In this Issue
- Codling moth: updated spray dates table for apple and pear
- Woolly apple aphid: treat before colonies get too out of hand
- Peach twig borer: treat now (if not already) for peach, apricot
- Walnut husk fly: treat now if a problem last year
- Greater peachtree borer: continue protecting lower trunks of peach and nectarine
- Spider mites: monitor activity on all fruit crops
- Raspberry horntail: prune out wilted canes
- Grape leafhopper: watch for nymphs in mid to late July
APPLE, PEAR
Codling Moth
Second generation egg hatch coming up; assess damage from first generation
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.
Codling moth in most sites in northern Utah are starting the second generation of egg hatch. To prevent resistance to insecticides, we recommend switching to a different chemical class for the second generation treatment. Note that the table includes a date range when “rapid egg hatch” occurs, and if you can tolerate higher injury or have a low population, you can protect the fruit just during this time period.
Otherwise, if you are not using mating disruption, provide continual protect of apples and pears from now until harvest or September 15, whichever is earliest.
Assess Damage from First Generation
Now is a great time to determine the results of your codling moth control so far.
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.
A codling moth sting is a small brown blemish on the fruit where the codling moth larva did not successfully enter the fruit, either because it was killed, or it moved to a different spot. Stings from first generation are usually not as noticeable at harvest.
If you cut into the fruit to look for the larva inside, you can sometimes tell when control failed. If larvae are large or there is no larva in the fruit, then the entry occurred approximately near the beginning of egg-hatch.
Medium-sized larvae (1/3-2/3-inch long) indicate that entry occurred at the early to mid egg-hatch period (early June), and if the larvae are small, they entered in late June.
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.
Treatment
- Residential growers: See the advisory from May 17 that includes a table of products.
- Options for commercial growers: click here.
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. This species of aphid occurs in the tree as well as below ground. They feed on the bark of the trunk, scaffold limbs, and succulent twigs, as well as on tree roots. Their feeding causes galls that may weaken trees. They are most common in trees that are not regularly sprayed.
If woolly apple aphids have increased to the point of covering more than 10-20% of the tree, they should be treated. Because of their waxy coating, it is important to spray trees to drip to allow the insecticide to be effective.
Treatment
- Residential growers can use insecticidal soap plus 1% oil, aimed directly at the colonies. Products for codling moth (Triazicide, Sevin) plus 0.5% oil is also effective.
- Options for commercial growers: click here.
PEACH/NECTARINE, APRICOT, PLUM, CHERRY
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.
Second generation egg hatch will begin in a few days to a few weeks at most locations. In high-population areas, two sprays may be required. The first spray should be applied at the earlier date in the date range provided, with the second application 7-21 days later, depending on the material used.
In low population areas, only one application is needed. Apply the spray at the later date shown in the date range.
Be sure to attention to apricots, which ripen earlier. At this time of year, peach twig borer larvae will be entering fruit as they ripen.
Treatment
- Residential growers can the same options as for codling moth. See the advisory from May 17 that includes a table.
- Options for commercial growers: click here.
Walnut Husk Fly
Where this pest has occurred before, treat walnuts and/or peach now
Walnut husk fly is typically a pest of walnuts, but in Utah, it has been found to attack soft apricots or peaches growing near walnuts. Now is the time in in all areas to target adults and prevent egg-laying.
Along the Wasatch Front, the peak fly emergence will occur in late July, so another application will be needed at that time.
In walnuts, populations of walnut husk fly can be reduced by removing all nuts that fall to the ground.
To make husk removal of infested nuts easier, store them in a damp burlap bag for 2 to 3 days.
Treatment
Options for residential growers:
- Peach, Apricot: Sprays for peach twig borer will also target walnut husk fly. Otherwise, a product containing spinosad (many brands) is an excellent option for both conventional and organic production.
- Walnuts: Spinosad can also be used on walnuts, and should be repeated every 10 days, ending up until one month before harvest.
Options for commercial producers:
- Peach, Apricot: from the USU commercial spray guide
- Walnut: from the Pacific Northwest handbook
Greater Peachtree Borer
Continue protection of lower trunks through September.
Continue to protect the lower trunks of peach/nectarine, apricot, and plum. through September. Make sure the spray covers the entire surface area, particularly close to ground level, and any exposed roots.
Young trees can be killed when trunks are girdled by feeding; older trees are weakened and become susceptible to attack by pathogens and bark beetles.
Treatment
Materials for residential growers include:
- Hi Yield permethrin products; apply once/month
- Spectracide Triazicide; apply every 3 weeks
- GardenTech Sevin (containing cyfluthrin); apply every 3 weeks
- Organic options are products containing spinosad or pyrethrins, or BioNeem (azadirachtin); apply every 7 to 10 days
Materials for commercial growers: click here
Other ways to prevent attack are:
- Remove all weeds, grass, and excess soil from around the base of the tree. Heat and dryness reduce the survival of eggs and larvae.
- Avoid mechanical and rodent-caused injuries to trunks.
- Keep trees healthy with optimal nutrition and irrigation
ALL FRUITS
Spider Mites
Spider mite activity is slowly increasing on apples, peaches, and cherries. Check for mites by examining the leaves on the lowest branches first. (Mites overwinter in groundcover and migrate up the tree in hot, dry weather.)
Look for leaves that are stippled, and turn them over. Using a hand lens, look for the slow-moving mites. Before making a decision on whether to treat, also look for predatory mites within the pest mite population. These are faster moving mites, about the same size, that can prevent spider mite densities from exceeding economic thresholds. If predators are present, then a treatment may not be necessary.
Treatment
- Residential growers: A 0.5-1% application of horticultural oil is very effective on mites, especially when populations are low, and when the spray coverage is good enough to cover the undersides of the leaves.
- Spider mite options for commercial growers. (Select crop, and then select “fruit present” stage.)
SMALL FRUITS
Raspberry Horntail
Prune off wilted tips to remove larvae
Raspberry fruits are in various stages of maturity in northern Utah. Damage from the raspberry horntail has been visible for a few weeks now.
Now is the time to prune out the wilted upper portions of the canes and destroy the prunings (or kill the larva inside). This will help to reduce the horntail population in your area. When pruning, note that the white larva might be farther down the stem than you think. To get a feel for where the larvae are feeding, slice a few cut stems vertically to locate the larva.
Where there is no borer, the pith will be creamy-white. A pith with loose brown material will indicate borer activity.
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 summer generation will 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 groundcover 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 85F), insecticidal soap, pyrethrin (Lilly Miller, Pyganic), carbaryl (Bayer Advanced Complete), Malathion
- Commercial: acetamiprid (Assail), pyrethrin (Azera, Pyganic, Tersus-good coverage is important), methomyl (Lannate), horticultural oil (1%)