Apples Diseases Insects Pest Management

Apple Update: July 1, 2016

Crop Stages

June drop is finishing up. Terminal buds have started to set in many locations across the province. Fruit continues to increase in size and are looking larger than normal for this time of year.


As terminal buds are starting to set, now is the time to sample tissue for nutrient analysis. It is also a good time to start applying foliar applications of calcium to help control bitter pit. Apply calcium at two week intervals up until harvest. For further details on tissue sampling and calcium application, click here.

Hand thinning has started across the province. Please be aware that re-entry intervals may be longer for hand thinning.

Lack of precipitation continues across the province. OMAFRA’s Water Quantity Engineer, Rebecca Shortt posted two ONfruit articles recently: an Irrigation Update on how much to irrigate based on crop, time of year and evapotranspiration; and How Long Do I Run My Drip Lines? which shows how to calculate length of time required to run a drip system.

Fire Blight

Fire blight continues to appear in many orchards across the province. In most cases, these strikes are being pruned out and left to dry in the row middles before being removed and burned or mowed down. However, particularly with older trees (>8 years) and those with many strikes, it is best to leave the pruning until new growth stops or when the tree is dormant. Excessive pruning during the summer can stimulate more growth which increases the risk of spreading the bacteria further. In some orchards, trees or even entire blocks will be removed due to the severity of fire blight infection. Once the fire blight has made its way to the leader, there is very little that can be done to salvage the tree. It is best to simply get the infected tree out.

Many are happy to see early terminal set to help slow the spread of fire blight infection. Generally after terminals harden off in July, there is less risk of new shoot infections and existing infections tend to spread less.

The next round of fire blight concern is the risk of trauma blight where some kind of event (hail, wind, etc.) causes a wound, or entry point for the bacteria to move in. Dr. Kari Peters, Penn State University warns days with gusty winds alone may be enough to spread infection and not just high winds common with storms. In a recent Tree Fruit Disease Update, Peters says research has shown “simple damage to leaf hairs along the midrib of pear leaves provides suitable wounds for bacteria to enter and incite infections”.

So, what can be done if trauma occurs? If it is possible, spray streptomycin or a copper within the first 24 hours of the event. Depending on the copper formulation, there is a risk of fruit russeting. If using Cueva, the addition of Double Nickel may help offset this fruit damage.

Other Diseases

We are getting into that time of the season for summer rot development. Black and bitter rot pathogens can infect fruit as early as bloom right up until harvest. However, symptoms really start to show July or August after a period of hot, humid weather accompanied by a rain event. The spores of these diseases cannot move without free water but can spread quickly under the right conditions. If an orchard has a history of rot problems, fungicides with good rot activity should be applied on a 10-14-day interval until harvest, especially if rain is forecasted. See Table 3-14. Activity of Fungicides on Apple Diseases in 2016-2017 Publication 360, Guide to Fruit Production for efficacy ratings of registered fungicides for rot management.


Cover sprays for obliquebanded leafroller continue to be applied across the province. As well, dogwood borer trunk sprays are being applied in problem orchards over the next week or two. Typically, a trunk spray of a pyrethoid, Delegate, Rimon or Altacor can be applied a week following peak flight and re-applied at 2-week intervals. For more information, refer to the following Hort Matters article.

Apple maggot has been caught in various earlier regions. It is still too early to tell what pressure will be like this year. However, insects that pupate underground, such as apple maggot, tend to thrive in water-logged, loose soils. With very little rain across the province, pupae can remain in the soil until environmental conditions become more favourable, even delaying emergence to next year. That said, as movement into the orchard is observed, control is still warranted in high pressure sites. Border sprays of organophosphates, such as Imidan applied to the outer 20 m of an orchard without a resident maggot population may sufficiently intercept any adults flying in from adjacent hosts. However, border sprays of other products, such as Calypso, Assail, Exirel, Altacor, Delegate or Surround are NOT recommended. Use a full cover spray with these products.

San Jose scale crawler activity is underway and fruitlet damage has been observed. Ideal timing for Sivanto Prime, Closer or TwinGuard would be now, if controls haven’t been applied yet. The window for Movento is closing quickly. Since this product is systemic, activity in the tissue is delayed slightly. Application should be made preventatively before fruit damage is observed. For all products registered for scale management, re-applying 10-14 days later is recommended since crawler activity can continue well into July, possibly even early August.

Apple leafcurling midge populations continue to increase as the second generation adults emerge. However, terminal set will help limit new damage since females tend to prefer laying eggs on new growth.

Mite activity is steadily increasing in some orchards while still relatively quiet in others.




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