Apple Pest Update: July 30, 2019

What a difference a few weeks can make! In the last Apple Pest Update, we were still experiencing cool, wet weather. Since then, temperatures have become hot and humid with a number of areas receiving very little rain. Irrigation has started in some orchards across the province. In other regions, the humidity has brought unsettling weather patterns resulting in heavy rains, thunderstorms and, in some cases, hail. In general, warmer temperatures have increased pest activity of those that thrive in these conditions.

Summer Diseases

Infection caused by summer diseases such as bitter rot, black rot, flyspeck and sooty blotch can occur in periods of high heat and humidity followed by a rain storm. Optimal infection conditions for these diseases are temperatures in the high 20s and 4-5 hours of leaf wetness. On very humid days, this length of leaf wetness required can very easily be met.

Continues spread can be extensive with these diseases as spores are produced on the fruit surface and rain splashed to other fruit resulting in further infections as the season progresses. If spores land on fruit just before or during harvest, infection can occur with symptoms developing slowly in storage. For bitter rot, small lesions will begin to enlarge within a few days after the fruit is removed from storage.

Black rot on fruit and leaves (known as frog-eye leaf spot) on apple.

Bitter rot

Sooty blotch

Fly speck

Summer diseases usually appear in orchards that have reduced summer fungicide programs due to a lack of apple scab. They can, however, also appears in September or October in orchards that have received summer sprays. In these cases, late summer rains often remove fungicide protection allowing fruit infection to occur prior to harvest. Studies have found fungicides applied in early summer for fly speck and sooty blotch do not eradicate pre-exisiting infections. These infections can resume growing and become visible late season when residues are depleted.

General chemical management recommendations include:

• Rotate between registered products such as high rate captan (e.g., Maestro, Supra Captan), Granuflo-T, strobilurin (e.g., Pristine) and Allegro fungicides; however, refer to Table 2-3. Activity of Fungicides on Apple Diseases (pg. 75-76) in the 2018-2019 Publication 360, Fruit Crop Protection Guide for all control options available.
• Follow a 14-21-day application interval until harvest to ensure fruit remains protected. Pristine can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan should not be pushed further than 14-days between sprays particularly since it is not as strong on fly speck and sooty blotch as other control products.
• Reduce interval to 7 days during times of hot, wet weather.
• Reapply if more than 5 cm (2 inches) of rain has occurred since the last fungicide was applied especially on late-maturing varieties.

Important cultural management recommendations include:

• Prune and thin clustered fruit to facilitate drying and improve fungicide coverage.
• Remove potential sources of inoculum such as dead branches, fruit mummies (where possible), infected fruit on the orchard floor and alternate hosts including brambles (blackberry, raspberry) from surrounding hedgerows or woodlots.
• Toss pruning cuts and thinned fruit in the row middle and mulch.

Apple Maggot

Apple maggot traps have been installed across the province and catch has begun. Emergence is closely linked to soil moisture with flushes in flight often following periods of significant rainfall loosening soil. With catch on yellow sticky boards, it is important to differentiate between male and female adult flies. Males generally begin emerging before the females, but by peak emergence (August), the sex ratio is about 1 to 1.

Timing for management depends on the type of trap:

• Sexually immature males and females are attracted to the yellow sticky boards, which mimic nectar sources. Insecticides are not needed until 7-10 days after first fly, particularly a female, is captured.
• Sexually mature females ready to lay their eggs are attracted to red spheres, which mimic ripe apples and indicate an insecticide should be applied immediately as damage is imminent.

Many growers make use of an Imidan border spray at this point in the year when the longer re-entry restrictions won’t interfere as much with work that needs to be done. Border sprays are not recommended for other registered apple maggot products.

The following table, adapted from John Wise, Michigan State University (2018), summarizes the characteristics of apple maggot products. Organophosphates (Imidan) and neonicotinoids (Assail, Calypso) are the only insecticide groups that have activity on the adults as well as a curative effect on the eggs and larvae due to their ability to penetrate into the flesh of the fruit.

Table 1. Summary of Insecticides Used to Control Apple Maggot (Adapted from John Wise, MSU: https://www.canr.msu.edu/news/managing-apple-maggots-with-insecticides)

Japanese Beetle

Japanese beetle damage can be easily found now in many regions. The characteristic leaf skeletonization is quite distinct. Look for damage and congregations of this pest at the top of the canopy as damage often moves down the tree. Honeycrisp is often the most preferred variety.

Most insecticides applied for codling moth should have good efficacy on Japanese beetle; however, the tendency of these beetles to move in from surrounding areas may make multiple applications necessary.  If applying a control product, target timing for early morning while beetles are still relatively inactive on the tree. Once feeding begins, the sex pheromones emitted by females combined with what numerous studies believe to be feeding-induced plant volatiles attract more beetles to congregate in the feeding area. Achieving knockdown before this occurs could help reduce the number of individuals coming into the orchard from surrounding areas.

Good weed control in and around the orchard will also help reduce Japanese beetle pressure. Populations tend to be more abundant in orchards where there is poor control of wild raspberry, blackberry, Virginia creeper and wild grape.

Japanese beetle

Skeletonized leaves caused by Japanese beetle feeding

Potato Leafhopper

Potato leafhopper are quite active. Hopper burn and leaf cupping can be easily found in many orchards. This is caused by a toxin in the leafhopper’s saliva that blocks vascular system flow, preventing normal movement of water and nutrients to the affected area. In most high vigour blocks, leafhopper damage is manageable, particularly once terminals harden off. However, nursery trees and non-bearing blocks require control at first sign of injury since vigour and shoot growth can be significantly impacted.

Potato leafhopper nymphs on underside of leaf

Damage to growing apple terminal caused by potato leafhopper

San Jose Scale

The second generation adult flight for San Jose scale is on the upswing in the early regions of the province. In previous years, crawler emergence has generally begun late July to early August. This year, activity seems to be approximately one week behind average in some monitoring orchards. Crawlers are expected early to mid August.

Fruit damage from San Jose scale has been relatively low to date this year, especially compared to the high pressure in many blocks in previous years. Those that have a history of damage from this pest may want to consider managing this generation to prevent fruit damage close to harvest. Registered products include Movento, Sivanto Prime, Closer and TwinGuard. For good resistance management, rotate to a different chemical group than what was used for the first generation. If using two consecutive sprays applied 14-days apart, be aware of the preharvest interval particularly on any early varieties.

Apple Leafcurling Midge

Orchards that still have not seen terminal set or are experiencing secondary growth may be noticing more apple leafcurling midge damage on the newest leaves. So long as there is new growth on either shoots or root suckers, leafcurling midge activity will continue into the fall. Watch young trees as this damage will impact growth and tree vigour.

Orange bullet-shaped apple leafcurling midge eggs laid in newest growth

Figure 3a. Scouting for apple leafcurling midge includes detecting presence of adult female layng eggs in unfurled leaves of terminal.

Leaf curling caused by leafcurling midge feeding

Orius or minute pirate bug is a predator of leafcurling midge, feeding on larva

Mites

The hot, humid weather has resulted in an increased activity of European red mite, two-spotted spider mite and apple rust mite in some orchards. Those growers that are seeing populations reach threshold are opting for miticides with relatively quick knock-down. For more information, see Table 2-6. Activity of Miticides Registered on Apple and/or Pear in Ontario in the 2018-2019 Publication 360, Fruit Crop Protection Guide. Note, only Envidor and Nexter are registered for apple rust mite.

Despite the lush, dense foliage this time of year, do not let mite populations cause extensive damage. Late-season mite pressure and leaf bronzing can result in poor fruit finish and reduce winter hardiness.