2022 Willamette Valley Pest Management Guide for Walnuts

This guide lists recommendations for insect, mite and disease control in walnut orchards. The chemicals, formulations and application rates listed here are based on label directions, research and orchard experience.

Pest management depends on producers and their knowledge of the orchard and its characteristics. Producers must weigh several factors: cultivar, tree size, tree density, canopy characteristics, pest complex and pest history. Consider all these factors when choosing which chemicals to apply and at what rates. Other variables include the amount of water used per acre and the method of application.

Trade name products are mentioned as examples only. Occasionally, manufacturers register different formulations of a product that contain a different concentration of active ingredient. This does not mean that OSU Extension either endorses these products or intends to discriminate against products not mentioned. Consult product labels to determine whether their use confers advantages over the products listed in this guide.

Always refer to the pesticide label for use instructions. It is the legal document.

Producers ask two common questions about the chemical control of insects and diseases:

• “How much chemical do I use per acre?”
• “What is the least amount of water I need per acre to apply in my concentrate sprayer?”

The schedule below suggests an amount of formulated product to use per acre, and not the amount of active ingredient. This amount is based on a typical orchard of middle age and average tree density, with moderate pest pressure. Less product may be needed in 1- to 4-year-old orchards. Conversely, more chemical (within label limits) may be required for large, mature trees experiencing heavy pressure from multiple pests.

Many insecticide labels today list the minimum amount of water needed per acre in concentrate sprays of insecticides. Labels also tell users how to calculate the amount of chemical needed per acre in a concentrate sprayer. Check the label before spraying! Some label directions indicate dilute applications only, such as the dimethoate labels for cherry fruit fly control. Also:

• Make sure any tank-mixes of pesticides are compatible. For example, the elevated pH of some boron spray solutions weakens many insecticides.
• Use adjuvants and spreader stickers with caution.

Important: Blackline of walnuts is a serious disease that can’t be controlled by use of pesticides. For more information, see Growing Walnuts in Oregon, EM 8907.

Walnut pest control recommendations

Use only one material except where a combination is indicated. Follow label precautions when tank-mixing oils, fungicides, and insecticides. Materials are not listed in order of preference.

Early prebloom: Late March to early April, when catkins begin to enlarge

Blight and downy leaf spot

Late prebloom: Early to mid-May, when shoots begin to expand

Anthracnose

Many of these chemicals have received registration for the nut crop group, may be efficacious, and are legal to use on walnut; however, most have not been tested for efficacy against anthracnose. Tank mix or alternate chemicals to prevent fungi from developing resistance. Limit the use of any one group during crop production.

Blight

See materials listed for Early prebloom stage.

Postbloom: Late May

Blight

See materials listed for Early prebloom stage.

June–July

Aphids

Note: When possible, rely on biological control from the aphid parasitoid Trioxys pallidus or reduced-risk materials.

Aphids, codling moth

Note: Monitor codling moth with pheromone traps beginning in June. See footnote 3.

Scales

Apply when crawlers appear; chemical control of scales usually is not necessary.

July–August

Walnut husk fly

Treatments may not be required every year; monitor with yellow sticky cards or other trap. See footnote 5.

Note: Baits can be combined with insecticides to enhance control and reduce reliance on coverage. Commercial baits include Brandt Insect Bait and NU-Lure Bait. Follow labels for mixing directions and rates.

Fall webworm

Insecticides labeled for walnut husk fly and Bacillus thuringiensis will control this pest. Only spot treatments are necessary. Completely drench the infested branch. Applications made when the larvae are small are most effective.

Footnotes

1. More than one type of formulation usually is available for most insecticides. Lower rates can be used on smaller trees.
2. Bordeaux 4-2-100 means 4 pounds of copper sulfate plus 2 pounds of hydrated lime in 100 gallons of water. In any bordeaux formula, ingredients always are listed in the same order — copper sulfate, hydrated lime, then gallons of water.
3. Early summer nut drop can be a result of codling moth infestation. Inspect nuts for larvae and monitor moths with pheromone traps. See Walnut Production Manual by David D. Ramos for information on codling moths as a pest of walnuts.
4. Resistance to copper products has been seen widely in California and may be a problem in the Pacific Northwest. However, copper-resistant bacteria do not seem to cause as much disease as ones that are copper sensitive. Adding mancozeb (such as Dithane or Manzate) will boost the copper ion concentration and may result in improved disease control. Bacteria, however, will become resistant to the higher copper concentrations.
5. Monitor yellow sticky cards placed high (upper half) in the canopy by late May or early June two times per week or more for walnut husk fly captures. Attraction to sticky cards can be enhanced with ammonium carbonate tubes (superchargers). Use captures of adult flies to time insecticide applications. All listed insecticides for walnut husk flies can be enhanced by tank mixing commercial fruit fly baits, or use GF-120, a bait/insecticide formulation. Coverage is less important when using insecticide with baits. You can squeeze captured female flies to determine if eggs are present, indicating impending egg laying and potential crop damage. Egg laying begins one to two weeks after adult emergence. Orchard sanitation practices such as flailing or removing dropped preharvest and postharvest nuts from the orchard floor can greatly reduce the number of overwintering flies.
6. Sprayers used for AFrame Plus, Quadris Top, Quilt Xcel or Willowood Azoxy should not be used on apples such as Gala, Cox’s Orange Pippin and McIntosh. Even a small amount of drift can severely impact these apple trees.
7. A model known as XanthoCast can determine blight risk. Temperatures during periods of leaf wetness are measured and a daily index is calculated. A sliding seven-day accumulation of the daily index is calculated. Estimates of inoculum levels can be done the year before in June (for California) by examining 10 trees, where low disease risk = less than 50 total blighted nuts per tree; moderate disease risk = 50 to 150 blighted nuts per tree; and high disease risk = 150 blighted nuts per tree or more.

Quick reference guide to herbicides labeled for use in fruit and nut crops

• An X indicates the herbicide is labeled for use in that crop.
• Nonbearing (NB) indicates the herbicide is labeled only for crops that will not be harvested for 1 year (365-day preharvest interval).
• Herbicides in bold, italic type are recommended for new plantings.
• For more complete information, please refer to the PNW Weed Management Handbook

OSU resources for plant protection

Information on plant protection is available from several sources at Oregon State University:

• OSU Integrated Plant Protection Center. Online weather data and degree day information for insect pests and diseases.
• Pacific Northwest Plant Disease Management Handbook.
• Pacific Northwest Insect Management Handbook.
• Pacific Northwest Weed Management Handbook.

Using pesticides safely

Always read the label

The single most important approach to pesticide safety is to read the pesticide label before each use and then follow the directions. If still in doubt after reading the label, contact a person qualified to help evaluate the hazard of the chemical and its use. Qualified people include Extension specialists, county educators, pesticide product representatives, and retailers.

Pesticides are toxic and should be handled with care — but they can be used safely if you follow recommended precautions. Follow all label requirements, and strongly consider any recommendations for additional personal protective clothing and equipment. In addition to reading and following the label, other major factors in the safe and effective use of pesticides are the pesticide applicator’s qualifications, common sense, and positive attitude. Always take all safety precautions when using pesticides.

In case of accidents involving pesticides, see your doctor at once. It will help your doctor to know exactly which pesticide is involved. The label on the container gives this information. Take to the physician the pesticide label or information from the label, such as the product name, registration number of the U.S. Environmental Protection Agency, common name and percentage of active ingredient, and first aid instructions. If the label cannot be removed, take along the pesticide container (if not contaminated), but do not take it into the hospital or doctor’s office.

Pesticide safety checklist

• Use pesticides only when necessary and as part of an Integrated Pest Management program.
• Always read the label and follow the instructions.
• Do not allow children to play around sprayers or mixing, storage and disposal areas.
• Wear appropriate protective clothing and equipment.
• Never eat, drink or smoke while handling pesticides.
• Avoid drift into nontarget areas and pesticide runoff into streams, rivers, lakes, irrigation ponds and canals.
• Avoid spilling materials on skin or clothing.
• Have access to clean water, soap and first-aid supplies.
• Keep pesticides in a dry and locked storage area away from food and feed.
• Triple rinse or pressure rinse empty containers and dispose or recycle in accordance with state and local regulations.
• Stay out of recently sprayed areas until the spray has dried, and observe the restricted entry intervals
  specified on the pesticide label.
• Follow the pre-harvest interval on the pesticide label before harvesting crops or gardens and before allowing livestock to graze fields.

Emergency response for exposure and spills

• For any pesticide exposure emergency, dial 911.
• First aid for exposure is indicated on the pesticide label.
• For information on poison emergency treatment call the National Poison Center Poison Help Line at 1-800-222-1222.
• For emergency information related to pesticide spills contact the Oregon Emergency Response System at 1-800-452-0311.

Non-emergency information

• General pesticide information — The National Pesticide Information Center provides objective, science-based information about pesticides and pesticide-related topics.
• Pesticide licensing and regulation — The Oregon Department of Agriculture regulates most aspects of pesticide use in the State of Oregon. Visit the ODA Pesticide and Fertilizers Programs web page or call 503-986-4635.
• Worker protection — The federal Worker Protection Standard for Agricultural Pesticides protects agricultural workers from pesticide exposure at work. The Oregon Occupational Safety and Health Administration is the state agency responsible for administering the WPS in Oregon. Call 1-800-922-2689.
• Pesticide waste — The Oregon Department of Environmental Quality regulates the disposal of pesticide waste in Oregon. Visit or call 503-229-5263.
• The Tricounty Hazardous Waste and Recycling Program conducts periodic collection events for unused pesticides in Hood River, Sherman, and Wasco counties. Call 541-506-2632. Most area chemical distributors offer plastic pesticide container recycling. For information on container preparation, contact your chemical supplier.