Peach Twig Borer, Cherry Fruit Fly, Greater Peachtree Borer

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In this Issue

Peach twig borer: first generation spray dates
Greater peachtree borer: treatment should start mid-June along Wasatch Front area
Thin peaches now
Western cherry fruit fly: treat when fruits develop a salmon blush color
Codling moth: updated dates
San Jose scale: crawlers active in early June
Fire blight: look for damage and prune it out
Rose stem girdler: adults laying eggs in early June

PEACH/NECTARINE, APRICOT, PLUM

Peach Twig Borer

Treatment dates for peach, nectarine, and apricot

Click here for a pdf table of treatment dates for protection of shoots and fruit against peach twig borer.

A halved apricot with peach twig borer damage. The peach twig borer has eaten the area around the pit, causing it to become pockmarked and darkened. — Peach twig borer damage to apricot.

Peach twig borer is the “worm in the peach”. It is a somewhat sporadic pest in Utah, where some locations have a low enough population that trees do not need to be treated.

In spring when peach and apricot fruits are still hard, peach twig borer larvae feeds within succulent twigs. You may notice wilted twigs and these are called shoot strikes. Later in the season, when twigs become hardened off and unpalatable, larvae feed inside the fruit.

If peach twig borer is sporadic, you can get away with a single (or no) application for each generation (up to 2 well-timed sprays). Otherwise, one spray is required for first generation, and multiple sprays may be required for the second generation (when the fruit is susceptible).

Treatment Options – Same as Codling Moth

Residential trees, Conventional:

GardenTech Sevin; Bonide Fruit Tree Spray Guard; Spectracide Triazicide, Monterey Bug-Buster II (all of these are pyrethroids): Each provides 14 days of protection

Residential trees, Organic:

spinosad: Gardens Alive Bull’s Eye; Monterey; Bonide Captain Jack’s, and more: Provides 7 days of protection
pyrethrin: Ortho Fruit Spray; Fertilome Fruit Tree Spray; Worry-free Insecticide: Provides 5 days of protection

Commercial

Commercial growers, click here.

Greater Peachtree Borer

Protect lower trunks of peach, nectarine, apricot, plum

The base of a tree with several orange spots. — Greater peachtree borer larvae feed on the wood at the base of the tree and on roots.

Greater peachtree borer moths lay eggs on the lower 12” of the peach trunk or on nearby soil, and larvae bore through the bark and feed on the cambium. Larvae pupate the following spring, and when they emerge, they sometimes leave their pupal case stuck in the tree.

Only the lower 12″ of the trunk (down to soil line) and any exposed roots need to be protected from peachtree borer. It is also very important to remove all weeds and grass away from the trunks because the moths prefer the dark, moist egg-laying environment.

Newly-planted trees should especially be protected.

The ranges of a predicted first treatment date (or date where mating disruption should be hung) are shown below.

Cache, Sanpete, Summit, Uinta, Wasatch counties: June 28 – July 4
Iron County: June 18 – 21
Wasatch Front warmer areas and Carbon County: June 15 – 20
Wasatch Front cooler areas: June 25 – 30
Grand, Kane,Wayne counties: June 5 – 10

Treatment

Female moths are actively laying eggs all summer long, so keep the trunk protected. Peach trees younger than 5 years are the most vulnerable. The last application should be on Sept 15.

Residential growers – the organic option is any product containing spinosad or pyrethrin (see Peach Twig Borer above; apply every 10 days); Otherwise, use a product containing permethrin, such as Hi Yield Garden & Farm Insect Control or Hi Yield Indoor/Outdoor (apply once per month)
Options for commercial growers who have not used mating disruption: click here.

Thinning Peaches (Residential Information)

Two pictures of a peach branch. The first picture shows very young peaches grouped closely together. The second picture shows the same branch with the peaches thinned to be six inches apart. — Top: unthinned; Bottom: thinned peaches to approximately 6 inches apart.

Apple trees should already be thinned (down to a single apple per cluster, and 6 inches between fruits).

It is also time (or past time in some areas) to thin peaches (4 weeks after full bloom, or when peaches are the size of a robin’s egg). Peach trees set far more fruit than the tree can carry to harvest. Thinning the extra fruit is very important not only to get a good crop of fruit this year, but to get a decent crop next year.

Excess fruit that remains too long on the tree will impact fruit size, formation of flower buds and crop potential for the following year, and overall tree health. An overload of peaches greatly reduces the tree’s carbohydrate reserves and can also affect the tree’s ability to withstand disease and winter injury.
Branch breakage can also occur from the weight of too many peaches.
Proper thinning ensures an even production of flower buds from year to year and provides larger fruit size. Although fruit will naturally drop from the tree (“June drop”), the amount is insufficient to assure optimal fruit size. Natural drops typically stem from unfertilized seed, cold injury, competition between fruit, or excessive shading.

Remove fruit by hand-twisting them off, or on taller trees, hitting unwanted fruit with children’s plastic bats, rubber hoses, or other soft object.

When thinning, pick off the smallest fruits as well as any that are mis-shaped or damaged. Then adequately space the remaining fruits to 4 to 6 inches apart. A moderate-sized peach tree should only produce 100 to 150 fruits on the entire tree.

CHERRY

Western Cherry Fruit Fly

Start treating when fruits in sunniest location color to a salmon blush

fruit salmon blush color — Western cherry fruit fly cannot lay eggs within fruit until they become soft enough, which is when a salmon-blush color appears.

The time to start treating to prevent “worms in the cherry” is based on the fruit development of your own tree. Fruit color will go from green to yellow, and then quickly develop a rosy blush. Once that rosy blush forms, then the female flies are able to penetrate the fruit skin and lay eggs inside. Therefore, watch your fruit and start spraying when fruits in the sunniest location (usually at the top of the tree or on the south side) turn a salmon-blush color.

Western cherry fruit fly is a serious pest of tart and sweet cherries. Please keep in mind that any commercial growers’ crop can be rejected by the processing plant if worms are detected. Therefore, if you have trees that are adjacent to commercial orchards, it is important they are treated for cherry fruit fly, or removed to preserve the livelihood of our farmers.

Treatment

Start treatment at salmon-blush color and continue, with the last spray providing protection until harvest.

Residential, Conventional:

Malathion (malathion): every 7 days
GardenTech Sevin; Bonide Fruit Tree Spray Guard; Spectracide Triazicide, Monterey Bug-Buster II (all of these are pyrethroids): Each provides 14 days of protection

Residential, Organic:

spinosad: Gardens Alive Bull’s Eye; Monterey; Bonide Captain Jack’s, and more: Provides 7 days of protection
pyrethrin: Ortho Fruit Spray; Fertilome Fruit Tree Spray; Worry-free Insecticide: Provides 5 days of protection

Commercial growers, click here

APPLE, PEAR

Codling Moth

Codling moth treatment dates updated for northern Utah locations.

View a pdf of the spray timing table. Be sure to read the instructions at the top of the page, for how to read the table.

Treatment

See the May 5 advisory for a table of spray options for backyard growers (scroll down).
Options for commercial growers.

San Jose Scale

Time to treat crawlers in early to mid June

Green fruit with pink coloring on the end of it. — San Jose scale nymphs have settled near the blossom end of this apple.

San Jose scale is an armored scale (immobile insect with hard covering) that mostly occurs on apple. It can be found feeding on bark, and when populations are high, it appears on fruit as small pepper-flake spots with a purple halo. The scales are often difficult to see with the naked eye and require magnification.

We always recommend a dormant oil spray, and this helps to knock down the scale population but does not control it. The oil only smothers the overwintering nymphs, whose protective “covering” is not as developed as adults. Overwintering adults will survive the dormant oil spray, and offspring laid by females (called crawlers) will need to be treated. Crawlers walk or are windblown to new sites to settle on twigs or fruit, insert their mouthparts, and feed for the remainder of their lives.

Cache, Summit, Uinta, Wasatch counties: June 10 – 14
Wasatch Front and Sevier counties: June 1 – 5
Carbon, Iron, Sanpete counties: June 4 – 8

Treatment

Backyard growers can use insecticidal soap plus 1% oil, neem oil, GardenTech Sevin plus 1% oil, or Spectracide Triazicide plus 1% oil.
In addition, in late fall or spring when there are no leaves, “scrub” the trunk with a stiff brush and very dilute soapy water to remove the scale bodies.
Options for commercial growers: click here.

Fire Blight – Post-Infection

Fire blight infection on a fruit tree. The leaves are wilted and the fruit clusters are shriveled. — This fire blight infection was caught 2 weeks after bloom. In this case, remove twice the length of the visible infection.

Inspect fruit clusters starting 2 weeks after full bloom for infections

We have not seen very many areas with fire blight infections, which is good news. They would typically be visible 2 to 3 weeks after full bloom. It is important to monitor your apple and pear trees every week. Look for wilted leaves, and fruit clusters that appear shriveled and brown.

Post-infection Treatment

Prune out all diseased plant parts as they are found. This will not only prevent the infections from expanding into the tree, but will also reduce the source of bacteria in the area.
This fire blight infection is about 3 to 4 weeks old. The bacteria has already entered the branch, so it should be pruned 12 inches below the visible canker.

For infections that are caught early, remove twice the length of the visible symptoms.
For infections that are caught late (that have expanded beyond the fruit cluster), it is important to make the pruning cut 10 to 12 inches beyond the visible symptoms.
Prune in dry weather only. To be safe, wipe pruners with disinfecting wipes between cuts.

If moisture is predicted after pruning, remove the debris rather than leaving it in the orchard. If conditions are hot and dry, it is OK to leave the debris on the ground.

BERRIES

Rose Stem Girdler

Adults will start laying eggs in early June

A major pest of raspberries is the rose stem girdler. This insect can also attack currants, black raspberry, and roses. The adult is a shiny, bronze-colored beetle. Adults will be starting to lay eggs on canes in early to mid June.

Females lay eggs near the base of the canes, and the larvae hatch and tunnel into the cane tissue. Canes may have swellings at the feeding sites, and infested canes may break at weak areas later in the season.

Treatment

The best treatment option is to remove and destroy infested canes late in the season and over the winter. There are a few insecticides that can be used to kill the eggs and newly hatched larvae, but use caution when spraying flowering plants by treating at dawn or dusk only to protect pollinators, or ideally, do not spray plants in bloom.

Options for commercial and residential include: malathion; pyrethrin (Pyrellin EC*, Bonide Liquid Pyrethrin Spray and more); products containing a pyrethroid (Spectracide Triazicide, GardenTech Sevin, Monterey Bug Buster II, Asana, Mustang, Warrior).
Treat two or three times, spaced 7 to 14 days apart (depending on material used) and target the base of the canes.