Tree Fruit IPM Advisory

August 17, 2011

In this Issue:

• Insect/Disease Activity
  • Codling Moth
  • Pear Psylla
  • Bitter Pit of Apple
  • San Jose Scale
  • Stink Bug on Apple
  • Shothole Borer
  • Peach Twig Borer
  • Greater Peachtree Borer
  • Post-Harvest Tart Cherry Spray
  • Stink Bugs on Peaches
  • Pests that Enter Ripening Peaches
  • Spider Mites
  • Walnut Husk Fly
    
• Upcoming Monitoring/Insect Activity
• Degree Day Accumulations and Insect Development
• When Do I Spray?
  • Codling Moth
  • Peach Twig Borer
• Sprays-Commercial
• Sprays-Residential

What to Look for/Do Now:

• No need to treat for codling moth or peach twig borer after September 15. 
• Continue protecting peach trunks from greater peachtree borer through September.
• Spider mites numbers are peaking now.
• Commercial growers: Utah County Tree Fruit Tour, Tuesday, August 23
   

Current Insect and Disease Activity

APPLE/PEAR

Codling Moth

Most of the warmer northern Utah locations are within or nearing the end of the period of greatest egg hatch, when it is essential to keep the fruit protected. The end of the second generation will occur later in September. So for the first time in many, many years, most areas of northern Utah will not have a partial third generation. In the hot summer of 2007, these same areas had almost 4 full generations of codling moth.

In general, keep fruit protected up until September 15. The shorter days and cooler nights will prevent any successful egg hatch after that time.

Pear Psylla

Pear psylla is a pest that is around all season, from April to October. It is a sporadic pest of pear in Utah, but where present, it can be difficult to control if it gets out of hand. At this time of year, a variety of life stages can be found. Nymphs are cream colored to small and brown, and typically feed on the undersides of leaves, sucking sap and excreting honeydew. Heavy feeding can lead to necrotic lesions on pear leaves.

Treatment: Commercial growers can use Nexter (PHI 7 days) plus 0.5% oil. Imidacloprid (PHI 7 days) plus 0.5% oil will primarily target the youngest nymphs. Backyard growers can use acetamiprid (Ortho Max) or 1% oil. If the problem is severe, apply lime sulfur after harvest to reduce overwintering psylla.

Bitter Pit of Apple

Lack of calcium in apple fruits can result in a physiological disorder of the fruit where depressed, brown lesions form on the skin, known as bitter pit. The lesions are located mainly on the calyx end of the fruit and are circular in shape. Lesions become worse after storage, turning dark brown to black.

Bitter pit can usually be found throughout an orchard and is most common on trees with low fruit set, excessive vigor, irregular soil moisture, or a certain variety.  Granny Smith, Golden Delicious, Mutsu, Gravenstein, Yellow Newtown, Jonathan, and Red Delicious are among the more susceptible varieties, although almost any young, extremely vigorous tree may exhibit symptoms.

Treatment: Calcium sprays have been shown to reduce bitter pit symptoms. Ideally, sprays should be spaced throughout the season, starting 1-2 weeks after bloom and continuing monthly until harvest. However, if bitter pit has been a nagging problem in your orchard and you have not applied calcium yet, consider 1-2 calcium sprays on expanding fruit before harvest (target the fruit, not the foliage). In some studies, calcium in the form of calcium nitrate has shown to work better when applied as late sprays (do not spray at temps above 80-85F). Avoid spraying Crispin and Golden Delicious with calcium nitrate, since fruit damage may result. After harvest, a 4% calcium chloride dip is also effective. (Store fruit immediately and wash before eating.) (Calcium chloride is corrosive to metal.)

For the best bitter pit prevention, an integrated approach of the following cultural practices is important to prevent bitte pit:

• during irrigation season, avoid wide fluctuations in soil moisture
• do not over-fertilize to avoid vigorous growth and oversized fruit
• do not over-prune
• try to prevent biennial bearing through proper thinning and pollination practices
• harvest at optimal timing because late harvested fruit is prone to bitter bit
• calcium sprays (calcium chloride, calcium nitrate, STOP-IT, Nutri-Cal, Miracal, etc.) should be applied monthly throughout the growing season only if the above practices do not alleviate the problem

San Jose Scale

If you have San Jose scale, you will have noticed small white pimples with a purple halo on your fruit by now. These are the immobile bodies of the scale insect, feeding sap from fruit, twigs, and scaffold limbs. This insect is best treated by targeting the newly hatched nymphs (crawlers), which are more susceptible to insecticides than the armored adults. Crawlers hatch at two different times during the growing season. One hatching occurred in June, and the second in occurring now.

If you have an extremely high population, or did not treat for the first generation of crawlers, consider a single insecticide application according to the timing below:

Box Elder County: September 12
Cache, Wasatch counties: no second generation
Carbon, Uintah counties: no second generation
Davis County: September 7
Salt Lake County: Aug. 31
Utah County: Sept. 3 (Payson) Sept. 10 (Orem) - Sept. 22 (American Fork)
Weber County: Sept. 6

Stink Bugs in Apple

Late season stink bug damage on apples appears as sunken spots on the skin that are green to brown. The flesh underneath the injury is corky and light colored. When you slice into the flesh, the damaged area forms a conical shape, with the widest area near the skin. Damage mostly occurs near the top third of the apple, and on fruits near the orchard borders or near natural areas.

Stink bugs will continue to move into orchards for the next month, feeding up until harvest, where they are present.

Treatment (commercial growers): Danitol is one option, but keep in mind that it will kill beneficial mites. Beleaf (flonicamid) is another option and has a PHI of 21 days.

Shothole Borer

The second generation of shothole borer (Scolytus sp.) is active now through September. This bark beetle attacks scaffold limbs of all tree fruits, preferring weakened or wounded trees. Adults lay eggs on the bark surface and hatched larvae tunnel through the bark to tunnel through and feed on the cambium. Entrance holes will be tiny, and require a hand lens to detect. On stone fruits, sometimes a small amount of sap will ooze out of entrance holes.

Treatment: Control of shothole borer with insecticides is not very effective, but options for commercial growers include Diazinon 50WP (R) or Thiodan 50WP or permethrin or carbaryl ro residential. The best management strategy is to keep trees healthy, and remove dead or dying trees immediately.

STONE FRUITS

Peach Twig Borer

Like codling moth, you do not need to spray after September 15. If you have recently (within 1-2 weeks) made an application for the second generation, you are probably all set for the season. But continue to check ripening fruit for larval entries (which look like codling moth entries, with sawdust-like frass).

Greater Peachtree Borer

We are still catching high numbers of peachtree borer in all areas of northern Utah. Maintain protection of the lower trunk of peach/nectarine and apricot (where necessary) through September.

Sometimes larvae enter the tree below the soil-line, so successful attacks may not be obvious. Determine the success of your control program by examining a select amount of trees this fall. Remove dirt from around the base of the tree down to about 4 inches. Look for oozing gum mixed with frass. Where you see entries, you will know that you need to improve your control program for next year.

There’s not much you can do about successful entries unless you want to carefully search for the larva under the bark. Cut a small amount of bark away (vertically) to find the larva, or insert a strong but thin wire into the borer hole. Take care in using these methods and do not damage the tree more than a single borer would.

Post-Harvest Tart Cherry Spray

Harvest of tart cherries continues this week, but that does not mean the end of the cherry fruit fly. Adult flies will continue (even increase) emergence for the next month, and any fruit left on the trees will be prime real estate for their larval babies. Washington State University recommends a spray (to dripping) no more than 7-10 days after harvest to reduce the overwintering populations of fruit flies. Options include Dimethoate 400 (¼ - ½ pint per 100 gallons or 2 pints/acre) or Provado (6-8 oz/acre).

If you combine this spray with 1% oil (200 gal/acre), you will also reduce the formation of overwintering powdery mildew inoculum (cleistothecia) as well as spider mites. 

Stink Bugs, Leaf-footed Plant Bugs, Boxelder Bugs on Peaches

Late-season feeding by these sap-feeding insects can cause depressed lesions that become watersoaked. Also, their feeding may introduce fruit rot. Adults are moving into orchards now, and activity will escalate through the end of August and into early September. In Utah, we have several species of stink bugs (green and brown) and have not yet detected the introduced brown marmorated stink bug.

Treament:  Insecticides for stink bug management in commercial orchards include Asana, Baythroid, Danitol, Lannate, Leverage, Proaxis, Voliam Xpress, Vydate, and Warrior. Surround (organic, kaolin clay) may provide some repellent activity. Start with treatment of the border rows only. Avoid using a pyrethroid if you have spider mites, as this could make the problem worse.

Pests That Enter Ripening Peaches

This season looks similar to last season in that the moist spring and dryer summer leads to fruit with split pits or soft sutures. The smallest openings (which would occur at the stem end in the case of split pits) or overripe fruit are invitations for sap beetles, comb-clawed beetles (Hymenorous sp.), and earwigs to enter and feed.

Sap beetles are tiny, brown to black beetles that feed on overripe fruit. When the fruit is handled, the beetles will scurry out. Comb-clawed beetles normally feed on organic matter, but there were reports of this insect invading apricots and peaches last year. During harvest, baskets and totes can become infested with beetles, moving from one fruit to another.

Earwigs will not only enter fruit through openings, but feed on soft fruit, leaving deep holes with small openings. Earwig damage is usually easy to tell because they leave behind black dots of excrement on the fruit surface.

Insects that are able to travel in and out of fruit will introduce saprophytic (not disease-causing) fungi into the fruit, causing it to decay. Nothing is worse than a customer biting into a fruit that has pennicillium spores on the inside!

Controlling adults can be difficult due to these insects’ limited exposure to surface applied insecticides. Carbaryl or spinosad have shown good control for earwigs, and a pyrethriod could be used (if necessary) for other opportunistic insects.

The best control measure for sap beetles and other opportunistic insects is good sanitation. Any damaged, splitting, or overripe fruit should be pulled from the tree and dropped to the ground immediately. On smaller farms or where possible, remove the fruits from the orchard. 

Spider Mites

Spider mites (two-spotted and McDaniel) are peaking now in tart cherry, peach, and apple orchards now due to the prolonged hot, dry weather. Use of broad-spectrum pesticides early in the season (pyrethroids, carbaryl) will also contribute to spider mite activity because they kill predatory mites. Starting in early September, mites will change over to their overwintering adult forms, which are orange in color, and migrate to groundcover.

View the undersides of leaves with a hand lens to see if a treatment is necessary. In general, a late-season threshold for most fruits would be an average of 10-30 mites per leaf (or when symptoms are seen on outer leaves) and for peaches, about 30 per leaf. Pear leaves infested with mites will turn black, and newer foliage may become distorted.

The best option for treatment is 1% horticultural oil, sprayed to dripping. A second application 10-14 days later may be required for heavy infestations. Overwintering forms are resistant to oil.

Walnut Husk Fly

Walnut husk flies will be actively flying and laying eggs through October. Some areas are trapping large numbers (more than 100/week), so those who wish to treat their walnuts should continue treatments until one month before harvest. (However, if you do not mind the extra work in removing the damaged husk, treatment of backyard trees is not always necessary.)

Upcoming Monitoring/Insect Activity

Degree Day Accumulations and Insect Development

Click here for information on degree days.

March 1 - August 16

Codling Moth - When to Spray

Continue to apply your chosen material(s) at the interval provided on the label up until Sept. 15.
  

Peach Twig Borer - When to Spray

The second generation egg hatch will end after mid-September for most locations.  You do not need to apply an insecticide after Sept. 15.
 

Spray Materials - Commercial Applicators

The options provided below are not all-inclusive and are not endorsements of USU.  Please check the label before mixing.

Spray Materials - Residential Applicators

Note that these treatments are only recommended if you know you have the particular pest in your trees.

Precautionary Statement:  Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document.  All pesticides are labeled with ingredients, instructions, and risks.  The pesticide applicator is legally responsible for proper use.  USU makes no endorsement of the products listed herein.