Diseases & Pests
Walnut Husk Fly - Findings of recent field trials by UC Cooperative Extension Farm Advisors.
- Trials in Sutter, San Joaquin and San Benito Counties found that out of two
lures and seven lures, Trece and Alpha Scents lures performed equally well.
- Alpha Scents ammonium carbonate and ammonium bicarbonate where the best performing lures.
- A trial in San Benito County comparing eight new and existing insecticides
found Danitol + Belay, Assail and Brigadier provided the highest WHF control.
Botryosphaeria - Botryosphaeria and Phomopsis are increasingly a problem for walnut growers in Yolo and Solano Counties. Symptoms include large sections of blighted branches, spur cankers, leaf and fruit blight, cankers below pruning wounds and branch dieback.
Both cultural controls and fungicide are recommended for dealing with Bot. Pruning out dead and dying wood decreases the inoculum load for new infections, and stops current infection from spreading. Fungicides can protect green tissue early in the season. UC is currently researching efficacy of different sprays and timing. A number of sprays that are effective at controlling Bot in pistachio are also labeled for use in walnut, including Pristine/Merivon, Luna Experience, Luna Sensation, Fontelis, Quilt Xcel, Abound, Quadris Top, Bumper, Quash, and Inspire Super.
Treating Crown Gall - Cost-Benefit analysis of whether it's worth the effort to remove galls and step-by-step instruction for gall removal
Root Rot Diseases - If a few trees in your orchard are declining or dying with no particular pattern in the orchard, a root rot disease is a likely cause. This presentation by UC Plant Pathologist Greg Browne lays out the difference between Phytophthora, Armillaria or Lethal Paradox Canker with pictures of disease symptoms you can find if you cut away at the crown: Phytophthora (Slides 4-5), Armillaria (Slide 9) or Lethal Paradox Canker (Slides 7, 31-34).
Other Pest & Disease Resources