In this Issue
- Codling moth: updated spray dates table for apple and pear
- Woolly apple aphid: treat before colonies get too out of hand
- Walnut husk fly: treat now if a problem last year
- Peach twig borer: updated spray dates for peach, apricot
- Summer pruning: remove excess growth from peach trees to improve light penetration
- Raspberry horntail: prune out wilted canes
- Grape leafhopper: watch for nymphs in mid to late July
- Spider mites: monitor activity on all fruit crops
- White apple leafhopper: nymphs present in late July
APPLE, PEAR
Codling Moth
Assess fruits for injury
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.
The end of the first generation egg hatch is a great time to assess your codling moth control by inspecting fruit for damage.
Commercial orchards should examine 5-10% of the fruit, and residential growers should check as many fruits as possible. Do not neglect fruit at the top of the tree where sprays may not have reached, or where residual insecticide may have broken down more quickly due to higher UV exposure.
A successful codling moth entry will show frass (sawdust-like excrement) pushed out of the apple at the entry hole. Most first generation entries are through the calyx end because, while fruit is still firm, it is easier for the larvae to enter at that location. Although not as common, side entries can also be found now, usually where two fruit touch or where leaves touch the fruit.
If you are finding a lot of damage, evaluate your management program to improve control for the second generation. Consider the material used, the spraying method, and the length of time between treatments. If you cut into the fruit to look for the larva inside, you can sometimes tell when your control failed.
- Large larvae or no larvae: The entry occurred approximately near the beginning of egg-hatch.
- Medium-sized larvae (1/3-2/3-inch long): Entry occurred at the early to mid egg-hatch period (early June)
- Small larvae: Entry occurred toward the end of the generation.
Treatment
- See the May 5 advisory for a table of spray options for backyard growers (scroll down).
- Options for commercial growers.
Woolly Apple Aphid
Treat before colonies get out of hand
Woolly apple aphid populations are rapidly increasing in the hot weather we have been having. They feed on the bark of the trunk, scaffold limbs, and succulent twigs, as well as on tree roots. They are most common in trees that are not regularly sprayed.
If woolly apple aphids have increased to the point of covering more than 10% of the tree, they should be treated, but it is better to get them before that point. When the colonies are large, insecticides are not able penetrate the cottony-waxy material.
Treatment
Mixing 0.5% oil (neem, horticultural oil) helps to penetrate into the aphids, as well as good coverage (spraying the affected areas of the tree to dripping).
- Residential growers can use insecticidal soap plus 0.5% oil, aimed directly at the colonies. Products for codling moth (Triazicide, Sevin) plus 0.5% oil are also effective.
- Options for commercial growers: click here.
PEACH/NECTARINE, APRICOT, PLUM, CHERRY
Walnut Husk Fly
Hosts include nuts of walnuts and fruits of peach and apricot; emergence begins now
Walnut husk flies are just starting their emergence from the soil in the Wasatch Front area, and in cooler areas, will start in mid-July. They will continue emerging There is a single generation per year.
Apricots, peaches, and walnuts (black, Japanese, and English) are all hosts for the husk fly. For fruits, the flies prefer them when they start to get soft, so if you found maggots in your fruits last year, count on treating this year.
In walnuts, the maggots do not damage walnut meat directly. Instead, they feed on the husk which causes hull removal difficult, and black staining of the nutshell. Maggots feed on the husk for 3 to 5 weeks and then drop to the soil to pupate.
Non-chemical Treatment (walnuts)
- Like cherry fruit fly, populations of walnut husk fly can be reduced by placing landscape fabric under the tree canopy in late summer to prevent larvae from entering the soil.
- Remove all walnuts that fall to the ground.
- To make husk removal easier, store infested nuts in a damp burlap bag for 2-3 days.
Treatment
The primary option for both commercial and backyard walnut trees is the organic product, spinosad (Captain Jack’s, Gardens Alive Bull’s Eye, Monterey, Entrust, Success), which is applied every 7 days. Make sure you cover the entire tree.
Another option is using a bait with spinosad. The bait attracts the adult flies to feed on the product, and the spinosad kills the flies. GF-120 is a prepared bait, but is only sold in gallon-sized containers for at least $100. Backyard growers could consider mixing a bait solution of the spinosad concentrate with about 4 to 6 tablespoons of molasses per gallon of water applied.
The GF-120 or homemade spray mix does not need to cover the entire tree. Instead, it should be applied as evenly spaced, large droplets.
For treatment of husk fly in apricots or peach, sprays for peach twig borer will also target walnut husk fly.
Peach Twig Borer
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 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.
Summer Pruning
Vigorous vegetative shoots that shade the interior of peach trees may need to be pruned out increase light penetration as well as to retain fruiting wood in the interior.
Research has shown that summer pruning of does not affect flowering, fruit set, or shoot growth the following season.
Summer pruning may stimulate new growth, so it should be finished by early to mid July. Trees that are pruned later in the summer will have delayed leaf senescence and reduced development of cold hardiness in the fall. This is very detrimental for peaches, and could leave them more susceptible to winter injury or to a disease called cytospora canker.
SMALL FRUITS
Raspberry Horntail
Prune out wilted tops until you see a white pith
Larvae of the raspberry horntail feed in the upper portion of canes, causing top-wilting. Damage has been visible for a few weeks now.
Now is the time to take care of these wilted portions of the cane to reduce the horntail population in your area. Some people have had success killing larvae by pinching the top area of the cane (with gloves!) where it feels softest (which is where the larva will be).
Otherwise, prune off the cane top and destroy the prunings. When cutting, be sure that the section you have cut includes the larva inside the stem. It may be farther down the cane than you think. To get a feel for where the larvae are feeding, slice a few cut stems vertically to locate the single larva inside.
Where there is no borer, the pith will be creamy-white. A pith with loose brown material will indicate that the borer may be farther down the stem.
If you see symptoms of crispy leaves near new healthy top-growth, then it is possible that the larva inside was attacked and killed by a beneficial insect called a parasitoid. Parasitoids include flies and wasps. The adult is able to penetrate the cane and lay her eggs on the horntail larva.
Grape Leafhopper
Monitor for nymphs starting in mid-July
The western grape leafhopper is sometimes mistaken for a whitefly in late August, when flying adults are present in grape plants. If this pest has been a problem in the past, do not wait until August. In mid to late July, nymphs of the summer generation will be visible on the undersides of the foliage. Nymphs don’t have wings and are much more susceptible to treatment.
Scout for nymphs by turning leaves over and looking for rice-shaped, cream-colored insects along the leaf veins.
Grape leafhoppers spend the winter as adults on weeds or ground-cover near grape plants. Eggs are laid inside foliage and hatch in late May, with egg-laying adults present in late June.
Nymphs and adults damage foliage by extracting sap and chlorophyll, leaving behind white stippled areas. With heavy feeding, the foliage may become speckled with dark excrement or become scorched. However, flying adults are especially a nuisance as you work in your grapevines.
Treatment
Plants can withstand a high population, and there are several beneficial insects that keep the population in check. A guideline for treatment is an average of 10 nymphs on 80% of the foliage.
- Residential: horticultural oil (1%, apply only when temperatures are below 85 degrees F), insecticidal soap, pyrethrin (Lilly Miller, Pyganic), Malathion
- Commercial: acetamiprid (Assail), pyrethrin (Azera, Pyganic, Tersus-good coverage is important), methomyl (Lannate), horticultural oil (1%)
ALL FRUITS
Spider Mites
In the heat we are experiencing, one pest is much happier than I am – spider mites. These tiny arachnids feed on almost all fruit crops. Right now, they are just beginning to move from ground-covers to plants.
Check for mites by examining the leaves on the lowest branches and plant parts first. (Mites overwinter in ground-cover and migrate up the tree in hot, dry weather.)
- Look for leaves that are stippled (clusters of tiny yellow dots), and turn them over. Using a hand lens, look for the slow-moving mites.
- Or, shake the plant material over white paper and if the tiny dots that fall can be smeared with your thumb, these are spider mites.
Treatment
Residential: Organic options are neem oil or insecticidal soap. Be sure to aim the product to the undersides of the leaves so it lands on the mites.
Commercial: Spider mite options for commercial growers. (Select crop, and then select “fruit present” stage.)
White Apple Leafhopper
Monitor for nymphs in late July
Leafhopper adults are active now in some areas and will be active in others soon, appearing as “white flies” that fly around when foliage is disturbed. Leafhoppers are a minor pest of apples, cherry, raspberry, roses, and other plants. They rarely cause economic damage. They feed on foliage with piercing-sucking mouthparts which causes stippling (tiny white spots).
Adults will soon begin to lay eggs, and the nymphs that hatch will also feed on foliage. But because nymphs are wingless, this pest is easier to manage by targeting this life stage. Most nymphs and adults are found on the undersides of the leaves.
Look for nymphs starting in mid to late July.
Treatment
- Residential: Insecticidal soap (many brands) or products containing pyrethrin are organic options, but must come into contact with the leafhoppers, which are on the undersides of the foliage. Good coverage is important and application should be repeated in 7 days. A few options for conventional treatment of codling moth also work on leafhoppers (Spectracide Triazicide, GardenTech Sevin, and related).
- Commercial: Options for leafhopper can be found by clicking here for apple, and here for cherry