.  It only takes one non-baited trapped fly to  determine that they have arrived to the orchard!  The apple maggot (AM) is native to the Midwestern US and is considered a primary pest, along with plum curculio (PC), and codling moth (CM), which have been covered in previous posts. The adult apple maggot fly resembles a small housefly in size, with a black body, eyes of dark red, with the thorax and abdomen having distinctive white or cream colored bands. The AM is distinguished from other similar, and closely related flies, like cherry fruit fly and black cherry fruit fly, by the variation in dark banding on its wings (See Fig. 1).  

Fig. 2

The AM overwinters in the pupal stage in soil. As soil temperatures rise in early spring, development of pupae commences. The adult fly first emergence begins shortly thereafter (early summer, mid to late June in upper Illinois). It takes about 7 to 10 days for the female to mature enough to mate and lay eggs.  So there is a 7 - 10 day window for spraying prior to egg laying.  A feeding and mating period (pre-oviposition) during this 7-10 days is followed by egg laying directly under the skin of the apple. Females may deposit eggs over an approximate 30 day period laying as many as 300-500 eggs.

Fig. 3

Egg-laying punctures cause dimples and distortion in the outer flesh of fruits. These punctures appear as pinpricks on the fruit surface. Larvae tunnel throughout the fruit leaving irregular trails.(Fig. 2) As eggs hatch, larvae funnel through fruit flesh leaving a winding brown trail.(Fig. 3)  Egg laying usually ceases in early to late August; however, it may continue longer if drought conditions exist throughout August.

Monitoring For Apple Maggot

Fig. 4

When monitoring for AM, the apple maggot fly tends to show a preference for golden delicious varieties, but no variety is immune from attack.  Sticky red spheres are effective monitoring devices for adult AM flies (Fig. 4). Females are attracted to the sphere for mating and egg laying activities and are trapped by the sticky coating. Hang traps shortly before expected adult emergence (mid to late June in upper Illinois). First emergence may be detected by checking traps daily until the first fly is spotted on the non-baited trap. 

Hang the sphere in the proximity to fruit at eye level on the perimeter of the south or southeast side of the tree. Attach the ball in a sturdy stem about 1 foot above a fruit cluster of approximately 6-10, cleaning out the foliage and other fruit for at least 18 inches to sides and top of the trap so it is easily visible. The spheres attract the insects that come within a few yards of them; therefore, the capture of ONE AM on any one non-baited trap at a time would indicate the need for an immediate control application. The capture of 5 flies on a baited trap would  indicate the need for an immediate control application. Once the pesticide is applied, AM captures are disregarded for the period during which the protective spray is effective (varies according to pesticide used).

Control for Apple Maggot

Fig 5.

Several insecticides can be used for apple maggot control including those used for codling moth control like   and/or spinosad.  Acetamiprid is a soft, conventional control and is available as  Ortho Flower, Fruit & Vegetable Insect Killer (Fig. 5).  This is a ready to use product that contains .006% acetamiprid, a synthetic organic compound of the family of chemicals that acts as neonicotinoid insecticides. Acetamiprid is a contact insecticide for sucking-type insects and can be applied as a foliar spray or a soil treatment. Acetamiprid acts on a broad spectrum of insects, including aphids, thrips, plum curculio, apple maggot and Lepidoptera, especially codling moth.  When sprayed in the evening at sunset, it will not harm bees or other beneficial insects.  Be sure to follow all label directions on the bottle for proper application.

Fig. 6

An all natural approach is available in the form of Bonide’s Captain Jack’s Dead Bug Brew (Fig. 6).  Captain Jack's Deadbug Brew® contains Spinosad (spin-OH-sid), a product first isolated from a naturally occurring soil dwelling bacterium that was collected on a Caribbean island from an abandoned rum distillery. Deadbug Brew® kills bagworms, borers, beetles, caterpillars, codling moth, gypsy moth, loopers, leaf miners, spider mites, tent caterpillars, thrips and more! Use on fruits, vegetables, berries, citrus, grapes, nuts and ornamentals and approved for organic gardening.

As always, be sure to follow all label directions on the bottle for proper application.

For additional information, see the following fact sheets and guides  which are available from local university extension services:

https://ecommons.cornell.edu/bitstream/handle/1813/43071/apple-maggot-FS-NYSIPM.pdf?sequence=1&isAllowed=y

http://extension.psu.edu/plants/tree-fruit/insects-mites/factsheets/apple-maggot

https://www.extension.purdue.edu/extmedia/ID/ID-146-W.pdf

______________________________________________
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.
 

It's July and Japanese Beetle is Beginning to Emerge

Figure 1.

Japanese Beetle emergence has begun here in Northern Illinois, but seems to be very spotty.  But once it has emerged in one location, it is only a matter of time before it emerges in another.  I noticed the first beetle last Monday and today they were still not in full on our Honeycrisp trees (Figure 1).  Due to the large amount of carbohydrates produced by the Honeycrisp trees, which is what makes the variety so sweet, the Japanese Beetle is seemingly attracted to it just like we are!  Honeycrisp seem to be the first leaves that attract them and then they move on to raspberries and several other berry varieties.   

Monitoring for Japanese Beetle

Adult Japanese beetles emerge from the soil and live from 30 to 45 days feeding on plants over a four-to-six-week period.  The adults produce aggregation pheromones that attract individuals (both males and females) to the same feeding location. Adults can fly up to five miles to locate a feeding site; however, they tend to fly only short distances to feed and lay eggs.   The adult beetles normally emerge during the last week of June through July. The first beetles out of the ground seek out that suitable food , like Honeycrisp, and begin to feed. These early arrivals then begin to release that aggregation pheromone (odor) that attracts additional adults. Newly emerged females also release a sex pheromone that attracts males. After feeding and mating for a day or two, the females burrow into the soil to lay eggs at a depth of 2 to 4 inches. Females lay 1 to 5 eggs before returning to plants to feed and mate. This cycle of feeding, mating and egg laying continues until the female has laid 40 to 60 eggs. Most of the eggs are laid by mid-August though adults may be found until the first frost. The eggs hatch in 8 to 14 days and the first instar larvae dig to the soil surface to feed on roots and organic material. The first instars shed their skin (molt) in 17 to 25 days. The second instars take 18 to 45 days to mature and molt again. Most of the grubs are in the third instar by late September and by October they dig deeper into the soil to overwinter. The grubs return to thesurface in the spring as the soil temperature warms, usually in mid-April. The grubs continue their development and form a pupa in an earthen cell 1 to 3 inches in the soil. 

Figure 2.

When you see those first few beetles, that is the time to begin you plan of attack.  Those first few beetles are the food source scouts that will emit the aggregation pheromone letting other beetles know that a feast is on! The Japanese beetle adults feed through the upper leaf surface (epidermis) and leaf center (mesophyll), leaving the lower epidermis intact. Adults usually avoid feeding on tissue between leaf veins, resulting in leaves appearing lace-like or skeletonized (Figure 2). Controlling those first few beetles can give you a head start on stopping the feeding/mating cycle.

 Control for Japanese Beetle

There are some control options for the adult life stage One is physical removal and/or trapping of adults:  Removing beetles by hand, or trapping, may provide adequate protection  for  small plantings  when  beetle  numbers are low.  However, Japanese  beetle  adults  are capable  of  migrating  from  other  areas,  and  the presence  of  beetles  on  or  near  a  plant  will  attract more   beetles.  Consequently,   use   of   Japanese beetle traps often attracts more beetles, and results in subsequent damage to plants.  

Figure 3.

The other alternative is chemical control of adults:  Several insecticides are labeled  for  use  against  adult  Japanese  beetles.  Always  follow  label  directions.    Typically, this may entail 2 treatments during the peak beetle flight. Homeowners should make their first application before damage becomes intolerable and beetles are still abundant. The need for repeated applications can be curtailed by inspecting plants for additional beetle damage prior to applying a second treatment. Neem products containing Azadirachtin can be effective repellents that can reduce defoliation when applied regularly (but no more than weekly) during beetle flight.  Apply before defoliation becomes intolerable. In years when beetle populations are very high, noticeable defoliation may occur because adults will consume a small amount of insecticide tainted leaves before they are killed.  Treat  foliage  and flowers thoroughly.  For optimal control, apply in the late afternoon when beetles are most active. Several other insecticides can be used for Japanese beetle control including those used for codling moth and apple maggot control like acetamaprid.  There are others like Sevin, but I do not recommend the use of Sevin since it is toxic to bees and to beneficial insects.   Acetamiprid is a soft, conventional control and is available as  Ortho Flower, Fruit & Vegetable Insect Killer (Figure 3).  This is a ready to use product that contains .006% acetamiprid, a synthetic organic compound of the family of chemicals that acts as neonicotinoid insecticides. Acetamiprid is a contact insecticide for sucking-type insects and can be applied as a foliar spray or a soil treatment.  When sprayed in the evening at sunset, it will not harm bees or other beneficial insects. 

If you do choose to use chemical controls make sure that the plant you are applying to is listed on the label as well as Japanese Beetles. If controlling Japanese Beetles on food crops such brambles or apples – make sure to follow the harvest-restriction date on the label. Always READ and FOLLOW the label and do not apply at rates higher than listed.

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.

Protecting Your Apple Fruit From Secondary Apple Scab

This 2020 growing season thus far is proving to be nearly as bad for apple scab as the 2019 season was.  We have received only 7.92" of rain since April 1, which is half the amount we received in 2019 for the same time period.  And, as of today, June 8, we have had  have had 8  apple scab infection periods as compared to 9 in 2019. But, with several of those infection periods lasting for more than 20 hours and one of them lasting more than 62 hours, which kept us from being able to get a cover spray on, resulting in over 3" of rain that washed off the previous spray, it has been pretty much impossible to control primary scab outbreaks.  With that being the case, we are at a point of now having to protect fruit from secondary scab.

Fig. 1

Season-long control is very difficult if primary infections develop, like those in Fig. 1, which produce secondary inoculum placing fruit at risk for secondary, conidial infections.   With primary ascospores possibly depleted, we will have to continue to monitor scab infection events and maintain spray coverage accordingly for at least two more weeks, if not longer, since we have found primary lesions,  like those in Fig. 2 on McIntosh and McIntosh hybrids like Cortland and Empire.  If you have seen lesions like those in Fig. 2, on your trees, then you will now need to protect your fruit from secondary lesions.

Fig. 2

The best product for protecting your fruit is Captan, a contact protectant. And that means that your trees will need to be sprayed with Captan at the full labelled rate prior to any rain event to protect your fruit.  If there are no rain events between sprays, a single contact protectant spray will last at least 10 days but not more than 14 days, based on the product's labeled information.  You will need to make sure that your trees and fruit are protected prior to any rain event  when using only a protectant. But, a protectant can lose its effectivness after 2" of rain, so you also want to reapply as soon as you can before the next rain event.   If no protection is available during the wetting event, then the liklihood of your fruit getting infected dramatically increases.

As always, be sure to follow the label directions on any spray product you may use.   For further information on control of apple scab, refer to:

 http://royaloakfarmorchard.blogspot.com/2018/04/apple-scab-season-approaches.html

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 for that product.

 

Codling Moth Arrival and Biofx Setting

Pheromone lure with trapped moths.

To determine when flight begins for codling moth, commercial growers make use of pheromone traps.  Once moths have been trapped for  two consecutive days in a row, a biofix is set  that initiates the beginning of growing-degree-day calculations.  We know that at approximately 100 degree days after the biofix date codling moths begin to lay eggs and those eggs begin to hatch at approximately 250 degree days after biofix.  It is this information that aids in the timing of necessary sprays for codling moth so they do not damage fruit.  Growers wishing to time sprays based on egg development and hatch (larval stage) should make an application of an insecticide at 250 DD (base 50 degrees F) after the first sustained capture of males in the sex pheromone traps.  Here is a Detailed Growing Degree Day Model for Codling Moth.   

 

We have now established a biofix for CM for this spring and it was May 26.  You may apply insecticides that need to be present before egg laying at about 50-75 DD or you may apply insecticides that target early egg laying period at 100-200 DD.  Since the biofix date, we have accumulated approximately 9 DD, but with the projected hot temperatures for the comming week, we will have to keep a close eye on the degree days for the first application of an ovicide.  It will soon be time time for the home grower to apply a spray to target early egg laying. 

For the home orchardist who does not have the benefit of a weather station or other means to calculate degree days, a simple tree growth stage time table can be followed.  Codling moths usually start flying at bloom time or just after bloom time at petal fall and approximately at the same time as plum curculio.  Eggs laid by these moths begin to hatch about two weeks after petal fall, depending on the weather. You can apply the first codling moth spray at this time, about two weeks after petal fall, to prevent larvae from entering the fruit. Because most insecticide residues last 7 to 10 days and moths are continuously present throughout the summer, apply a spray every 7 to 10 days to prevent later broods of codling moth larvae from entering apple and pear fruits. If using a natural product like Spinosad, then spray after every rain due to washoff.  Always follow the label directions of any spray you may use.

Several insecticides can be used for codling moth control including acetmaprid and/or spinosad.  Acetamiprid is a soft, conventional control and is available as  Ortho Flower, Fruit and Vegetable Insect Killer.  This is a ready to use product that contains .006% acetamiprid, and is also available in a concentrate containing .5% acetamiprid.  Acetamiprid is a synthetic organic compound of the family of chemicals that acts as neonicotinoid insecticides. Acetamiprid is a contact, translaminar insecticide for sucking-type insects and can be applied as a foliar spray.  Translaminar insecticides are absorbed by leaves and can move through the leaf to the opposite surface they contact. They are not truly systemic and do not move throughout the entire plant. Acetamiprid acts on a broad spectrum of insects, including aphids, thrips, plum curculio, apple maggot and Lepidoptera, especially codling moth.  When sprayed in the evening at sunset, it will not harm bees or other beneficial insects once it is dry. Be sure to follow all label directions on the bottle for proper application.

An all natural approach is also available in the form of Bonide’s Captain Jack’s Dead Bug Brew.  Captain Jack's Deadbug Brew® contains Spinosad (spin-OH-sid), a product first isolated from a naturally occurring soil dwelling bacterium that was collected on a Caribbean island from an abandoned rum distillery. Deadbug Brew® kills bagworms, borers, beetles, caterpillars, codling moth, gypsy moth, loopers, leaf miners, spider mites, tent caterpillars, thrips and more! Use on fruits, vegetables, berries, citrus, grapes, nuts and ornamentals and approved for organic gardening.  

Both of the above products will kill Codling Moth larvae and need to be sprayed just prior to the emergence of the larvae,  which is between 100 to 250 DD after biofix.  Since we are not yet at or near 100 DD after biofix, your trees can be sprayed in about 7 to 10 days, depending on the amount of rain that may fall at night between now and then.  Typically after 1" of rain, these sprays will have been washed off and will need to be sprayed again to be effective.

For additional information, see the following fact sheets which are available from local university extension services:

https://ecommons.cornell.edu/bitstream/handle/1813/43086/codling-moth-FS-NYSIPM.pdf

http://extension.psu.edu/plants/tree-fruit/insects-mites/factsheets/codling-moth

 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.

Plum Curculio Season is On the Horizon

Plum Curculio Ovipositing Egg

With apple scab season in our midst, and petal fall coming to an end, it is time to turn our attention to several insect pests. Plum curculio (PC) is one of the most difficult insect pests to contain.  They enter the orchard from the perimeter after the adults pass the winter hidden under leaves, along fence rows, in brush piles, rock walls and in other protected places. In spring when the weather warms up (mean temperature 60°F. or maximum temperature above 75°F.), about the same time apples are blooming, the adults become active. The adult plum curculio beetles, pictured to the left, emerge right around or just after petal fall, to feed on apple buds, flowers, leaves and young fruit.  The duration of full bloom to petal fall is usually about 5 to 10 days.  From petal fall to fruit set is generally another 5 to 10 days, depending on temperatures.  Once the fruit sets, female beetles cut holes in the young fruit and deposit one egg in each cavity. 

 

 

These sites, called oviposition stings, are easily identified by their crescent shaped cuts. Unlike codling moth, the larvae of plum curculio rarely cause damage to the fruit. The fruit is primarily damaged superficially by the egg-laying and feeding by the adults. These "stings" will cork over and cause an indentation in the fruit as it matures making it look deformed and unsightly.

The question then becomes, how do we control them??  Pesticide application at this time is very important for plum curculio control. To prevent fruit drop, and due to toxicity to bees if there are still blooms on the trees, do not use carbaryl (Sevin®) or any pyrethrin based spray as these are highly toxic to honey bees and other pollinators as well as any beneficial insects. Any other pesticides should be applied int he evening when the honey bees have returned tot heor hives.  For home growers, an acetamiprid spray such as Ortho® Flower, Fruit & Vegetable Insect Killer Ready-Spray is a deterrent.  If no blooms are present  on any trees, a pyrethrin based spray can be used as a deterrent, even though there may be no fruit.  Picking up and disposing of any fallen fruit will reduce problems with plum curculio, other insects, and many plant diseases. For conventional growers, Avaunt or Assail are two choices you might use, based on your codling moth protocol and your apple maggot protocol.

For a pure organic spray, the two most frequently used insecticides are Surround® and Pyganic®, both certified organic. The organic products may need to be sprayed multiple times for complete control at 7 to 10 day intervals or after any rain. And, as always, follow all label directions on any spray product. 

For a complete Fact Sheet on Plum Curculio, consult the Cornell University Plum Curculio Fact Sheet and for an in depth look at this pest.
__________________________________________

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.

Tree Growth Stages, Main Pests, 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 apple scab, plum curculio, codling moth and apple maggot, in that order. 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 “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.

Revisiting Critical Temperatures for Fruit Trees

With the predicted colder night temperatures we are about 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 tight cluster to pink to bloom here in northern Illinois with a forecast of night temperatures in the high 20's this weekend. Fortunately, our trees haven't progressed to far this spring, but we could see some bloom this weekend.   This spring has marked another unprecedented weather pattern that raised our temperatures in late March and early April and is dropping our temperatures going into mid-May to way below normal.  The early warm temperatures accelerated bud swell, and the lower temperatures that are anticipated present the threat of frost or freeze damage to new leaf and bloom 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 this 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.  

Apple Scab Has Arrived to Northern Illinois

Based on our NEWA (Network for Environment and Weather Applications) Apple Scab Model, we have had multiple scab infection events beginning March 9 with spore maturity being very low (see chart below). But, the scab season has officially begun!  With no leaf tissue showing prior to green tip, any previous infection period would have no immediate effect on the leaf tissue, but we now know that there are spores out there.  Since we had our copper spray put on right at green tip the evening of April 10, we were protected from the infection once the spores began to mature.  With spore maturity and discharge being very low, the risk is also very low, but we still need to be protected because any high temperature day can cause the spores to mature very quickly. 

Ascospores mature as spring progresses with a few ascospores usually maturing by bud break (green tip). The proportion of ascospores maturing progresses slowly until about the tight cluster stage of blossom development. From tight cluster through bloom the percentage of mature ascospores rapidly increases with most ascospores matured by the end of bloom. 

Unusual weather conditions may contribute to significant ascospore discharges earlier than or later than the model predicts. 

Mature ascospores begin to discharge into the air within 30 minutes during periods of rain. When rainfall begins at night, discharge may be delayed until daybreak. Ascospore discharge usually peaks from pink through bloom, and nearly all ascospores have been discharged within 1 or 2 weeks after petal fall.

Copper has been shown to be a protectant against scab on the tissue that has been covered, but not on any new tissue that would have grown since that copper spray was put on.   If no copper spray has been put on your trees as of today, and you have not put any other protectant on like Captan or Mancozeb, you still have time to get an eradicant fungicide put on your trees in the form of Immunox, which has a 72 to 96 hour reach back ability.  That means that you have up to 72 to 96 hours to get a spray on which will still be effective against any scab infection event 72 to 96 hours previous. Immunox is a xylum mobile fungicide which means when applied to leaves it will move throughout the leaves it was deposited on but will not move out of that leaf.  

For the home grower who may not have a weather station or scab model to help predict the apple scab infection periods, monitoring for apple scab can be quite complicated.  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 an eradicant on hand like a myclobutanil, which is available as Spectracide Immunox, which I mention above.  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 72 to 96 hours as I have stated above.  That means that it can still have an effect on the scab pathogen for up to 96 hours after a wetting event, although it is a good practice to use the shorter 72 hours.. 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. 

 But, 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.

_____________________________________________________________

 
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.

 

Apple Scab Season is Upon Us

We are now officially emerging into the apple scab season as green tip and 1/4" green leaf tissue is seen on the apple trees.  In some cases, due to our uncertain weather pattern, some trees are still at silver tip and others are near 1/2" green, but as long as any leaf tissue is exposed, there is a chance for primary scab to set in.  Apple scab is the most prevalent and most damaging disease to apples we have in the Midwest and pretty much all apple growing locations east of the Rocky Mountains.  At this point, scab sprays should be applied according to the Apple Spray Guide found in  "Managing Pests in Home Fruit Plantings".  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 apple trees 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 an 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.

©Janna Beckerman, Department of Botany and Plant Pathology, Purdue University

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.
________________________________________________________________

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.