Apple Scab -- Pay attention!!!

Jon Ipema • August 31, 2024

The evidence is now, the cure is a phone call away!!

Now is the time when Apple scab is evident. These trees are screaming for your help. This is also the time of year I hear people state that treatment will be a priority next season. The problem is that the tree greens up in the spring (as it did this year), mid summer symtoms return, but another year goes by as the tree continues its decline. The best time for treatment for apple scab starts as soon as possible, the reason for this is that treatment is a multifaceted approach. I will explain more in the “What’s the Solution” part of the text.

Venturia inaequalis, commonly known as apple scab, is a serious disease attacking apples and crabapple trees. There are several other similar fungal pathogens that ravage other fruit and ornamental trees. Venturia pirina, or pear scab, is a prime example. Scab is very common, even on “scab resistant” trees. Treatment is necessary and proper treatment pertinent to any type of control. Getting 100% cured from scab is not a reality, instead suppression using a systematic approach is the most practical strategy.

Spotting on leaves, maldeveloped fruit, loss of leaves and fruit during the growing season, and thinning of the canopy. Initially the disease is not fatal in and of itself, but It does lead to stress on the plant leaving it susceptible to multiple secondary diseases. Stressed trees do not develop in a healthy manner and are impossible to keep aesthetically pleasing. If edible fruit is desired, scab will ruin any chances of a successful harvest.

Scab overwinters in fallen leaves and in the soil around the trees. Spring brings cool and wet conditions, which are optimum for disease development. Fungal spores are spread to leaves, flowers and fruit by wind, rain, and splashing water. The prevalence of fungal spores and time of desirable environment have a direct correlation with the severity of disease. Temperatures between 55- and 75-degrees Fahrenheit with high humidity cause the infections to spread rapidly, and this process can be repeated multiple times during a single season. As the disease progresses, spotting on leaves get larger. When fruit develops, spotting can be apparent. As the fruit grows, the shape and quality of fruit declines very abruptly. Leaf drop of stressed trees typically happens during mid-summer, typically July/August. The leaf drop is a defense mechanism of the tree and an attempt to push out healthy leaves during the current growing season. This process takes a large amount of energy during a time in the growing season when resources are typically not abundant. Although healthy leaves may be nurtured, the toll of stress can be difficult to recover from. Neglect of treatment results in defoliation, decreased growth, decreased canopy density, reduced blooms, increased susceptibility to other diseases including winter injury. The appearance of trees that have gone through years of this defoliation and stress, tend to look uneven, unkempt, disarranged, and terribly shaped.

What’s the solution??

There are several options to mitigate the damage from scab. Crabapples as ornamentals are irreplaceable and as a fruit tree there’s no way to get an apple without an apple tree. If you are in the planning stages trying to figure out what trees to use, select scab resistant trees if possible. This will not eliminate scab and treatment will certainly be part of the care of your tree, but treatments would be more effective. Even scab resistant trees will get scab, just to a more limited degree. Scab resistant trees naturally have a thicker leaf cuticle (waxy covering on the leaf), this makes it more difficult for infection to occur. If you have a crabapple/apple tree already, there is no reason to cut it down and start over.

Often the advice is put out there that good housekeeping is the best way to limit the spread and intensity of scab. Thoroughly cleaning up all leaves and branches, especially of infected trees isn’t a bad idea, but won’t have much effect on scab. The amount of cleanliness necessary to have an impact would be impractical.

The best way is using a systematic approach. Starting with a growth regulator, which should be applied as soon as the decision is made that control is desired. The effects of this application will not be noticed until at least the following growing season. It is the delayed reaction to the growth regulator that is the reason for the ASAP approach. Delaying this part of the treatment, as well as not being scheduled for spring fungicide application, which is a timely application, will certainly result in symtoms the following season and continued tree decline. The reason a growth regulator is warranted is mostly due to the secondary effects. The growth regulator is a gibberellin inhibitor. Gibberellin is a plant growth hormone that regulate cell elongation. When used there is a noticeable difference in internodal growth (length of new growth on branches, compared to other years. The primary effects of this application are less pruning and a thicker canopy, this makes for a more aesthetically pleasing tree that is not getting stressed by excessive pruning. The secondary effects are increased chlorophyll production, increase in fine root density (fine roots are responsible for not only water uptake, but micro and macro nutrient absorption), and thicker leaf cuticle development. The last of these is the most desired effect for this particular application. Due to restrictions, we do not use this method for edibles, but we have a very effective protocol for edibles as well.

The next step is fungicide applications in spring. Proper scab control applications are time sensitive. They must be applied as the tips of the branches are greening up in the spring (a phenomena we refer to as “green tip”, because arborists are very original), and when the buds open up (once again a very original term, “bud break”). A second application is made two weeks later. Certain products require more applications some every two weeks until the flower petals fall off (petal drop). The number of applications can be restrictive due to the cost of each application. The Green Advantage utilizes top-of-the-line products which allow us to limit this to two applications, thereby keeping the costs more reasonable.

While not utilizing a growth regulator for edibles, The Green Advantage instead recommends 3-4 applications of the fungicide.

The Green Advantage has performed years and years of research to develop our protocols. Ranging from the frequency of applications to the choice of products. We are a family business so we understand the concerns between chemicals and loved ones. We prioritize safety for people and the environment. The Green Advantage is NWI’s most qualified pest control professions. We are local, We support OUR community, and We are here for YOU!!!!

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The Cycle

By Jon Ipema • September 12, 2025

The goal of this article is not to berate other professionals; instead, it is to get a better understanding of how to get desired results while avoiding counterproductive measures that often impede progress, increase maintenance, and are detrimental to the goals of plant cultivation and land management. Often, attention is applied strictly to climate and aesthetics. The decisions are typically made based on whether a plant is known to survive in a particular zone and results from successful cultivation (often photos of established plants). Although these are important issues, the results are often compromised by disregard for soil type, soil quality, maintenance requirements, desired results, and specific strengths and weaknesses of individual species and subspecies. Proper consideration of the process and costs of achieving desired outcomes can be oversimplified to the detriment of that outcome. Observing this time and again, a cycle has been noticed that seems to repeat itself. Analyzing this cycle has given insight into how to avoid this cycle and the frustration that goes along with it. Signs of this cycle are increases in maintenance, costs, and frustration while experiencing decreased aesthetics, plant health, and recurring issues. Here is an example: 1. A lawn does not appeal to its owner and steps are taken to improve the situation. 2 . The first step is often to incorporate a fertilization program. 3. A generalized fertilization program is implemented, with the primary focus being macro-nutrients for turf and weed control. 4. Initially this seems productive and seems to be leading to satisfactory results especially in the beginning of the season, when temperatures are lower and natural irrigation is sufficient. 5. As the season progresses and temperatures increase the results seem to diminish. The color of the lawn appears fair at best, weeds become more of an issue, and general satisfaction declines. Watering is increased, chemical applications to control weeds are rendered, and some choose to increase fertilization to achieve what seemed to be improving results earlier in the season. 6. During midseason, temperatures are at extremes, and the focus gets shifted to irrigation, with some increase to the length of time for irrigation but mostly on the frequency. 7. As the end of summer approaches, nighttime temperatures decrease, while temperatures during the day still feel extreme. Turf appears to be recovering and looking better. Weeds continue to be an issue and additional weed control measures are often taken, usually spot treating as even selective herbicides can damage turf in the heat of the day. At this point fungal issues appear and many opt to apply fungicides to control the matter. 8. Some satisfaction with weed control seems to take place although grassy weeds remain persistent and fungal issues come and go. Overall, the turf seems better than previous seasons and staying on the course seems to be the correct action for the next season. 9. Year 2 - In spring pre-emergent weed control is applied to keep grassy weeds controlled (primarily crabgrass). Patches of inconsistent turf seem to be taking hold, and the turf color continues to decline. Spring is often when other fungal issues are noticed, especially cold season fungal issues that take place throughout the winter (snow molds). 10. Increases in fertilizer are often recommended to return color to turf while weed control becomes a larger issue. Irrigation is more frequent, as it seemed to help the stressed turf during the previous season. 11. Although recommendations are followed, by midseason it is apparent that turf quality is not improving, there may be a noticeable “boost” to aesthetics for a short period after fertilization, but not much further. 12. When evening temperatures begin dropping but daytime temperatures are still high, fungal issues return. It may be recommended to add fungicidal applications to the fertilization program annually to “get ahead” of the problem. 13. Turf doesn’t seem to improve any further and is often declining at this point. During the 3rd season some owners begin looking at other options, but some stay on this course and continue, many of these individuals simply get accustomed to a subpar lawn. Others contemplate discontinuing service, as the programs appear to be a gimmick. 14. By the fourth season many have had enough. Many companies will continue to offer more services claiming that they will solve the issues. By this point the customers usually have had enough, even more convinced that their lawn will just never look the way they would like. This pattern may vary from what is indicated above. The main point is that this system is reactive rather than proactive. Certain people experience a degree of success. This is typically short-lived, and they don't even realize the added maintenance and costs. My experience is that these results vary from lawn to lawn, which are not replicable, and lack consistency. This brings us to the main point of this article…How do we stop the cycle and get the results we want, without constantly increasing the need for more maintenance? Let's start at the same point as we did earlier. 1. A lawn does not appeal to its owner and steps are taken to improve the situation. 2. Soil tests are taken to provide information as to what is going on currently, how to adjust, and what type of grasses fit the purpose of the lawn. 3. Soil amendments are made to correct micro-nutrient deficiencies and correct soil chemistry. Aeration is completed to aid the microbial processes in the soil, reduce compaction, and maintain the thatch layer. Lawn is overseeded with turfgrass that fits the desired outcome, thrives in the climate, and resists disease. 4. Fertilizer program is implemented to address macronutrients and help maintain chemical adjustments performed in previous step. At the beginning of this process, pre-emergent weed controls should be avoided and only implemented in the future if annual weeds are an issue. Even then I personally am not a proponent of preemergent weed control in turf, unless absolutely necessary as this hinders seed germination and causes issues with overseeding. 5. Instructions are given on maintenance information. Turfgrass needs to be maintained at a certain height and cut at regular intervals to maintain that height. Sharp blades and maintained equipment are important for turf grass health. This thickens the grass not only for aesthetic purposes, but also for weed control. 6. In spring when conditions are optimum for turf grass growth, the desired grass species will begin to take hold. As temps increase and are less favorable to the other grasses, this will become the dominant. With the corrections in the soil chemistry and condition this species will thrive, not allowing area for weeds to encroach. This is not to say weed control is not necessary, but it is drastically minimized. 7. Aeration needs to be performed on a regular basis, 1 to 2 times a year minimum, based on grass species, soil conditions, thatch conditions, and activities on the turf. 8. As the heat of the summer stresses the turf grass, correct watering is pertinent. Root systems of all plants require water, but they also require oxygen. A flooded root system will kill plants. Less frequent, deep watering is what plants including turf need. Turf grass varieties that are more tolerant of temperature extremes are the best solution to this issue. As these grasses grow and begin to dominate the turf ecosystem, other non-desirable plants will not have room to get a foot hold, limiting the need for weed control. Short frequent irrigation creates the environment for fungal disease. Without fungal disease the use of fungicide would be minimal if not irrelevant, avoiding the damage to mycorrhizae. These beneficial fungi aid in oxygen and nutrient transfer in root systems. 9. Year 2 - Turf appearance drastically improves as does the health of the grasses. Soil amendments are not necessary unless problems exist. Soil test should be done regularly (I recommend every 3 years, unless issues are present). Aeration and overseed are recommended in spring and fall, continue to feed (general purpose fertilizer, 4 application slow release sulfur coated urea), and continue maintenance as described above. 10. Lastly, enjoy. Healthy plants resist disease. Working with nature, controlling what we can, and mitigating what we can’t is the answer to all turf and landscaping. Overall maintenance will be far less chaotic as the days of chasing symptoms will come to a close. Any issues that arise can be dealt with systematically.