Orchard diseases in July and August: what becomes more severe before harvest?

At a glance

Not every disease noticed in summer began in July or August. Scab and powdery mildew are usually a continuation of problems that developed earlier, while brown rot of stone fruit and storage diseases become more significant as the fruit ripens. The absence of visible lesions at harvest does not rule out a latent infection.

• Scab remains active in summer if lesions in the orchard are producing inoculum for secondary infections.
• Brown rot can develop rapidly on ripening and damaged stone fruit.
• Rainfall before harvest increases the risk of storage diseases in apples.
• Fruit inspections should be considered alongside the weather history and events in each individual orchard block.

How does the infection calendar change from May to August?

Disease pressure is not evenly distributed throughout the season. In spring, young leaves, flowers and developing fruitlets are the main concern. In the second half of summer, attention shifts towards ripening fruit, skin damage and infections that can reduce the quality of a batch in storage.

One of the biggest mistakes is to assume that clean-looking fruit in July means the problem is over. A late infection may remain invisible until harvest. Symptoms may appear as the fruit ripens, during grading or after several weeks in storage.

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Which orchard diseases remain active in July?

July often does not bring an entirely new problem. Instead, the effects of infections that began in spring remain visible, while further secondary infections occur. This is why inspections need to take account of the history of the individual orchard block, rather than relying only on the fruit's current appearance.

Apple and pear scab

Scab does not disappear once the main period of primary infection has ended. Lesions already present on leaves and fruit can produce conidia that cause further infections. Rain spreads these spores to new tissue, so an orchard with active lesions still requires monitoring in July and August.

Late fruit infections are not always visible before harvest. They may only become apparent as storage scab after apples or pears have been placed in cold storage.

Apple powdery mildew

Powdery mildew primarily affects young leaves and shoots. In July, it remains important in blocks where trees are still growing vigorously, heavily infected shoots have not been removed, or the variety being grown is particularly susceptible.

White fungal growth, curling leaves and stunted growth are easy to spot. It is harder to assess how severe infection affects shoot condition and bud formation for the following season. Powdery mildew should therefore not be treated simply as a cosmetic defect of the leaves.

Cherry leaf spot

In stone-fruit orchards, leaf inspection remains important during harvest and immediately afterwards. Increasing numbers of lesions and premature leaf fall weaken the trees and shorten the period in which they can build up reserves for the next season.

Which diseases become more severe before fruit harvest?

As fruit ripens, it becomes more susceptible to cracking, abrasion and other damage. Wounds make it easier for some pathogens to develop, while fruit touching each other can create localised pockets of rot. At the same time, latent infections become increasingly important.

Brown rot of stone fruit

Brown rot can develop rapidly on ripening sour cherries, sweet cherries and plums. Warm, humid weather favours infection, while cracking, hail damage, insect feeding and abrasions provide entry points for the pathogen.

Infection can originate from mummified fruit left on the trees and from infected shoots. When an infected fruit touches another fruit, the disease focus can spread more quickly. The way brown rot develops on stone fruit is described by Penn State Extension in its guidance on brown rot.

Apple lenticel rot

In Polish orchard guidance, apple lenticel rot is associated primarily with fungi of the genus Neofabraea. Infection takes place in the orchard, but the characteristic lesions often develop only during storage.

The disease becomes more significant with frequent rainfall before harvest, susceptible varieties and the presence of infection sources such as cankers. Instytut Ogrodnictwa – PIB lists lenticel rot among the most important apple storage diseases in its current integrated apple protection methodology for growers.

Grey mould in apples

Grey mould can occur in two forms that are important to growers. The first is a dry summer calyx-end rot: the lesion develops around the calyx, remains relatively dry and may still be visible while the fruit is on the tree. The second is soft storage rot, which develops after harvest and can spread between fruit that are touching.

This spread from one fruit to the next is known as nest rot. Cold storage slows many biological processes, but it does not eliminate an infection brought in with the fruit. A damaged apple can therefore become a source of infection for a whole group of fruit in a crate or storage chamber.

How do rainfall, temperature and humidity affect orchard diseases?

Monthly rainfall totals alone are not enough to assess the risk. The duration of leaf and fruit wetness, the temperature during wet periods, humidity within the canopy, and localised damage caused by storms or hail are also important.

Several rainfall events interspersed with warm periods are particularly problematic, especially as fruit enters the ripening stage. Under these conditions, a disease focus can develop between two routine inspections.

Modelled data for the nearest town may not reflect rainfall in a particular orchard block. The differences between local measurements and modelled data are discussed in the article on physical and virtual weather stations.

How should fruit be inspected before harvest?

Inspections should cover orchard blocks with different levels of risk. Walking a single outside row provides a quick overview, but it can miss areas with poorer air circulation, hail damage or a previous history of scab.

1. Check blocks where scab, powdery mildew or rots have previously been observed.
2. Assess fruit after hail, strong winds and pest feeding.
3. Inspect the inside of the canopy and areas where fruit touch each other.
4. Mark trees with infected shoots and mummified fruit.
5. Separate observations relating to leaves from lesions that directly affect fruit quality.
6. Record the date, orchard block, variety, photograph and weather conditions preceding the symptoms.

A photograph without a date or orchard block quickly loses its value. By the end of the season, there may be dozens of similar photos on a phone, with no way to tell whether they came from an early or late variety, or from a part of the orchard damaged by hail.

What are the benefits of structured disease monitoring?

For the grower

The grower can focus inspections on the highest-risk orchard blocks and reconstruct the sequence of events before harvest. This is not an automatic diagnosis, but it reduces the need to make decisions based solely on memory or a single photograph.

For the fruit adviser

The adviser receives photographs linked to the crop, weather and treatment history. The discussion can then start with a specific orchard block, variety and date when symptoms appeared, rather than a general description of the entire holding.

For the fruit buyer

For deliveries to a packhouse or processor, it is important to be able to link a batch to its orchard block, harvest and quality-control records. FarmPortal can work with FoodPass for quality management and batch traceability.

How does FarmPortal support orchard disease monitoring?

FarmPortal brings together orchard-block and crop data with weather information, field observations, photographs, treatment history and adviser recommendations. In one place, users can see where a problem occurred, when it was noticed and what actions were taken afterwards.

Features related to alerts, disease models and collaboration with advisers are described on the page covering crop health and safety in FarmPortal. Fruit growers may also find the overview of FarmPortal features for orchard farms useful.

A disease model should not make decisions on behalf of the grower. Its purpose is to identify periods when a specific orchard block needs to be checked more promptly. The final assessment requires an inspection, knowledge of the variety and growth stage, and the current label for the relevant plant protection product.

Illustrative example: inspection after a rainy week

This illustrative example was prepared for the purposes of this article. The data are intended to demonstrate the process and should be verified before being presented as the result of a real-world implementation.

The holding manages 24 ha of orchards: 14 ha of apples, 4 ha of pears, 4 ha of sour cherries and 2 ha of plums. Over six days, there were three rainfall events and a brief hailstorm affected part of the holding. The owner begins the inspection in the area where previous scab symptoms, high humidity and fruit damage coincide.

During the inspection, 28 observations were recorded across eight orchard blocks. Two blocks were marked as priorities: apple trees with extensive skin damage and plum trees showing the first pockets of brown rot. Follow-up inspections were scheduled in the remaining blocks after several days.

The metric is not a claimed increase in yield. It is the completeness of the documentation: every block affected by hail has a photograph, date, location and link to the relevant weather conditions. The limitations of this example are the absence of laboratory confirmation of the causal agent and the lack of comparison with a control holding.

FAQ

Glossary

Primary infection

The first infection that initiates disease development during the season, often associated with infectious material that has overwintered in the orchard.

Secondary infection

A subsequent infection caused by spores produced on tissue infected earlier in the same season.

Latent infection

An infection with no immediate symptoms. Symptoms may become apparent as the fruit ripens or during storage.

Calyx-end rot

A lesion that develops around the calyx end of the fruit. In the case of grey mould, it may take the form of a dry lesion that is already visible in the orchard.

Nest rot

The development of rot in a group of fruit that are touching, as the pathogen spreads from one infected apple to another during storage.

Pre-harvest period

The period immediately before harvest, when fruit quality, the pre-harvest interval and post-harvest keeping quality become particularly important.

Leaf wetness

The period during which water remains on the surface of the plant. Its duration, together with temperature, affects the potential development of many infections.

Disease model

An algorithm that uses weather and biological data to assess infection risk. It is not a laboratory diagnosis.

What should be checked before harvest begins?

Summer diseases of fruit trees need to be assessed at two levels. The first covers symptoms visible on leaves, shoots and fruit. The second concerns infections that may have occurred after rainfall or damage but will only become apparent during ripening and storage.

Before harvest, select the highest-risk orchard blocks, inspect them after the most recent rainfall and label batches from trees bearing damaged fruit. Organise photographs and observation records. These records do not replace the advice of a fruit specialist, but they provide the information needed to assess the situation.